Patent Application
20110033575
Polypeptides, specifically amylase polypeptides and nucleic acids encoding these, and their uses in producing food products are provided. An α-amylase from Pseudomonas saccharophila, thermostable mutations thereof, and nucleic acids encoding the same are useful in several processes such as in a process of baking or a process of liquefaction and saccharification of corn syrup to make ethanol, among other things.
Improved amylases can ameliorate problems inherent in certain processes, such as in conversion of vegetable starches or baking.
Crystallisation of amylopectin takes place in starch granules days after baking, which leads to increased firmness of bread and causes bread staling. When bread stales, bread loses crumb softness and crumb moisture. As a result, crumbs become less elastic, and bread develops a leathery crust.
Enzymatic hydrolysis (by amylases, for example) of amylopectin side chains can reduce crystallization and increase anti-staling. Crystallization depends upon the length of amylopectin side chains: the longer the side chains, the greater the crystallization. Most starch granules are composed of a mixture of two polymers: amylopectin and amylose, of which about 75% is amylopectin. Amylopectin is a very large, branched molecule consisting of chains of α-D-glucopyranosyl units joined by (1-4) linkages, where the chains are attached by α-D-(1-6) linkages to form branches. Amylose is a linear chain of (1-4) linked α-D-glucopyranosyl units having few α-D-(1-6) branches.
Baking of farinaceous bread products such as white bread, bread made from bolted rye flour and wheat flour and rolls is accomplished by baking the bread dough at oven temperatures in the range of from 180 to 250° C. for about 15 to 60 minutes. During the baking process a steep temperature gradient (200→120° C.) prevails over the outer dough layers where the crust of the baked product is developed. However, due to steam, the temperature in the crumb is only about 100° C. at the end of the baking process. Above temperatures of about 85° C., enzyme inactivation can take place and the enzyme will have no anti-staling properties. Only thermostable amylases, thus, are able to modify starch efficiently during baking.
Endoamylase activity can negatively affect the quality of the final bread product by producing a sticky or gummy crumb due to the accumulation of branched dextrins. Exo-amylase activity is therefore preferred with regards to baking, because it accomplishes the desired modification of starch that leads to retardation of staling, with fewer of the negative effects associated with endo-amylase activity. Reduction of endoamylase activity can lead to greater exospecifity, which can reduce branched dextrins and produce a higher quality bread.
The conversion of vegetable starches, especially cornstarch, to ethanol is a rapidly expanding industry. The current process consists of two sequential enzyme-catalyzed steps that result in the production of glucose. Yeast can then be used to ferment the glucose to ethanol.
The first enzyme-catalyzed step is starch liquefaction. Typically, a starch suspension is gelatinized by rapid heating to 85° C. or more. α-Amylases (EC 3.2.1.1) are used to degrade the viscous liquefact to maltodextrins. α-amylases are endohydrolases that catalyze the random cleavage of internal α-1,4-D-glucosidic bonds. As α-amylases break down the starch, the viscosity decreases. Because liquefaction typically is conducted at high temperatures, thermostable α-amylases, such as an α-amylase from Bacillus sp., are preferred for this step.
The maltodextrins produced in this manner generally cannot be fermented by yeast to form alcohol. A second enzyme-catalyzed saccharification step thus is required to break down the maltodextrins. Glucoamylases and/or maltogenic α-amylases commonly are used to catalyze the hydrolysis of non-reducing ends of the maltodextrins formed after liquefaction, releasing D-glucose, maltose and isomaltose. Debranching enzymes, such as pullulanases, can be used to aid saccharification. Saccharification typically takes place under acidic conditions at elevated temperatures, e.g., 60° C., pH 4.3.
One of the yeasts used to produce ethanol is Saccharomyces cerevisiae. S. cerevisiae contains α-glucosidase that has been shown to utilize mono-, di-, and tri-saccharides as substrates. Yoon et al., Carbohydrate Res. 338: 1127-32 (2003). The ability of S. cerevisiae to utilize tri-saccharides can be improved by Mg2+ supplementation and over-expression of AGT1 permease (Stambuck et al., Lett. Appl. Microbiol. 43: 370-76 (2006)), over-expression of MTT1 and MTT1alt to increase maltotriose uptake (Dietvorst et al., Yeast 22: 775-88 (2005)), or expression of the maltase MAL32 on the cell surface (Dietvorst et al., Yeast 24: 27-38 (2007)). The saccharification step could be omitted altogether, if the liquefaction step produced sufficient levels of mono-, di-, or tri-saccharides and S. cerevisiae or its genetically modified variants were used for the fermentation step.
Pseudomonas saccharophila expresses a maltotetraose-forming maltotetraohydrolase (EC 3.2.1.60; G4-forming amylase; G4-amylase; “Amy3A”; or “PS4” herein). The nucleotide sequence of the P. saccharophila gene encoding PS4 has been determined. Zhou et al., “Nucleotide sequence of the maltotetraohydrolase gene from Pseudomonas saccharophila,” FEBS Lett. 255: 37-41 (1989); GenBank Acc. No. X16732. PS4 is expressed as a precursor protein with an N-terminal 21-residue signal peptide. The mature form of PS4, as set forth in SEQ ID NO: 1, contains 530 amino acid residues with a catalytic domain at the N-terminus and a starch binding domain at the C-terminus. PS4 displays both endo- and exo-α-amylase activity. Endo-α-amylase activity is useful for decreasing the viscosity of gelatinized starch, and exo-α-amylase activity is useful for breaking down maltodextrins to smaller saccharides. The exo-α-amylase activity of PS4, however, has been thought to produce only maltotetraoses, which are not suitable substrates for the S. cerevisiae α-glucosidase. For this reason, PS4 has been thought to be unsuitable in a process of liquefaction of corn syrup to produce ethanol.
A PS4 variant polypeptide as set out in the claims is provided. In a further aspect, the use of such a PS4 variant polypeptide, including in and as food additives, food products, bakery products, improver compositions, feed products including animal feeds, etc as set out in the claims, is provided. In yet a further aspect, nucleic acids which encode and which relate to PS4 variant polypeptides, as set out in the claims, are provided. Methods for producing such PS4 variant polypeptides, as well as other aspects, are also set out in the claims.
As set forth herein, conditions are provided under which P. saccharophila G4-forming amylase (PS4) advantageously can be used in an enzyme-catalyzed liquefaction step to produce ethanol from starch, e.g., cornstarch, wheat starch, or barley starch. In the present methods, wild-type PS4 produces significant amounts of maltotrioses, which can be utilized by S. cerevisiae in a subsequent fermentation step to produce ethanol. This property of PS4 advantageously allows ethanol to be produced from liquefied starch in the absence of a saccharification step.
Typically, starch liquefaction is performed at ˜85° C. The melting temperature (Tm) of PS4, however, is 65° C. at pH 5.5. Yet, in one embodiment, PS4 can liquefy cornstarch in a process in which the starch is pre-heated to 70° C., then mixed with PS4 and rapidly heated to 85° C., and held at this temperature for 30 minutes. HPLC analysis of the products of this liquefaction shows that PS4 produces significant amounts of maltotriose in addition to maltotetraose.
In another embodiment, variants of PS4 that are more thermostable than the wild-type PS4 show improved performance in liquefaction, as measured by the viscosity of the liquefact. Particular variants include a truncation of PS4, where the C-terminal starch-binding domain is removed. Other thermostable variants comprise one or more amino acid modifications to the wild-type PS4 enzyme sequence, or modifications to the sequence of the C-terminal truncated PS4 variant.
Compared to wild-type PS4, PS4 variants advantageously may produce more maltotriose than maltotetraose. Further, PS4 variants can produce more glucose and maltose even than currently used amylases, such as SPEZYME™ Xtra (Danisco US Inc., Genencor Division). This results in a higher observed ethanol yield from fermentation, which can exceed 2.5% v/v ethanol in embodiments using yeast that ferment glucose and maltose. It is expected that the ethanol yield can be further increased by fermenting liquefacts produced by PS4 variants with a yeast strain that can metabolize maltotrioses, such as S. cerevisiae.
The PS4 variant may have an altered thermostability, an altered endo-amylase activity, an altered exo-amylase activity, and/or an altered ratio of exo- to endo amylase activity compared to the amino acid sequence of SEQ ID NO: 1, residues 1-429 of SEQ ID NO: 1, or SEQ ID NO: 2. The PS4 variant may comprise one or more amino acid substitutions at following positions: 7, 8, 32, 38, 49, 62, 63, 64, 67, 72, 73, 74, 75, 76, 104, 106, 107, 110, 112, 116, 119, 122, 123, 124, 125, 126, 128, 130, 137, 138, 140, 142, 143, 144, 148, 149, 150, 151, 154, 156, 163, 164, 168, 169, 182, 183, 192, 195, 196, 200, 202, 208, 213, 220, 222, 225, 226, 227, 232, 233, 234, 236, 237, 239, 253, 255, 257, 260, 264, 267, 269, 271, 276, 282, 285, 295, 297, 300, 302, 305, 308, 312, 323, 324, 325, 341, 358, 367, 379, 390, of SEQ ID NO: 1, 2, 3, 4, 5, or 6; one or more following amino acid substitutions: A3T, G9A, H13R, I46F, D68E, G69A/E/H/I/K/M/R/T, G70A/E/L/P/Q/S/V, K71M, G100A/S, G121I/P/R, A131T, G134C, A141S, N145S, Y146D/E, G153A/D, G158C/F/I/L/P/Q/V, S161G/H/K/P/R/TN, G166N, I170E/K/L/M/N, L178N/Q/W, A179E/N/P/R/S, A179S, G184Q, G188A, A199P, G223C/F/H/M/N/Q/W/Y, S229N, W238E/G/K/P/Q/R, G303L, H307D/E/F/G/K/M/P/Q/R/S/W/Y, A309E/I/M/T/V, S334A/H/K/L/M/Q/R/T, and/or H335M of SEQ ID NO: 1, 2, 3, 4, 5, or 6; and/or one or more amino acid substitutions at positions of 420, 422, and/or 424 of SEQ ID NO: 1. The presently disclosed PS4 variant may comprise one or more following amino acid substitutions: A3T, P7S, A8N, G9A, H13R, P32S, I38M, I46F, D49V, D62N, F63A/D/E/L/V, S64N/T, T67G/H/K/N/Q/R/V, D68E, G69A/E/H/I/K/M/R/T, G70A/E/L/P/Q/S/V, K71M, S72E/K/N/T, G73D/E/L/M/N/S/T, G74S, G75C/E/F/R/S/W/Y, E76V, G100A/S, G104N/R, G106K, V107M, L110F, D112E, N116D, N119E/G/S/Y, G121I/P/R, Y122A/E/Q/W, P123S, D124S, K125A/D/E/G/P/Q/W, E126D/N, N128E, P130S, A131T, G134C, R137c, N138D/E/S, C140A/R, A141S, D142E/G/N, P143T, G144E, N145S, Y146D/E, N148K/S, D149H/L/V, C150A, D151A/V/W, G153A/D, D154E/G/Y, F156Y, G158C/F/I/L/P/Q/V, S161G/H/K/P/R/TN, L163M, N164R, G166N, P168L, Q169D/E/G/K/N/R/V, I170E/K/L/M/N, L178N/Q/W, A179E/N/P/R/S, R182D/G/H/M/S, S183G, G184Q, G188A, F192M/Y, V195D, R196A/G/K/P/Q/S/T/V/Y, A199P, P200A/G, R202K, 5208T, S213N, L220A/T, K222M/Y, G223C/F/H/M/N/Q/W/Y, S225E/G/V, E226C/D/G/W, Y227C/D/G/K/T, S229N, W232F/G/H/I/K/L/N/P/Q/R/S/T/Y, R233H, N234R, A236E, S237D/G, W238E/G/K/P/Q/R, Q239L, V253G, D255V, A257V, E260K/R, N264D, V267I, D269N/S/V, K271A/L/Q, G276R, W282S, V285A, T295C, Y297H, G300E, N302K, G303L, Q305E/L/T, H307D/E/F/G/K/M/P/Q/R/S/W/Y, W308A/C/G/K/N/Q/R/S/T, A309E/I/M/T/V, D312E, W323M, T324A/L/M, S325G, S334A/H/K/L/M/Q/R/T, H335M, Y341C/E, R358A/E/G/L/N/Q/T/V, S367Q/R, S379G, and/or D390E of SEQ ID NO: 1, 2, 3, 4, 5, or 6; and/or one or more substitutions of S420G, D422N/P/Q, and/or G424D/S of SEQ ID NO: 1. In one aspect, the PS4 variant may comprise one or more amino acid substitutions at following positions: 7, 32, 49, 62, 63, 64, 72, 73, 74, 75, 76, 107, 110, 112, 116, 119, 122, 123, 125, 128, 130, 137, 138, 140, 142, 143, 144, 148, 149, 150, 151, 154, 156, 163, 164, 168, 169, 182, 183, 192, 195, 196, 202, 220, 222, 226, 227, 232, 233, 234, 236, 237, 239, 253, 255, 257, 260, 264, 269, 271, 276, 282, 285, 297, 300, 302, 305, 308, 312, 323, 324, 325, 341, 358, 367, and/or 379 of SEQ ID NO: 1, 2, 3, 4, 5, or 6; one or more following amino acid substitutions: A3T, H13R, I38M, I46F, T67G/H/K/N/Q/R/V, G69A/E/H/I/K/M/R/T, G70E/L/P/Q/V, K71M, G100A/S, G104R, G106K, G121I/P/R, D124S, E126D/N, A131T, G134C, A141S, N145S, Y146D/E, G153A/D, G158C/F/I/L/P/Q/V, S161G/H/K/P/R/TN, G166N, I170E/K/L/M/N, L178N/Q/W, A179E/N/P/R/S, G188A, A199P, P200A, G223C/F/H/M/N/Q/W/Y, S225E/G/V, W238E/G/K/P/Q/R, T295C, G303L, H307D/G/M/P/S, A309E/I/M/T/V, S334A/H/K/L/M/Q/R/T, H335M, and/or D390E of SEQ ID NO: 1, 2, 3, 4, 5, or 6; one or more amino acid substitutions S420G and/or D422/N/P/Q of SEQ ID NO: 1; and/or an amino acid substitution at position 424 of SEQ ID NO: 1. In another aspect, the PS4 variant may comprise one or more following amino acid substitutions: A3T, P7S, H13R, P32S, I38M, I46F, D49V, D62N, F63A/D/E/L/V, S64N/T, T67G/H/K/N/Q/R/V, G69A/E/H/I/K/M/R/T, G70E/L/P/Q/V, K71M, S72E/K/N/T, G73D/E/L/M/N/S/T, G74S, G75C/E/F/R/S/W/Y, E76V, G100A/S, G104R, G106K, V107M, L110F, D112E, N116D, N119E/G/S/Y, G121I/P/R, Y122A/E/Q/W, P123S, D124S, K125A/D/E/G/P/Q/W, E126D/N, N128E, P130S, A131T, G134C, R137C, N138D/E/S, C140A/R, A141S, D142E/G/N, P143T, G144E, N145S, Y146D/E, N148K/S, D149H/L/V, C150A, D151A/V/W, G153A/D, D154E/G/Y, F156Y, G158C/F/I/L/P/Q/V, S161G/H/K/P/R/TN, L163M, N164R, G166N, P168L, Q169D/E/G/K/N/R/V, I170E/K/L/M/N, L178N/Q/W, A179E/N/P/R/S, R182D/G/H/M/S, S183G, G188A, F192M/Y, V195D, R196A/G/K/P/Q/S/T/V/Y, A199P, P200A, R202K, L220A/T, K222M/Y, G223C/F/H/M/N/Q/W/Y, S225E/G/V, E226C/D/G/W, Y227C/D/G/K/T, W232F/G/H/I/K/L/N/P/Q/R/S/T/Y, R233H, N234R, A236E, S237D/G, W238E/G/K/P/Q/R, Q239L, V253G, D255V, A257V, E260K/R, N264D, D269N/S/V, K271A/L/Q, G276R, W282S, V285A, T295C, Y297H, G300E, N302K, G303L, Q305E/L/T, H307D/G/M/P/S, W308A/C/G/K/N/Q/R/S/T, A309E/I/M/T/V, D312E, W323M, T324A/L/M, S325G, S334A/H/K/L/M/Q/R/T, H335M, Y341C/E, R358A/E/G/L/N/Q/T/V, S367Q/R, S379G, and/or D390E of SEQ ID NO: 1, 2, 3, 4, 5, or 6; and/or one or more following amino acid substitutions: S420G, D422N/P/Q, and/or G424D/S of SEQ ID NO: 1. In a further aspect, the PS4 variant may comprise one or more amino acid substitutions at following positions: 49, 62, 63, 64, 72, 73, 74, 75, 76, 107, 112, 116, 119, 122, 123, 125, 128, 130, 137, 140, 143, 144, 148, 149, 150, 151, 154, 156, 163, 164, 168, 169, 182, 183, 192, 195, 196, 202, 257, 282, 285, 297, 300, 305, 308, 312, 323, and/or 325 of SEQ ID NO: 1, 2, 3, 4, 5, or 6; one or more following amino acid substitutions: A3T, P7S, H13R, I38M, I46F, T67G/H/K/N/Q/R/V, G69A/E/H/I/K/M/R/T, G70E/L/P/Q/V, K71M, G100A/S, G104R, G106K, L110F, G121I/P/R, D124S, E126D/N, A131T, G134C, N138D/E, D142/E/G/N, N145S, Y146D/E, G153A/D, G158C/F/I/L/P/Q/V, S161G/H/K/P/R/TN, G166N, I170E/K/L/M, L178N/Q/W, A179E/N/P/R/S, G188A, A199P, P200A, L220T, K222M/Y, G223C/F/H/M/N/Q/W/Y, S225E/V, E226C/D/G/W, Y227C/D/G/K/T, W232F/G/H/I/K/N/P/Q/R/S/T/Y, R233H, N234R, A236E, S237D/G, W238E/G/K/P/Q/R, Q239L, V253G, D255V, E260K/R, N264D, D269N/S/V, K271A/L/Q, G276R, T295C, N302K, G303L, H307D/G/M/P/S, A309E/I/M/T/V, T324L/M, S334A/H/K/L/M/Q/R/T, H335M, Y341C/E, R358A/E/G/L/N/Q/T/V, S367Q/R, S379G, and/or D390E of SEQ ID NO: 1, 2, 3, 4, 5, or 6; and one or more following amino acid substitutions: S420G, D422/N/P/Q, and/or G424S of SEQ ID NO: 1. In yet another aspect, the PS4 variant may comprise one or more following amino acid substitutions: A3T, P7S, H13R, I38M, I46F, D49V, D62N, F63A/D/E/L/V, S64N/T, T67G/H/K/N/Q/R/V, G69A/E/H/I/K/M/R/T, G70E/L/P/Q/V, K71M, S72E/K/N/T, G73D/E/L/M/N/S/T, G74S, G75C/E/F/R/S/W/Y, E76V, G100A/S, G104R, G106K, V107M, L110F, D112E, N116D, N119E/G/S/Y, G121I/P/R, Y122A/E/Q/W, P123S, D124S, K125A/D/E/G/P/Q/W, E126D/N, N128E, P130S, A131T, G134C, R137c, N138D/E, C140A/R, D142E/G/N, P143T, G144E, N145S, Y146D/E, N148K/S, D149H/L/V, C150A, D151A/V/W, G153A/D, D154E/G/Y, F156Y, G158C/F/I/L/P/Q/V, S161G/H/K/P/R/TN, L163M, N164R, G166N, P168L, Q169E/G/K/N/R/V, I170E/K/L/M, L178N/Q/W, A179E/N/P/R/S, R182D/G/H/M/S, S183G, G188A, F192M/Y, V195D, R196A/G/K/P/Q/S/T/V/Y, A199P, P200A, R202K, L220T, K222M/Y, G223C/F/H/M/N/Q/W/Y, S225E/V, E226C/D/G/W, Y227C/D/G/K/T, W232F/G/H/I/K/N/P/Q/R/S/T/Y, R233H, N234R, A236E, S237D/G, W238E/G/K/P/Q/R, Q239L, V253G, D255V, A257V, E260K/R, N264D, D269N/S/V, K271A/L/Q, G276R, W282S, V285A, T295C, Y297H, G300E, N302K, G303L, Q305E/L/T, H307D/G/M/P/S, W308A/C/G/K/N/Q/R/S/T, A309E/I/M/T/V, D312E, W323M, T324L/M, S325G, S334A/H/K/L/M/Q/R/T, H335M, Y341C/E, R358A/E/G/L/N/Q/T/V, S367Q/R, S379G, and/or D390E of SEQ ID NO: 1, 2, 3, 4, 5, or 6, and/or one or more following amino acid substitutions: S420G, D422N/P/Q, and/or G424S of SEQ ID NO: 1. The PS4 variant may have up to 25, 23, 21, 19, 17, 15, 13, or 11 amino acid deletions, additions, insertions, or substitutions compared to the amino acid sequence of SEQ ID NO: 1, 2, 3, 4, 5, or 6.
The present disclosure contemplates a PS4 variant that may comprise additional one or more amino acid substitutions at the following positions: N33, D34, G70, G121, G134, A141, Y146, I157, S161, L178, A179, G223, S229, L307, A309, and/or 5334 of SEQ ID NO: 1 or 2. In one aspect, the PS4 variant comprises one or more following amino acid substitutions: N33Y, D34N, G70D, G121F, G134R, A141P, Y146G, I157L, S161A, L178F, A179T, G223E, S229P, L307K, A309P, and/or S334P of SEQ ID NO: 1 or 2.
The present disclosure also contemplates a PS4 variant that may have an altered thermostability compared to the amino acid sequence of SEQ ID NO: 1, residues 1 to 429 of SEQ ID NO: 1, or SEQ ID NO: 2. The PS4 variant may be more thermostable than the amino acid sequence of SEQ ID NO: 1, residues 1 to 429 of SEQ ID NO: 1, or SEQ ID NO: 2. In one aspect, the PS4 variant that is more thermostable may comprise one or more following amino acid substitutions: A3T, I38M, G70L, Q169K/R, R182G/H, P200G, G223N, S237D, D269V, K271A/Q, S367Q/R, S379G, and/or S420G of SEQ ID NO: 1 or 2. In another aspect, the PS4 variant that is more thermostable may comprise additional one or more amino acid substitutions at following positions: G134, A141, I157, G223, H307, S334, and/or D343 of SEQ ID NO: 1 or 2. In a further aspect, the PS4 variant that is more thermostable may comprise one or more following amino acid substitutions: G134R, A141P, I157L, G223A, H307L, S334P, and/or D343E of SEQ ID NO: 1 or 2. In yet another aspect, the PS4 variant may further comprise one or more amino acid substitutions at following positions: N33, D34, K71, L178, and/or A179 of SEQ ID NO: 1 or 2. The PS4 variant may comprises one or more amino acid substitutions: N33Y, D34N, K71R, L178F, and/or A179T of SEQ ID NO: 1 or 2.
The present disclosure further contemplates a PS4 variant that may have an altered endo-amylase activity, an altered exo-amylase activity, and/or an altered ratio of exo- to endo-amylase activity compared to the amino acid sequence of SEQ ID NO: 1, residues 1 to 429 of SEQ ID NO: 1, or SEQ ID NO: 2. The PS4 variant may comprise one or more following amino acid substitutions: A3T, G69K, G70E, K71M, G73D/E, G75C/E, Y122A, C140A, G144E, Y146D/E, N148K, C150A, D151A/V/W, G153A, G158I/P, S161G/H/K/P/R, Q169D/E/G/N/R, R196Q/S/T, R202K, 5208T, S213N, K222M, G223C/F/H/M/Q/W/Y, E226D, Y227D/G/K/T, S229N, W232Q/S/T, T295C, Q305T, W308A/C/G/Q/R/S/T, A3091N, W323M, T324L/M, S334A/H/M/Q, and/or R358E/L/N/Q/T/V of SEQ ID NO: 1 or 2. The PS4 variant may comprise additional one or more amino acid substitutions at following positions: W66, I157, E160, S161, R196, W221, K222, E226, D254, Q305, H307, and/or W308 of SEQ ID NO: 1 or 2. The PS4 variant may comprise one or more following amino acid substitutions: W66S, E160F/G/L/P/R/S, S161A, R196H/P/V, W221A, K222T, Q305T/L, H307L, and/or W308A/L/S of SEQ ID NO: 1 or 2.
In one aspect the PS4 variant may have an increased endo-amylase activity or a decreased ratio of exo- to endo-amylase activity compared to the amino acid sequence of SEQ ID NO: 1, residues 1 to 429 of SEQ ID NO: 1, or SEQ ID NO: 2. The PS4 variant may comprise one or more following amino acid substitutions: G69K, G73D/E, Y122A, C140A, C150A, G153A, G158I/P, S161G/H/K/P/R, Q169R, S208T, S229N, T295C, Q305T, and/or R358E/L/Q/T/V of SEQ ID NO: 1 or 2. The PS4 variant may comprise additional one or more amino acid substitutions at following positions: substitutions: W66S, R196H/P/V, W221A, K222T, H307L, and/or W308 of SEQ ID NO: 1 or 2.
In another aspect, the PS4 variant may have an increased exo-amylase activity or an increased ratio of exo- to endo-amylase activity compared to the amino acid sequence of SEQ ID NO: 1, residues 1 to 429 of SEQ ID NO: 1, or SEQ ID NO: 2. The PS4 variant may comprise one or more following amino acid substitutions: A3T, G70E, K71M, G75C/E, G144E, Y146D/E, N148K, D151A/V/W, Q169D/E/G/N, R196Q/S/T, R202K, S213N, K222M, G223C/F/H/M/Q/W/Y, E226D, Y227D/G/K/T, W232Q/S/T, W308A/C/G/Q/R/S/T, A309I/V, W323M, T324L/M, S334A/H/M/Q, and/or R358N of SEQ ID NO: 1 or 2. The PS4 variant may comprise additional one or more following amino acid substitutions: E160F/G/L/P/R/S, S161A, and/or Q305T/L of SEQ ID NO: 1 or 2.
In one aspect, a method of processing starch comprising liquefying a starch and/or saccharifying a starch liquefact to form a saccharide syrup by adding a disclosed Pseudomonas saccharophila amylase (PS4) variant is provided.
In a further aspect, the starch processing method may further comprise adding a debranching enzyme, an isoamylase, a pullulanase, a protease, a cellulase, a hemicellulase, a lipase, a cutinase, or any combination of said enzymes, to the starch liquefact. The starch processing method may be suitable for starch from corns, cobs, wheat, barley, rye, milo, sago, cassava, tapioca, sorghum, rice, peas, bean, banana, or potatoes.
In yet another aspect, the disclosed starch processing method may comprise fermenting the saccharide syrup to produce ethanol. The disclosed method may further comprise recovering the ethanol. The ethanol may be obtained by distilling the starch, wherein the fermenting and the distilling are carried out simultaneously, separately, or sequentially.
The accompanying drawings are incorporated in and constitute a part of this specification and illustrate various embodiments. In the drawings below, “PS4” is replaced with the abbreviation “SAS.” The abbreviations refer to the same protein and are interchangeable.
PS4, a C-terminal truncated variant thereof, and thermostable variants thereof, are provided. The PS4 and variants thereof are useful in processing starch that advantageously produces significant amounts of maltotrioses, which can be utilized by S. cerevisiae or a genetically engineered variant thereof in a subsequent fermentation step to produce ethanol. The process of producing ethanol advantageously does not require the use of glucoamylases and/or maltogenic α-amylases in a saccharification step to convert maltodextrins to mono-, di-, and tri-saccharides. PS4 may occasionally be referred to as SAS in the specification and figures. “PS4” and “SAS” are synonymous.
In accordance with this detailed description, the following abbreviations and definitions apply. It should be noted that as used herein, the singular forms “a,” “an,” and “the” include plural referents unless the context clearly dictates otherwise. Thus, for example, reference to “an enzyme” includes a plurality of such enzymes, and reference to “the formulation” includes reference to one or more formulations and equivalents thereof known to those skilled in the art, and so forth.
Unless defined otherwise, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art. The following terms are provided below.
“Amylase” means an enzyme that is, among other things, capable of catalyzing the degradation of starch. An endo-acting amylase activity cleaves α-D-(1→4) O-glycosidic linkages within the starch molecule in a random fashion. In contrast, an exo-acting amylolytic activity cleaves a starch molecule from the non-reducing end of the substrate. “Endo-acting amylase activity,” “endo-activity,” “endo-specific activity,” and “endo-specificity” are synonymous, when the terms refer to PS4. The same is true for the corresponding terms for exo-activity.
A “variant” or “variants” refers to either polypeptides or nucleic acids. The term “variant” may be used interchangeably with the term “mutant.” Variants include insertions, substitutions, transversions, truncations, and/or inversions at one or more locations in the amino acid or nucleotide sequence, respectively. The phrases “variant polypeptide,” and “variant enzyme” mean a PS4 protein that has an amino acid sequence that has been modified from the amino acid sequence of a wild-type PS4. The variant polypeptides include a polypeptide having a certain percent, e.g., 80%, 85%, 90%, 91%, 92%, 93%, 94%, 95%, 96%, 97%, 98%, or 99%, of sequence identity with the parent enzyme. As used herein, “parent enzymes,” “parent sequence,” “parent polypeptide,” “wild-type PS4,” and “parent polypeptides” mean enzymes and polypeptides from which the variant polypeptides are based, e.g., the PS4 of SEQ ID NO: 1. A “parent nucleic acid” means a nucleic acid sequence encoding the parent polypeptide. A “wild-type” PS4 occurs naturally and includes naturally occurring allelic variants of the PS4 of SEQ ID NO: 1. The signal sequence of a “variant” may be the same (SEQ ID NO: 8) or may differ from the wild-type PS4. A variant may be expressed as a fusion protein containing a heterologous polypeptide. For example, the variant can comprise a signal peptide of another protein or a sequence designed to aid identification or purification of the expressed fusion protein, such as a His-Tag sequence.
To describe the various PS4 variants that are contemplated to be encompassed by the present disclosure, the following nomenclature will be adopted for ease of reference. Where the substitution includes a number and a letter, e.g., 141P, then this refers to {position according to the numbering system/substituted amino acid}. Accordingly, for example, the substitution of an amino acid to proline in position 141 is designated as 141P. Where the substitution includes a letter, a number, and a letter, e.g., A141P, then this refers to {original amino acid/position according to the numbering system/substituted amino acid}. Accordingly, for example, the substitution of alanine with proline in position 141 is designated as A141P.
Where two or more substitutions are possible at a particular position, this will be designated by contiguous letters, which may optionally be separated by slash marks “/”, e.g., G303ED or G303E/D.
Sequence identity is determined using standard techniques known in the art (see e.g., Smith and Waterman, Adv. Appl. Math. 2: 482 (1981); Needleman and Wunsch, J. Mol. Biol. 48: 443 (1970); Pearson and Lipman, Proc. Natl. Acad. Sci. USA 85: 2444 (1988); programs such as GAP, BESTHT, FASTA, and TFASTA in the Wisconsin Genetics Software Package (Genetics Computer Group, Madison, Wis.); and Devereux et al., Nucleic Acid Res., 12: 387-395 (1984)).
The “percent (%) nucleic acid sequence identity” or “percent (%) amino acid sequence identity” is defined as the percentage of nucleotide residues or amino acid residues in a candidate sequence that are identical with the nucleotide residues or amino acid residues of the starting sequence (e.g., PS4). The sequence identity can be measured over the entire length of the starting sequence.
“Sequence identity” is determined herein by the method of sequence alignment. For the purpose of the present disclosure, the alignment method is BLAST described by Altschul et al., (Altschul et al., J. Mol. Biol. 215: 403-410 (1990); and Karlin et al, Proc. Natl. Acad. Sci. USA 90: 5873-5787 (1993)). A particularly useful BLAST program is the WU-BLAST-2 program (see Altschul et al, Meth. Enzymol. 266: 460-480 (1996)). WU-BLAST-2 uses several search parameters, most of which are set to the default values. The adjustable parameters are set with the following values: overlap span=1, overlap fraction=0.125, word threshold (T)=11. The HSP S and HSP S2 parameters are dynamic values and are established by the program itself depending upon the composition of the particular sequence and composition of the particular database against which the sequence of interest is being searched. However, the values may be adjusted to increase sensitivity. A % amino acid sequence identity value is determined by the number of matching identical residues divided by the total number of residues of the “longer” sequence in the aligned region. The “longer” sequence is the one having the most actual residues in the aligned region (gaps introduced by WU-Blast-2 to maximize the alignment score are ignored).
Other methods find use in aligning sequences. One example of a useful algorithm is PILEUP. PILEUP creates a multiple sequence alignment from a group of related sequences using progressive, pair-wise alignments. It can also plot a tree showing the clustering relationships used to create the alignment. PILEUP uses a simplification of the progressive alignment method of Feng and Doolittle (Feng and Doolittle, J. Mol. Evol. 35: 351-360 (1987)). The method is similar to that described by Higgins and Sharp (Higgins and Sharp, CABIOS 5: 151-153 (1989)). Useful PILEUP parameters including a default gap weight of 3.00, a default gap length weight of 0.10, and weighted end gaps.
“Variant nucleic acids” can include sequences that are complementary to sequences that are capable of hybridizing to the nucleotide sequences presented herein. For example, a variant sequence is complementary to sequences capable of hybridizing under stringent conditions, e.g., 50° C. and 0.2×SSC (1×SSC=0.15 M NaCl, 0.015 M sodium citrate, pH 7.0), to the nucleotide sequences presented herein. More particularly, the term variant encompasses sequences that are complementary to sequences that are capable of hybridizing under highly stringent conditions, e.g., 65° C. and 0.1×SSC, to the nucleotide sequences presented herein. The melting point (Tm) of a variant nucleic acid may be about 1, 2, or 3° C. lower than the Tm of the wild-type nucleic acid. The variant nucleic acids include a polynucleotide having a certain percent, e.g., 80%, 85%, 90%, 95%, or 99%, of sequence identity with the nucleic acid encoding the parent enzyme.
As used herein, the term “expression” refers to the process by which a polypeptide is produced based on the nucleic acid sequence of a gene. The process includes both transcription and translation.
“Isolated” or “Non-naturally occurring” means that the sequence is at least substantially free from at least one other component that the sequence is naturally associated and found in nature, e.g., genomic sequences or has been modified in any manner from its natural state.
“Purified” means that the material is in a relatively pure state, e.g., at least about 90% pure, at least about 95% pure, or at least about 98% pure.
“Thermostable” means the enzyme retains activity after exposure to elevated temperatures. The thermostability of an enzyme is measured by its half-life (t1/2), where half of the enzyme activity is lost by the half-life. The half-life value is calculated under defined conditions by measuring the residual amylase activity. To determine the half-life of the enzyme, the sample is heated to the test temperature for 1-10 min, and activity is measured using a standard assay for PS4 activity, such as the Betamyl® assay (Megazyme, Ireland).
As used herein, “optimum pH” means the pH at which PS4 or a PS4 variant displays the activity in a standard assay for PS4 activity, measured over a range of pH's.
As used herein, “amino acid sequence” is synonymous with the term “polypeptide” and/or the term “protein.” In some instances, the term “amino acid sequence” is synonymous with the term “peptide”; in some instances, the term “amino acid sequence” is synonymous with the term “enzyme.” As used herein, “nucleotide sequence” or “nucleic acid sequence” refers to an oligonucleotide sequence or polynucleotide sequence and variants, homologues, fragments and derivatives thereof. The nucleotide sequence may be of genomic, synthetic or recombinant origin and may be double-stranded or single-stranded, whether representing the sense or anti-sense strand. As used herein, the term “nucleotide sequence” includes genomic DNA, cDNA, synthetic DNA, and RNA.
“Homologue” means an entity having a certain degree of identity or “homology” with the subject amino acid sequences and the subject nucleotide sequences. A “homologous sequence” includes a polynucleotide or a polypeptide having a certain percent, e.g., 80%, 85%, 90%, 95%, or 99%, of sequence identity with another sequence. Percent identity means that, when aligned, that percentage of bases or amino acid residues are the same when comparing the two sequences. Amino acid sequences are not identical, where an amino acid is substituted, deleted, or added compared to the subject sequence. The percent sequence identity typically is measured with respect to the mature sequence of the subject protein, i.e., following removal of a signal sequence, for example. Typically, homologues will comprise the same active site residues as the subject amino acid sequence. Homologues also retain amylase activity, although the homologue may have different enzymatic properties than the wild-type PS4.
As used herein, “hybridization” includes the process by which a strand of nucleic acid joins with a complementary strand through base pairing, as well as the process of amplification as carried out in polymerase chain reaction (PCR) technologies. The variant nucleic acid may exist as single- or double-stranded DNA or RNA, an RNA/DNA heteroduplex or an RNA/DNA copolymer. As used herein, “copolymer” refers to a single nucleic acid strand that comprises both ribonucleotides and deoxyribonucleotides. The variant nucleic acid may be codon-optimized to further increase expression.
As used herein, a “synthetic” compound is produced by in vitro chemical or enzymatic synthesis. It includes, but is not limited to, variant nucleic acids made with optimal codon usage for host organisms, such as a yeast cell host or other expression hosts of choice.
As used herein, “transformed cell” includes cells, including both bacterial and fungal cells, which have been transformed by use of recombinant DNA techniques. Transformation typically occurs by insertion of one or more nucleotide sequences into a cell. The inserted nucleotide sequence may be a heterologous nucleotide sequence, i.e., is a sequence that is not natural to the cell that is to be transformed, such as a fusion protein.
As used herein, “operably linked” means that the described components are in a relationship permitting them to function in their intended manner. For example, a regulatory sequence operably linked to a coding sequence is ligated in such a way that expression of the coding sequence is achieved under condition compatible with the control sequences.
As used herein, “biologically active” refers to a sequence having a similar structural, regulatory or biochemical function as the naturally occurring sequence, although not necessarily to the same degree.
As used herein the term “starch” refers to any material comprised of the complex polysaccharide carbohydrates of plants, such as corn, comprised of amylose and amylopectin with the formula (C6H10O5)x, where X can be any number. The term “granular starch” refers to raw, i.e., uncooked starch, e.g., starch that has not been subject to gelatinization.
The term “liquefaction” refers to the stage in starch conversion in which gelatinized starch is hydrolyzed to give low molecular weight soluble dextrins. As used herein the term “saccharification” refers to enzymatic conversion of starch to glucose. The term “degree of polymerization” (DP) refers to the number (n) of anhydroglucopyranose units in a given saccharide. Examples of DP1 are the monosaccharides glucose and fructose. Examples of DP2 are the disaccharides maltose and sucrose.
As used herein the term “dry solids content” (ds) refers to the total solids of a slurry in a dry weight percent basis. The term “slurry” refers to an aqueous mixture containing insoluble solids.
The phrase “simultaneous saccharification and fermentation (SSF)” refers to a process in the production of biochemicals in which a microbial organism, such as an ethanol producing microorganism and at least one enzyme, such as PS4 or a variant thereof, are present during the same process step. SSF refers to the contemporaneous hydrolysis of granular starch substrates to saccharides and the fermentation of the saccharides into alcohol, for example, in the same reactor vessel.
As used herein “ethanologenic microorganism” refers to a microorganism with the ability to convert a sugar or oligosaccharide to ethanol.
The following abbreviations apply unless indicated otherwise:
In one aspect, a polypeptide having a substitution at one or more positions which effect an altered property, which may be any combination of altered exospecificity, endospecifity or altered thermostability, or an altered handling property, relative to the parent enzyme, is provided. Such variant polypeptides are referred to in this document for convenience as “PS4 variant polypeptides” or “PS4 variants”.
In one aspect, the PS4 variants exhibit enzyme activity. In one aspect, the PS4 variant polypeptides comprise amylase activity. In a further aspect, the PS4 variant polypeptides comprise exoamylase activity. In a further aspect, the PS4 variant polypeptides exhibit non-maltogenic exoamylase activity.
Compositions, including food additives, food products, bakery products, improver compositions, feed products including animal feeds, etc comprising such altered PS4 variant polypeptides, such as those which have non-maltogenic exoamylase activity, as well as methods of making and using such polypeptides and the compositions, are provided herein.
As noted above, the PS4 variant polypeptides may comprise one or more improved handling properties, preferably improved baking properties. Thus, the PS4 variant polypeptides are such that the food products so treated have one or more of (preferably all of) a lower firmness, a higher resilience, a higher cohesiveness, a lower crumbliness or a higher foldability. Such improved handling or baking properties exhibited by the PS4 variant polypeptides are described in further detail below.
Furthermore a treatment of food products, particularly doughs and bakery products with such polypeptides, and such that the food products exhibit the desired qualities set out above, is provided.
Further is provided other uses of such compositions such as in the preparation of detergents, as sweeteners, syrups, etc. The compositions include the polypeptide together with at least one other component. In particular, food or feed additives comprising the polypeptides, are provided.
An isolated and/or purified polypeptide comprising a PS4 or variant thereof is provided. In one embodiment, the PS4 is a mature form of the polypeptide (SEQ ID NO: 1), wherein the 21 amino acid leader sequence is cleaved, so that the N-terminus of the polypeptide begins at the aspartic acid (D) residue. Variants of PS4 include a PS4 in which the C-terminal starch binding domain is removed. A representative amino acid sequence of a mature PS4 variant in which the starch binding domain is removed is the one having an amino acid sequence of residues 1 to 429 of SEQ ID NO: 1, or SEQ ID NO: 2 with residues 419-429 of SEQ ID NO:1 fused at the C-terminus. Other PS4 variants include variants wherein between one and about 25 amino acid residues have been added or deleted with respect to wild-type PS4 or the PS4 having an amino acid sequence of residues 1 to 429 of SEQ ID NO: 1, or SEQ ID NO: 2 with residues 419-429 of SEQ ID NO:1 fused at the C-terminus. In one aspect, the PS4 variant has the amino acid sequence of residues 1 to 429 of SEQ ID NO: 1, wherein any number between one and about 25 amino acids have been substituted. Representative embodiments of these variants include CF135 (SEQ ID NO: 3 with residues 419-429 of SEQ ID NO:1 fused at the C-terminus), CF143(SEQ ID NO: 4 with residues 419-429 of SEQ ID NO:1 fused at the C-terminus), CF149(SEQ ID NO: 5 with residues 419-429 of SEQ ID NO:1 fused at the C-terminus), and CF154(SEQ ID NO: 6 with residues 419-429 of SEQ ID NO:1 fused at the C-terminus).
In another aspect, the PS4 variant has the sequence of wild-type PS4, wherein any number between one and about 25 amino acids have been substituted. Representative examples of PS4 variants having single amino acid substitutions are shown in TABLE 3. Examples of PS4 variants having combinations of amino acid substitutions are shown in TABLES 4 and 7. TABLE 4 depicts various amino acids that have been modified to form a core variant sequence, which is additionally modified as indicated for the PS4 variants listed in TABLE 7. TABLE 7 further summarizes the effect of various mutations on endo- or exo-amylase activity, as well as the ratio of exo- to endo-amylase activity. In addition to the amino acid residue modifications listed in TABLES 3-4, additional specific PS4 residues that may be modified include A3, S44, A93, G103, V109, G172, A211, G265, N302, G313, and G342. PS4 variants may have various combinations of the amino acid substitutions disclosed herein. A process of using a PS4 variant may comprise the use of a single PS4 variant or a combination, or blend, of PS4 variants.
PS4 variants advantageously may produce more maltotriose than maltotetraose. Further, the PS4 variants can produce more glucose and maltose than currently used amylases, such as SPEZYME™ Xtra (Danisco US Inc., Genencor Division). This results in a higher observed ethanol yield from fermentation, which can exceed 2.5% (v/v) ethanol in embodiments using yeast that ferment glucose and maltose. PS4 variants are provided that have substantial endo-amylase activity, compared to wild-type PS4, and/or have a lower ratio of exo- to endo-amylase activity compared to wild-type PS4. Such PS4 variants may be particularly useful in a liquefaction process, when used alone or combination with other PS4 variants, where internal cleavage of complex branching saccharides lowers the viscosity of the substrate.
Representative examples of amino acid substitutions that maintain or increase thermostability include the substitutions made to the variants CF135, CF143, CF149, and CF154. The PS4 variant CF135 has an amino acid sequence of SEQ ID NO: 3 with residues 419-429 of SEQ ID NO: 1 fused at the C-terminus. This variant contains the amino acid substitution A141P. The variant CF143, having an amino acid sequence of SEQ ID NO: 4 with residues 419-429 of SEQ ID NO: 1 fused at the C-terminus, has the additional substitution G223A. The variant CF149, having an amino acid sequence of SEQ ID NO: 5 with residues 419-429 of SEQ ID NO: 1 fused at the C-terminus, has seven substitutions: G134R, A141P, G223A, I157L, H307L, S334P, and D343E. The variant CF154, having an amino acid sequence of SEQ ID NO: 6 with residues 419-429 of SEQ ID NO: 1 fused at the C-terminus, has the same seven substitutions as CF149, plus the substitutions N33Y, D34N, K71R, L178F, and A179T.
Other particularly useful variants include those in which residues affecting substrate binding are substituted. PS4 residues involved in substrate binding include those depicted in
The PS4 variant may comprises a sequence having at least 80%, 85%, 90%, 91%, 92%, 93%, 94%, 95%, 96%, 97%, 98%, or 99% sequence identity to the amino acid sequence of SEQ ID NO: 1, residues 1 to 429 of SEQ ID NO: 1, or SEQ ID NO: 2. The PS4 variant may have an altered thermostability, an altered endo-amylase activity, an altered exo-amylase activity, and/or an altered ratio of exo- to endo amylase activity compared to the amino acid sequence of SEQ ID NO: 1, residues 1-429 of SEQ ID NO: 1, or SEQ ID NO: 2.
In some embodiments, the PS4 variant may comprise one or more amino acid substitutions at following positions: 7, 8, 32, 38, 49, 62, 63, 64, 67, 72, 73, 74, 75, 76, 104, 106, 107, 110, 112, 116, 119, 122, 123, 124, 125, 126, 128, 130, 137, 138, 140, 142, 143, 144, 148, 149, 150, 151, 154, 156, 163, 164, 168, 169, 182, 183, 192, 195, 196, 200, 202, 208, 213, 220, 222, 225, 226, 227, 232, 233, 234, 236, 237, 239, 253, 255, 257, 260, 264, 267, 269, 271, 276, 282, 285, 295, 297, 300, 302, 305, 308, 312, 323, 324, 325, 341, 358, 367, 379, 390, of SEQ ID NO: 1, 2, 3, 4, 5, or 6; one or more following amino acid substitutions: A3T, G9A, H13R, I46F, D68E, G69A/E/H/I/K/M/R/T, G70A/E/L/P/Q/S/V, K71M, G100A/S, G121I/P/R, A131T, G134C, A141S, N145S, Y146D/E, G153A/D, G158C/F/I/L/P/Q/V, S161G/H/K/P/R/TN, G166N, I170E/K/L/M/N, L178N/Q/W, A179E/N/P/R/S, A179S, G184Q, G188A, A199P, G223C/F/H/M/N/Q/W/Y, S229N, W238E/G/K/P/Q/R, G303L, H307D/E/F/G/K/M/P/Q/R/S/W/Y, A309E/I/M/T/V, S334A/H/K/L/M/Q/R/T, and/or H335M of SEQ ID NO: 1, 2, 3, 4, 5, or 6; and/or one or more amino acid substitutions at positions of 420, 422, and/or 424 of SEQ ID NO: 1. Representative substitutions may include: A3T, P7S, A8N, G9A, H13R, P32S, I38M, I46F, D49V, D62N, F63A/D/E/L/V, S64N/T, T67G/H/K/N/Q/R/V, D68E, G69A/E/H/I/K/M/R/T, G70A/E/L/P/Q/S/V, K71M, S72E/K/N/T, G73D/E/L/M/N/S/T, G74S, G75C/E/F/R/S/W/Y, E76V, G100A/S, G104N/R, G106K, V107M, L110F, D112E, N116D, N119E/G/S/Y, G121I/P/R, Y122A/E/Q/W, P123S, D124S, K125A/D/E/G/P/Q/W, E126D/N, N128E, P130S, A131T, G134C, R137C, N138D/E/S, C140A/R, A141S, D142E/G/N, P143T, G144E, N145S, Y146D/E, N148K/S, D149H/L/V, C150A, D151A/V/W, G153A/D, D154E/G/Y, F156Y, G158C/F/I/L/P/Q/V, S161G/H/K/P/R/TN, L163M, N164R, G166N, P168L, Q169D/E/G/K/N/R/V, I170E/K/L/M/N, L178N/Q/W, A179E/N/P/R/S, R182D/G/H/M/S, S183G, G184Q, G188A, F192M/Y, V195D, R196A/G/K/P/Q/S/T/V/Y, A199P, P200A/G, R202K, 5208T, S213N, L220A/T, K222M/Y, G223C/F/H/M/N/Q/W/Y, 5225E/G/V, E226C/D/G/W, Y227C/D/G/K/T, S229N, W232F/G/H/I/K/L/N/P/Q/R/S/T/Y, R233H, N234R, A236E, S237D/G, W238E/G/K/P/Q/R, Q239L, V253G, D255V, A257V, E260K/R, N264D, V267I, D269N/S/V, K271A/L/Q, G276R, W282S, V285A, T295C, Y297H, G300E, N302K, G303L, Q305E/L/T, H307D/E/F/G/K/M/P/Q/R/S/W/Y, W308A/C/G/K/N/Q/R/S/T, A309E/I/M/T/V, D312E, W323M, T324A/L/M, S325G, S334A/H/K/L/M/Q/R/T, H335M, Y341C/E, R358A/E/G/L/N/Q/T/V, S367Q/R, S379G, and/or D390E of SEQ ID NO: 1, 2, 3, 4, 5, or 6, and/or one or more substitutions of S420G, D422N/P/Q, and/or G424D/S of SEQ ID NO: 1.
In some embodiments, the PS4 variant may comprise one or more amino acid substitutions at following positions: 7, 32, 49, 62, 63, 64, 72, 73, 74, 75, 76, 107, 110, 112, 116, 119, 122, 123, 125, 128, 130, 137, 138, 140, 142, 143, 144, 148, 149, 150, 151, 154, 156, 163, 164, 168, 169, 182, 183, 192, 195, 196, 202, 220, 222, 226, 227, 232, 233, 234, 236, 237, 239, 253, 255, 257, 260, 264, 269, 271, 276, 282, 285, 297, 300, 302, 305, 308, 312, 323, 324, 325, 341, 358, 367, and/or 379 of SEQ ID NO: 1, 2, 3, 4, 5, or 6; one or more following amino acid substitutions: A3T, H13R, I38M, I46F, T67G/H/K/N/Q/R/V, G69A/E/H/I/K/M/R/T, G70E/L/P/Q/V, K71M, G100A/S, G104R, G106K, G121I/P/R, D124S, E126D/N, A131T, G134C, A141S, N145S, Y146D/E, G153A/D, G158C/F/I/L/P/Q/V, S161G/H/K/P/R/TN, G166N, I170E/K/L/M/N, L178N/Q/W, A179E/N/P/R/S, G188A, A199P, P200A, G223C/F/H/M/N/Q/W/Y, 5225E/G/V, W238E/G/K/P/Q/R, T295C, G303L, H307D/G/M/P/S, A309E/I/M/T/V, 334A/H/K/L/M/Q/R/T, H335M, and/or D390E of SEQ ID NO: 1, 2, 3, 4, 5, or 6; one or more amino acid substitutions S420G and/or D422/N/P/Q of SEQ ID NO: 1; and/or an amino acid substitution at position 424 of SEQ ID NO: 1. Representative substitutions may include: A3T, P7S, H13R, P32S, I38M, I46F, D49V, D62N, F63A/D/E/L/V, S64N/T, T67G/H/K/N/Q/R/V, G69A/E/H/I/K/M/R/T, G70E/L/P/Q/V, K71M, S72E/K/N/T, G73D/E/L/M/N/S/T, G74S, G75C/E/F/R/S/W/Y, E76V, G100A/S, G104R, G106K, V107M, L110F, D112E, N116D, N119E/G/S/V, G121I/P/R, Y122A/E/Q/W, P123S, D124S, K125A/D/E/G/P/Q/W, E126D/N, N128E, P130S, A131T, G134C, R137C, N138D/E/S, C140A/R, A141S, D142E/G/N, P143T, G144E, N145S, Y146D/E, N148K/S, D149H/L/V, C150A, D151A/V/W, G153A/D, D154E/G/V, F156Y, G158C/F/I/L/P/Q/V, S161G/H/K/P/R/TN, L163M, N164R, G166N, P168L, Q169D/E/G/K/N/R/V, I170E/K/L/M/N, L178N/Q/W, A179E/N/P/R/S, R182D/G/H/M/S, S183G, G188A, F192MN, V195D, R196A/G/K/P/Q/S/T/V/Y, A199P, P200A, R202K, L220A/T, K222M/Y, G223C/F/H/M/N/Q/W/Y, S225E/G/V, E226C/D/G/W, Y227C/D/G/K/T, W232F/G/H/I/K/L/N/P/Q/R/S/T/Y, R233H, N234R, A236E, S237D/G, W238E/G/K/P/Q/R, Q239L, V253G, D255V, A257V, E260K/R, N264D, D269N/S/V, K271A/L/Q, G276R, W282S, V285A, T295C, Y297H, G300E, N302K, G303L, Q305E/L/T, H307D/G/M/P/S, W308A/C/G/K/N/Q/R/S/T, A309E/I/M/T/V, D312E, W323M, T324A/L/M, S325G, S334A/H/K/L/M/Q/R/T, H335M, Y341C/E, R358A/E/G/L/N/Q/T/V, S367Q/R, S379G, and/or D390E of SEQ ID NO: 1, 2, 3, 4, 5, or 6, and/or one or more following amino acid substitutions: S420G, D422N/P/Q, and/or G424D/S of SEQ ID NO: 1.
In other embodiments, the PS4 variant may comprise one or more amino acid substitutions at following positions: 49, 62, 63, 64, 72, 73, 74, 75, 76, 107, 112, 116, 119, 122, 123, 125, 128, 130, 137, 140, 143, 144, 148, 149, 150, 151, 154, 156, 163, 164, 168, 169, 182, 183, 192, 195, 196, 202, 257, 282, 285, 297, 300, 305, 308, 312, 323, and/or 325 of SEQ ID NO: 1, 2, 3, 4, 5, or 6; one or more following amino acid substitutions: A3T, P7S, H13R, I38M, I46F, T67G/H/K/N/Q/R/V, G69A/E/H/I/K/M/R/T, G70E/L/P/Q/V, K71M, G100A/S, G104R, G106K, L110F, G121I/P/R, D124S, E126D/N, A131T, G134C, N138D/E, D142/E/G/N, N145S, Y146D/E, G153A/D, G158C/F/I/L/P/Q/V, S161G/H/K/P/R/TN, G166N, I170E/K/L/M, L178N/Q/W, A179E/N/P/R/S, G188A, A199P, P200A, L220T, K222M/Y, G223C/F/H/M/N/Q/W/Y, S225EN, E226C/D/G/W, Y227C/D/G/K/T, W232F/G/H/I/K/N/P/Q/R/S/TN, R233H, N234R, A236E, S237D/G, W238E/G/K/P/Q/R, Q239L, V253G, D255V, E260K/R, N264D, D269N/S/V, K271A/L/Q, G276R, T295C, N302K, G303L, H307D/G/M/P/S, A309E/I/M/T/V, T324L/M, S334A/H/K/L/M/Q/R/T, H335M, Y341C/E, R358A/E/G/L/N/Q/T/V, S367Q/R, S379G, and/or D390E of SEQ ID NO: 1, 2, 3, 4, 5, or 6; and one or more following amino acid substitutions: S420G, D422/N/P/Q, and/or G424S of SEQ ID NO: 1. Representative substitutions may include: A3T, P7S, H13R, I38M, I46F, D49V, D62N, F63A/D/E/L/V, S64N/T, T67G/H/K/N/Q/R/V, G69A/E/H/I/K/M/R/T, G70E/L/P/Q/V, K71M, S72E/K/N/T, G73D/E/L/M/N/S/T, G74S, G75C/E/F/R/S/W/Y, E76V, G100A/S, G104R, G106K, V107M, L110F, D112E, N116D, N119E/G/S/Y, G121I/P/R, Y122A/E/Q/W, P123S, D124S, K125A/D/E/G/P/Q/W, E126D/N, N128E, P130S, A131T, G134C, R137C, N138D/E, C140A/R, D142E/G/N, P143T, G144E, N145S, Y146D/E, N148K/S, D149H/L/V, C150A, D151A/V/W, G153A/D, D154E/G/Y, F156Y, G158C/F/I/L/P/Q/V, S161G/H/K/P/R/TN, L163M, N164R, G166N, P168L, Q169E/G/K/N/R/V, I170E/K/L/M, L178N/Q/W, A179E/N/P/R/S, R182D/G/H/M/S, S183G, G188A, F192M/Y, V195D, R196A/G/K/P/Q/S/T/V/Y, A199P, P200A, R202K, L220T, K222M/Y, G223C/F/H/M/N/Q/W/Y, S225EN, E226C/D/G/W, Y227C/D/G/K/T, W232F/G/H/I/K/N/P/Q/R/S/T/Y, R233H, N234R, A236E, S237D/G, W238E/G/K/P/Q/R, Q239L, V253G, D255V, A257V, E260K/R, N264D, D269N/S/V, K271A/L/Q, G276R, W282S, V285A, T295C, Y297H, G300E, N302K, G303L, Q305E/L/T, H307D/G/M/P/S, W308A/C/G/K/N/Q/R/S/T, A309E/I/M/T/V, D312E, W323M, T324L/M, S325G, S334A/H/K/L/M/Q/R/T, H335M, Y341C/E, R358A/E/G/L/N/Q/T/V, S367Q/R, S379G, and/or D390E of SEQ ID NO: 1, 2, 3, 4, 5, or 6, and/or one or more following amino acid substitutions: S420G, D422N/P/Q, and/or G424S of SEQ ID NO: 1.
The PS4 variant may have up to 25, 23, 21, 19, 17, 15, 13, or 11 amino acid deletions, additions, insertions, or substitutions compared to the amino acid sequence of SEQ ID NO: 1, 2, 3, 4, 5, or 6.
The PS4 variant may comprise additional one or more amino acid substitutions at the following positions: N33, D34, G70, G121, G134, A141, Y146, I157, S161, L178, A179, G223, S229, L307, A309, and/or 5334 of SEQ ID NO: 1 or 2. Representative substitutions may include: N33Y, D34N, G70D, G121F, G134R, A141P, Y146G, I157L, S161A, L178F, A179T, G223E, S229P, L307K, A309P, and/or S334P of SEQ ID NO: 1 or 2.
In other embodiments, the PS4 variant may have an altered thermostability compared to the amino acid sequence of SEQ ID NO: 1, residues 1 to 429 of SEQ ID NO: 1, or SEQ ID NO: 2. The altered thermostability may be elevated thermostability compared to the amino acid sequence of SEQ ID NO: 1, residues 1 to 429 of SEQ ID NO: 1, or SEQ ID NO: 2. The PS4 variant that is more thermostable may comprise one or more following amino acid substitutions: A3T, I38M, G70L, Q169K/R, R182G/H, P200G, G223N, S237D, D269V, K271A/Q, S367Q/R, S379G, and/or S420G of SEQ ID NO: 1 or 2. Moreover, the PS4 variant may comprise additional one or more amino acid substitutions at following positions: G134, A141, I157, G223, H307, 5334, and/or D343 of SEQ ID NO: 1 or 2. Representative substitutions may include: G134R, A141P, I157L, G223A, H307L, S334P, and/or D343E of SEQ ID NO: 1 or 2. The PS4 variant may further comprise one or more amino acid substitutions at following positions: N33, D34, K71, L178, and/or A179 of SEQ ID NO: 1 or 2. Representative substitutions may include: N33Y, D34N, K71R, L178F, and/or A179T of SEQ ID NO: 1 or 2.
In yet other embodiments, the PS4 variant that may have an altered endo-amylase activity, an altered exo-amylase activity, and/or an altered ratio of exo- to endo-amylase activity compared to the amino acid sequence of SEQ ID NO: 1, residues 1 to 429 of SEQ ID NO: 1, or SEQ ID NO: 2. The PS4 variant may comprise one or more following amino acid substitutions: A3T, G69K, G70E, K71M, G73D/E, G75C/E, Y122A, C140A, G144E, Y146D/E, N148K, C150A, D151A/V/W, G153A, G158I/P, S161G/H/K/P/R, Q169D/E/G/N/R, R196Q/S/T, R202K, 5208T, S213N, K222M, G223C/F/H/M/Q/W/Y, E226D, Y227D/G/K/T, S229N, W232Q/S/T, T295C, Q305T, W308A/C/G/Q/R/S/T, A3091N, W323M, T324L/M, S334A/H/M/Q, and/or R358E/L/N/Q/T/V of SEQ ID NO: 1 or 2. Moreover, the PS4 variant may comprise additional one or more amino acid substitutions at following positions: W66, I157, E160, S161, R196, W221, K222, E226, D254, Q305, H307, and/or W308 of SEQ ID NO: 1 or 2. Representative substitutions may include: W66S, E160F/G/L/P/R/S, S161A, R196H/P/V, W221A, K222T, Q305T/L, H307L, and/or W308A/L/S of SEQ ID NO: 1 or 2. In one embodiment, a PS4 variant additional having an amino acid substitution in position 141 is provided. In one aspect, a PS4 variant additional having the amino acid substitution A141P is provided. In one embodiment, a PS4 variant additional having an amino acid substitution in position 223 is provided. In one embodiment, a PS4 variant additional having the amino acid substitution G223A is provided. In one embodiment, a PS4 variant further having amino acid substitution(s) in one or more of the following position(s) selected from the group consisting of 134, 141, 223, 157, 307, and 334 is provided. In one embodiment, a PS4 variant further having one or more of the amino acid substitution(s) selected from the group consisting of G134R, A141P, G223A, I157L, H307L, S334P, and D343E is provided. In one embodiment, a PS4 variant further having the following amino acid substitution(s) G134R, A141P, G223A, I157L, H307L, S334P, and D343E is provided. In one embodiment, a PS4 variant additional having amino acid substitution(s) in one or more of the following position(s) selected from the group consisting of 157, 158, 160, 161, and 307 is provided.
The present disclosure also relates to each and every core variant sequence or backbone as shown in TABLE 4 comprising the substitution patterns as shown for each variant in TABLE 7. The disclosure further relates to the exact recited variants as shown in TABLE 4 with the substitutions as recited in TABLE 7, i.e., the core variant sequence containing only the recited mutations or substitution patterns as shown in TABLE 7. The disclosure further relates to PS4 variants comprising the amino acid sequence of SEQ ID NO: 1, residues 1 to 429 of SEQ ID NO: 1, or SEQ ID NO: 2, and comprising the substitution patterns as shown in TABLE 7. Furthermore, the disclosure relates to PS4 variants comprising the amino acid sequence of SEQ ID NO: 1, residues 1 to 429 of SEQ ID NO: 1, or SEQ ID NO: 2, and containing only the substitution patterns as shown in TABLE 7.
Nucleic acids encoding the polypeptides above also are provided. In one embodiment, a nucleic acid encoding a PS4 variant is a cDNA encoding the protein comprising an amino acid sequence of residues 1-429 of SEQ ID NO: 1. For example, the cDNA may have the corresponding sequence of the native mRNA, set forth in SEQ ID NO: 7. See GenBank Acc. No. X16732. As is well understood by one skilled in the art, the genetic code is degenerate, meaning that multiple codons in some cases may encode the same amino acid. Nucleic acids include genomic DNA, mRNA, and cDNA that encodes a PS4 variant.
2.1. PS4 Variant Characterization
Enzyme variants can be characterized by their nucleic acid and primary polypeptide sequences, by three dimensional structural modeling, and/or by their specific activity. Additional characteristics of the PS4 variant include stability, pH range, oxidation stability, and thermostability, for example. Levels of expression and enzyme activity can be assessed using standard assays known to the artisan skilled in this field. In another aspect, variants demonstrate improved performance characteristics relative to the wild-type enzyme, such as improved stability at high temperatures, e.g., 65-85° C. PS4 variants are advantageous for use in liquefaction or other processes that require elevated temperatures, such as baking. For example, a thermostable PS4 variant can degrade starch at temperatures of about 55° C. to about 85° C. or more.
An expression characteristic means an altered level of expression of the variant, when the variant is produced in a particular host cell. Expression generally relates to the amount of active variant that is recoverable from a fermentation broth using standard techniques known in this art over a given amount of time. Expression also can relate to the amount or rate of variant produced within the host cell or secreted by the host cell. Expression also can relate to the rate of translation of the mRNA encoding the variant enzyme.
A nucleic acid complementary to a nucleic acid encoding any of the PS4 variants set forth herein is provided. Additionally, a nucleic acid capable of hybridizing to the complement is provided. In another embodiment, the sequence for use in the methods and compositions described here is a synthetic sequence. It includes, but is not limited to, sequences made with optimal codon usage for expression in host organisms, such as yeast.
The PS4 variants provided herein may be produced synthetically or through recombinant expression in a host cell, according to procedures well known in the art. The expressed PS4 variant optionally is isolated prior to use. In another embodiment, the PS4 variant is purified following expression. Methods of genetic modification and recombinant production of PS4 variants are described, for example, in U.S. Pat. Nos. 7,371,552, 7,166,453; 6,890,572; and 6,667,065; and U.S. Published Application Nos. 2007/0141693; 2007/0072270; 2007/0020731; 2007/0020727; 2006/0073583; 2006/0019347; 2006/0018997; 2006/0008890; 2006/0008888; and 2005/0137111. The relevant teachings of these disclosures, including PS4-encoding polynucleotide sequences, primers, vectors, selection methods, host cells, purification and reconstitution of expressed PS4 variants, and characterization of PS4 variants, including useful buffers, pH ranges, Ca2+ concentrations, substrate concentrations and enzyme concentrations for enzymatic assays, are herein incorporated by reference.
In another embodiment, suitable host cells include a Gram positive bacterium selected from the group consisting of Bacillus subtilis, B. licheniformis, B. lentus, B. brevis, B. stearothermophilus, B. alkalophilus, B. amyloliquefaciens, B. coagulans, B. circulans, B. lautus, B. thuringiensis, Streptomyces lividans, or S. murinus; or a Gram negative bacterium, wherein said Gram negative bacterium is Escherichia coli or a Pseudomonas species. In one aspect, the host cell is a B. subtilis or B. licheniformis. In one embodiment, the host cell is B. subtilis, and the expressed protein is engineered to comprise a B. subtilis signal sequence, as set forth in further detail below. In one aspect, the host cell expresses the polynucleotide as set out in the claims.
In some embodiments, a host cell is genetically engineered to express an PS4 variant with an amino acid sequence having at least about 80%, 85%, 90%, 91%, 92%, 93%, 94%, 95%, 96%, 97%, 98% or 99% identity with the wild-type PS4. In some embodiments, the polynucleotide encoding a PS4 variant will have a nucleic acid sequence encoding the protein of SEQ ID NO: 1 or 2 or a nucleic acid sequence having at least about 80%, 85%, 90%, 95%, 96%, 97%, 98% or 99% sequence identity with a nucleic acid encoding the protein of SEQ ID NO: 1 or 2. In one embodiment, the nucleic acid sequence has at least about 80%, 85%, 90%, 95%, 96%, 97%, 98% or 99% sequence identity to the nucleic acid of SEQ ID NO: 7.
3.1. Vectors
In one aspect, the invention relates to a vector comprising a polynucleotide. In one aspect, of the invention a bacterial cell comprises the vector. In some embodiments, a DNA construct comprising a nucleic acid encoding a PS4 variant is transferred to a host cell in an expression vector that comprises regulatory sequences operably linked to a PS4 encoding sequence. The vector may be any vector that can be integrated into a fungal host cell genome and replicated when introduced into the host cell. The FGSC Catalogue of Strains, University of Missouri, lists suitable vectors. Additional examples of suitable expression and/or integration vectors are provided in Sambrook et al., M
In some embodiments, a nucleic acid encoding a PS4 variant is operably linked to a suitable promoter, which allows transcription in the host cell. The promoter may be derived from genes encoding proteins either homologous or heterologous to the host cell. Suitable non-limiting examples of promoters include cbh1, cbh2, egl1, and egl2 promoters. In one embodiment, the promoter is one that is native to the host cell. For example, when P. saccharophila is the host, the promoter is a native P. saccharophila promoter. An “inducible promoter” is a promoter that is active under environmental or developmental regulation. In another embodiment, the promoter is one that is heterologous to the host cell.
In some embodiments, the coding sequence is operably linked to a DNA sequence encoding a signal sequence. A representative signal peptide is SEQ ID NO: 8, which is the native signal sequence of the PS4 precursor. In other embodiments, the DNA encoding the signal sequence is replaced with a nucleotide sequence encoding a signal sequence from a species other than P. saccharophila. In this embodiment, the polynucleotide that encodes the signal sequence is immediately upstream and in-frame of the polynucleotide that encodes the polypeptide. The signal sequence may be selected from the same species as the host cell. In one non-limiting example, the signal sequence is a cyclodextrin glucanotransferase (CGTase; EC 2.4.1.19) signal sequence from Bacillus sp., and the PS4 variant is expressed in a B. subtilis host cell. A methionine residue may be added to the N-terminus of the signal sequence.
In additional embodiments, a signal sequence and a promoter sequence comprising a DNA construct or vector to be introduced into a fungal host cell are derived from the same source. In some embodiments, the expression vector also includes a termination sequence. In one embodiment, the termination sequence and the promoter sequence are derived from the same source. In another embodiment, the termination sequence is homologous to the host cell.
In some embodiments, an expression vector includes a selectable marker. Examples of suitable selectable markers include those that confer resistance to antimicrobial agents, e.g., hygromycin or phleomycin. Nutritional selective markers also are suitable and include amdS, argB, and pyr4. In one embodiment, the selective marker is the amdS gene, which encodes the enzyme acetamidase; it allows transformed cells to grow on acetamide as a nitrogen source. The use of an A. nidulans amdS gene as a selective marker is described in Kelley et al., EMBO J. 4: 475-479 (1985) and Penttila et al., Gene 61: 155-164 (1987).
A suitable expression vector comprising a DNA construct with a polynucleotide encoding a PS4 variant may be any vector that is capable of replicating autonomously in a given host organism or integrating into the DNA of the host. In some embodiments, the expression vector is a plasmid. In some embodiments, two types of expression vectors for obtaining expression of genes are contemplated. The first expression vector comprises DNA sequences in which the promoter, PS4 coding region, and terminator all originate from the gene to be expressed. In some embodiments, gene truncation is obtained by deleting undesired DNA sequences, e.g., DNA encoding the C-terminal starch-binding domain, to leave the domain to be expressed under control of its own transcriptional and translational regulatory sequences. The second type of expression vector is preassembled and contains sequences required for high-level transcription and a selectable marker. In some embodiments, the coding region for a PS4 gene or part thereof is inserted into this general-purpose expression vector, such that it is under the transcriptional control of the expression construct promoter and terminator sequences. In some embodiments, genes or part thereof are inserted downstream of the strong cbh1 promoter.
3.2. Transformation, Expression and Culture of Host Cells
Introduction of a DNA construct or vector into a host cell includes techniques such as transformation; electroporation; nuclear microinjection; transduction; transfection, e.g., lipofection mediated and DEAE-Dextrin mediated transfection; incubation with calcium phosphate DNA precipitate; high velocity bombardment with DNA-coated microprojectiles; and protoplast fusion. General transformation techniques are known in the art. See, e.g., Ausubel et al. (1987), supra, chapter 9; Sambrook et al. (2001), supra; and Campbell et al., Curr. Genet. 16: 53-56 (1989). The expression of heterologous protein in Trichoderma is described, for example, in U.S. Pat. No. 6,022,725; U.S. Pat. No. 6,268,328; Harkki et al., Enzyme Microb. Technol. 13: 227-233 (1991); Harkki et al., BioTechnol. 7: 596-603 (1989); EP 244,234; and EP 215,594. In one embodiment, genetically stable transformants are constructed with vector systems whereby the nucleic acid encoding a PS4 variant is stably integrated into a host cell chromosome. Transformants are then purified by known techniques.
In one non-limiting example, stable transformants including an amdS marker are distinguished from unstable transformants by their faster growth rate and the formation of circular colonies with a smooth, rather than ragged outline on solid culture medium containing acetamide. Additionally, in some cases a further test of stability is conducted by growing the transformants on solid non-selective medium, e.g., a medium that lacks acetamide, harvesting spores from this culture medium and determining the percentage of these spores that subsequently germinate and grow on selective medium containing acetamide. Other methods known in the art may be used to select transformants.
3.3. Identification of PS4 Activity
To evaluate the expression of a PS4 variant in a host cell, assays can measure the expressed protein, corresponding mRNA, or α-amylase activity. For example, suitable assays include Northern and Southern blotting, RT-PCR (reverse transcriptase polymerase chain reaction), and in situ hybridization, using an appropriately labeled hybridizing probe. Suitable assays also include measuring PS4 activity in a sample. Suitable assays of the exo-activity of the PS4 variant include, but are not limited to, the Betamyl® assay (Megazyme, Ireland). Suitable assays of the endo-activity of the PS4 variant include, but are not limited to, the Phadebas blue assay (Pharmacia and Upjohn Diagnostics AB). Assays also include HPLC analysis of liquefact prepared in the presence of the PS4 variant. HPLC can be used to measure amylase activity by separating DP-3 and DP-4 saccharides from other components of the assay.
3.4. Methods for Purifying PS4
In general, a PS4 variant produced in cell culture is secreted into the medium and may be purified or isolated, e.g., by removing unwanted components from the cell culture medium. In some cases, a PS4 variant may be recovered from a cell lysate. In such cases, the enzyme is purified from the cells in which it was produced using techniques routinely employed by those of skill in the art. Examples include, but are not limited to, affinity chromatography, ion-exchange chromatographic methods, including high resolution ion-exchange, hydrophobic interaction chromatography, two-phase partitioning, ethanol precipitation, reverse phase HPLC, chromatography on silica or on a cation-exchange resin, such as DEAE, chromatofocusing, SDS-PAGE, ammonium sulfate precipitation, and gel filtration using Sephadex G-75, for example.
A PS4 variant produced and purified by the methods described above is useful for a variety of industrial applications. In one embodiment, the PS4 variant is useful in a starch conversion process, particularly in a liquefaction process of a starch, e.g., cornstarch, wheat starch, or barley starch. The desired end-product may be any product that may be produced by the enzymatic conversion of the starch substrate. For example, the desired product may be a syrup rich in saccharides useful for fermentation, particularly maltotriose, glucose, and/or maltose. The end product then can be used directly in a fermentation process to produce alcohol for fuel or drinking (i.e., potable alcohol). The skilled artisan is aware of various fermentation conditions that may be used in the production of ethanol or other fermentation end-products. A microbial organism capable of fermenting maltotrioses and/or less complex sugars, such as S. cerevisiae or a genetically modified variant thereof, is particularly useful. Suitable genetically altered variants of S. cerevisiae particularly useful for fermenting maltotrioses include variants that express AGT1 permease (Stambuck et al., Lett. Appl. Microbiol. 43: 370-76 (2006)), MTT1 and MTT1 alt (Dietvorst et al., Yeast 22: 775-88 (2005)), or MAL32 (Dietvorst et al., Yeast 24: 27-38 (2007)). PS4 variants also are useful in compositions and methods of food preparation, where enzymes that express amylase activity at high temperatures are desired.
The desirability of using a particular PS4 variant will depend on the overall properties displayed by the PS4 variant relative to the requirements of a particular application. As a general matter, PS4 variants useful for a starch conversion process have substantial endo-amylase activity compared to wild-type PS4, and/or have a lower exo- to endo-amylase activity compared to wild-type PS4. Such PS4 variants may be particularly useful in a liquefaction process, when used alone or combination with other PS4 variants, where internal cleavage of complex branching saccharides lowers the viscosity of the substrate. Some PS4 variants useful for liquefaction, however, are expected to have an endo-amylase activity comparable or even lower than wild-type PS4. Useful PS4 variants include those with more or less exo-amylase activity than the wild-type PS4, depending on the application. Compositions may include one or a combination of PS4 variants, each of which may display a different set of properties.
4.1. Preparation of Starch Substrates
Those of skill in the art are well aware of available methods that may be used to prepare starch substrates for use in the processes disclosed herein. For example, a useful starch substrate may be obtained from tubers, roots, stems, legumes, cereals or whole grain. More specifically, the granular starch comes from plants that produce high amounts of starch. For example, granular starch may be obtained from corns, cobs, wheat, barley, rye, milo, sago, cassava, tapioca, sorghum, rice, peas, bean, banana, or potatoes. Corn contains about 60-68% starch; barley contains about 55-65% starch; millet contains about 75-80% starch; wheat contains about 60-65% starch; and polished rice contains 70-72% starch. Specifically contemplated starch substrates are cornstarch, wheat starch, and barley starch. The starch from a grain may be ground or whole and includes corn solids, such as kernels, bran and/or cobs. The starch may be highly refined raw starch or feedstock from starch refinery processes. Various starches also are commercially available. For example, cornstarch is available from Cerestar, Sigma, and Katayama Chemical Industry Co. (Japan); wheat starch is available from Sigma; sweet potato starch is available from Wako Pure Chemical Industry Co. (Japan); and potato starch is available from Nakaari Chemical Pharmaceutical Co. (Japan).
The starch substrate can be a crude starch from milled whole grain, which contains non-starch fractions, e.g., germ residues and fibers. Milling may comprise either wet milling or dry milling. In wet milling, whole grain is soaked in water or dilute acid to separate the grain into its component parts, e.g., starch, protein, germ, oil, kernel fibers. Wet milling efficiently separates the germ and meal (i.e., starch granules and protein) and is especially suitable for production of syrups. In dry milling, whole kernels are ground into a fine powder and processed without fractionating the grain into its component parts. Dry milled grain thus will comprise significant amounts of non-starch carbohydrate compounds, in addition to starch. Most ethanol comes from dry milling. Alternatively, the starch to be processed may be a highly refined starch quality, for example, at least about 90%, at least 95%, at least 97%, or at least 99.5% pure.
4.2. Gelatinization and Liquefaction of Starch
As used herein, the term “liquefaction” or “liquefy” means a process by which starch is converted to less viscous and shorter chain dextrins. This process involves gelatinization of starch simultaneously with or followed by the addition of a PS4 variant. A thermostable PS4 variant is preferably used for this application. Additional liquefaction-inducing enzymes optionally may be added.
In some embodiments, the starch substrate prepared as described above is slurried with water. The starch slurry may contain starch as a weight percent of dry solids of about 10-55%, about 20-45%, about 30-45%, about 30-40%, or about 30-35%. The α-amylase is usually supplied, for example, at about 1500 units per kg dry matter of starch. To optimize α-amylase stability and activity, the pH of the slurry may be adjusted to the optimal pH for the PS4 variant. Other α-amylases may be added and may require different optimal conditions. Bacterial α-amylase remaining in the slurry following liquefaction may be deactivated by lowering pH in a subsequent reaction step or by removing calcium from the slurry.
The slurry of starch plus the PS4 variant may be pumped continuously through a jet cooker, which is steam heated from about 85° C. to up to 105° C. Gelatinization occurs very rapidly under these conditions, and the enzymatic activity, combined with the significant shear forces, begins the hydrolysis of the starch substrate. The residence time in the jet cooker is very brief. The partly gelatinized starch may be passed into a series of holding tubes maintained at about 85-105° C. and held for about 5 min. to complete the gelatinization process. These tanks may contain baffles to discourage back mixing. As used herein, the term “secondary liquefaction” refers the liquefaction step subsequent to primary liquefaction, when the slurry is allowed to cool to room temperature. This cooling step can be about 30 minutes to about 180 minutes, e.g. about 90 minutes to 120 minutes.
4.3. Processes of Fermentation
Yeast typically from Saccharomyces spp. is added to the mash and the fermentation is ongoing for 24-96 hours, such as typically 35-60 hours. The temperature is between about 26-34° C., typically at about 32° C., and the pH is from about pH 3-6, typically around about pH 4-5.
In one embodiment, a batch fermentation process is used in a closed system, where the composition of the medium is set at the beginning of the fermentation and is not altered during the fermentation. At the beginning of the fermentation, the medium is inoculated with the desired microbial organism(s). In this method, fermentation is permitted to occur without the addition of any components to the system. Typically, a batch fermentation qualifies as a “batch” with respect to the addition of the carbon source, and attempts are often made to control factors such as pH and oxygen concentration. The metabolite and biomass compositions of the batch system change constantly up to the time the fermentation is stopped. Within batch cultures, cells progress through a static lag phase to a high growth log phase and finally to a stationary phase, where growth rate is diminished or halted. If untreated, cells in the stationary phase eventually die. In general, cells in log phase are responsible for the bulk of production of product.
A suitable variation on the standard batch system is the “fed-batch fermentation” system. In this variation of a typical batch system, the substrate is added in increments as the fermentation progresses. Fed-batch systems are useful when catabolite repression likely inhibits the metabolism of the cells and where it is desirable to have limited amounts of substrate in the medium. Measurement of the actual substrate concentration in fed-batch systems is difficult and is therefore estimated on the basis of the changes of measurable factors, such as pH, dissolved oxygen and the partial pressure of waste gases, such as CO2. Batch and fed-batch fermentations are common and well known in the art.
Continuous fermentation is an open system where a defined fermentation medium is added continuously to a bioreactor, and an equal amount of conditioned medium is removed simultaneously for processing. Continuous fermentation generally maintains the cultures at a constant high density, where cells are primarily in log phase growth. Continuous fermentation allows for the modulation of one or more factors that affect cell growth and/or product concentration. For example, in one embodiment, a limiting nutrient, such as the carbon source or nitrogen source, is maintained at a fixed rate and all other parameters are allowed to moderate. In other systems, a number of factors affecting growth can be altered continuously while the cell concentration, measured by media turbidity, is kept constant. Continuous systems strive to maintain steady state growth conditions. Thus, cell loss due to medium being drawn off should be balanced against the cell growth rate in the fermentation. Methods of modulating nutrients and growth factors for continuous fermentation processes, as well as techniques for maximizing the rate of product formation, are well known in the art of industrial microbiology.
Following the fermentation, the mash is distilled to extract the ethanol. The ethanol obtained according to the process of the disclosure may be used as, e.g., fuel ethanol; drinking ethanol, i.e., potable neutral spirits or industrial ethanol. Left over from the fermentation is the grain, which is typically used for animal feed, either in liquid form or dried. Further details on how to carry out liquefaction, saccharification, fermentation, distillation, and recovery of ethanol are well known to the skilled person. According to the process of the disclosure, the saccharification and fermentation may be carried out simultaneously or separately.
In one aspect, compositions, including food additives, food products, bakery products, improver compositions, feed products including animal feeds, etc comprising such altered PS4 variants according to the invention, such as those which have non-maltogenic exoamylase activity, as well as methods of making and using such polypeptides and the compositions are provided.
As noted above, the PS4 variant polypeptides may comprise one or more improved handling properties, preferably improved baking properties. Thus, the PS4 variant polypeptides may provide that the food products so treated have one or more of (preferably all of) a lower firmness, a higher resilience, a higher cohesiveness, a lower crumbliness or a higher foldability. Such improved handling or baking properties exhibited by the PS4 variant polypeptides are described in further detail below. In one aspect, a PS4 variant, in which the half life (t½), preferably at 60 degrees C., is increased by 15% or more, preferably 50% or more, most preferably 100% or more, compared to the amino acid sequence of SEQ ID NO: 1, residues 1 to 429 of SEQ ID NO: 1, or SEQ ID NO: 2, is provided.
In one aspect, a PS4 variant, in which a food product treated with the PS4 variant has any one or more, preferably all of the following properties: (a) lower firmness; (b) higher resilience; (c) higher cohesiveness; (d) lower crumbliness; and (e) higher foldability compared to a food product which has been treated with the amino acid sequence of SEQ ID NO: 1, residues 1 to 429 of SEQ ID NO: 1, or SEQ ID NO: 2 is provided.
In one aspect, a PS4 variant, in which the resilience, cohesiveness or foldability of the food product is independently increased by 15% or more, preferably 50% or more, most preferably 100% or more, compared to a food product which has been treated with the amino acid sequence of SEQ ID NO: 1, residues 1 to 429 of SEQ ID NO: 1, or SEQ ID NO: 2 is provided.
In one aspect, a PS4 variant, in which each of resilience cohesiveness and foldability of a food product treated with the PS4 variant is increased compared to a food product which has been treated with the amino acid sequence of SEQ ID NO: 1, residues 1 to 429 of SEQ ID NO: 1, or SEQ ID NO: 2, is provided.
In one aspect, a PS4 variant, in which the firmness or the crumbliness of the food product is independently decreased by 15% or more, preferably 50% or more, most preferably 100% or more, relative to a food product which has been treated with the amino acid sequence of SEQ ID NO: 1, residues 1 to 429 of SEQ ID NO: 1, or SEQ ID NO: 2, is provided.
In one aspect, a PS4 variant, in which each of the firmness and crumblines of a food product treated with the polypeptide is decreased compared to a food product which has been treated with the amino acid sequence of SEQ ID NO: 1, residues 1 to 429 of SEQ ID NO: 1, or SEQ ID NO: 2, is provided.
In one aspect, a PS4 variant comprising a fragment of at least 20 residues of a polypeptide as set out in the claims, in which the polypeptide has non-maltogenic exoamylase activity, is provided.
In one aspect of the invention the PS4 variants disclosed herein has non-maltogenic exoamylase activity. Such as activity may be determined by the methods described in U.S. Pat. No. 6,667,065 which is incorporated by reference herein.
In one aspect, the treatment of food products, particularly doughs and bakery products with such polypeptides, and such that the food products exhibit the desired qualities set out above are provided.
In one aspect, a process for treating a starch comprising contacting the starch with a PS4 variant as set out in any of the claims and allowing the polypeptide to generate from the starch one or more linear products, is provided. In one aspect, the use of a PS4 variant as set out in any of the claims in preparing a food or feed product, is provided. In one aspect, a process of preparing a food or feed product comprising admixing a PS4 variant as set out in any of the claims with a food or feed ingredient, is provided. In one aspect, the use, or a process, in which the food product comprises a dough or a dough product, preferably a processed dough product, is provided. In one aspect, the use or process, in which the food product is a bakery product, is provided. In one aspect, a process for making a bakery product comprising: (a) providing a starch medium; (b) adding to the starch medium a PS4 variant as set out in any of the claims; and (c) applying heat to the starch medium during or after step (b) to produce a bakery product, is provided. In one aspect, a food product, feed product, dough product or a bakery product obtained by a process as defined in the claims, is provided.
In one aspect, the use of a PS4 variant as set out in any of the claims, in a dough product to retard or reduce staling, preferably detrimental retrogradation, of the dough product, is provided.
In one aspect, the use of a PS4 variant as set out in any of claims, in a dough product to improve any one or more of firmness, resilience, cohesiveness, crumbliness or foldability of the dough product, is provided.
In one aspect, a combination of a PS4 variant as set out in any of the claims, together with any one or more of the following:
(a) maltogenic alpha-amylase also called glucan 1,4-α-maltohydrolase (EC 3.2.1.133) from Bacillus stearothermophilus, or a variant, homologue, or mutants thereof which have maltogenic alpha-amylase activity;
(b) a bakery xylanase (EC 3.2.1.8) from e.g. Bacillus sp., Aspergillus sp., Thermomyces sp. or Trichoderma sp.;
(c) α-amylase (EC 3.2.1.1) from Bacillus amyloliquefaciens or from Aspergillus sp. or a variant, homologue, or mutants thereof which have alpha-amylase activity; and
(d) a lipase such as glycolipase from Fusarium heterosporum, is provided.
The PS4 variants described here preferably comprise one or more improved handling properties compared to a parent polypeptide or a wild type polypeptide. The improved handling properties may in preferred embodiments comprise improved baking properties.
Thus, the PS4 variants are such that a food product treated with the PS4 variant polypeptide an improved handling or preferably baking property compared to a food product which has been treated with a parent polypeptide or a wild type polypeptide. The handling or baking property may be selected from the group consisting of: firmness, resilience, cohesiveness, crumbliness and foldability.
These handling properties may be tested by any means known in the art. For example, firmness, resilience and cohesiveness may be determined by analysing bread slices by Texture Profile Analysis using for example a Texture Analyser, as e.g. described in example 12.
Firmness
The PS4 variants described here are in one aspect such that a food product treated with the PS4 variant polypeptide lower firmness compared to a food product which has been treated with a parent polypeptide or a wild type polypeptide.
The firmness is in preferred embodiments inversely correlated with the softness of the food product; thus, a higher softness may reflect a lower firmness, and vice versa.
Firmness may be measured by the “Firmness Evaluation Protocol” set out in example 13.
In one aspect, the PS4 variants described herein are such that a food product treated with the PS4 variant polypeptide has a 10%, 20%, 30%, 40%, 50%, 60%, 70%, 80%, 90%, 100%, 200% or more lower firmness compared to a food product which has been treated with a parent polypeptide or a wild type polypeptide. A food product treated with the PS4 variant polypeptide may have a 1.1×, 1.5×, 2×, 3×, 4×, 5×, 6×, 7×, 8×, 9×, 10× or more lower firmness compared to a food product which has been treated with a parent polypeptide or a wild type polypeptide.
Resilience
In one aspect, the PS4 variants are such that a food product treated with the PS4 variant polypeptide has a higher resilience compared to a food product which has been treated with a parent polypeptide or a wild type polypeptide.
Resilience may be measured by the “Resilience Evaluation Protocol” set out in example 14.
Thus in one aspect, the PS4 variants described here are such that a food product treated with the PS4 variant polypeptide has a 10%, 20%, 30%, 40%, 50%, 60%, 70%, 80%, 90%, 100%, 200% or more higher resilience compared to a food product which has been treated with a parent polypeptide or a wild type polypeptide. A food product treated with the PS4 variant polypeptide may have a 1.1×, 1.5×, 2×, 3×, 4×, 5×, 6×, 7×, 8×, 9×, 10× or more higher resilience compared to a food product which has been treated with a parent polypeptide or a wild type polypeptide.
Cohesiveness
In one aspect, the PS4 variants are such that a food product treated with the PS4 variant polypeptide has higher cohesiveness compared to a food product which has been treated with a parent polypeptide or a wild type polypeptide.
Cohesiveness may be measured by the “Cohesiveness Evaluation Protocol” set out in example 15.
Thus in one aspect, the PS4 variants described here are such that a food product treated with the PS4 variant polypeptide has a 10%, 20%, 30%, 40%, 50%, 60%, 70%, 80%, 90%, 100%, 200% or more higher cohesiveness compared to a food product which has been treated with a parent polypeptide or a wild type polypeptide. A food product treated with the PS4 variant polypeptide may have a 1.1×, 1.5×, 2×, 3×, 4×, 5×, 6×, 7×, 8×, 9×, 10× or more higher cohesiveness compared to a food product which has been treated with a parent polypeptide or a wild type polypeptide.
Crumbliness
In one aspect, the PS4 variants described here are such that a food product treated with the PS4 variant polypeptide has lower crumbliness compared to a food product which has been treated with a parent polypeptide or a wild type polypeptide.
Crumbliness may be measured by the “Crumbliness Evaluation Protocol” set out in example 16.
Thus in one aspect, the PS4 variants described here are such that a food product treated with the PS4 variant polypeptide has a 10%, 20%, 30%, 40%, 50%, 60%, 70%, 80%, 90%, 100%, 200% or more lower crumbliness compared to a food product which has been treated with a parent polypeptide or a wild type polypeptide. A food product treated with the PS4 variant polypeptide may have a 1.1×, 1.5×, 2×, 3×, 4×, 5×, 6×, 7×, 8×, 9×, 10× or more lower crumbliness compared to a food product which has been treated with a parent polypeptide or a wild type polypeptide.
Foldability
In one aspect, the PS4 variants described here are such that a food product treated with the PS4 variant polypeptide has higher foldability compared to a food product which has been treated with a parent polypeptide or a wild type polypeptide.
Foldability is preferably measured by the “Foldability Evaluation Protocol” set out in example 17.
Thus, the PS4 variants described here are such that a food product treated with the PS4 variant polypeptide has a 10%, 20%, 30%, 40%, 50%, 60%, 70%, 80%, 90%, 100%, 200% or more higher foldability compared to a food product which has been treated with a parent polypeptide or a wild type polypeptide. A food product treated with the PS4 variant polypeptide may have a 1.1×, 1.5×, 2×, 3×, 4×, 5×, 6×, 7×, 8×, 9×, 10× or more higher foldability compared to a food product which has been treated with a parent polypeptide or a wild type polypeptide.
In one aspect, the use of the PS4 variant polypeptides described here in combination with a xylanase for improving foldability are provided.
Further, a method for preparing a food product, the method comprising: (a) obtaining a non-maltogenic exoamylase; (b) introducing a mutation at any one or more of the positions of the non-maltogenic exoamylase as set out in this document; (c) admixing the resulting polypeptide with a food ingredient is provided.
The PS4 variant polypeptides may be used to enhance the volume of bakery products such as bread. While not wishing to be bound by any particular theory, we believe that this results from the reduction in viscosity of the dough during heating (such as baking) as a result of the amylase shortening amylose molecules. This enables the carbon dioxide generated by fermentation to increase the size of the bread with less hindrance.
Thus, food products comprising or treated with PS4 variant polypeptides are expanded in volume when compared to products which have not been so treated, or treated with parent polypeptides. In other words, the food products have a larger volume of air per volume of food product. Alternatively, or in addition, the food products treated with PS4 variant polypeptides have a lower density, or weight (or mass) per volume ratio. In particularly preferred embodiments, the PS4 variant polypeptides are used to enhance the volume of bread. Volume enhancement or expansion is beneficial because it reduces the gumminess or starchiness of foods. Light foods are preferred by consumers, and the customer experience is enhanced. In preferred embodiments, the use of PS4 variant polypeptides enhances the volume by 10%, 20%, 30% 40%, 50% or more.
The PS4 variant polypeptides and nucleic acids described here may be used as—or in the preparation of—a food. In particular, they may be added to a food, i.e., as a food additive. The term “food” is intended to include both prepared food, as well as an ingredient for a food, such as a flour. In a preferred aspect, the food is for human consumption. The food may be in the form of a solution or as a solid—depending on the use and/or the mode of application and/or the mode of administration.
The PS4 variant polypeptides and nucleic acids may be used as a food ingredient. As used herein the term “food ingredient” includes a formulation, which is or can be added to functional foods or foodstuffs and includes formulations which can be used at low levels in a wide variety of products that require, for example, acidifying or emulsifying. The food ingredient may be in the from of a solution or as a solid—depending on the use and/or the mode of application and/or the mode of administration.
The PS4 variant polypeptides and nucleic acids disclosed here may be—or may be added to—food supplements. The PS4 variant polypeptides and nucleic acids disclosed here may be—or may be added to—functional foods. As used herein, the term “functional food” means food which is capable of providing not only a nutritional effect and/or a taste satisfaction, but is also capable of delivering a further beneficial effect to consumer. Although there is no legal definition of a functional food, most of the parties with an interest in this area agree that they are foods marketed as having specific health effects.
The PS4 variant polypeptides may also be used in the manufacture of a food product or a foodstuff. Typical foodstuffs include dairy products, meat products, poultry products, fish products and dough products. The dough product may be any processed dough product, including fried, deep fried, roasted, baked, steamed and boiled doughs, such as steamed bread and rice cakes. In highly preferred embodiments, the food product is a bakery product.
Preferably, the foodstuff is a bakery product. Typical bakery (baked) products include bread—such as loaves, rolls, buns, bagels, pizza bases etc. pastry, pretzels, tortillas, cakes, cookies, biscuits, crackers etc.
The food products preferably benefit from one or more of the improved handling or baking properties of the PS4 variant polypeptides described here. The improved handling or baking property may be selected from the group consisting of: improved firmness, improved resilience, improved cohesiveness, improved crumbliness and improved foldability.
Further in one aspect, a method of modifying a food additive comprising a non-maltogenic exoamylase, the method comprising introducing a mutation at any one or more of the positions of the non-maltogenic exoamylase as set out in this document is provided. The same method can be used to modify a food ingredient, or a food supplement, a food product, or a foodstuff.
In one aspect, the use of PS4 variant polypeptides that are capable of retarding the staling of starch media, such as starch gels are provided. The PS4 variant polypeptides are especially capable of retarding the detrimental retrogradation of starch.
Most starch granules are composed of a mixture of two polymers: an essentially linear amylose and a highly branched amylopectin. Amylopectin is a very large, branched molecule consisting of chains of α-D-glucopyranosyl units joined by (1-4) linkages, wherein said chains are attached by α-D-(1-6) linkages to form branches. Amylopectin is present in all natural starches, constituting about 75% of most common starches. Amylose is essentially a linear chain of (1-4) linked α-D-glucopyranosyl units having few α-D-(1-6) branches. Most starches contain about 25% amylose.
Starch granules heated in the presence of water undergo an order-disorder phase transition called gelatinization, where liquid is taken up by the swelling granules. Gelatinization temperatures vary for different starches. Upon cooling of freshly baked bread the amylose fraction, within hours, retrogrades to develop a network. This process is beneficial in that it creates a desirable crumb structure with a low degree of firmness and improved slicing properties. More gradually crystallisation of amylopectin takes place within the gelatinised starch granules during the days after baking. In this process amylopectin is believed to reinforce the amylose network in which the starch granules are embedded. This reinforcement leads to increased firmness of the bread crumb. This reinforcement is one of the main causes of bread staling.
It is known that the quality of baked products gradually deteriorates during storage As a consequence of starch recystallisation (also called retrogradation), the water-holding capacity of the crumb is changed with important implications on the organoleptic and dietary properties. The crumb loses softness and elasticity and becomes firm and crumbly. The increase in crumb firmness is often used as a measure of the staling process of bread.
The rate of detrimental retrogradation of amylopectin depends on the length of the side chains of amylopectin. Thus, enzymatic hydrolysis of the amylopectin side chains, for example, by PS4 variant polypeptides having non-maltogenic exoamylase activity, can markedly reduce their crystallisation tendencies.
Accordingly, the use of PS4 variant polypeptides as described here when added to the starch at any stage of its processing into a food product e.g., before during or after baking into bread can retard or impede or slow down the retrogradation. Such use is described in further detail below.
In one aspect, a method of improving the ability of a non-maltogenic exoamylase to prevent staling, preferably detrimental retrogradation, of a dough product, the method comprising introducing a mutation at any one or more of the positions of the non-maltogenic exoamylase as set out in this document are provided.
For evaluation of the antistaling effect of the PS4 variant polypeptides such a PS4 variant having non-maltogenic exoamylase activity described here, the crumb firmness can be measured 1, 3 and 7 days after baking by means of an Instron 4301 Universal Food Texture Analyzer or similar equipment known in the art.
Another method used traditionally in the art and which is used to evaluate the effect on starch retrogradation of a PS4 variant polypeptide having such as a variant having exoamylase activity is based on DSC (differential scanning calorimetry). Here, the melting enthalpy of retrograded amylopectin in bread crumb or crumb from a model system dough baked with or without enzymes (control) is measured. The DSC equipment applied in the described examples is a Mettler-Toledo DSC 820 run with a temperature gradient of 10° C. per min. from 20 to 95° C. For preparation of the samples 10-20 mg of crumb are weighed and transferred into Mettler-Toledo aluminium pans which then are hermetically sealed.
The model system doughs used in the described examples contain standard wheat flour and optimal amounts of water or buffer with or without the PS4 variant. They are mixed in a 10 or 50 g Brabender Farinograph for 6 or 7 min., respectively. Samples of the doughs are placed in glass test tubes (15*0.8 cm) with a lid. These test tubes are subjected to a baking process in a water bath starting with 30 min. incubation at 33° C. followed by heating from 33 to 95° C. with a gradient of 1.1° C. per min. and finally a 5 min. incubation at 95° C. Subsequently, the tubes are stored in a thermostat at 20° C. prior to DSC analysis.
In one embodiment, the PS4 variants described here have a reduced melting enthalpy, compared to the control. In a further embodiment, the PS4 variants have a 10% or more reduced melting enthalpy. In yet a further aspect, they have a 20% or more, 30%, 40%, 50%, 60%, 70%, 80%, 90% or more reduced melting enthalpy when compared to the control.
In one aspect, the use of PS4 variant polypeptides in the preparation of food products, in particular, starch products is provided. The method comprises forming the starch product by adding a non-maltogenic exoamylase enzyme such as a PS4 variant polypeptide, to a starch medium. If the starch medium is a dough, then the dough is prepared by mixing together flour, water, the non-maltogenic exoamylase which is a PS4 variant polypeptide and optionally other possible ingredients and additives.
The term “starch” should be taken to mean starch per se or a component thereof, especially amylopectin. The term “starch medium” means any suitable medium comprising starch. The term “starch product” means any product that contains or is based on or is derived from starch. Preferably, the starch product contains or is based on or is derived from starch obtained from wheat flour. The term “flour” as used herein is a synonym for the finely-ground meal of wheat or other grain. Preferably, however, the term means flour obtained from wheat per se and not from another grain. Thus, and unless otherwise expressed, references to “wheat flour” as used herein preferably mean references to wheat flour per se as well as to wheat flour when present in a medium, such as a dough.
A preferred flour is wheat flour or rye flour or mixtures of wheat and rye flour. However, dough comprising flour derived from other types of cereals such as for example from rice, maize, barley, and durra are also contemplated. Preferably, the starch product is a bakery product. More preferably, the starch product is a bread product. Even more preferably, the starch product is a baked farinaceous bread product. The term “baked farinaceous bread product” refers to any baked product based on a dough obtainable by mixing flour, water, and a leavening agent under dough forming conditions. Further components can of course be added to the dough mixture.
Thus, if the starch product is a baked farinaceous bread product, then the process comprises mixing—in any suitable order—flour, water, and a leavening agent under dough forming conditions and further adding a PS4 variant polypeptide, optionally in the form of a premix. The leavening agent may be a chemical leavening agent such as sodium bicarbonate or any strain of Saccharomyces cerevisiae (Baker's Yeast).
The PS4 variant polypeptide can be added together with any dough ingredient including the water or dough ingredient mixture or with any additive or additive mixture. The dough can be prepared by any conventional dough preparation method common in the baking industry or in any other industry making flour dough based products.
Baking of farinaceous bread products such as for example white bread, bread made from bolted rye flour and wheat flour, rolls and the like is typically accomplished by baking the bread dough at oven temperatures in the range of from 180 to 250 C for about 15 to 60 minutes. During the baking process a steep temperature gradient (200 120 C) is prevailing in the outer dough layers where the characteristic crust of the baked product is developed. However, owing to heat consumption due to steam generation, the temperature in the crumb is only close to 100 C at the end of the baking process.
A process for making a bread product comprising: (a) providing a starch medium; (b) adding to the starch medium a PS4 variant polypeptide as described in this document; and (c) applying heat to the starch medium during or after step (b) to produce a bread product is provided. A process for making a bread product comprising adding to a starch medium a PS4 variant polypeptide as described is also provided.
In one aspect, the PS4 variant polypeptide can be added as a liquid preparation or as a dry pulverulent composition either comprising the enzyme as the sole active component or in admixture with one or more additional dough ingredient or dough additive.
In a further aspect, the improver compositions, which include bread improving compositions and dough improving compositions are provided. These comprise a PS4 variant polypeptide, optionally together with a further ingredient, or a further enzyme, or both.
In one aspect, an improver composition for a dough, in which the improver composition comprises a PS4 variant as set out in any of the claims, and at least one further dough ingredient or dough additive, is provided.
In one aspect, a composition comprising a flour and a PS4 variant as set out in any of the claims, is provided.
In a further aspect, the use of such a bread and dough improving compositions in baking is provided. In a further aspect, a baked product or dough obtained from the bread improving composition or dough improving composition is provided. In another aspect, a baked product or dough obtained from the use of a bread improving composition or a dough improving composition is provided.
A dough may be prepared by admixing flour, water, a dough improving composition comprising PS4 variant polypeptide (as described above) and optionally other ingredients and additives.
The dough improving composition can be added together with any dough ingredient including the flour, water or optional other ingredients or additives. The dough improving composition can be added before the flour or water or optional other ingredients and additives. The dough improving composition can be added after the flour or water, or optional other ingredients and additives. The dough can be prepared by any conventional dough preparation method common in the baking industry or in any other industry making flour dough based products.
The dough improving composition can be added as a liquid preparation or in the form of a dry powder composition either comprising the composition as the sole active component or in admixture with one or more other dough ingredients or additive.
The amount of the PS4 variant polypeptide that is added is normally in an amount which results in the presence in the finished dough of 50 to 100,000 units per kg of flour, preferably 100 to 50,000 units per kg of flour. Preferably, the amount is in the range of 200 to 20,000 units per kg of flour. Alternatively, the PS4 variant polypeptide is added in an amount which results in the presence in the finished dough of 0.02-50 ppm of enzyme based on flour (0.02-50 mg enzyme per kg of flour), preferably 0.2-10 ppm.
In the present context, 1 unit of the non-maltogenic exoamylase is defined as the amount of enzyme which releases hydrolysis products equivalent to 1 μmol of reducing sugar per min. when incubated at 50 degrees C. in a test tube with 4 ml of 10 mg/ml waxy maize starch in 50 mM MES, 2 mM calcium chloride, pH 6.0 as described hereinafter.
The dough as described here generally comprises wheat meal or wheat flour and/or other types of meal, flour or starch such as corn flour, corn starch, maize flour, rice flour, rye meal, rye flour, oat flour, oat meal, soy flour, sorghum meal, sorghum flour, potato meal, potato flour or potato starch. The dough may be fresh, frozen, or part-baked.
The dough may be a leavened dough or a dough to be subjected to leavening. The dough may be leavened in various ways, such as by adding chemical leavening agents, e.g., sodium bicarbonate or by adding a leaven (fermenting dough), but it is preferred to leaven the dough by adding a suitable yeast culture, such as a culture of Saccharomyces cerevisiae (baker's yeast), e.g. a commercially available strain of S. cerevisiae.
The dough may comprise fat such as granulated fat or shortening. The dough may further comprise a further emulsifier such as mono- or diglycerides, sugar esters of fatty acids, polyglycerol esters of fatty acids, lactic acid esters of monoglycerides, acetic acid esters of monoglycerides, polyoxethylene stearates, or lysolecithin.
A pre-mix comprising flour together with the combination as described herein are furthermore provided. The pre-mix may contain other dough-improving and/or bread-improving additives, e.g. any of the additives, including enzymes, mentioned herein.
In order to improve further the properties of the baked product and impart distinctive qualities to the baked product further dough ingredients and/or dough additives may be incorporated into the dough. Typically, such further added components may include dough ingredients such as salt, grains, fats and oils, sugar or sweetener, dietary fibres, protein sources such as milk powder, gluten soy or eggs and dough additives such as emulsifiers, other enzymes, hydrocolloids, flavouring agents, oxidising agents, minerals and vitamins
The emulsifiers are useful as dough strengtheners and crumb softeners. As dough strengtheners, the emulsifiers can provide tolerance with regard to resting time and tolerance to shock during the proofing. Furthermore, dough strengtheners will improve the tolerance of a given dough to variations in the fermentation time. Most dough strengtheners also improve on the oven spring which means the increase in volume from the proofed to the baked goods. Lastly, dough strengtheners will emulsify any fats present in the recipe mixture.
Suitable emulsifiers include lecithin, polyoxyethylene stearat, mono- and diglycerides of edible fatty acids, acetic acid esters of mono- and diglycerides of edible fatty acids, lactic acid esters of mono- and diglycerides of edible fatty acids, citric acid esters of mono- and diglycerides of edible fatty acids, diacetyl tartaric acid esters of mono- and diglycerides of edible fatty acids, sucrose esters of edible fatty acids, sodium stearoyl-2-lactylate, and calcium stearoyl-2-lactylate.
The further dough additive or ingredient can be added together with any dough ingredient including the flour, water or optional other ingredients or additives, or the dough improving composition. The further dough additive or ingredient can be added before the flour, water, optional other ingredients and additives or the dough improving composition. The further dough additive or ingredient can be added after the flour, water, optional other ingredients and additives or the dough improving composition.
The further dough additive or ingredient may conveniently be a liquid preparation. However, the further dough additive or ingredient may be conveniently in the form of a dry composition.
In one aspect the further dough additive or ingredient is at least 1% the weight of the flour component of dough. In a further aspect, the further dough additive or ingredient is at least 2%, preferably at least 3%, preferably at least 4%, preferably at least 5%, preferably at least 6%. If the additive is a fat, then typically the fat may be present in an amount of from 1 to 5%, typically 1 to 3%, more typically about 2%.
For the commercial and home use of flour for baking and food production, it is important to maintain an appropriate level of α-amylase activity in the flour. A level of activity that is too high may result in a product that is sticky and/or doughy and therefore unmarketable. Flour with insufficient α-amylase activity may not contain enough sugar for proper yeast function, resulting in dry, crumbly bread, or baked products. Accordingly, a PS4 variant, by itself or in combination with another α-amylase(s) or another PS4 variant, may be added to the flour to augment the level of endogenous α-amylase activity in flour. The PS4 variant in this embodiment can have a temperature optimum in the presence of starch in the ranges of about 30-90° C., 40-80° C., 40-50° C., 45-65° C., or 50-60° C., for example. The pH optimum in a 1% solution of soluble starch may be between pH 4.5 to 6.0, for example.
Grains, such as barley, oats, wheat, as well as plant components, such as corn, hops, and rice, also are used for brewing, both in industry and for home brewing. The components used in brewing may be unmalted or may be malted, i.e., partially germinated, resulting in an increase in the levels of enzymes, including α-amylase. For successful brewing, adequate levels of α-amylase enzyme activity are necessary to ensure the appropriate levels of sugars for fermentation. A PS4 variant, by itself or in combination with another α-amylase(s), accordingly may be added to the components used for brewing.
As used herein, the term “flour” means milled or ground cereal grain. The term “flour” also may mean Sago or tuber products that have been ground or mashed. In some embodiments, flour may also contain components in addition to the milled or mashed cereal or plant matter. An example of an additional component, although not intended to be limiting, is a leavening agent. Cereal grains include wheat, oat, rye, and barley. Tuber products include tapioca flour, cassava flour, and custard powder. The term “flour” also includes ground corn flour, maize-meal, rice flour, whole-meal flour, self-rising flour, tapioca flour, cassava flour, ground rice, enriched flower, and custard powder.
As used herein, the term “stock” means grains and plant components that are crushed or broken. For example, barley used in beer production is a grain that has been coarsely ground or crushed to yield a consistency appropriate for producing a mash for fermentation. As used herein, the term “stock” includes any of the aforementioned types of plants and grains in crushed or coarsely ground forms. The methods described herein may be used to determine α-amylase activity levels in both flours and stock.
One or more further enzymes may be used in combination with the PS4 variant polypeptides. Such combinations may for example be added to the food, dough preparation, foodstuff or starch composition.
The further enzymes may be selected from, for example, any combination of the following: (a) Novamyl, or a variant, homologue, or mutants thereof which have maltogenic alpha-amylase activity; (b) a xylanase such as GRINDAMYL™ POWERBake 900 (Danisco A/S); (c) a bacterial α-amylase such as Max-Life U4 (Danisco A/S); and (d) a lipase such as GRINDAMYL™ POWERBake 4050 (Danisco A/S).
In one embodiment a PS4 variant polypeptide is used in combination with at least one enzyme selected from the list consisting of oxidoreductases, hydrolases, lipases, esterases, glycosidases, amylases, pullulanases, xylanases, cellulases, hemicellulases, starch degrading enzymes, proteases and lipoxygenases. In one embodiment, the composition comprises at least one PS4 variant and a maltogenic amylase from Bacillus, as disclosed in WO91/04669. One embodiment comprises a PS4 variant and flour.
Further enzymes that may be added to the dough include oxidoreductases, hydrolases, such as lipases and esterases as well as glycosidases like α-amylase, pullulanase, and xylanase. Oxidoreductases, such as for example glucose oxidase and hexose oxidase, can be used for dough strengthening and control of volume of the baked products and xylanases and other hemicellulases may be added to improve dough handling properties, crumb firmness and bread volume. Lipases are useful as dough strengtheners and crumb softeners and α-amylases and other amylolytic enzymes may be incorporated into the dough to control bread volume and further reduce crumb firmness.
Further enzymes that may be used may be selected from the group consisting of a cellulase, a hemicellulase, a starch degrading enzyme, a protease, a lipoxygenase.
A PS4 variant further can be added alone or in a combination with other amylases, including other PS4 variants, to prevent or retard staling, i.e., crumb firming of baked products. The amount of anti-staling amylase will typically be in the range of 0.01-10 mg of enzyme protein per kg of flour, e.g., 0.5 mg/kg ds. Additional anti-staling amylases that can be used in combination with a PS4 variant include an endo-amylase, e.g., a bacterial endo-amylase from Bacillus. The additional amylase can be a maltogenic α-amylase (EC 3.2.1.133), e.g., from Bacillus. Novamyl® is an exemplary maltogenic α-amylase from B. stearothermophilus strain NCIB 11837 and is described in Christophersen et al., Starch 50: 39-45 (1997). Other examples of anti-staling endo-amylases include bacterial α-amylases derived from Bacillus, such as B. licheniformis or B. amyloliquefaciens. The anti-staling amylase may be an exo-amylase, such as β-amylase, e.g., from plant sources, such as soybean, or from microbial sources, such as Bacillus.
The baking composition comprising a PS4 variant further can comprise a phospholipase. The phospholipase may have A1 or A2 activity to remove fatty acid from the phospholipids, forming a lysophospholipid. It may or may not have lipase activity, i.e., activity on triglyceride substrates. The phospholipase typically has a temperature optimum in the range of 30-90° C., e.g., 30-70° C. The added phospholipases can be of animal origin, for example, from pancreas, e.g., bovine or porcine pancreas, snake venom or bee venom. Alternatively, the phospholipase may be of microbial origin, e.g., from filamentous fungi, yeast or bacteria, such as the genus or species. Exemplary sources of phospholipases include Aspergillus, A. niger; Dictyostelium, D. discoideum; Mucor, M. javanicus, M. mucedo, M. subtilissimus; Neurospora, N. crassa; Rhizomucor, R. pusillus; Rhizopus, R. arrhizus, R. japonicus, R. stolonifer; Sclerotinia, S. libertiana; Trichophyton, T. rubrum; Whetzelinia, W. sclerotiorum; Bacillus, B. megaterium, B. subtilis; Citrobacter, C. freundii; Enterobacter, E. aerogenes, E. cloacae; Edwardsiella, E. tarda; Etwinia, E. herbicola; Escherichia, E. coli; Klebsiella, K. pneumoniae; Proteus, P. vulgaris; Providencia, P. stuartii; Salmonella, S. typhimurium; Serratia, S. liquefasciens, S. marcescens; Shigella, S. flexneri; Streptomyces, S. violeceoruber; Yersinia, Y. enterocolitica; Fusarium, and F. oxysporum (strain DSM 2672, for example).
The phospholipase is added in an amount that improves the softness of the bread during the initial period after baking, particularly the first 24 hours. The amount of phospholipase will typically be in the range of about 0.01-10 mg of enzyme protein per kg of flour, e.g., 0.1-5 mg/kg. Phospholipase activity generally will be in the range of about 20-1000 Lipase Unit (LU)/kg of flour, where a Lipase Unit is defined as the amount of enzyme required to release 1 μmol butyric acid per minute at 30° C., pH 7.0, with gum arabic as emulsifier and tributyrin as substrate.
Compositions of dough generally comprise wheat meal or wheat flour and/or other types of meal, flour or starch such as corn flour, cornstarch, rye meal, rye flour, oat flour, oatmeal, soy flour, sorghum meal, sorghum flour, potato meal, potato flour or potato starch. The dough may be fresh, frozen or par-baked. The dough can be a leavened dough or a dough to be subjected to leavening. The dough may be leavened in various ways, such as by adding chemical leavening agents, e.g., sodium bicarbonate or by adding a leaven, i.e., fermenting dough. Dough also may be leavened by adding a suitable yeast culture, such as a culture of Saccharomyces cerevisiae (baker's yeast), e.g., a commercially available strain of S. cerevisiae.
The dough may also comprise other conventional dough ingredients, e.g., proteins, such as milk powder, gluten, and soy; eggs (e.g., whole eggs, egg yolks or egg whites); an oxidant, such as ascorbic acid, potassium bromate, potassium iodate, azodicarbonamide (ADA) or ammonium persulfate; an amino acid such as L-cysteine; a sugar; or a salt, such as sodium chloride, calcium acetate, sodium sulfate or calcium sulfate. The dough further may comprise fat, e.g., triglyceride, such as granulated fat or shortening. The dough further may comprise an emulsifier such as mono- or diglycerides, diacetyl tartaric acid esters of mono- or diglycerides, sugar esters of fatty acids, polyglycerol esters of fatty acids, lactic acid esters of monoglycerides, acetic acid esters of monoglycerides, polyoxyethylene stearates, or lysolecithin. In particular, the dough can be made without addition of emulsifiers.
Optionally, an additional enzyme may be used together with the anti-staling amylase and the phospholipase. The additional enzyme may be a second amylase, such as an amyloglucosidase, a β-amylase, a cyclodextrin glucanotransferase, or the additional enzyme may be a peptidase, in particular an exopeptidase, a transglutaminase, a lipase, a cellulase, a hemicellulase, in particular a pentosanase, such as xylanase, a protease, a protein disulfide isomerase, e.g., a protein disulfide isomerase as disclosed in WO 95/00636, for example, a glycosyltransferase, a branching enzyme (1,4-α-glucan branching enzyme), a 4-α-glucanotransferase (dextrin glycosyltransferase) or an oxidoreductase, e.g., a peroxidase, a laccase, a glucose oxidase, a pyranose oxidase, a lipooxygenase, an L-amino acid oxidase or a carbohydrate oxidase. The additional enzyme(s) may be of any origin, including mammalian and plant, and particularly of microbial (bacterial, yeast or fungal) origin and may be obtained by techniques conventionally used in the art.
The xylanase is typically of microbial origin, e.g., derived from a bacterium or fungus, such as a strain of Aspergillus, in particular of A. aculeatus, A. niger (cf. WO 91/19782), A. awamori (e.g., WO 91/18977), or A. tubigensis (e.g., WO 92/01793); from a strain of Trichoderma, e.g., T. reesei, or from a strain of Humicola, e.g., H. insolens (e.g., WO 92/17573). Pentopan® and Novozym 384® are commercially available xylanase preparations produced from Trichoderma reesei. The amyloglucosidase may be an A. niger amyloglucosidase (such as AMG®). Other useful amylase products include Grindamyl® A 1000 or A 5000 (available from Grindsted Products, Denmark) and Amylase® H or Amylase® P (available from Gist-Brocades, The Netherlands). The glucose oxidase may be a fungal glucose oxidase, in particular an Aspergillus niger glucose oxidase (such as Gluzyme®). An exemplary protease is Neutrase®. An exemplary lipase can be derived from strains of Thermomyces (Humicola), Rhizomucor, Candida, Aspergillus, Rhizopus, or Pseudomonas, in particular from Thermomyces lanuginosus (Humicola lanuginosa), Rhizomucor miehei, Candida antarctica, Aspergillus niger, Rhizopus delemar or Rhizopus arrhizus, or Pseudomonas cepacia. In specific embodiments, the lipase may be Lipase A or Lipase B derived from Candida antarctica as described in WO 88/02775, for example, or the lipase may be derived from Rhizomucor miehei as described in EP 238,023, for example, or Humicola lanuginosa, described in EP 305,216, for example, or Pseudomonas cepacia as described in EP 214,761 and WO 89/01032, for example.
The process may be used for any kind of baked product prepared from dough, either of a soft or a crisp character, either of a white, light or dark type. Examples are bread, particularly white, whole-meal or rye bread, typically in the form of loaves or rolls, such as, but not limited to, French baguette-type bread, pita bread, tortillas, cakes, pancakes, biscuits, cookies, pie crusts, crisp bread, steamed bread, pizza and the like.
In another embodiment, a PS4 variant may be used in a pre-mix, comprising flour together with an anti-staling amylase, a phospholipase and a phospholipid. The pre-mix may contain other dough-improving and/or bread-improving additives, e.g., any of the additives, including enzymes, mentioned above. In one aspect, the PS4 variant is a component of an enzyme preparation comprising an anti-staling amylase and a phospholipase, for use as a baking additive.
The enzyme preparation is optionally in the form of a granulate or agglomerated powder. The preparation can have a narrow particle size distribution with more than 95% (by weight) of the particles in the range from 25 to 500 μm. Granulates and agglomerated powders may be prepared by conventional methods, e.g., by spraying the PS4 variant onto a carrier in a fluid-bed granulator. The carrier may consist of particulate cores having a suitable particle size. The carrier may be soluble or insoluble, e.g., a salt (such as NaCl or sodium sulfate), a sugar (such as sucrose or lactose), a sugar alcohol (such as sorbitol), starch, rice, corn grits, or soy.
Another aspect contemplates the enveloping of particles comprising a PS4 variant, i.e., α-amylase particles. To prepare the enveloped α-amylase particles, the enzyme is contacted with a food grade lipid in sufficient quantity to suspend all of the α-amylase particles. Food grade lipids, as used herein, may be any naturally organic compound that is insoluble in water but is soluble in non-polar organic solvents such as hydrocarbon or diethyl ether. Suitable food grade lipids include, but are not limited to, triglycerides either in the form of fats or oils that are either saturated or unsaturated. Examples of fatty acids and combinations thereof which make up the saturated triglycerides include, but are not limited to, butyric (derived from milk fat), palmitic (derived from animal and plant fat), and/or stearic (derived from animal and plant fat). Examples of fatty acids and combinations thereof which make up the unsaturated triglycerides include, but are not limited to, palmitoleic (derived from animal and plant fat), oleic (derived from animal and plant fat), linoleic (derived from plant oils), and/or linolenic (derived from linseed oil). Other suitable food grade lipids include, but are not limited to, monoglycerides and diglycerides derived from the triglycerides discussed above, phospholipids and glycolipids.
The food grade lipid, particularly in the liquid form, is contacted with a powdered form of the α-amylase particles in such a fashion that the lipid material covers at least a portion of the surface of at least a majority, e.g., 100% of the α-amylase particles. Thus, each α-amylase particle is individually enveloped in a lipid. For example, all or substantially all of the α-amylase particles are provided with a thin, continuous, enveloping film of lipid. This can be accomplished by first pouring a quantity of lipid into a container, and then slurrying the α-amylase particles so that the lipid thoroughly wets the surface of each α-amylase particle. After a short period of stirring, the enveloped α-amylase particles, carrying a substantial amount of the lipids on their surfaces, are recovered. The thickness of the coating so applied to the particles of α-amylase can be controlled by selection of the type of lipid used and by repeating the operation in order to build up a thicker film, when desired.
The storing, handling and incorporation of the loaded delivery vehicle can be accomplished by means of a packaged mix. The packaged mix can comprise the enveloped α-amylase. However, the packaged mix may further contain additional ingredients as required by the manufacturer or baker. After the enveloped α-amylase has been incorporated into the dough, the baker continues through the normal production process for that product.
The advantages of enveloping the α-amylase particles are two-fold. First, the food grade lipid protects the enzyme from thermal denaturation during the baking process for those enzymes that are heat labile. Consequently, while the α-amylase is stabilized and protected during the proving and baking stages, it is released from the protective coating in the final baked good product, where it hydrolyzes the glucosidic linkages in polyglucans. The loaded delivery vehicle also provides a sustained release of the active enzyme into the baked good. That is, following the baking process, active α-amylase is continually released from the protective coating at a rate that counteracts, and therefore reduces the rate of, staling mechanisms.
In general, the amount of lipid applied to the α-amylase particles can vary from a few percent of the total weight of the α-amylase to many times that weight, depending upon the nature of the lipid, the manner in which it is applied to the α-amylase particles, the composition of the dough mixture to be treated, and the severity of the dough-mixing operation involved.
The loaded delivery vehicle, i.e., the lipid-enveloped enzyme, is added to the ingredients used to prepare a baked good in an effective amount to extend the shelf-life of the baked good. The baker computes the amount of enveloped α-amylase, prepared as discussed above, that will be required to achieve the desired anti-staling effect. The amount of the enveloped α-amylase required is calculated based on the concentration of enzyme enveloped and on the proportion of α-amylase to flour specified. A wide range of concentrations has been found to be effective, although, as has been discussed, observable improvements in anti-staling do not correspond linearly with the α-amylase concentration, but above certain minimal levels, large increases in α-amylase concentration produce little additional improvement. The α-amylase concentration actually used in a particular bakery production could be much higher than the minimum necessary in order to provide the baker with some insurance against inadvertent under-measurement errors by the baker. The lower limit of enzyme concentration is determined by the minimum anti-staling effect the baker wishes to achieve.
A method of preparing a baked good may comprise: (a) preparing lipid-coated α-amylase particles, where substantially all of the α-amylase particles are coated; (b) mixing a dough containing flour; (c) adding the lipid-coated α-amylase to the dough before the mixing is complete and terminating the mixing before the lipid coating is removed from the α-amylase; (d) proofing the dough; and (e) baking the dough to provide the baked good, where the α-amylase is inactive during the mixing, proofing and baking stages and is active in the baked good.
The enveloped α-amylase can be added to the dough during the mix cycle, e.g., near the end of the mix cycle. The enveloped α-amylase is added at a point in the mixing stage that allows sufficient distribution of the enveloped α-amylase throughout the dough; however, the mixing stage is terminated before the protective coating becomes stripped from the α-amylase particle(s). Depending on the type and volume of dough, and mixer action and speed, anywhere from one to six minutes or more might be required to mix the enveloped α-amylase into the dough, but two to four minutes is average. Thus, several variables may determine the precise procedure. First, the quantity of enveloped α-amylase should have a total volume sufficient to allow the enveloped α-amylase to be spread throughout the dough mix. If the preparation of enveloped α-amylase is highly concentrated, additional oil may need to be added to the pre-mix before the enveloped α-amylase is added to the dough. Recipes and production processes may require specific modifications; however, good results generally can be achieved when 25% of the oil specified in a bread dough formula is held out of the dough and is used as a carrier for a concentrated enveloped α-amylase when added near the end of the mix cycle. In bread or other baked goods, particularly those having a low fat content, e.g., French-style breads, an enveloped α-amylase mixture of approximately 1% of the dry flour weight is sufficient to admix the enveloped α-amylase properly with the dough. The range of suitable percentages is wide and depends on the formula, finished product, and production methodology requirements of the individual baker. Second, the enveloped α-amylase suspension should be added to the mix with sufficient time for complete mixture into the dough, but not for such a time that excessive mechanical action strips the protective lipid coating from the enveloped α-amylase particles.
Also contemplated are compositions and methods of treating fabrics (e.g., to desize a textile) using PS4 variant. In one aspect, a method of desizing textiles, comprising contacting the PS4 variant of the invention with a textile for a time sufficient to desize the textile, is provided.
Fabric-treating methods are well known in the art (see, e.g., U.S. Pat. No. 6,077,316). For example, in one aspect, the feel and appearance of a fabric is improved by a method comprising contacting the fabric with a PS4 variant in a solution. In one aspect, the fabric is treated with the solution under pressure.
In one aspect, a PS4 variant is applied during or after the weaving of a textile, or during the desizing stage, or one or more additional fabric processing steps. During the weaving of textiles, the threads are exposed to considerable mechanical strain. Prior to weaving on mechanical looms, warp yarns are often coated with sizing starch or starch derivatives to increase their tensile strength and to prevent breaking A PS4 variant can be applied during or after the weaving to remove these sizing starch or starch derivatives. After weaving, a PS4 variant can be used to remove the size coating before further processing the fabric to ensure a homogeneous and wash-proof result.
A PS4 variant can be used alone or with other desizing chemical reagents and/or desizing enzymes to desize fabrics, including cotton-containing fabrics, as detergent additives, e.g., in aqueous compositions. A PS4 variant also can be used in compositions and methods for producing a stonewashed look on indigo-dyed denim fabric and garments. For the manufacture of clothes, the fabric can be cut and sewn into clothes or garments, which are afterwards finished. In particular, for the manufacture of denim jeans, different enzymatic finishing methods have been developed. The finishing of denim garment normally is initiated with an enzymatic desizing step, during which garments are subjected to the action of amylolytic enzymes to provide softness to the fabric and make the cotton more accessible to the subsequent enzymatic finishing steps. A PS4 variant can be used in methods of finishing denim garments (e.g., a “bio-stoning process”), enzymatic desizing and providing softness to fabrics, and/or finishing process.
The invention is further described by the following numbered paragraphs:
1. A Pseudomonas saccharophila amylase (PS4) variant, wherein the variant comprises a sequence having at least 90% sequence identity to the amino acid sequence of SEQ ID NO: 1, residues 1 to 429 of SEQ ID NO: 1, or SEQ ID NO: 2, and wherein the PS4 variant comprises one or more amino acid substitutions at the following positions: 7, 8, 32, 38, 49, 62, 63, 64, 67, 72, 73, 74, 75, 76, 104, 106, 107, 110, 112, 116, 119, 122, 123, 124, 125, 126, 128, 130, 137, 138, 140, 142, 143, 144, 148, 149, 150, 151, 154, 156, 163, 164, 168, 169, 182, 183, 192, 195, 196, 200, 202, 208, 213, 220, 222, 225, 226, 227, 232, 233, 234, 236, 237, 239, 253, 255, 257, 260, 264, 267, 269, 271, 276, 282, 285, 295, 297, 300, 302, 305, 308, 312, 323, 324, 325, 341, 358, 367, 379, and/or 390 of SEQ ID NO: 1, 2, 3, 4, 5, or 6; and/or one or more of the following amino acid substitutions: A3T, G9A, H13R, I46F, D68E, G69A/E/H/I/K/M/R/T, G70A/E/L/P/Q/S/V, K71M, G100A/S, G121I/P/R, A131T, G134C, A141S, N145S, Y146D/E, G153A/D, G158C/F/I/L/P/Q/V, S161G/H/K/P/R/TN, G166N, I170E/K/L/M/N, L178N/Q/W, A179E/N/P/R/S, A179S, G184Q, G188A, A199P, G223C/F/H/M/N/Q/W/Y, S229N, W238E/G/K/P/Q/R, G303L, H307D/E/F/G/K/M/P/Q/R/S/W/Y, A309E/I/M/T/V, S334A/H/K/L/M/Q/R/T, and/or H335M of SEQ ID NO: 1, 2, 3, 4, 5, or 6; and/or one or more amino acid substitutions at the following positions: 420, 422, and/or 424 of SEQ ID NO: 1.
2. The PS4 variant of paragraph 1 comprising a sequence having at least 95% sequence identity to the amino acid sequence of SEQ ID NO: 1, residues 1 to 429 of SEQ ID NO: 1, or SEQ ID NO: 2.
3. The PS4 variant according to any one of paragraphs 1-2 comprising one or more of the following amino acid substitutions: A3T, P7S, A8N, G9A, H13R, P32S, I38M, I46F, D49V, D62N, F63A/D/E/L/V, S64N/T, T67G/H/K/N/Q/R/V, D68E, G69A/E/H/I/K/M/R/T, G70A/E/L/P/Q/S/V, K71M, S72E/K/N/T, G73D/E/L/M/N/S/T, G74S, G75C/E/F/R/S/W/Y, E76V, G100A/S, G104N/R, G106K, V107M, L110F, D112E, N116D, N119E/G/S/Y, G121I/P/R, Y122A/E/Q/W, P123S, D124S, K125A/D/E/G/P/Q/W, E126D/N, N128E, P130S, A131T, G134C, R137C, N138D/E/S, C140A/R, A141S, D142E/G/N, P143T, G144E, N145S, Y146D/E, N148K/S, D149H/L/V, C150A, D151A/V/W, G153A/D, D154E/G/Y, F156Y, G158C/F/I/L/P/Q/V, S161G/H/K/P/R/TN, L163M, N164R, G166N, P168L, Q169D/E/G/K/N/R/V, I170E/K/L/M/N, L178N/Q/W, A179E/N/P/R/S, R182D/G/H/M/S, S183G, G184Q, G188A, F192M/Y, V195D, R196A/G/K/P/Q/S/T/V/Y, A199P, P200A/G, R202K, 5208T, S213N, L220A/T, K222M/Y, G223C/F/H/M/N/Q/W/Y, S225E/G/V, E226C/D/G/W, Y227C/D/G/K/T, S229N, W232F/G/H/I/K/L/N/P/Q/R/S/T/Y, R233H, N234R, A236E, S237D/G, W238E/G/K/P/Q/R, Q239L, V253G, D255V, A257V, E260K/R, N264D, V267I, D269N/S/V, K271A/L/Q, G276R, W282S, V285A, T295C, Y297H, G300E, N302K, G303L, Q305E/L/T, H307D/E/F/G/K/M/P/Q/R/S/W/Y, W308A/C/G/K/N/Q/R/S/T, A309E/I/M/T/V, D312E, W323M, T324A/L/M, S325G, S334A/H/K/L/M/Q/R/T, H335M, Y341C/E, R358A/E/G/L/N/Q/T/V, S367Q/R, S379G, and/or D390E of SEQ ID NO: 1, 2, 3, 4, 5, or 6, and/or one or more substitutions of S420G, D422N/P/Q, and/or G424D/S of SEQ ID NO: 1.
4. The PS4 variant according to any one of paragraphs 1-3 comprising one or more amino acid substitutions at the following positions: 7, 32, 49, 62, 63, 64, 72, 73, 74, 75, 76, 107, 110, 112, 116, 119, 122, 123, 125, 128, 130, 137, 138, 140, 142, 143, 144, 148, 149, 150, 151, 154, 156, 163, 164, 168, 169, 182, 183, 192, 195, 196, 202, 220, 222, 226, 227, 232, 233, 234, 236, 237, 239, 253, 255, 257, 260, 264, 269, 271, 276, 282, 285, 297, 300, 302, 305, 308, 312, 323, 324, 325, 341, 358, 367, and/or 379 of SEQ ID NO: 1, 2, 3, 4, 5, or 6; and/or one or more of the following amino acid substitutions: A3T, H13R, I38M, I46F, T67G/H/K/N/Q/R/V, G69A/E/H/I/K/M/R/T, G70E/L/P/Q/V, K71M, G100A/S, G104R, G106K, G121I/P/R, D124S, E126D/N, A131T, G134C, A141S, N145S, Y146D/E, G153A/D, G158C/F/I/L/P/Q/V, S161G/H/K/P/R/TN, G166N, I170E/K/L/M/N, L178N/Q/W, A179E/N/P/R/S, G188A, A199P, P200A, G223C/F/H/M/N/Q/W/Y, S225E/G/V, W238E/G/K/P/Q/R, T295C, G303L, H307D/G/M/P/S, A309E/I/M/T/V, S334A/H/K/L/M/Q/R/T, H335M, and/or D390E of SEQ ID NO: 1, 2, 3, 4, 5, or 6; and/or one or more of the amino acid substitutions S420G and/or D422/N/P/Q of SEQ ID NO: 1; and/or an amino acid substitution at position 424 of SEQ ID NO: 1.
5. The PS4 variant according to any one of paragraphs 1-4 comprising one or more of the following amino acid substitutions: A3T, P7S, H13R, P32S, I38M, I46F, D49V, D62N, F63A/D/E/L/V, S64N/T, T67G/H/K/N/Q/R/V, G69A/E/H/I/K/M/R/T, G70E/L/P/Q/V, K71M, S72E/K/N/T, G73D/E/L/M/N/S/T, G74S, G75C/E/F/R/S/W/Y, E76V, G100A/S, G104R, G106K, V107M, L110F, D112E, N116D, N119E/G/S/Y, G121I/P/R, Y122A/E/Q/W, P123S, D124S, K125A/D/E/G/P/Q/W, E126D/N, N128E, P130S, A131T, G134C, R137C, N138D/E/S, C140A/R, A141S, D142E/G/N, P143T, G144E, N145S, Y146D/E, N148K/S, D149H/L/V, C150A, D151A/V/W, G153A/D, D154E/G/Y, F156Y, G158C/F/I/L/P/Q/V, S161G/H/K/P/R/TN, L163M, N164R, G166N, P168L, Q169D/E/G/K/N/R/V, I170E/K/L/M/N, L178N/Q/W, A179E/N/P/R/S, R182D/G/H/M/S, S183G, G188A, F192M/Y, V195D, R196A/G/K/P/Q/S/T/V/Y, A199P, P200A, R202K, L220A/T, K222M/Y, G223C/F/H/M/N/Q/W/Y, S225E/G/V, E226C/D/G/W, Y227C/D/G/K/T, W232F/G/H/I/K/L/N/P/Q/R/S/T/Y, R233H, N234R, A236E, S237D/G, W238E/G/K/P/Q/R, Q239L, V253G, D255V, A257V, E260K/R, N264D, D269N/S/V, K271A/L/Q, G276R, W282S, V285A, T295C, Y297H, G300E, N302K, G303L, Q305E/L/T, H307D/G/M/P/S, W308A/C/G/K/N/Q/R/S/T, A309E/I/M/T/V, D312E, W323M, T324A/L/M, S325G, S334A/H/K/L/M/Q/R/T, H335M, Y341C/E, R358A/E/G/L/N/Q/T/V, S367Q/R, S379G, and/or D390E of SEQ ID NO: 1, 2, 3, 4, 5, or 6, and/or one or more of the following amino acid substitutions: S420G, D422N/P/Q, and/or G424D/S of SEQ ID NO: 1.
6. The PS4 variant according to any one of paragraphs 1-5 comprising one or more of the amino acid substitutions at the following positions: 49, 62, 63, 64, 72, 73, 74, 75, 76, 107, 112, 116, 119, 122, 123, 125, 128, 130, 137, 140, 143, 144, 148, 149, 150, 151, 154, 156, 163, 164, 168, 169, 182, 183, 192, 195, 196, 202, 257, 282, 285, 297, 300, 305, 308, 312, 323, and/or 325 of SEQ ID NO: 1, 2, 3, 4, 5, or 6; and/or one or more of the following amino acid substitutions: A3T, P7S, H13R, I38M, I46F, T67G/H/K/N/Q/R/V, G69A/E/H/I/K/M/R/T, G70E/L/P/Q/V, K71M, G100A/S, G104R, G106K, L110F, G121I/P/R, D124S, E126D/N, A131T, G134C, N138D/E, D142/E/G/N, N145S, Y146D/E, G153A/D, G158C/F/I/L/P/Q/V, S161G/H/K/P/R/TN, G166N, I170E/K/L/M, L178N/Q/W, A179E/N/P/R/S, G188A, A199P, P200A, L220T, K222M/Y, G223C/F/H/M/N/Q/W/Y, S225EN, E226C/D/G/W, Y227C/D/G/K/T, W232F/G/H/I/K/N/P/Q/R/S/T/Y, R233H, N234R, A236E, S237D/G, W238E/G/K/P/Q/R, Q239L, V253G, D255V, E260K/R, N264D, D269N/S/V, K271A/L/Q, G276R, T295C, N302K, G303L, H307D/G/M/P/S, A309E/I/M/T/V, T324L/M, S334A/H/K/L/M/Q/R/T, H335M, Y341C/E, R358A/E/G/L/N/Q/T/V, S367Q/R, S379G, and/or D390E of SEQ ID NO: 1, 2, 3, 4, 5, or 6; and/or one or more of the following amino acid substitutions: S420G, D422/N/P/Q, and/or G424S of SEQ ID NO: 1.
7. The PS4 variant according to any one of paragraphs 1-6 comprising one or more of the following amino acid substitutions: A3T, P7S, H13R, I38M, I46F, D49V, D62N, F63A/D/E/L/V, S64N/T, T67G/H/K/N/Q/R/V, G69A/E/H/I/K/M/R/T, G70E/L/P/Q/V, K71M, S72E/K/N/T, G73D/E/L/M/N/S/T, G74S, G75C/E/F/R/S/W/Y, E76V, G100A/S, G104R, G106K, V107M, L110F, D112E, N116D, N119E/G/S/Y, G121I/P/R, Y122A/E/Q/W, P123S, D124S, K125A/D/E/G/P/Q/W, E126D/N, N128E, P130S, A131T, G134C, R137C, N138D/E, C140A/R, D142E/G/N, P143T, G144E, N145S, Y146D/E, N148K/S, D149H/L/V, C150A, D151A/V/W, G153A/D, D154E/G/Y, F156Y, G158C/F/I/L/P/Q/V, S161G/H/K/P/R/TN, L163M, N164R, G166N, P168L, Q169E/G/K/N/R/V, I170E/K/L/M, L178N/Q/W, A179E/N/P/R/S, R182D/G/H/M/S, S183G, G188A, F192M/Y, V195D, R196A/G/K/P/Q/S/T/V/Y, A199P, P200A, R202K, L220T, K222M/Y, G223C/F/H/M/N/Q/W/Y, S225EN, E226C/D/G/W, Y227C/D/G/K/T, W232F/G/H/I/K/N/P/Q/R/S/T/Y, R233H, N234R, A236E, S237D/G, W238E/G/K/P/Q/R, Q239L, V253G, D255V, A257V, E260K/R, N264D, D269N/S/V, K271A/L/Q, G276R, W282S, V285A, T295C, Y297H, G300E, N302K, G303L, Q305E/L/T, H307D/G/M/P/S, W308A/C/G/K/N/Q/R/S/T, A309E/I/M/T/V, D312E, W323M, T324L/M, S325G, S334A/H/K/L/M/Q/R/T, H335M, Y341C/E, R358A/E/G/L/N/Q/T/V, S367Q/R, S379G, and/or D390E of SEQ ID NO: 1, 2, 3, 4, 5, or 6, and/or one or more of the following amino acid substitutions: S420G, D422N/P/Q, and/or G424S of SEQ ID NO: 1.
8. The PS4 variant according to any one of paragraphs 1-7 comprising additional one or more amino acid substitutions at the following positions: N33, D34, G70, G121, G134, A141, Y146, I157, S161, L178, A179, G223, S229, L307, A309, and/or 5334 of SEQ ID NO: 1 or 2.
9. The PS4 variant according to any one of paragraphs 1-8 comprising one or more of the following amino acid substitutions: N33Y, D34N, G70D, G121F, G134R, A141P, Y146G, I157L, S161A, L178F, A179T, G223E, S229P, L307K, A309P, and/or S334P of SEQ ID NO: 1 or 2.
10. The PS4 variant according to any one of paragraphs 1-9, wherein the PS4 variant has up to 25 amino acid deletions, additions, insertions, or substitutions compared to the amino acid sequence of SEQ ID NO: 1, 2, 3, 4, 5, or 6.
11. The PS4 variant according to any one of paragraphs 1-10, wherein the PS4 variant has an altered thermostability compared to the amino acid sequence of SEQ ID NO: 1, residues 1 to 429 of SEQ ID NO: 1, or SEQ ID NO: 2.
12. The PS4 variant according to any one of paragraphs 1-11, wherein the PS4 variant is more thermostable than the amino acid sequence of SEQ ID NO: 1, residues 1 to 429 of SEQ ID NO: 1, or SEQ ID NO: 2.
13. The PS4 variant according to paragraph 12, wherein the PS4 variant comprises one or more of the following amino acid substitutions: A3T, I38M, G70L, Q169K/R, R182G/H, P200G, G223N, S237D, D269V, K271A/Q, S367Q/R, S379G, and/or S420G of SEQ ID NO: 1 or 2.
14. The PS4 variant according to paragraph 12, wherein the PS4 variant comprises additional one or more amino acid substitutions at the following positions: G134, A141, I157, G223, H307, S334, and/or D343 of SEQ ID NO: 1 or 2.
15. The PS4 variant according to paragraph 14, wherein the PS4 variant comprises one or more of the following amino acid substitutions: G134R, A141P, I157L, G223A, H307L, S334P, and/or D343E of SEQ ID NO: 1 or 2.
16. The PS4 variant according to paragraph 14, wherein the PS4 variant further comprises one or more amino acid substitutions at the following positions: N33, D34, K71, L178, and/or A179 of SEQ ID NO: 1 or 2.
17. The PS4 variant according to paragraph 16, wherein the PS4 variant comprises one or more following amino acid substitutions: N33Y, D34N, K71R, L178F, and/or A179T of SEQ ID NO: 1 or 2.
18. The PS4 variant according to any one of paragraphs 1-17, wherein the PS4 variant has an altered endo-amylase activity, an altered exo-amylase activity, and/or an altered ratio of exo- to endo-amylase activity compared to the amino acid sequence of SEQ ID NO: 1, residues 1 to 429 of SEQ ID NO: 1, or SEQ ID NO: 2.
19. The PS4 variant according to paragraph 18, wherein the PS4 variant comprises one or more of the following amino acid substitutions: A3T, G69K, G70E, K71M, G73D/E, G75C/E, Y122A, C140A, G144E, Y146D/146E, N148K, C150A, D151A/V/W, G153A, G158I/P, S161G/H/K/P/R, Q169D/E/G/N/R, R196Q/S/T, R202K, 5208T, S213N, K222M, G223C/F/H/M/Q/W/Y, E226D, Y227D/G/K/T, S229N, W232Q/S/T, T295C, Q305T, W308A/C/G/Q/R/S/T, A309I/V, W323M, T324L/M, S334A/H/M/Q, and/or R358E/L/N/Q/TN of SEQ ID NO: 1 or 2.
20. The PS4 variant according to paragraph 18, wherein the PS4 variant has an increased endo-amylase activity or a decreased ratio of exo- to endo-amylase activity compared to the amino acid sequence of SEQ ID NO: 1, residues 1 to 429 of SEQ ID NO: 1, or SEQ ID NO: 2.
21. The PS4 variant according to paragraph 18, wherein the PS4 variant comprises one or more following amino acid substitutions: G69K, G73D/E, Y122A, C140A, C150A, G153A, G158I/P, S161G/H/K/P/R, Q169R, S208T, S229N, T295C, Q305T, and/or R358E/L/Q/T/V of SEQ ID NO: 1 or 2.
22. The PS4 variant according to paragraph 18, wherein the PS4 variant has an increased exo-amylase activity or an increased ratio of exo- to endo-amylase activity compared to the amino acid sequence of SEQ ID NO: 1, residues 1 to 429 of SEQ ID NO: 1, or SEQ ID NO: 2.
23. The PS4 variant according to paragraph 18, wherein the PS4 variant comprises one or more of the following amino acid substitutions: A3T, G70E, K71M, G75C/E, G144E, Y146D/E, N148K, D151A/V/W, Q169D/E/G/N, R196Q/S/T, R202K, S213N, K222M, G223C/F/H/M/Q/W/Y, E226D, Y227D/G/K/T, W232Q/S/T, W308A/C/G/Q/R/S/T, A3091/V, W323M, T324L/M, S334A/H/M/Q, and/or R358N of SEQ ID NO: 1 or 2.
24. The PS4 variant according to paragraph 18, wherein the PS4 variant comprises additional one or more amino acid substitutions at the following positions: W66, I157, E160, S161, R196, W221, K222, E226, D254, Q305, H307, and/or W308 of SEQ ID NO: 1 or 2.
25. The PS4 variant according to paragraph 24, wherein the PS4 variant comprises one or more of the following amino acid substitutions: W66S, E160F/G/L/P/R/S, S161A, R196H/P/V, W221A, K222T, Q305T/L, H307L, and/or W308A/L/S of SEQ ID NO: 1 or 2.
26. The PS4 variant according to paragraph 20, wherein the PS4 variant comprises additional one or more of the following amino acid substitutions: W66S, R196H/P/V, W221A, K222T, H307L, and/or W308 of SEQ ID NO: 1 or 2.
27. The PS4 variant according to paragraph 22, wherein the PS4 variant comprises additional one or more of the following amino acid substitutions: E160F/G/L/P/R/S, S161A, and/or Q305T/L of SEQ ID NO: 1 or 2.
28. The PS4 variant according to any one of paragraphs 1-27 additional having an amino acid substitution in position 141.
29. The PS4 variant according to any one of paragraphs 1-28 additional having the amino acid substitution A141P.
30. The PS4 variant according to any one of paragraphs 1-29 additional having an amino acid substitution in position 223.
31. The PS4 variant according to any one of paragraphs 1-30 additional having the amino acid substitution G223A.
32. The PS4 variant according to any one of paragraphs 1-31 further having amino acid substitution(s) in one or more of the following position(s) selected from the group consisting of 134, 141, 223, 157, 307, and 334.
33. The PS4 variant according to any one of paragraphs 1-32 further having one or more of the amino acid substitution(s) selected from the group consisting of G134R, A141P, G223A, I157L, H307L, S334P, and D343E.
34. The PS4 variant according to any one of paragraphs 1-33 further having the following amino acid substitution(s) G134R, A141P, G223A, I157L, H307L, S334P, and D343E.
35. The PS4 variant according to any one of paragraphs 1-34 additional having amino acid substitution(s) in one or more of the following position(s) selected from the group consisting of 157, 158, 160, 161, and 307.
36. The PS4 variant according to any one of paragraphs 1-35, in which the half life (t½), preferably at 60 degrees C., is increased by 15% or more, preferably 50% or more, most preferably 100% or more, compared to the amino acid sequence of SEQ ID NO: 1, residues 1 to 429 of SEQ ID NO: 1, or SEQ ID NO: 2.
37. The PS4 variant according to any one of paragraphs 1-30, in which a food product treated with the PS4 variant has any one or more, preferably all of the following properties: (a) lower firmness; (b) higher resilience; (c) higher cohesiveness; (d) lower crumbliness; and (e) higher foldability compared to a food product which has been treated with the amino acid sequence of SEQ ID NO: 1, residues 1 to 429 of SEQ ID NO: 1, or SEQ ID NO: 2.
38. The PS4 variant according to any one of paragraphs 1-30, in which the resilience, cohesiveness or foldability of the food product is independently increased by 15% or more, preferably 50% or more, most preferably 100% or more, compared to a food product which has been treated with the amino acid sequence of SEQ ID NO: 1, residues 1 to 429 of SEQ ID NO: 1, or SEQ ID NO: 2.
39. The PS4 variant according to any one of paragraphs 37 or 38, in which each of resilience cohesiveness and foldability of a food product treated with the PS4 variant is increased compared to a food product which has been treated with the amino acid sequence of SEQ ID NO: 1, residues 1 to 429 of SEQ ID NO: 1, or SEQ ID NO: 2.
40. The PS4 variant according to paragraph 39, in which the firmness or the crumbliness of the food product is independently decreased by 15% or more, preferably 50% or more, most preferably 100% or more, relative to a food product which has been treated with the amino acid sequence of SEQ ID NO: 1, residues 1 to 429 of SEQ ID NO: 1, or SEQ ID NO: 2
41. The PS4 variant according to any one of paragraphs 37 or 40, in which each of the firmness and crumblines of a food product treated with the polypeptide is decreased compared to a food product which has been treated with the amino acid sequence of SEQ ID NO: 1, residues 1 to 429 of SEQ ID NO: 1, or SEQ ID NO: 2
42. The PS4 variant comprising a fragment of at least 20 residues of a polypeptide according to any preceding paragraph, in which the polypeptide has non-maltogenic exoamylase activity.
43. Use of a PS4 variant as set out in any preceding paragraph as a food or feed additive.
44. A process for treating a starch comprising contacting the starch with a PS4 variant as set out in any of paragraphs 1 to 42 and allowing the polypeptide to generate from the starch one or more linear products.
45. Use of a PS4 variant as set out in any of paragraphs 1 to 42 in preparing a food or feed product.
46. A process of preparing a food or feed product comprising admixing a PS4 variant as set out in any of paragraphs 1 to 42 with a food or feed ingredient.
47. Use according to paragraph 45, or a process according to paragraph 46, in which the food product comprises a dough or a dough product, preferably a processed dough product.
48. A use or process according to any of paragraphs 43 to 47, in which the food product is a bakery product.
49. A process for making a bakery product comprising: (a) providing a starch medium; (b) adding to the starch medium a PS4 variant as set out in any of paragraphs 1 to 42; and (c) applying heat to the starch medium during or after step (b) to produce a bakery product.
50. A food product, feed product, dough product or a bakery product obtained by a process according to any of paragraphs 43 to 49.
51. An improver composition for a dough, in which the improver composition comprises a PS4 variant as set out in any of paragraphs 1 to 42, and at least one further dough ingredient or dough additive.
52. A composition comprising a flour and a PS4 variant as set out in any of paragraphs 1 to 42.
53. Use of a PS4 variant as set out in any of paragraphs 1 to 42, in a dough product to retard or reduce staling, preferably detrimental retrogradation, of the dough product.
54. Use of a PS4 variant as set out in any of paragraphs 1 to 42, in a dough product to improve any one or more of firmness, resilience, cohesiveness, crumbliness or foldability of the dough product.
55. A combination of a PS4 variant as set out in any of paragraphs 1 to 42, together with any one or more of the following:
56. A method of desizing textiles, comprising contacting the PS4 variant of paragraph 1 with a textile for a time sufficient to desize the textile.
57. A polynucleotide that encodes a polypeptide according to any one of paragraphs 1 to 42.
58. A vector comprising the polynucleotide of paragraph 57.
59. A bacterial cell comprising the vector of paragraph 58.
60. A host cell that expresses the polynucleotide of paragraph 57.
61. The host cell of paragraph 60, wherein the host cell is a B. subtilis or B. licheniformis.
62. A starch processing composition comprising the PS4 variant of paragraph 1.
63. A method of baking, comprising adding the PS4 variant of paragraph 1 to a substance to be baked, and baking the substance.
The invention will now be further described by way of the following non-limiting examples.
Determination of thermal melting points. Differential scanning calorimetry was used to characterize the thermal unfolding midpoint (Tm) of wild-type PS4 and the PS4 variants: CF135 (SEQ ID NO: 3 with residues 419-429 of SEQ ID NO:1 fused at the C-terminus), CF143 (SEQ ID NO: 4 with residues 419-429 of SEQ ID NO:1 fused at the C-terminus), CF149 (SEQ ID NO: 5 with residues 419-429 of SEQ ID NO:1 fused at the C-terminus), and CF154 (SEQ ID NO: 6 with residues 419-429 of SEQ ID NO:1 fused at the C-terminus). The Tm was used as an indicator of the thermal stability of the various enzymes. Excess heat capacity curves were measured using an ultrasensitive scanning high-throughput microcalorimeter, VP-Cap DSC (MicroCal, Inc., Northampton, Mass.). Approximately 500 μL of 500 ppm of protein was needed per DSC run, and the samples were scanned over a 30-120° C. temperature range using a scan rate of 200° C./hr. The same sample was then rescanned to check the reversibility of the process. For the wild-type and variant proteins, the thermal unfolding process was irreversible. The buffer was 10 mM sodium acetate, pH 5.5, with 0.002% Tween-20. Tm values for the wild-type PS4 and PS4 variants, as well as the increase in the Tm due to the mutations (ΔTm), are shown in TABLE 1.
All the PS4 variants showed an increase in the thermal unfolding midpoint relative to the wild-type PS4. The Tm for the wild-type PS4 relative to the mutations was wild-type PS4<PS4 CF 135<PS4 CF143<PS4 CF149<PS4 CF154.
Measurement of thermostability. Alternatively, the thermostability of a given PS4 variant was evaluated by measuring its half-life under an elevated temperature, because heat inactivation follows a 1st order reaction. For this, the residual amylase activity of a given variant was measured after it was incubated for 1-30 minutes at 72° C., 75° C., 80° C., or 85° C. in (1) 50 mM sodium citrate, 5 mM calcium chloride, pH 6.5, (2) 50 mM sodium citrate, 0.5 M sodium chloride, 5 mM calcium chloride, pH 6.5, or (3) 50 mM sodium acetate, 0.5 M sodium chloride, 2 mM calcium chloride, pH 5.0. The Betamyl® assay (Megazyme, Ireland) was used to determine the residual amylase activity. The assay mix contains 50 μL of 50 mM sodium citrate, 5 mM calcium chloride, pH 6.5, with 25 μL enzyme sample and 25 μL Betamyl substrate (paranitrophenol(PNP)-coupled maltopentaose (Glc5) and alpha-glucosidase). One Betamyl unit is defined as activity degrading 0.0351 mole/min of PNP-coupled maltopentaose. The assay contained 50 μL of 50 mM sodium citrate, 5 mM calcium chloride, pH 6.5, and 25 μL of Betamyl substrate. The assay mixture was incubated for 30 min at 40° C., then stopped by the addition of 150 μL of 4% Tris. Absorbance at 420 nm was measured using an ELISA-reader, and the Betamyl activity was calculated according to the formula Activity=A420×d in Betamyl units/ml of enzyme sample assayed, with “d” being the dilution factor of the enzyme sample. The half-lives of various PS4 variants are shown in Table 7.
Determination of starch liquefaction performance. Starch liquefaction performance was measured for the wild-type PS4 and thermostable PS4 variants by the rate of reduction in viscosity of a starch liquefact. A Thermo VT550 viscometer was used to determine viscosity. A slurry comprising starch substrate and an appropriate amount of enzyme was poured into the viscometer vessel. The temperature and viscosity were recorded during heating to 85° C., and incubation was continued for additional 60 to 120 minutes. Viscosity was measured as μNm as a function of time.
Wild-type PS4 liquefied starch at high temperature, e.g., 70-85° C. This result was significant, in view of the melting temperature of the wild-type PS4 of 66.5° C. The relatively high final viscosity obtained with the wild-type PS4, however, suggests that the wild-type PS4 has limited performance at these temperatures.
Liquefaction performance was compared between the full length, wild-type PS4 (“Amy3A”) and the PS4 variants CF135 and CF143. As shown in
Starch liquefaction with CF149 and CF154 versus SPEZYME™ Xtra. To test the ability of yeast to produce ethanol from corn liquefact generated using PS4 as an alpha-amylase, the thermostable PS4 variants CF135, CF143, CF149, and CF154 were compared to SPEZYME™ Xtra (Danisco US Inc., Genencor Division) in a conventional ethanol fermentation process run on liquefacts generated in a viscometer. A solution of Xtra at 4.86 mg/mL was added to 2.0 μg/g dry solids. PS4 variant CF149 (purified, 32.7 mg/mL) was added to 46.7 μg/g dry solids, and PS4 variant CF154 (purified, 15.9 mg/ml) was added to 46.7 μg/g dry solids. The starch solution was 30% dry solids corn flour (15 g total dry solids), pH 5.8, where the pH was adjusted with H2SO4 or NH4OH, as necessary. The starch solution was preincubation for 10 min at 70° C. before the enzyme was added. The viscometer holding the reaction was held 1 min at 70° C., 100 rpm rotation. The temperature was ramped to 85° C. over 12 min, with 75 rpm rotation. The reaction then proceeded at 85° C. for 20 min at 75 rpm rotation.
Fermentation using the CF149, CF154, or SPEZYME™ Xtra liquefacts. Two viscometer runs were performed for each enzyme in order to generate enough liquefact for one 50 g fermentation. After each viscometer run, liquefact was collected; liquefact from each pair of viscometer runs was pooled. Fermentations were run in duplicate in 125 mL Erlenmeyer flasks. Replicate fermentations were started on separate days due to timing constraints.
For each individual 50 g fermentation, the pH was adjusted to pH 4.3. The % dry solids was left unadjusted. Urea was added at 400 ppm final concentration. Red Star Ethanol Red yeast were added at a ratio of 0.33% (w/w); the yeast were prehydrated as a 33% (w/v) slurry before aliquoting 500 μL into flasks.
Flasks were incubated at 32° C. with stirring at 400 rpm for 48 h fermentation. The PS4 liquefact fermentations slowed slow stirring, whereas the Xtra liquefact fermentations did not stir at all. Samples were taken at t=0, 14 h, 23 h, 39 h, and 48 h and analyzed by HPLC.
Results. Final ethanol yields from the fermentations using PS4 liquefacts averaged 3.2% and 3.3% (v/v), whereas the final ethanol yields from the fermentations using Xtra liquefact averaged 2.2% (v/v). See
HPLC analysis of the liquefaction reaction was used to determine levels of high-DP sugars.
Crystallization and structure determination of native PS4. Crystals were obtained for the wild-type PS4 catalytic core using the Hampton PEG6000 screen. Large single crystals were obtained in 10-30% PEG6000, over the pH range 6-8. Crystals with similar morphology also were obtained by storing the protein stock solution at 4° C. without precipitant.
Data were collected at room temperature with an R-AXIS IV using CuKα radiation from an RU200 generator, and processed with d*TREK (MSC, The Woodland, Tex.). The cell dimensions were almost identical to those of crystal form II of the P. stutzeri G4-amylase. See Yoshioka et al., J. Mol. Biol. 271: 619-28 (1997); Hasegawa et al., Protein Eng. 12: 819-24 (1999). Molecular replacement calculations thus were not necessary, and rigid body refinement was used to begin structure refinement. The G4-amylase structure from RCSB Protein Database Base (PDB) Accession No. 1JDC was used with the ligand deleted. The amino acid differences between each homologue were readily apparent in 2Fo-Fc difference maps, and the correct P. saccharophila structure was built manually using COOT. The structure was subsequently refined using REFMAC5, included in the Collaborative Computational Project, Number 4 (CCP4) suite of programs. See CCP4, “The CCP4 Suite: Programs for Protein Crystallography,” Acta Cryst. D50: 760-63 (1994). Water molecules were identified using COOT, and refinement was completed with REFMAC5. Ligand atom labels and the geometry file for REFMAC5 were generated using PRODRG, available at the Dundee PRODRG2 Server.
Overall structure of PS4. The native structure of the PS4 catalytic core consists of 418 amino acids 2 calcium atoms and 115 water molecules. The structure of native PS4 with acarbose, a pseudo-tetra-saccharide, consists of 418 amino acids, 2 calcium atoms, 76 water molecules, and an acarbose derived inhibitor with 7 sugar residues. The catalytic core of PS4 has a conserved 3 domain structure common to GH13 enzymes. Domain A consists of a (β/α)8 barrel. Domain B is an insertion into this barrel, between β-sheet 3 and α-helix 3, which is relatively unstructured in this enzyme, and which contains the conserved calcium ion. Domain C is a five-stranded anti-parallel β-sheet in a Greek key motif. Domain C packs against the C-terminus of Domain A. In common with P. stutzeri MO-19 G4-amylase, there is a second calcium ion bound at the N-terminal region.
Preparation of inhibitor-bound PS4. Acarbose was added to the mother liquor of crystals grown in storage buffer, and the liquor was left to incubate at 4° C. for 24 hours. Data were collected at room temperature and processed as described above. The ligand was fitted manually into the observed difference density, and the protein ligand complex was refined with REFMAC5. See
Analysis of enzyme inhibitor interactions. Enzyme-inhibitor interactions were analyzed and characterized using the Chemical Computing Group (Montreal, Canada) Molecular Operating Environment (MOE) program, according to the parameters and instructions supplied with the program. Inhibitor binding to PS4 is depicted at
Conformation of the inhibitor at the non-reducing end. A bifurcation in the positive difference density in the Fo-Fc difference map was seen when the data obtained for PS4 without inhibitor was refined to the data obtained with the bound inhibitor. In the −4 sugar conformation, there was a positive density corresponding to the C1, O1, C3, O3, and O6 atoms, but not the C2, O2, C4, O5, and C6 atoms. See
Enzyme/inhibitor interactions. The types of interactions between the PS4 enzyme and the inhibitor can be divided into hydrogen bonding, hydrophobic interactions, and water-mediated interactions. There were 20 hydrogen bonds between the protein and the inhibitor. The conserved GH13 catalytic residues, D193, E219, and D294, were found clustered around the −1 and +1 sugars. See
Enzyme recognition of the −4 sugar at the non-reducing end of the inhibitor occurred via hydrogen bonding between (1) the side chain carboxylate oxygen OE1 of E160 and the O1 and O6 of the −4 sugar residue, (2) the OG of S161 and the O6, and (3) the main-chain nitrogen of G158 to O1 of the same sugar residue. Other key hydrogen bond interactions were hydrogen bonds between the backbone carbonyl oxygen of H307 and the O3 oxygen of the +3 sugar, OE2 of E226 and O1 of the +2 sugar, NH1 of R196 and O3 of the −1 sugar, OE1 of E219 and O2 of the −1 sugar, NE2 of H293 to O3 of the −1 sugar, and OE1 of Q305 to O2 of the −2 sugar. See
Five water molecules mediated further hydrogen bonds from the protein to the inhibitor. In the crystal structure, H2O number 456 hydrogen bonded to the O2 and O3 of the +1 sugar, the backbone carbonyl oxygen atom of E219, and the backbone nitrogen atom of W221. H2O number 464 hydrogen bonded to the O5 and O6 of the −3 sugar, the O6 of the −2 sugar, and the OG of 564. H2O number 472 hydrogen bonded to the O6 of the −2 sugar, the NE1 of W66, and OE1 of E76. H2O number 516 hydrogen bonded to the O6 of the −2 sugar, the OD2 of D62, and the OE1 of E76. See
There were nine significant hydrophobic interactions. Of these, four were co-planar stacking interactions between sugar residues +3, +2, −1, and −3 with W308, W221, Y78 and W66, respectively. There were four additional non-planar interactions of the inhibitor with W25, F79, F156, I157, and F194. Notably, F156 and I157 formed a hydrophobic peninsula around which the inhibitor wraps, allowing its non-reducing end to hydrogen bond to the protein. See
Altering the exo- and endo-activity of PS4 by protein engineering. Enzymes with exo-activity generally have an active-site cleft that is blocked at one end, only allowing substrate binding at the ends of macromolecular chains. In PS4, the non-reducing end of the active-site was restricted by the large loop between S64 and G75, but it was not completely blocked. There was indeed sufficient space for an amylose chain to pass between this loop and the loop formed by residues 155-163. In PS4, the exo-amylase activity appeared to be driven by hydrogen bonding of the non-reducing end of the amylose chain to G158, E160, and S161, which was very similar to that seen in the P. stutzeri G4-amylase. Given the total number of interactions between the substrate, as mimicked by the enzyme inhibitor complex, the energy involved in recognition of the non-reducing end of the amylase chain appeared small compared to the total energy involved in binding, amounting to only four hydrogen bonds out of a total of 23, as well as four coplanar stacking interactions. The F(acarbose)-F(native) difference map showed two conformations for the inhibitor at the non-reducing end. Together this suggested that the hydrogen bonding to the non-reducing end of the amylose chain was insufficiently strong to provide for 100% exo-specificity, which was reported in the enzymological characterization of the enzyme. Thus, the crystal structure of an inhibitor complex of PS4 provided additional evidence for mixed exo- and endo-cleavage of starch by this enzyme. This further suggested that protein engineering can be used to alter the exo- and endo-activity of the enzyme, and thus the products of the reaction.
Site-directed mutagenesis. Site-directed mutagenesis was used to produce PS4 variants. Representative examples of PS4 variants having single amino acid substitutions are shown in TABLE 3. Mutations were introduced into a nucleic acid encoding the PS4 enzyme, using the Quick Change™ method (Stratagene, California), according to instructions supplied with the kit with some modifications. Briefly, a single colony was picked and inoculated in 3 ml LB (22 g/l Lennox L Broth Base, Sigma) supplemented with 50 μg/ml kanamycin (Sigma) in a 10 ml Falcon tube. After overnight incubation at 37° C. at 200 rpm, the culture was spin down at 5000 rpm for 5 min. The medium was removed and the double-stranded DNA template was prepared using QIAGEN columns (QIAGEN). Primers were designed according to the manufacturers' protocol. For example, TABLE 5 lists primers that were used to generate backbone pMS382 based on the sequence of PS4 as shown in SEQ ID NO: 1 or 2; and TABLE 6 lists primers that were used to generate variants of pMS382 at position E223.
Next, PCR was performed to synthesize the mutant strand. The PCR reaction mix contained the following:
The PCR reaction was performed in an Eppendorf thermal cycler for 35 cycles of denaturation (96° C. for 1 min), primer annealing (62.8° C. for 1 min), and elongation (65° C. for 15 min), and then hold at 4° C. For each amplification reaction, 2 μl of DpnI restriction enzyme (10 U/μl) was added, and the mixture was incubated at 37° C. for ˜3 hr.
The DpnI-treated DNA was then used to transform XL10-Gold® Ultracompetent cells (Stratagene). XL10-Gold® cells were thawed on ice. For each mutagenesis reaction, 45 μl cells were added to a pre-chilled Falcon tube. Subsequently, 2 μl of beta-mercaptoethanol mix was added to each tube. The mixture was incubated on ice for 10 min with swirling every 2 min. Then, 1.5 μl DpnI-treated DNA was added to each aliquot of cells, and the mixture was incubated on ice for 30 min. The sample was subject to a heat-pulse of 30 sec at 42° C., and was placed on ice for another 2 min. 0.5 ml of preheated NZY+ broth was added to each sample, and incubation was carried at 37° C. for 1 hr with shaking at 225-250 rpm. 200 μl of each transformation reaction were plated on LB plates (33.6 g/l Lennox L Agar, Sigma) supplemented with 1% starch and 50 μg/ml kanamycin. The plates were incubated overnight at 37° C. Individual colonies harboring the desired mutations were identified by DNA sequencing and subjected to plasmid preps to harvest plasmids with the desired mutations.
Transformation into Bacillus subtilis. Bacillus subtilis (strain DB104A; Smith et al., Gene 70, 351-361 (1988)) is transformed with the mutated plasmid DNA according to the following protocol.
A. Media for Protoplasting and Transformation
B. Media for Plating/Regeneration
Add appropriate antibiotics: chloramphenicol and tetracycline, 5 μg/ml; erythromycin, 1 μg/ml. Selection on kanamycin is problematic in DM3 medium: concentrations of 250 μg/ml may be required.
C. Preparation of Protoplasts
Use detergent-free plastic or glassware throughout.
Inoculate 10 ml of 2×YT medium in a 100-ml flask from a single colony. Grow an overnight culture at 25-30° C. in a shaker (200 rev/min).
Dilute the overnight culture 20 fold into 100 ml of fresh 2×YT medium (250-ml flask) and grow until OD600=0.4-0.5 (approx. 2 h) at 37° C. in a shaker (200-250 rev/min).
Harvest the cells by centrifugation (9000 g, 20 min, 4° C.).
Remove the supernatant with pipette and resuspend the cells in 5 ml of SMMP+5 mg lysozyme, sterile filtered.
Incubate at 37° C. in a waterbath shaker (100 rpm).
After 30 min and thereafter at 15 min intervals, examine 25 μl samples by microscopy. Continue incubation until 99% of the cells are protoplasted (globular appearance). Harvest the protoplasts by centrifugation (4000 g, 20 min, RT) and pipet off the supernatant. Resuspend the pellet gently in 1-2 ml of SMMP.
The protoplasts are now ready for use. Portions (e.g. 0.15 ml) can be frozen at −80° C. for future use (glycerol addition is not required). Although this may result in some reduction of transformability, 106 transformants per ug of DNA can be obtained with frozen protoplasts).
D. Transformation
Transfer 450 μl of PEG to a microtube.
Mix 1-10 μl of DNA (0.2 μg) with 150 μl of protoplasts and add the mixture to the microtube with PEG. Mix immediately, but gently.
Leave for 2 min at room temperature, and then add 1.5 ml of SMMP and mix.
Harvest protoplasts by microfuging (10 min, 13,000 rpm (10,000-12,000 g)) and pour off the supernatant. Remove the remaining droplets with a tissue.
Add 300 μl of SMMP (do not vortex) and incubate for 60-90 min at 37° C. in a waterbath shaker (100 rpm) to allow for expression of antibiotic resistance markers. (The protoplasts become sufficiently resuspended through the shaking action of the waterbath.) Make appropriate dilutions in 1×SSM and plate 0.1 ml on DM3 plates
Fermentation of PS4 Variants in Shake Flasks. The shake flask substrate is prepared by dissolving the following in water:
The substrate is adjusted to pH 6.8 with 4 N sulfuric acid or sodium hydroxide before autoclaving. 100 ml of substrate is placed in a 500 ml flask with one baffle and autoclaved for 30 minutes. Subsequently, 6 ml of sterile dextrose syrup is added. The dextrose syrup is prepared by mixing one volume of 50% w/v dextrose with one volume of water followed by autoclaving for 20 minutes.
The shake flasks are inoculated with the variants and incubated for 24 hours at 35° C. and 180 rpm in an incubator. After incubation cells are separated from broth by centrifugation (10.000 g in 10 minutes) and finally, the supernatant is made cell free by microfiltration at 0.2 μm. The cell free supernatant is used for assays and application tests.
Enzymatic characterization of PS4 variants. Exo-amylase activity of PS4 variants produced by mutagenesis was assayed using the Betamyl® assay (Megazyme, Ireland). One Betamyl unit is defined as activity degrading 0.0351 mole/min of PNP-coupled maltopentaose. The assay contained 50 μL of 50 mM sodium citrate, 5 mM calcium chloride, pH 6.5, and 25 μL of Betamyl substrate. The assay mixture was incubated for 30 min at 40° C., then stopped by the addition of 150 μL of 4% Tris. Absorbance at 420 nm was measured using an ELISA-reader, and the Betamyl activity was calculated according to the formula Activity=A420×d in Betamyl units/ml of enzyme sample assayed, with “d” being the dilution factor of the enzyme sample. Endo-amylase activity was determined using the Phadebas blue assay (Pharmacia and Upjohn Diagnostics AB), performed according to the manufacturer's instructions. The exo-activity index is the ratio of Betamyl activity to Phadebas activity. The wild-type PS4 had a Betamyl/Phadebas activity ratio of 50. Variants with ratios lower than 50 are more endo-specific than the wild-type. Those with a ratio greater than 50 are more exo-specific. The Betamyl and Phadebas activity measured for the PS4 variants and their ratios of Betamyl to Phadebas activity are listed in Table 7. The mutations in TABLE 7 are listed with reference to the sequence of the respective backbone that is noted at the upper left corner of each table. “Na-Acet.” stands for sodium acetate; “Na-citr.” stands for sodium citrate; 72, 75, 80, or 85 indicates the temperature in ° C. at which the half-lives have been determined as described in Example 1; “Beta” stands for the Betamyl activity as described in Example 10; “Phad” stands for the Phadebas activity as described in Example 10; and “B/P” stands for the ratio of Betamyl activity to Phadebas activity.
Protein engineering of PS4. Active site residues close to the hydrolyzed glycosidic bond between the +1 and −1 residues were not mutated, as changes to these residues would be expected to affect the catalytic reaction itself, rather than the degree of exo-specificity. See
Mutations to the −4 binding-site. An analysis of the mutant E160D revealed no effect on the Betamyl/Phadebas activity ratio. To test if exo-activity required non-reducing sugar recognition by residue 160, the mutant E160G also was made. In this case, the Betamyl/Phadebas ratio was 12, representing a significant increase in endo-activity. Confirmation that an E or D at residue 160 was critical for exo-specificity was confirmed by the mutations of E160 to P, F, R, S, and L, which significantly increased endo-specificity. This clearly demonstrated the requirement of recognition of the non-reducing end sugar by E/D160 for exo-specificity. The mutation S161A likewise had a significant effect on endo-activity, with a Betamyl/Phadebas ratio of 18.
Mutations to the −3 binding-site. Five mutations of W66 were obtained. The conservative mutations to L, V, F, and M had little effect on exo-specificity. The mutation W66S, however, increased exo-specificity and exhibited a lower expressed activity.
Mutations to the −2 binding site. Three mutations to Q305 were made. Mutations Q305T and Q305L reduced exo-specificity significantly. By contrast, Q305E had no appreciable effect on exo-specificity.
Mutations to the +2 binding-site. Three mutations at R196 exhibited a large increase in exo-specificity. R196V had greatest exo-specificity, followed by R196H and R196P. The mutant H307L had a similar exo-specificity to these R196 mutants.
Mutations to the +3 binding-site. Mutations to W221 had very low expressed activity. Only W221A had sufficient expressed activity for characterization, and it had modestly increased exo-activity. Four mutations to W308, W308A, W308S, W308L and W308S, had significant expressed activity. All four mutations showed significant improvement in exo-specificity, the best being W308S.
The mutation K222T exhibited the most exo-activity. The side-chain of K222 did not interact directly with the substrate, yet mutation of this residue gave the largest positive increase in exo-specificity. The increase in exo-activity was not likely an effect on the neighboring W221, as mutation of W221 had only a modest effect on specificity. An analysis of the region around K222 revealed that it was part of an ion-pair network. K222 ion-paired with D254, which also ion-paired with R196. R196 in turn ion-paired with E226. R196 was positioned to hydrogen bond with the O2 and O3 of the +2 sugar. E226 hydrogen bonded to the +2 sugar. Accordingly, the large increase in exo-specificity of the K222T mutation may be due to a simultaneous reorientation of R196 and E226, which weakens substrate binding to the +2 sugar.
In summary, mutations to the − binding sub-sites increased the endo-specificity of the enzyme. The data also revealed that mutations to the + binding sub-sites could greatly increase exo-specificity. Strong interactions between the substrate binding-site and the amylose chain end promoted exospecificity. Similarly, weakening these interactions increased the endo-specificity of the enzyme. The effect of mutations to the “+” binding sub-sites revealed a delicate balancing of interactions throughout the substrate binding-site. Further, the relative strength of substrate interactions in the − binding sub-sites versus the strength of interactions in the + binding sub-sites determined the degree of exo-specificity of the enzyme. Changes that decrease the affinity of the “−” binding sub-sites relative to the + binding sub-sites increased endo-specificity. Conversely, changes that decrease the affinity of the + binding sub-sites relative to the − binding sub-sites increased exo-specificity.
It will be apparent to those skilled in the art that various modifications and variation can be made to the compositions and methods of using the same without departing from the spirit or scope of the intended use. Thus, it is the modifications and variations provided they come within the scope of the appended claims and their equivalents.
Firmness, resilience and cohesiveness are determined by analysing bread slices by Texture Profile Analysis using a Texture Analyser From Stable Micro Systems, UK. Calculation of firmness and resilience is done according to preset standard supplied by Stable Micro System, UK. The probe used is aluminium 50 mm round.
Bread is sliced with the width of 12.5 mm. The slices are stamped out to a circular piece with a diameter of 45 mm and measured individually.
The following settings are used:
Pre Test Speed: 2 mm/s
Test Speed: 2 mm/s
Post Test Speed: 10 mm/s
Rupture Test Distance: 1%
Distance: 40%
Force: 0.098 N
Time: 5.00 sec
Count: 5
Load Cell: 5 kg
Trigger Type Auto −0.01 N
The mode of compression is a modification to the one used in Standard method AACC 74-09. The sample is compressed twice in the test.
Firmness is determined at 40% compression during the first compression. The figure is the force needed to compress the slice to 40% of the total thickness. The lower the value, the softer the bread. The firmness is expressed as a pressure, for example, in hPa.
This assay may be referred to as the “Firmness Evaluation Protocol”.
Area under the curve is a measure of work applied during the test. The area under the curve in the compression part (A1) and the withdrawal part (A2) during the first compression are shown in
The ratio between A1 and A2 is defined as the resilience of the sample, and is expressed as Resilience Units. True elastic material will give a symmetric curve, as the force applied during the first part will be equal to the force in the second part. For bread and bread-like material, A2 is normally smaller than A2 due to disturbance of the structure during compression. Hence, resilience is always lower than 1.
This assay may be referred to as the “Resilience Evaluation Protocol”.
The cohesiveness is defined as the ratio between the area under second compression to the area under first compression (A3/A1+A2), and is expressed as Cohesiveness Units. It is a measure of the decay of the sample during compression. The higher the ability of the sample to regain its shape after first compression the closer the value will be to 1. For bread and bread-like material cohesiveness is always lower than 1.
This assay may be referred to as the “Cohesiveness Evaluation Protocol”.
Two slices of bread are placed on a piece of paper. Each slice is divided into 4 squares by vertical and subsequent horizontal tears of the slice.
Tearing is done by pulling the crumb apart by the fingers. First the slice is torn from the middle of the top bread surface to the middle of the bottom bread surface. Thereafter, each half of the original slice is torn from the crust side to the inside of the slice. The small crumb pieces, which are separated from the 4 squares, are removed by shaking each piece after a tear at least 3 times by moving the hand up and down.
The weight of the separated small crumb pieces is determined as a measure of crumbliness. This assay may be referred to as the “Crumbliness Evaluation Protocol”.
The toast bread is sliced using an automatic bread slicer with set slice thickness of 15 mm. The slice is folded by hand from the top of the slice towards the bottom, so that the direction of the crease is from side to side.
The foldability is visually assessed using the following scoring system:
This assay may be referred to as the “Foldability Evaluation Protocol”.
This application is a continuation-in-part application of international patent application Serial No. PCT/EP2008/068375 filed Dec. 30, 2008, which published as PCT Publication No. WO2009/083592 on Jul. 9, 2009, which claims benefit of U.S. application Ser. No. 61/006,240 filed Jan. 2, 2008. The foregoing applications, and all documents cited therein or during their prosecution (“appln cited documents”) and all documents cited or referenced in the appln cited documents, and all documents cited or referenced herein (“herein cited documents”), and all documents cited or referenced in herein cited documents, together with any manufacturer's instructions, descriptions, product specifications, and product sheets for any products mentioned herein or in any document incorporated by reference herein, are hereby incorporated herein by reference, and may be employed in the practice of the invention.
| Number | Date | Country | |
|---|---|---|---|
| 61006240 | Jan 2008 | US |
| Number | Date | Country | |
|---|---|---|---|
| Parent | PCT/EP2008/068375 | Dec 2008 | US |
| Child | 12829696 | US |
