Patent Application
20170204380
The present invention relates to novel glycosyl transferases from Vitis vinifera that are capable of catalyzing the formation of certain glycosides with high efficiency, to nucleic acid molecules encoding such glycosyl transferases, to vectors, host cells and transgenic plants comprising nucleic acid sequences coding for such glycosyl transferases, to methods for preparing and to uses of such glycosyl transferases.
Due to their manifold physiological activities, glycosylated natural products are important components of e.g. foodstuffs, pharmaceutical products and cosmetics. Thus, glycosylated diterpenes, steroids and flavonoids are for example used in the food industry as sweeteners (steviosides, glycyrrhizin, neohesperidin, dihydrochalcone) and glycosylated flavonoids as bitterns (neohesperidin), while steroid glycosides and glycosides of antibiotics are employed as medicaments and glycoside extracts as cosmetic products. Moreover, since many terpenes are important fragrance and flavor compounds, the corresponding terpene glycosides can be useful as “slow release” aroma compounds, or can be utilized as antimicrobials, detergents and emulsifier. Glycoside esters of terpene, on the other hand, have antimicrobial activity.
Typically, industrial production of glycosides is carried out by the Koenigs-Knorr process (i.e. organic-chemical substitution of a glycosyl halide with an alcohol to yield a glycoside) or reversed enzymatic hydrolysis or transglycosylation employing glycosidases. However, such methods have a low efficiency, require heavy metal catalysts and anhydrous conditions in the case of chemical synthesis, and thus do not allow to prepare large quantities of glycosides, in particular (mono)terpene glycosides, in a cost-efficient manner.
In nature, regioselective and enantioselective transfer of sugars is catalyzed by nucleoside diphosphate carbohydrate dependent glycosyl transferases, such as UDP-glucose dependent glycosyl transferases (UGTs). Glycosyl transferases of small molecules transfer sugar to a multitude of acceptors, such as antibiotics, lipids, hormones, secondary metabolites or toxins In plants, a remarkably large array of different small molecules is glycosylated, including terpenoids, alkaloids, cyanohydrins and glucosinolates as well as flavonoids, isoflavonoids, anthocyanidins, phenylpropanoids and phytohormones. The transfer of a carbohydrate group onto a lipophilic acceptor modifies the chemical characteristics and bioactivity of the acceptor and enables it to access membrane transport systems. Some glycosyl transferases are considered highly specific with respect to substrate-, regio- and stereospecificity, whereas others glycosylate a broad range of acceptors (a phenomenon called promiscuity).
Although glycosylation of plant hormones, phenylpropanoids, flavonoids, betalains and coumarins with recombinant UGTs has frequently been described, enzymatic transfer to monoterpenes has been observed quite rarely.
Moreover, glycosyl transferases known from the prior art only have relatively low glycosylation and esterification activities, in particular for the glycosylation of terpenes or monoterpenes and the formation of glycose esters of terpenes or monoterpenes. Thus, the glycosyl transferases available do not allow for cost-efficient preparation of glycosides or glycose esters, in particular of terpene and monoterpene glycosides or terpene and monoterpene glycose esters, and thus do not allow for biotechnological preparation of such glycosides or glycose esters at an industrial scale.
Thus, there is a need in the art for improved ways and reagents for the preparation of glycosides and glycose esters, in particular (mono)terpene glycosides and (mono)terpene glycose esters. Moreover, there is a need in the art for ways and reagents that allow for the preparation of glycosides and glycose esters, in particular (mono)terpene glycosides and (mono)terpene glycose esters, on an industrial scale by biotechnological processes. Moreover, there is a need in the art for glycosyl transferases with high activity for the preparation of glycosides and glycose esters, in particular (mono)terpene glycosides and (mono)terpene glycose esters. Moreover, there is a need in the art for reaction product compositions obtained by a method for forming/producing a terpene glycoside, terpene glycose ester, octanyl glycoside, furaneyl glycoside or hexanyl glycoside, wherein said reaction product composition includes said terpene glycoside, terpene glycose ester, octanyl glycoside, furaneyl glycoside or hexanyl glycoside at higher purity than reaction product compositions known from the prior art.
These objects are solved by the below-described aspects of the present invention, in particular by a glycosyl transferase according to claim 1, a nucleic acid molecule according to claim 6, a vector according to claim 7, a host cell according to claim 8, a transgenic plant according to claim 10, the use of a glycosyl transferase according to claim 12, a method of forming a terpene glycoside, terpene glycose ester, octanyl glycoside, furaneyl glycoside or hexanyl glycoside according to claim 13, a method of producing a terpene glycoside, terpene glycose ester, octanyl glycoside, furaneyl glycoside or hexanyl glycoside according to claim 14, a method of producing a protein having glycosyl transferase activity according to claim 15, and a reaction product composition according to claim 16. Preferred embodiments are defined in the dependent claims and below.
In a first aspect, the present invention relates to a glycosyl transferase having an amino acid sequence that
In some embodiments, said glycosyl transferase is a small molecule glycosyl transferase.
In some embodiments, the glycosyl transferase is a terpene glycosyl transferase, preferably a monoterpene glycosyl transferase, more preferably a UDP-glucose:monoterpene β-D-glucosyltransferase.
In some embodiments, said glycosyl transferase is capable of using UDP-glucose as sugar donor. Preferably, said glycosyl transferase uses UDP-glucose more efficiently as sugar donor than UDP-xylose, UDP-glucuronic acid, UDP-arabinose, UDP-rhamnose, UDP-galactose, GDP-fucose, GDP-mannose and/or CMP-sialic acid, as seen by radiochemical analysis. In such radiochemical analysis, individual reactions are carried out in which different radiolabelled sugar donors (such as radiolabelled UDP-glucose, UDP-xylose and UDP-glucuronic acid) that carry a radionuclide in their sugar group are reacted under appropriate conditions and in the presence of the glycosyl transferase with a certain acceptor molecule. By comparing the amount of radiolabel that was transferred from the different sugar donors to the acceptor molecule, it can be determined which sugar donor the glycosyl transferase uses more efficiently than the others.
In some embodiments, the glycosyl transferase is capable of catalyzing transfer of a sugar group from a sugar donor to a hydroxyl group of a hydroxy-containing terpene and/or a carboxyl group of a carboxy-containing terpene.
In some embodiments, the glycosyl transferase is capable of catalyzing formation of a glycoside in which a sugar is linked to a hydroxy-containing terpene through a β-D-glycosyl linkage and/or formation of a glycose ester in which a sugar is linked to a carboxy-containing terpene through a β-D-glycose ester linkage.
In some embodiments, the glycosyl transferase is capable of catalyzing glycosylation, preferably glucosylation, of geraniol, (R-)linalool, (R- and/or S-)citronellol, nerol, hexanol and/or octanol, preferably geraniol and/or (R- and/or S-)citronellol, wherein, preferably, said glycosyl transferase has an amino acid sequence that
In some embodiments, the glycosyl transferase is capable of catalyzing glycosylation, preferably glucosylation, of furaneol, wherein, preferably, said glycosyl transferase has an amino acid sequence that
In some embodiments, said glycosyl transferase is capable of catalyzing glycosylation, preferably glucosylation, of eugenol, wherein, preferably, said glycosyl transferase has an amino acid sequence that
In some embodiments, the glycosyl transferase is not capable of catalyzing glycosylation, preferably glucosylation, of cyanidin, pelargonodin, quercetin and/or kaempferol, wherein, preferably, said glycosyl transferase has an amino acid sequence that
In some embodiments, the glycosyl transferase is capable of catalyzing glycosylation, preferably glucosylation, of geraniol, (R- and/or S-)citronellol, nerol, hexanol, octanol, 8-hydroxylinalool, trans 2-hexenol, and/or farnesol, preferably geraniol, wherein, preferably, said glycosyl transferase has an amino acid sequence that
In some embodiments, the glycosyl transferase is not capable of catalyzing glycosylation, preferably glucosylation, of cyanidin, pelargonodin, quercetin, kaempferol, linalool, terpineol, benzyl alcohol, phenyl ethanol, eugenol, mandelonitrile, 3-methyl-2-butenol, 3-methyl-3-butenol, cis-3-hexenol and/or furaneol, wherein, preferably, said glycosyl transferase has an amino acid sequence that
In some embodiments, the glucosyl transferase activity (kcat/KM) of said glycosyl transferase for geraniol, citronellol and/or nerol is higher than the glucosyl transferase activity of said glycosyl transferase for benzyl alcohol by at least a factor of 2. In some embodiments, the glucosyl transferase activity (kcat/KM) of said glycosyl transferase for geraniol is higher than the glucosyl transferase activity of said glycosyl transferase for hexanol by at least a factor of 4.
In some embodiments, said glycosyl transferase has a glucosyl transferase activity (kcat/KM) for geraniol, that is by at least a factor of 2, preferably by at least a factor of 5, more preferably by at least a factor of 10, more preferably by at least a factor of 20, more preferably by at least a factor of 30, more preferably by at least a factor of 40 higher than the glucosyl transferase activity of the glycosyl transferase UGT85B1 of Sorghum bicolor for geraniol.
In some embodiments, said glycosyl transferase has a glucosyl transferase activity (Kcat/KM) for nerol that is by at least a factor of 2, preferably by at least a factor of 3, more preferably by at least a factor of 4, more preferably by at least a factor of 5 higher than the glucosyl transferase activity of the glycosyl transferase UGT85B1 of Sorghum bicolor for nerol.
In some embodiments, said glycosyl transferase has a glucosyl transferase activity (Kcat/KM) for citronellol that is by at least a factor of 2, preferably by at least a factor of 3 higher than the glucosyl transferase activity of the glycosyl transferase UGT85B1 of Sorghum bicolor for citronellol.
In some embodiments, said glycosyl transferase can be expressed more efficiently as a recombinant protein in E. coil cells than the glycosyl transferase UGT85B1 of Sorghum bicolor.
In a second aspect, the present invention relates to an (isolated) nucleic acid molecule encoding a glycosyl transferase as defined in any of the embodiments described above, wherein, preferably, said nucleic acid molecule is a DNA molecule.
In a third aspect, the present invention relates to a vector comprising a DNA sequence encoding a glycosyl transferase as defined in any of the embodiments described above.
Preferably, said vector is an expression vector, preferably an expression vector for expression of a glycosyl transferase as defined in any of the embodiments described above.
In a fourth aspect, the present invention relates to a host cell containing or transfected with the nucleic acid molecule according to the second aspect of the invention described above or the vector according to the third aspect of the invention described above, wherein, preferably, said host cell is not a cell of Vitis vinifera, more preferably not a cell of a grape vine, and/or wherein, preferably, said host cell is a non-human cell, preferably a bacterial cell, more preferably an E. coli cell.
In some embodiments, said host cell produces/expresses a glycosyl transferase as defined in any of the embodiments above.
In a fifth aspect, the present invention relates to a transgenic plant comprising a nucleic acid molecule as defined above or a vector as defined above, wherein, preferably, said plant is not a Vitis vinifera plant, more preferably not a grape vine.
In some embodiments, said transgenic plant produces/expresses a glycosyl transferase as defined in any of the embodiments above.
In a sixth aspect, the present invention relates to the use of a glycosyl transferase as defined in any of the embodiments above or a nucleic acid molecule as defined in the second aspect of the invention or a vector as defined in the third aspect of the invention or a host cell as defined in any of the embodiments above or a transgenic plant as defined in any of the embodiments above for producing a terpene glycoside, terpene glycose ester, octanyl glycoside, furaneyl glycoside or hexanyl glycoside.
Preferably, said terpene glycoside is selected from the group consisting of geranyl β-D-glucoside, (R-)linaloyl β-D-glucoside, (R- and/or S-)citronellyl β-D-glucoside, neryl β-D-glucoside, 8-hydroxylinaloyl glucoside and farnesyl glucoside, more preferably said terpene glycoside is geranyl β-D-glucoside and/or (R- and/or S-)citronellyl β-D-glucoside, more preferably said terpene glycoside is geranyl β-D-glucoside.
Preferably, said octanyl glycoside is octanyl glucoside. Preferably, said furaneyl glycoside is furaneyl glucoside. Preferably, said hexanyl glycoside is hexanyl glucoside.
Preferably, said production of said terpene glycoside, terpene glycose ester, octanyl glycoside, furaneyl glycoside or hexanyl glycoside does not involve steps carried out in vivo. Preferably, said production of said terpene glycoside, terpene glycose ester, octanyl glycoside, furaneyl glycoside or hexanyl glycoside is carried out in a host cell or transgenic plant as defined above, preferably in an E. coli cell.
In a seventh aspect, the present invention relates to a method of forming
Preferably, said glycosyl transferase is a recombinantly expressed glycosyl transferase.
Preferably, said terpene glycoside is selected from the group consisting of geranyl β-D-glucoside, (R-)linaloyl β-D-glucoside, (R- and/or S-)citronellyl β-D-glucoside, neryl β-D-glucoside, 8-hydroxylinaloyl glucoside and farnesyl glucoside, said sugar group is glucose and said sugar donor is UDP-glucose, and said hydroxy-containing terpene is selected from the group consisting of geraniol, (R-) linalool, (R- and/or S-)citronellol, nerol, 8-hydroxylinalool and farnesol.
More preferably, said terpene glycoside is geranyl β-D-glucoside or (R- and/or S-)citronellyl β-D-glucoside,
said sugar group is glucose and said sugar donor is UDP-glucose,
and said hydroxy-containing terpene is geraniol or (R- and/or S-)citronellol.
More preferably, said terpene glycoside is geranyl β-D-glucoside,
said sugar group is glucose and said sugar donor is UDP-glucose,
and said hydroxy-containing terpene is geraniol.
Preferably, said sugar group is glucose, said sugar donor is UDP-glucose, and said octanyl glycoside is octanyl glucoside. Preferably, said sugar group is glucose, said sugar donor is UDP-glucose, and said furaneyl glycoside is furaneyl glucoside. Preferably, said sugar group is glucose, said sugar donor is UDP-glucose, and said hexanyl glycoside is hexanyl glucoside.
In some embodiments, said method is an in vitro method which, preferably, does not involve any steps carried out in vivo. In some embodiments, said method is an in vivo method carried out in a host cell or transgenic plant as defined above, more preferably an in vivo method carried out in E. coli.
In an eighth aspect, the present invention relates to a method of producing a terpene glycoside, terpene glycose ester, octanyl glycoside, furaneyl glycoside or hexanyl glycoside, said method comprising the steps of:
Preferably, said terpene glycoside is a terpene glycoside in which a hydroxy-containing terpene is covalently linked to a sugar group. Preferably, said terpene glycose ester is a terpene glycose ester in which a carboxy-containing terpene is covalently linked to a sugar group.
In some embodiments, said hydroxy-containing terpene is a monoterpene, preferably geraniol, (R-)linalool, (R- and/or S-)citronellol, nerol, 8-hydroxylinalool or farnesol, more preferably geraniol or citronellol, more preferably geraniol, and/or said sugar group is a glucosyl group. In some embodiments, said terpene glycoside is selected from the group consisting of geranyl β-D-glucoside, (R-)linaloyl β-D-glucoside, (R- and/or S-)citronellyl β-D-glucoside, neryl β-D-glucoside, 8-hydroxylinaloyl glucoside and farnesyl glucoside, preferably geranyl β-D-glucoside or (R- and/or S-)citronellyl β-D-glucoside, more preferably geranyl β-D-glucoside.
In some embodiments, said octanyl glycoside is octanyl glucoside. In some embodiments, said furaneyl glycoside is furaneyl glucoside. In some embodiments, said hexanyl glycoside is hexanyl glucoside.
Preferably, during said culturing or growing said host cell or transgenic plant said hydroxy-containing terpene is present in said host cell or transgenic plant. Preferably, during said culturing or growing said host cell or transgenic plant said carboxy-containing terpene is present in said host cell or transgenic plant. Preferably, during said culturing or growing said host cell or transgenic plant octanol is present in said host cell or transgenic plant. Preferably, during said culturing or growing said host cell or transgenic plant furaneol is present in said host cell or transgenic plant. Preferably, during said culturing or growing said host cell or transgenic plant hexanol is present in said host cell or transgenic plant. Preferably, during said culturing or growing said host cell or transgenic plant UDP-glucose is present in the culture medium used for culturing said host cell or in the water used for watering that transgenic plant.
In some embodiments, said culturing or growing said host cell is carried out in a bioreactor.
In a ninth aspect, the present invention relates to a method of producing a protein having glycosyl transferase activity and/or enzymatic activity for the catalysis of glycose esterification, said method comprising the steps of:
Preferably, said glycosyl transferase activity is an activity of transferring the sugar group of a sugar donor to a hydroxyl group of a hydroxy-containing terpene under formation of a glycosidic bond between said hydroxy-containing terpene and said sugar group.
Preferably, said hydroxy-containing terpene is a monoterpene, preferably geraniol, (R-)linalool, (R- and/or S-)citronellol, nerol, 8-hydroxylinalool or farnesol, more preferably geraniol or citronellol, more preferably geraniol, and/or said sugar donor is UDP-glucose. Preferably, said glycosyl transferase activity is an activity of transferring the sugar group of a sugar donor to a hydroxyl group of octanol, furaneol or hexanol under formation of a glycosidic bond between said octanol, furaneol or hexanol and said sugar group.
Preferably, said sugar donor is UDP-glucose and said sugar group is a glucosyl group.
Preferably, said enzymatic activity for the catalysis of glycose esterification is an activity of transferring the sugar group of a sugar donor to a carboxyl group of a carboxy-containing terpene under formation of a glycose ester bond between said carboxy-containing terpene and said sugar group.
Preferably, said protein having glycosyl transferase activity and/or enzymatic activity for the catalysis of glycose esterification is a glycosyl transferase as defined in any of the embodiments above. A “glycosyl transferase” in an enzyme of EC class 2.4 that catalyzes the transfer of a monosaccharide moiety from a sugar donor to an acceptor molecule under formation of a glycosidic linkage between the sugar (the glycone) and the acceptor molecule (the aglycone) (see, e.g., Bowles et al., 2006). The sugar donor is typically an activated sugar precursor and can be, for example, UDP (uridine diphosphate)-glucose wherein the sugar is glucose, UDP-xylose wherein the sugar is xylose, UDP-glucuronic acid wherein the sugar is glucuronic acid, UDP-arabinose wherein the sugar is arabinose, UDP-rhamnose wherein the sugar is rhamnose, UDP-galactose wherein the sugar is galactose, GDP (guanosin diphosphate)-fucose wherein the sugar is fucose, GDP-mannose wherein the sugar is mannose or CMP (cytidine monophosphate)-sialic acid wherein the sugar is sialic acid. If the glycosyl transferase is a glucosyl transferase, then the sugar donor is UDP-glucose. The acceptor molecule may be an alcohol, such as the alcohol of a terpenoid, alkaloid, cyanohydrin, glucosinolate, flavonoid, isoflavonoid, anthocyanidin, phenylpropanoid, polyphenol, hydroquinone, amine, carbohydrate (monomeric or oligomeric), fatty acid or lipids. Examples of glycosyl transferases are UDP-glucosyltransferases, UDP-arabinosyltransferases, UDP-glucuronosyltransferases, UDP-xylosyltransferases, UDP-galactosyltransferases, UDP-rhamnosyltransferases, GDP-fucosyltransferase, GDP-mannosyltransferase, or CMP-sialyltransferase. A glycosyl transferase may or may not have an additional enzymatic activity for the catalysis of glycose esterification, i.e. for transferring the sugar group of a sugar donor to a carboxyl group of a carboxy-containing acceptor molecule under formation of a glycose ester bond between said carboxy-containing acceptor molecule and said sugar group.
In a tenth aspect, the present invention relates to a reaction product composition obtainable by a method of forming
Preferably, said method, said terpene glycoside, said terpene glycose ester, said octanyl glycoside, said furaneyl glycoside, said hexanyl glycoside, said hydroxy-containing terpene, said carboxy-containing terpene, said sugar group, said sugar donor and said glycosyl transferase are as defined in any of the embodiments above.
Preferably, said method is a method of forming a terpene glycoside and said reaction product composition comprises said terpene glycoside at a purity of at least 90%. Preferably, said method is a method of forming a terpene glycose ester and said reaction product composition comprises said terpene glycose ester at a purity of at least 90%. Preferably, said method is a method of forming an octanyl glycoside and said reaction product composition comprises said octanyl glycoside at a purity of at least 90%. Preferably, said method is a method of forming a furaneyl glycoside and said reaction product composition comprises said furaneyl glycoside at a purity of at least 90%. Preferably, said method is a method of forming a hexanyl glycoside and said reaction product composition comprises said hexanyl glycoside at a purity of at least 90%.
In an eleventh aspect, the present invention relates to a reaction product composition obtainable by a method of producing a terpene glycoside, terpene glycose ester, octanyl glycoside, furaneyl glycoside or hexanyl glycoside, said method comprising the steps of:
Preferably, said method, said terpene glycoside, said terpene glycose ester, said octanyl glycoside, said furaneyl glycoside, said hexanyl glycoside, said culturing, said growing, said host cell, said transgenic plant and said collecting are as defined in any of the embodiments above.
A “small molecule glycosyl transferase” is a glycosyl transferase that catalyzes the transfer of a monosaccharide moiety from a sugar donor to a small molecule as acceptor molecule. A small molecule is a molecule that has a molecular weight below 1 500 Dalton, preferably below 1 000 Dalton. A “terpene glycosyl transferase” is a glycosyl transferase that catalyzes the transfer of a monosaccharide moiety from a sugar donor to a terpene as acceptor molecule. A “monoterpene glycosyl transferase” is a glycosyl transferase that catalyzes the transfer of a monosaccharide moiety from a sugar donor to a monoterpene as acceptor molecule. An “UDP-glucose:monoterpene β-D-glucosyltransferase” is a glycosyl transferase that catalyzes the transfer of a glucose moiety from a UDP-glucose as sugar donor to a monoterpene as acceptor molecule under formation of covalent a β-D-glycosidic bond.
At some instance, the present invention refers to a glycosyl transferase “having” a certain amino acid sequence. This is meant to designate that the amino acid sequence of said glycosyl transferase consists of said certain amino acid sequence, i.e. the glycosyl transferase comprises only said certain amino acid sequence and no further amino acid sequence(s) beyond said certain amino acid sequence.
Glycosyl transferases having an amino acid sequence comprising SEQ ID NO: 1 (i.e. the sequence of VvGT14) or SEQ ID NO: 2 (i.e. the sequence of VvGT15) or a related amino acid sequence can be obtained by standard methods of recombinant DNA technology, for example as described in Example 1 below.
If the present application refers to a specific allelic/splice form of VvGT14 by the general designation “VvGT14”, this is meant to refer to VvGT14a. If the present application refers to a specific allelic/splice form of VvGT15 by the general designation “VvGT15”, this is meant to refer to VvGT15a.
A “glycoside”, as used herein, is a molecule in which a sugar (the “glycone” part or “glycone component” of the glycoside) is bonded to a non-sugar (the “aglycone” part or “aglycone component”) via a glycosidic bond. Accordingly, a glycoside may consist of a sugar as glycone component (designated “Z” in the general chemical structure below) linked through its anomeric carbon atom to the hydroxy group of an alcohol (chemical structure R—OH) as aglycone component, thus resulting in a glycoside of the general chemical structure R—O—Z. For example, in the glycoside linaloyl β-D-glucoside, the glycone component glucose is linked to the aglycone component linalool.
A glycoside can be produced by carrying out a reaction in which an aglycone component (such as a terpene, for example geraniol or citronellol) is mixed under appropriate conditions with a sugar donor (an activated sugar precursor such as UDP-glucose or UDP-glucuronic acid, preferably UDP-glucose) in the presence of a glycosyl transferase as enzymatic catalyzer. For example, 100 μL purified enzyme (50 μg), 100-150 μL Tris-HCl buffer (100 mM, pH 7.5, 10 mM 2-mercaptoethanol), 37 pmol UDP-glucose and 50 μg substrate (dissolved in methyl-tert-butylether) can be incubated at 30° C. for 24 hr. This results in the formation of glycosides composed of an aglycone component linked to a glycone component. The glycoside can subsequently be isolated from the reaction mixture by standard methods of extraction and chromatography (see also Example 1).
Alternatively, a glycoside can be produced by culturing or growing a host cell or transgenic plant expressing a glycosyl transferase according to the invention. During culture/growth, such a host cell or transgenic plant will generate glycosides. The glycoside(s) generated in such a host cell or transgenic plant can subsequently be collected from said host cell or transgenic plant by standard methods of extraction and/or chromatography (such as solvent extraction, solid phase extraction and reversed phase chromatography). In such a method for producing a glycoside, the present application may indicate that during said culturing or growing a host cell or transgenic plant a certain compound or substrate (such as the aglycone component) used for formation of the glycoside “is present in said host cell or transgenic plant”. This means that the compound or substrate is either produced by said host cell or transgenic plant such that it is present in said host cell/in the cells of said transgenic plant, or that it is added to the host cell or transgenic plant in such a manner that it is taken up by the host cell or transgenic plant and enters into the host cell/cells of the transgenic plant. This may for example be achieved by including the compound or substrate to the culture medium used for culturing the host cells (for example the growth medium used for culturing E. coli cells) or, in the case of a transgenic plant, by adding the compound or substrate to the water used for watering the plant (for example, an aqueous solution containing the compound/substrate or an aqueous solution with a low content of ethanol containing the compound/substrate may be added to the culture medium used for culturing the host cells or to the water used for watering the plant).
If the present application refers to “collecting” a certain glycoside, glycose ester or protein from a host cell or transgenic plant, this is meant to designate that said glycoside, glycose ester or protein is separated and/or isolated from other components of said host cell or transgenic plant. This can be achieved by standard methods of extraction and chromatography known to a person of skill in the art (see e.g. Example 1).
As used herein, a “bioreactor” is a vessel in which a (bio)chemical process is carried out which involves organisms (such as host cells) or biochemically active substances derived from such organisms.
A “terpene”, as used herein, is a hydrocarbon having a carbon skeleton formally derived by combination of several isoprene units. The term includes hydrocarbons having a carbon skeleton formally derived by combination of several isoprene units covalently linked to at least one hydroxy group, preferably covalently linked to one hydroxy group and/or covalently linked to at least one carboxyl group, preferably covalently linked to one carboxyl group. In some embodiments, the term “terpene” also includes hydrocarbons having a carbon skeleton formally derived by combination of several isoprene units in which up to three, preferably up to two, more preferably one, methyl groups have been moved or removed. In other embodiments, the term “terpene” does not include hydrocarbons having a carbon skeleton formally derived by combination of several isoprene units in which methyl groups have been moved or removed. In some embodiments, the term “terpene” also includes hydrocarbons having a carbon skeleton formally derived by combination of several isoprene units which comprise up to three, preferably up to two, more preferably one, oxygen atom. In some embodiments the term “terpene” does not include hydrocarbons having a carbon skeleton formally derived by combination of several isoprene units which comprise additional oxygen atoms besides the oxygen atom that is part of the above-mentioned hydroxy group. In some embodiments the term “terpene” does not include compounds comprising more than one oxygen atom.
As used herein, a “hydroxy-containing terpene” is a terpene that comprises one or more, preferably one, hydroxy group. As used herein, a “carboxy-containing terpene” is a terpene that comprises one or more, preferably one, carboxyl group. The term “terpene glycoside” refers to a glycoside the aglycone component of which is a terpene. In some embodiments, the term does not include glycosides the aglycone component of which is a terpene in which methyl groups have been moved or removed compared to a terpene formally derived from isoprene units. In some embodiments, the term does not include glycosides the aglycone component of which includes further functional groups in addition to the functional group forming the linkage to the glycone component of the terpene glycoside. In some embodiments, the term does not include glycosides the aglycone component of which includes further oxygen atoms in addition to oxygen atom(s) that are part of the functional group forming the linkage to the glycone component of the terpene glycoside. The term “monoterpene glycoside” refers to a glycoside the aglycone component of which is a monoterpene (formally comprising two isoprene units, such as geraniol, citronellol or linalool). The term “sesquiterpene glycoside” refers to a glycoside the aglycone component of which is a terpene formally comprising three isoprene units (such as farnesol). The term “diterpene glycoside” refers to a glycoside the aglycone component of which is a diterpene (formally comprising four isoprene units, such as steviol).
A “glycose ester”, as used herein, is a molecule in which an aglycone component is linked via an ester bond to a sugar component, preferably to a monosaccharide. A “terpene glycose ester” is a glycose ester the aglycone component of which is a terpene.
“Glycose esterification”, as used herein, refers to a reaction in which a molecule is linked to a sugar, preferably a monosaccharide, under formation of an ester bond between said molecule and said sugar.
At some instances, the present application refers to a glycosyl transferase being “capable of catalyzing” a certain reaction. For example, the present application may state that a glycosyl transferase is capable of catalyzing transfer of a sugar group from a sugar donor to a certain acceptor. This is meant to designate that under appropriate reaction conditions the rate at which the reaction product (in the example the adduct of the sugar group and the acceptor) is formed is at least 10-fold higher in the presence of said glycosyl transferase than the rate at which the reaction product is formed in a control experiment in the absence of said glycosyl transferase.
At some instances, the present application indicates that a certain glycosyl transferase “has a glucosyl transferase activity” for a substrate A that is “by at least a factor X higher” than the glucosyl transferase activity for a substrate B. This means that, if the kcat/KM values (i.e. the specificity constants) of said glycosyl transferase for substrate A and B are measured under appropriate conditions and the kcat/KM value obtained for the glycosyl transferase with substrate A is divided by the kcat/KM value obtained for the glycosyl transferase with substrate B, the resulting value is X or greater than X.
Similarly, the present application may indicate that a certain glycosyl transferase G “has a glucosyl transferase activity” for a certain substrate A that is “by at least a factor X higher” than the glucosyl transferase activity of another glycosyl transferase H for substrate A. This means that, if the kcat/KM values of glycosyl transferase G and of glycosyl transferase H for substrate A are measured under appropriate conditions and the kcat/KM value obtained for glycosyl transferase G with substrate A is divided by the kcat/KM value obtained for glycosyl transferase H with substrate A, the resulting value is X or greater than X.
The kcat/KM value can be determined by standard procedures known to the person of skilled in the art. Preferably, recombinant glycosyl transferases are used for determining the kcat/KM values.
Preferably, the following procedure is used:
The kinetic data are determined with increasing concentrations of the substrates from 1 μM to 500 μM and a fixed concentration of sugar precursor (for example an UDP-glucose concentration of 108 μM (100 μM unlabeled UDP-glucose and 8 μM UDP-[14C] glucose), 833 μM (825 μM unlabeled UDP-glucose and 8 μM UDP-[14C] glucose) or 512.5 μM (500 μM unlabeled UDP-glucose and 12.5 μM UDP-[14C] glucose)). The total volume is 40 μL and 0.2 μg, 0.5 μg or 5 μg of purified protein is used. The measurements are performed under the following conditions: The assays are carried out at 30° C. for 1.5 h, 30 min or 10 min using a Tris-HCl buffer (100 mM, 10 mM 2-mercaptoethanol, pH 8.5 or pH 7.5). The amount of the purified enzyme and the incubation time can be adapted depending on the counting sensibility. The reaction is stopped by adding 1 μL 24% trichloroacetic acid and glucosides are extracted with 100 μL ethyl acetate. Radioactivity is determined by LSC.
To determine the kinetic data of a sugar precursor (e.g. UDP-glucose), the value of the substrate used (e.g. geraniol) is fixed (1.25 mM or 0.1 mM) and radiolabeled sugar precursor (e.g. UDP-[14C] glucose) is mixed with non-radiolabeled sugar precursor (in the example UDP-glucose) to obtain concentrations ranging from 5 μM to 100 μM or 25 μM to 500 μM. The KM- and vmax-values are calculated from Lineweaver-Burk plots, Hanes-Woolf plots and non-linear fitting of the experimental data.
At some instances, the present application indicates that a certain glycosyl transferase can be “expressed more efficiently as a recombinant protein in E. coli cells” than another glycosyl transferase. The efficiency of recombinant protein expression in E. coli can be compared as follows: Recombinant expression of the different glycosyl transferases is carried out in E. coli cells by standard methods known to the skilled person, preferably according to the methods described in Example 1 below. Whole-cell extracts from the E. coli cells are prepared and proteins in the whole-cell extract are compared after gel-electrophoresis and visualization by coomassie-staining.
As “host cell” transfected with the nucleic acid molecule as described above, the cell of a prokaryotic or eukaryotic organism may be used. As the prokaryotic organism, bacteria, for example, commonly used hosts such as bacteria belonging to genus Escherichia such as Escherichia coli can be used. Alternatively, a cell of a lower eukaryotic organism such as eukaryotic microorganisms including, for example, yeast (e.g. Saccharomyces cerevisiae) or fungi like Aspergillus oryzae and Aspergillus niger can be used. Animal cells or plant cells also can be used as a host. Examples of animal cells that can be used include cell lines of mouse, hamster, monkey, human, etc., as well as insect cells such as silkwoiin cells and adult silkworm per se.
Construction of a vector may be performed using a restriction enzyme, ligase etc. according to a standard method known in the art. An “expression vector” is a vector that allows expression of a protein encoded by the DNA sequence of the vector in a target cell. The transformation of a host with an (expression) vector can be performed according to standard methods.
At some instances, the present application refers to a host cell being “transfected”. This refers to a situation where foreign DNA is introduced into a cell. A transfected host cell may be “stably transfected”. This refers to the introduction and integration of foreign DNA into the genome of the transfected cell. Alternatively, a transfected host cell may be “transiently transfected”. This refers to the introduction of foreign DNA into a cell where the foreign DNA fails to integrate into the genome of the transfected cell.
As used herein, the term “transgenic plant” refers to a plant that has a heterologous gene integrated into its genome and that transmits said heterologous gene to its progeny. A “heterologous gene” is a gene that is not in its natural environment. For example, a heterologous gene includes a gene from one species introduced into another species. In some embodiments, a heterologous gene also includes a gene native to an organism that has been altered in some way (e.g., mutated, added in multiple copies, or linked to non-native regulatory sequences). Heterologous genes are distinguished from endogenous genes in that the heterologous gene sequences are typically joined to DNA sequences that are not found naturally associated with the gene sequences in the chromosome or are associated with portions of the chromosome not found in nature (e.g., genes expressed in loci where the gene is not normally expressed).
A “protein having glycosyl transferase activity” is a protein that is capable of catalyzing a glycosylation reaction in which the sugar group of a sugar donor is transferred to an acceptor molecule. A protein having glycosyl transferase activity can be obtained by culturing, cultivating or growing a host cell or organism that expresses such a protein (for example a host cell transformed with a vector as described in the above embodiments), and then by recovering and/or purifying the protein from the host cell, host organism or culture medium according to standard methods, such as filtration, centrifugation, cell disruption, gel filtration chromatography, ion exchange chromatography and the like. For example, the methods described in Example 1 of the present application can be used.
A “recombinantly expressed” glycosyl transferase is a glycosyl transferase protein that has been expressed from a recombinant DNA molecule, i.e. from a DNA molecule formed by laboratory methods of genetic engineering (such as molecular cloning) to bring together genetic material from multiple sources, creating a DNA sequence that would not be found naturally in a biological organism. Typically, a recombinantly expressed glycosyl transferase is expressed by heterologous expression (i.e. in a host organism which is different from the organism from which said glycosyl transferase is originally derived), such as by expression in e.g. E. coli, Saccharomyces cerevisiae, Pichia pastoris or insect cells, preferably in E. coli. Preferably, said recombinantly expressed glycosyl transferase is expressed by heterologous expression. Preferably, said recombinantly expressed glycosyl transferase is isolated after expression from other proteins of the host organism by methods of protein purification.
The term “reaction product composition”, as used herein, refers to a composition obtained from a method for forming/producing said reaction product upon completion of the reaction step in which said reaction product is actually formed, wherein said composition is not subjected to any further steps of purifying or separating the components of the reaction mixture obtained after said reaction step in which said reaction product is actually formed. If used in the context of a method to produce a product in a host cell or transgenic plant, the term “reaction product composition” refers to the culture supernatant, host cell extract or transgenic plant extract in which said product is harvested from said host cell or transgenic plant.
The present inventors have surprisingly found that VvGT14 and VvGT15 have glucosyl transferase activities (kcat/KM) for the substrates geraniol, nerol and citronellol that are higher by a factor of 2.6 to 44 compared to known terpene glycosyl transferases, such as UGT85B1 of Sorghum bicolor (see Table 5). Moreover, the present inventors have surprisingly found that the glycosyl transferases VvGT14 and VvGT15 are expressed more efficiently than other known terpene glycosyl transferases as recombinant proteins in E. coli cells or other host cells. Moreover, the present inventors have surprisingly found that the glycosyl transferase VvGT14 is capable of catalyzing glucosylation of furaneol, whereas plant glycosyl transferases that are capable of catalyzing glucosylation of furaneol are otherwise not known.
In the following, reference is made to the figures:
All methods mentioned in the figure descriptions below were carried out as described in detail in the examples.
The relative expression was quantified in Gewurztraminer 11-18 Gm (black bars) and White Riesling 239-34 Gm (grey bars). Sampled tissues: Inflorescences four weeks (I1) and two weeks (I2) before flowering and at full bloom (I3), leaves at the age of approximately one week (L1), three weeks (L2) and five weeks (L3) and roots (R). The mean values+SD of three independent experiments are shown, o.o.r. out of range.
Different stages of berry development are given as weeks post flowering. Expression was determined in berry skins (exocarp) of five different varieties and clones. Mean values±SD of three independent experiments are shown, o.o.r. out of range.
The relative activities refer to the highest level of extractable radioactivity which was measured for the conversion of geraniol (100%) in case of VvGT14a and VvGT15a-c (order of the columns 15c, 15b, 15a) and benzyl alcohol (100%) in the case of VvGT16. Data for two biological and two technical replicates are shown. Black and white bars represent monoterpenoids and non-monoterpenoids, respectively. (D): Chemical structures of geraniol, nerol, 3S-citronellol, α-terpineol and 3S-linalool.
LC-MS analysis of citronellyl B-D-glucoside (A), geranyl β-D-glucoside (B), neryl β-D-glucoside (C), linaloyl β-D-glucoside (D) formed by VvGT14a, VvGT15a and VvGT16 and a mixture of synthesized monoterpenyl β-D-glucosides (E); chromatograms display an overlay of single product measurements, traces show the total ion current of the characteristic transitions (refer to Example 1), Gaussian smoothing was partly applied.
A) Racemic mixture of R,S-citronellol was used as substrate for VvGT14a and VvGT15a, enantiomerically pure R-citronellol was used as reference.
B, C) racemic citronellol is released by acid catalyzed hydrolysis of citronellyl-β-D-glucoside formed by VvGT14a and VvGT15a. Signals labeled with “x” are hydrolysis by-products. Chromatograms are shown in SIM mode by using the characteristic ion traces m/z 69, 81 and 123 for citronellol.
D) Racemic mixture of R,S-linalool was used as substrate for VvGT14a.
E) Enantiomerically pure R-linalool was used as reference material.
F) A slight preference for the R-linalool is revealed after enzymatic hydrolysis with AR 2000. Chromatograms are shown in SIM mode (m/z 71, 93).
Radio-TLC analysis (A) of products formed by VvGT14a (1,2,3), VvGT15a (4,5,6) and VvGT16 (7,8,9) after incubation with the aglycone library obtained from grape berries of Gewurztraminer 11-18 Gm (1,4,7); Positive control: geraniol (2,5,8); negative control: no acceptor molecule (3,6); UDP [14C]-glucose (9; approximately: 3000 dpm). The plates were analyzed by digital autoradiograph. The products formed from citronellol, geraniol and nerol were verified by LC-MS analysis. GC-MS analysis (B, total ion chromatogram) of volatiles that were enzymatically released from glucosides which were formed by incubation of an aglycone library obtained from grape berries of Gewurztraminer 11-18 Gm with UDP-glucose and VvGT14 (gray) or heat-inactivated VvGT14a (black) as control 1: linalool; 2: citronellol; 3: nerol; 4: geraniol; 5: benzyl alcohol; 6: phenylethanol.
In the following, reference is made to the examples, which are given to illustrate, not to limit the present invention.
Plant Material
Vitis vinifera grapevines of cultivars Gewurztraminer 11-18 Gm, Gewurztraminer FR 46-107, White Riesling 239-34 Gm, White Riesling 24-196 Gm and Muscat a petit grains blancs FR 90 were grown during vintages 2011 and 2012. Grape berries, leaves, inflorescences and roots were collected. Sampling was conducted for a total of six dates between 6 and 17 weeks after bloom including berries from pea-size to harvest ripeness. Muscat a petit grains blancs FR 90 was additionally sampled every two weeks from week 4 to week 18 after bloom.
After veraison (the onset of ripening) 100 berries were collected for the determination of ripening related parameters like sugar content. For terpenoid analysis 250 g of berries were stored at −20° C., while three replicates consisting of ten berries were peeled and skins immediately frozen in liquid nitrogen for subsequent RNA extraction. Roots were obtained from scions of White Riesling 239-34 Gm and Gewurztraminer 11-18 Gm grown in the greenhouse. Leaves were sampled from the same cultivars at the approximate age of one, three and five weeks. In addition, inflorescences four and two weeks before flowering and at full bloom were collected. Samples were stored at −20° C. until work-up.
Chemicals
UDP-[14C]glucose (300 mCi/mmol, 0.1 mCi/mL) was obtained from American Radiolabelled Compounds (St Louis, Mo., USA). (R,S)-3,7-dimethyl-1,6-octadien-3-ol (linalool) and (E)-3,7-dimethyl-2,6-octadien-1-ol (geraniol) were obtained from Roth (Karlsruhe, Germany). (R,S)-3,7-dimethyl-6-octen-1-ol (citronellol) and pure (R)-(+)-B-citronellol were purchased from Sigma Aldrich (Steinheim, Germany). (Z)-3,7-dimethyl-2,6-octadien-1-ol (nerol) was purchased from Alfa Aesar (Karlsruhe, Germany). (R,S)-3,7-dimethyl-6-octenyl β-D-glucopyranoside (citronellyl β-D-glucoside), (Z)-3,7-dimethyl-2,6-octadienyl β-D-glucopyranoside (neryl β-D-glucoside) and (E)-3,7-dimethyl-2,6-octadienyl β-D-glucopyranoside (geranyl β-D-glucoside) were synthesized according to the Koenigs-Knorr-procedure, (R,S)-3,7-dimethyl-1,6-octadienyl B-D-glucopyranoside (linaloyl β-D-glucoside), according to a modified Koenigs-Knorr-procedure.
Sample Preparation for Metabolite Analysis
Grapes berries were peeled and 10 g (fresh weight) of the grape skins were taken for one analysis. In case of root, leaf and inflorescence, 4 g plant material was taken per analysis. The material was frozen in liquid nitrogen, ground and extracted with a mixture of phosphate buffer (0.1 M, pH 7) and 13% ethanol for 24 h under nitrogen with exclusion of light (Jesús Ibarz et al., 2006). 2-Octanol was used as internal standard for the determination of free monoterpenes. For the determination of monoterpenyl β-D-glucosides, stable isotope dilution analysis (SIDA) was applied, using [2H2]-citronellyl β-D-glucoside as a labeled, internal standard. The concentration of the internal standards was adapted for the variety, the tissue and the ripening stage of the plant material. 2-Octanol was added in a range of 0.3 to 6.8 mg/kg plant material, [2H2]-citronellyl-β-D-glucoside in a range of 0.1 to 3.5 mg/kg plant material.
To purify the sample, Carrez reagents (Merck Millipore, Darmstadt, Germany) were added (1 mL each) and the sample was then centrifuged at 14500 rpm for 20 min at 5° C. The supernatant was taken for subsequent solid phase extraction (SPE) to isolate and separate free monoterpenes from glycosidically bound monoterpenes. Therefore, a 200 mg Lichrolut EN column (Merck, Darmstadt, Germany) was conditioned as described (Piñeiro et al., 2004). Free monoterpenols were eluted with dichloromethane and glycosidically bound monoterpenols with methanol.
For GC-MS detection, the dichloromethane fractions were dried with Na2SO4, concentrated using nitrogen to 200 μL and analyzed. For LC-MS detection, the methanolic fractions were concentrated under reduced pressure and the residues were dissolved in water/acetonitrile (7/3; v:v). The samples were analyzed by LC-MS.
Nucleic Acid Extraction
For total RNA extraction plant material was ground to a fine powder in liquid nitrogen using mortar and pestle. One g of the powder was used for RNA extraction with the CTAB (cetyltrimethylammonium bromide) method following an established protocol (Zeng and Yang, 2002, adapted by Reid et al. 2006) to meet the requirements of different grape tissues. Remaining genomic DNA was digested by DNase I and cleaned up with the High Pure RNA Isolation kit (Roche, Mannheim, Germany).
Transcription Analysis
Transcription analysis was performed using the Genome Lab GeXP Genetic Analysis System (Beckman Coulter, Krefeld, Germany), a multiplex quantitative gene expression analysis system. The gene expression patterns of the VvGT genes VvGT14, VvGT15 and VvGT16 and five reference genes (VvActin, VvAP47, VvPP2A, VvSAND, and VvTIP41) were analyzed simultaneously from one sample of total RNA.
Reverse transcription was carried out with the GenomeLab™ GeXP Start kit (Beckman Coulter) following the manufacturer's instructions. As an internal control gene KANr RNA was co-reverse transcribed and subsequently amplified together with the reference genes and genes of interest. The gene specific primers for reverse transcription are chimeric, providing a 19 nt universal tag for the binding of universal reverse primers in the subsequent PCR reaction. The final concentration of the primers ranged from 0.1 nM to 100 nM to compensate for the different transcription levels of the analyzed genes (Table 3). Multiplex PCR reactions were conducted with Thermo-Start DNA Polymerase (Thermo Fisher Scientific, Dreieich, Germany). Each reaction contained 9.3 μL of reverse transcription products as template and 10.7 μL of a PCR reaction mix including gene specific forward primers providing an 18 nt universal tag (Table 3). The universal forward primer is labeled with a fluorescent dye for detection during subsequent capillary electrophoresis. Primer pairs were designed to yield PCR products ranging from 119 bp to 374 bp and differing in size by at least 8 bp. Of each PCR product, 4 μL were separated by capillary electrophoresis using the GenomeLab Genetic Analysis System (Beckman Coulter).
Individual standard curves for each gene in the multiplex were performed with serial two-fold dilutions ranging from 3.91 ng to 500 ng of an RNA mixture from all samples. Raw data were analyzed using the fragment analysis tool. The fragment data of the standard curves and samples were then normalized to the peak area of KANr RNA with the express analysis tool. Subsequently, the relative signal level of each sample replicate was interpolated from the standard curve. The data was further normalized to the geometric mean of the five reference genes with quant tool. All software for GeXP data analysis was purchased from Beckman Coulter.
Cloning of VvGT14, VvGT15 and VvGT16 DNA Sequences from Vitis vinifera
The reference genome of Vitis vinifera sequenced genome PN40024 was used to design gene specific primers in the untranslated regions of the three putative VvGT genes, VvGT14, VvGT15, and VvGT16 using the tool Primer-BLAST. Primers (Table 4) were purchased from Eurofins MWG Operon (Ebersberg, Germany). The cDNA-synthesis was performed with the SuperScript® III First-Strand Synthesis SuperMix (Life Technologies, Darmstadt, Germany) following the manufacturer's instructions. The template for cDNA-synthesis was total RNA, extracted from grape exocarp. The cDNA was used as template in the following PCR-reaction. PCR was performed with Phusion DNA Polymerase (Thermo Fisher Scientific, Dreieich, Germany) using high-fidelity (HF)-buffer and the following thermal cycling conditions: 98° C. for 30 s followed by 32 cycles consisting of 98° C. for 5 s, 60° C. for 5 s and 72° C. for 30 s and a final elongation step of 72° C. for 1 min.
PCR products were gel purified with the Wizard SV Gel and PCR Clean-Up System (Promega, Madison, USA). A-tailing of purified PCR-products was performed with Taq DNA Polymerase (Thermo Fisher Scientific). A-tailed PCR-products were ligated into pGEM-T Easy vector (Promega, Madison, USA) and cloned in One Shot TOP10 Chemically Competent E. Coli (Life Technologies, Darmstadt, Germany). Plasmids were isolated with the PureYield Plasmid Miniprep System (Promega, Madison, USA) and sequenced with the vector specific primers M13 uni (—21) and M13 rev (−29) on an ABI 3730 capillary sequencer (StarSEQ, Mainz, Germany). Raw data was edited with the FinchTV software (Geospiza, Seattle, USA). Sequences were assembled with SeqMan and aligned with MegAlign (DNASTAR, Madison, USA).
Construction of Expression Plasmids
The full-length ORFs of the VvGT sequences were subcloned into the pGEM-Teasy vector (Promega, Madison, Wis., USA). All genes were amplified with primer introducing BamHI and Notl restriction sites. Subsequently, the genes were cloned in frame with the N-terminal GST-tag into the pGEX-4T-1 expression vector (Amersham Bioscience, Freiburg, Germany). The gene identity was confirmed by sequencing (Eurofins MWG Operon, Ebersberg, Germany).
Heterologous Protein Expression
Recombinant protein was expressed in E. coli BL21 (DE3) pLysS (Novagen, Schwalbach, Germany). Pre-cultures were grown overnight at 37° C. in Luria Bertani medium containing 100 μg/mL ampicillin and 23 μg/mL chloramphenicol. The next day, 1 L Luria Bertani solution containing the appropriate antibiotics was inoculated with 50 mL of the pre-culture. The culture was grown at 37° C. at 160 rpm until OD600 reached 0.6-0.8. After cooling the culture to 16° C., 1 mM IPTG was added to induce protein expression. Cultures were incubated over night at 16-18° C. at 160 rpm. Cells were harvested by centrifugation and stored at −80° C. Negative controls were carried out with E. coli BL21 (DE3) pLysS cells containing the empty expression vector pGEX-4T-1.
Cell Lysis and Purification
Recombinant GST-fusion proteins were purified by GST Bind resin (Novagen) following the manufacturer's instructions. Briefly, the cells were re-suspended in the binding buffer containing 10 mM 2-mercaptoethanol. Cells were disrupted by sonication. The crude protein extract was incubated for 2 h with the GST Bind resin to bind GST fusion protein. The recombinant protein was eluted with GST elution buffer containing reduced glutathione and quantified by Bradford solution (Sigma-Aldrich, Steinheim, Germany). The presence of the expressed proteins was confirmed by SDS-PAGE and Western Blot using anti-GST antibody.
Activity Assay and Kinetics
In the initial screening, each reaction mixture (200 μL in total) contained Tris-HCl buffer (100 mM, pH 8, 10 mM 2-mercaptoethanol), 37 pmol UDP-[14C]glucose (0.01 μCi, Biotrend, Köln, Germany), substrate (50 μL of a 1 mg/mL stock solution) and purified protein (0.5-0.8 μg/μL). The reaction mixture was incubated at 30° C. for 18.5 hours. The assays were stopped by adding 1 μL 24% trichloroacetic acid and extracted with 500 μL water-saturated 1-butanol. The organic phase was mixed with 2 mL Pro Flow P+ cocktail (Meridian Biotechnologies Ltd., Epsom, UK) and radioactivity was determined by liquid scintillation counting (LSC, Tri-Carb 2800TR, Perkin Elmer, Waltham Mass., USA). Additionally, negative controls without substrate were performed. After determining the optimal conditions for the best substrate of each gene, the substrate screening was repeated under these conditions.
The kinetic data were determined with increasing concentrations of the substrates (VvGT14a: citronellol, geraniol, 8-hydroxylinalool, linalool, nerol and terpineol; VvGT15a-c: S-citronellol, geraniol, 8-hydroxylinalool and nerol; VvGT16: citronellol, geraniol and nerol) from 1 μM to 100 μM (VvGT14a and VvGT15a-c) or 50 μM to 500 μM (VvGT16) and a fixed UDP-glucose concentration of 108 μM (100 μM unlabeled UDP-glucose and 8 μM UDP-[14C] glucose; VvGT14a), 833 μM (825 μM unlabeled UDP-glucose and 8 μM UDP-[14C] glucose;VvGT15a-c) or 512.5 μM (500 μM unlabeled UDP-glucose and 12.5 μM UDP-[14C] glucose; VvGT16). The total volume was 40 μL and 0.2 μg (VvGT14a), 0.5 μg (VvGT15a-c) or 5 μg (VvGT16) of purified protein. The measurements were performed under the following conditions. The assays were carried out at 30° C. for 1.5 h using a Tris-HCl buffer (100 mM, 10 mM 2-mercaptoethanol, pH 8.5 for VvGT14a and VvGT16). The assay of VvGT15a-c was performed at 30° C. using a Tris-HCl buffer (100 mM, 10 mM 2-mercaptoethanol, pH 7.5) and 10 min (VvGT15c) or 30 min (VvGT15a-b) of incubation for the best substrates. The amount of the purified enzyme and the incubation time were adapted depending on the counting sensibility. The reaction was stopped by adding 1 μL 24% trichloroacetic acid and glucosides were extracted with 100 μL ethyl acetate. Radioactivity was determined by LSC.
To determine the kinetic data of UDP-glucose, the value of geraniol was fixed (1.25 mM for VvGT15a-c and VvGT16; 0.1 mM for VvGT14a) and UDP-[14C] glucose was mixed with non-radiolabeled UDP-glucose to obtain concentrations ranging from 5 μM to 100 μM (VvGT14a and VvGT15a-c) or 25 μM to 500 μM (VvGT16). The KM- and vmax-values were calculated from Lineweaver-Burk plots, Hanes-Woolf plots and non-linear fitting of the experimental data.
Preparation of Aglycone Libraries
For the preparation of aglycone extracts 50 g (fresh weight) grape skins or 4 g (fresh weight) inflorescences of Gewurztraminer Gm 11-18 were ground to a fine powder in liquid nitrogen. The isolation of glycosides was carried out as described above (see metabolite analysis). The methanolic fraction, which was obtained after SPE, was enzymatically hydrolysed. Therefore, the dried sample was dissolved in citric-acid buffer (0.1 M, pH 4), 50 mg AR 2000 (an enzyme preparation with glucosidase activity prepared from Aspergillus niger; DSM Food Specialties Beverage Ingredients, Delft, Netherlands) was added and incubated for 24 h with exclusion of light. The liberated aglycones were extracted by 20 mL methyl-tert-butyl ether and the organic phase was reduced to 1000 μL using a gentle stream of nitrogen.
Activity Based Profiling using a Physiologic Aglycone Library
Aliquots of this aglycone extract were incubated with UDP-glucose and various VvGT-enzymes. Optimum conditions at 30° C. for 24 hours were applied. Each solution contained 100 μL purified enzyme, 100-150 μL Tris-HCl buffer (100 mM, pH7.5 or 8.5, 10 mM 2-mercaptoethanol), 37 pmol UDP-[14C]glucose (0.01 μCD and 50-100 μL extract (dissolved in methyl-tert-butylether). The buffer was mixed with the extract and the organic solvent was gently vaporized with nitrogen. The missing volume was adjusted with buffer before the enzyme was added. The reaction was stopped by adding 1 μL 24% trichloroacetic acid and extracted with 500 μL ethyl acetate. After termination of the reaction free aglycones, which were not converted by VvGT14 and VvGT15, were measured via SPME-(Solid Phase Microextraction)-GC-MS. These residual, free aglycones were completely removed by extraction with dichloromethane. Enzymatically formed glucosides were extracted by ethyl acetate, which was removed under nitrogen. The residue was dissolved in methanol and analyzed by LC-MS to detect the generated monoterpenol glucosides. Enzymatic hydrolysis of the glucosides was performed using AR 2000 and 2 mL citric-acid-buffer. After hydrolysis, a 100 μL aliquot was used to detect volatile aglycones via SPME-GC-MS. The remaining solution was extracted with methyl-tert-butyl ether and reduced under nitrogen to approximately 200 μL. One μL were measured by GC-MS via liquid injection.
Enantioselectivity of VvGT14a, VvGT15a-c
To determine the enantioselectivity of VvGT14 and VvGT15 the enantiomeric ratio of glucosidically bound citronellol and linalool was determined by enantioselective GC-MS. Following the incubation, residual citronellol and linalool were completely removed by extraction with dichloromethane. Chronellyl β-D-glucoside which remained in the aqueous phase was hydrolyzed by HCl (2 mL, 0.1 M, pH 1) for one hour at 100° C. to release citronellol (Skouroumounis and Sefton, 2000). In case of linalyl β-D-glucoside an enzymatic hydrolysis (AR 2000, citric acid buffer pH 4, 24 h) was applied due to the instability of linalool in acid solutions (Williams et al., 1982). Hydrolysis of a synthetic 1:1 mixture of R- and S-linalyl β-D-glucoside revealed that AR 2000 does not discriminate between the two diastereomeric glucosides. After hydrolysis, citronellol and linalool were analyzed by SPME-GC-MS as described above.
LC-MS Analysis
For LC-MS analysis of monoterpenyl β-D-glucosides a Shimadzu LC2OAD HPLC system coupled to an API 2000 (Applied Biosystems, AB Sciex, Framingham, USA) triple-quadrupol-MS was used. Data acquisition was performed using Analyst software version 1.6.1. (Applied Biosystems, AB Sciex, Framingham, USA). The column (Phenomenex Gemini-NX 5u C18, 250×3 mm, Aschaffenburg, Germany) was eluted with a linear gradient starting at water/acetonitrile (7/3; v:v) containing 0.2% ammonia till 12 min to water/acetonitrile (4/6; v:v; 0.2% ammonia) at 18 min. The column temperature was maintained at 40° C. The mass spectrometer was operated in ESI-MRM negative ion mode. Nitrogen was used as curtain (setting 20), nebulizing and collision gas (collision energy was −20 eV). Monoterpenyl β-D-glucosides were identified by the following, characteristic MRM transitions {LinGlc: m/z 315→161(Glu), 315→113(Glu); NerGlc: m/z 315→119(Glu), 315→113(Glu); GerGlc: m/z 315→119(Glu), 315→113(Glu); CitrGlc: m/z 317→101(Glu), 317→161(Glu)} (Cole et al., 1989; Domon and Costello, 1988; Salles et al., 1991).
GC-MS Analysis
GC-MS analysis was performed with a Varian GC-450 coupled to a Varian MS-240 ion-trap employing a Phenomenex Zebron ZB-WAXplus column (30 m×0.25 mm×0.25 μm, Aschaffenburg, Germany). Helium flow rate was 1 mL/min. The analysis was carried out in split mode (liquid injections) or splitless mode (SPME measurements) with 220° C. injector temperature. EI (electron impact ionization)-MS spectra were recorded from m/z 40 to 300 (ionization energy 70 eV; trap temperature 170° C.). The oven temperature program was 60° C. (3 min), 10° C./min up to 250° C. (5 min). In case of SPME measurements, liberated aglycones were isolated for 10 min at 60° C. using a fiber coated with a 85 μm film of polyacrylate (SUPELCO, Bellefonte, USA). After extraction the SPME fiber was desorbed for 10 min at 250° C. in the injection port of the GC-MS system and the column oven program was carried out as described above. Enantioselective GC-MS analysis was performed with a Varian GC-450 coupled to a Varian MS-240 ion-trap. The column was a DiAcB (heptakis-(2,3-di-O-acetyl-6-O-tert.-butyldimethylsilyl)-B-cyclodextrin), 26 m×0.32 mm i.d. with a 0.1 μm film. Helium was used as carrier gas at a flow rate of 1 mL/min, injector temperature was 250° C. with a split ratio of 1/100 (liquid injections), or splitless (SPME measurement). The oven temperature program was 70° C. (3 min), 0.5° C./min to 130° C. 20° C./min up to 200° C. (3 min). GC-MS measurements were recorded in full scan mode. Selected ion monitoring (SIM) mode was used for quantification.
Radio-TLC Analysis
Assays containing UDP-[14C]glucose and aglycone libraries or substrates were performed as described above and subsequently extracted with 500 μL ethyl acetate. The organic solvent was vaporized and the pellet was re-suspended in 10 μL methanol and was applied on Silica Gel 60 F254 plates (Merck, Darmstadt, Germany). The dried plates were developed in a solvent system chloroform:acetic acid:water (50/45/5, v:v:v). Plates were dried and analyzed by digital autoradiograph (digital autoradiograph, EG&G Berthold, Wildbad, Germany).
All methods mentioned in this example were carried out as described in Example 1.
The transcript levels of VvGT genes VvGT14 (designation in Vitis vinifera genome project: VIT_18s0001g06060), VvGT15 (VIT_06s0004g05780) and VvGT16 (VIT_03s0017g01130) of Vitis vinifera cv. Pinot noir were analyzed using GeXP profiling in up to five cultivars in three different tissues (
The same is true for the ripening related parameters such as sugar content and pH value. Thus, VvGT14-16 appear to play an important role in grape berry ripening as their expression levels peak after veraison and they are barely expressed in other tissues, except VvGT16.
All methods mentioned in this example were carried out as described in Example 1.
To correlate the expression profiles of putative UGTs with terpenyl glucoside concentration metabolite analysis was performed in five cultivars during grape ripening (Table 1). Solid phase extraction was used to isolate free (non-glycosylated) and glycosylated monoterpenes from grape skins (exocarp) of various grapevine cultivars (Gunata et al., 1988; Mateo and Jimenez, 2000). Since grape skins (exocarp) accumulate the majority of terpene metabolites detected in grape berries they were separated from the flesh and extracted (Wilson et al., 1986). Geraniol, nerol, linalool and citronellol were quantified by GC-MS analysis whereas their non-volatile monoterpenyl glucosides were determined by a stable isotope dilution analysis (SIDA) method using LC-MS. Isotopically labelled internal standards were chemically synthesized.
Grape berries of the V. vinifera cultivars differed not only in their amounts of total terpenes, but also in their terpene profiles at different developmental stages (Table 1). Monoterpenols (free and glucosidically bound) were hardly detected (less than 0.25 mg/kg grape skins) in grape exocarp of Gewurztraminer FR 46-107, probably due to impaired monoterpene biosynthesis of this clone. Gewurztraminer 11-18 Gm and Muscat a petits grains blanc FR 90 skins accumulated significant levels of geraniol, citronellol and nerol derivatives (up to 5.5 mg/kg grape skins) and displayed a heterogenous spectrum of monoterpenes at every stage of ripening. Both Riesling clones produced smaller amounts of the metabolites that were mainly observed at weeks 15-17. In general, the highest concentration of free and bound terpenols was found in the late stages of ripening in all investigated cultivars, whereupon geraniol and its β-D-glucoside were the predominant terpene metabolites. The ratios of the amount of free to glucosidically bound forms of individual monoterpenes varied considerably at week 15 and 17 post flowering. These values provide a first indication of variable UGT activity in different varieties and/or differential preference of the UGTs for their monoterpene substrates.
Notably, the evolution of monoterpenyl β-D-glucosides in grape exocarp of the Riesling clones (Table 1) correlated well with the expression pattern of VvGT14 in the same tissue (
All methods mentioned in this example were carried out as described in Example 1.
The alleles of VvGT14a-c, 15a-c and 16 were isolated from V. vinifera cultivars and cloned in the expression vector pGEX-4T-1. The recombinant proteins were expressed with an N-terminal GST-tag, affinity purified and verified by SDS-PAGE and Western Blot using GST-specific antibody. Enzyme activity studies were performed with UDP-[14C]glucose and various putative substrates (terpenols, flavonoids and different mono-alcohols) that are known to be glycosidically bound and present in grapes (Gunata et al., 1988).
Recombinant VvGT14a, VvGT15a-c and VvGT16 converted several of the tested substrates (
The KM and kcat values of VvGT14a for geraniol (9 μM; 0.02 sec−1), citronellol (9 μM; 0.02 sec'1), nerol (10 μM; 0.02 sec−1) and UDP-glucose (16 μM; 0.03 sec−1) were alike (Table 2) and resembled the kinetic data of VvGT1 (Offen et al., 2006) and CaUGT2 (Catharanthus roseus) (Masada et al., 2007) for their natural substrates quercetin (31 μM; 0.075 sec−1) and curcumin (43.9 μM; 0.0165 sec−1), respectively. The data were also similar to those of VvGT5 (5.6 μM; 7.16 sec−1), VvGT6 (9.24 μM; 0.76) and UGT71G1 (57 μM; 0.0175 sec−1) from Medicago truncatula (He et al., 2006) for the conversion of quercetin (Ono et al., 2010). Hence, the specificity constants (kcat/Km) identified the monoterpenols as most probable in vivo substrates of VvGT14a as the kcat/KM values of geraniol, citronellol and nerol are 4, 4, and 40 fold higher, respectively than the values of the monoterpenols for UGT85B1 from Sorghum bicolor (Hansen et al., 2003) (see Table 5). Thus, VvGT14a shows unprecedented glucosyltransferase activity toward geraniol, citronellol and nerol.
The sequence comparison of the active VvGT14a allele with the two inactive alleles showed one point mutation at position 391 (P391L) in VvGT14b and a deletion of 21 aa at position 165 in VvGT14c rendering them inactive (
The allelic forms of VvGT15a-c showed a similar substrate spectrum (
Notably, the glucosylation of monoterpenols by UGT85B1, the cyanohydrins (mandelonitrile) GT from Sorghum bicolor, can be seen as promiscuous activity (Hansen et al., 2003). However, the KM data of VvGT14a and VvGT15a-c were 1.6 to 125-fold lower and the kcat/KM values up to 78 times higher than the data obtained for the glucosylation of terpenoids by UGT85B1. Mandelonitrile was only a poor substrate of VvGT14a and was not accepted at all by VvGT15a-c.
VvGT16 glucosylated monoterpenols, some short-chained and aromatic alcohols, albeit with low efficiency (
The formation of monoterpenyl glucosides was confirmed by LC-MS analysis in comparison with chemically synthesized glucosides (
Besides, selected glucosides of the transformed terpenoids were visualized by radio-TLC (
All methods mentioned in this example were carried out as described in Example 1.
Grape berries accumulate free and bound S-citronellol and S-linalool, albeit in lower levels than nerol and geraniol (Table 1). To elucidate the enantiomeric preference of VvGT14a and VvGT15a, racemic citronellol was used as substrate and racemic linalool was transformed by VvGT14a. Chiral phase GC-MS analysis of liberated citronellol after acid hydrolysis of citronellyl B-D-glucoside demonstrated no enantio-discrimination by VvGT14a and 15a if the reaction mixture is incubated for a prolonged time (24 h;
Furthermore, liberated linalool, after enzymatic hydrolysis of linaloyl β-D-glucoside (formed by VvGT14a), showed a slight enrichment of the R-enantiomer (
While VvGT14a and VvGT15a-c preferentially glucosylated S-citronellol in short time assays enantioselectivity of these enzymes for citronellol was not observe in long tend studies (
All methods mentioned in this example were carried out as described in Example 1.
The assay conditions were optimized for the conversion of geraniol to determine the kinetic constants of the active enzymes. The highest activity of VvGT14a, 15a-c and 16 was found in Tris-HCl buffer (pH 8.5, 7.5 and 8.5, respectively) at 30° C. The product formation of VvGT14a (0.2 μg purified enzyme) was linear for at least 90 minutes. KM and kcat values were obtained for geraniol, citronellol, nerol, terpineol, 8-hydroxylinalool, and linalool with a constant UDP-glucose level (108 μM) and for UDP-glucose with a fixed geraniol concentration (100 μM; Table 2). The kinetic parameters were deteiiiiined from a hyperbolic Michaelis-Menten saturation curves. Due to the low conversion rates of 8-hydroxylinalool, terpineol and linalool, the amount of purified enzyme was increased (2, 2, and 10 μg protein, respectively).
Interestingly, the KM and kcat value of VvGT14a for citronellol. geraniol, nerol and UDP-glucose was quite similar (KM 9-10 μM; kcat 0.02 sec−1; kcat/Km 2.0-2.6 sec−1 mM−1), while the kinetic data for 8-hydroxylinalool, terpineol and linalool explained the significantly lower enzyme activity towards these substrates. The kinetic data of VvGT15a-c (0.5 or 1 μg purified enzyme) were maintained for geraniol, S-citronellol, nerol and 8-hydroxylinalool with a fixed UDP-glucose amount (833 μM) and for UDP-glucose with a constant geraniol concentration (1.25 mM; Table 2). The formation of geranyl, neryl, and citronellyl β-D-glucoside was linear for at least 10 minutes (VvGT15c) and 20 minutes (VvGT15a and b), but was extended for 8-hydroxylinaloyl β-D-glucoside up to 30 min (VvGT15c) and 60 min (VvGT15a and b). The kinetic data confirmed the high enzymatic activity of the VvGT15 alleles towards geraniol and UDP-glucose. The KM and kcat value for S-citronellol and nerol was similar, whereas 8-hydroxylinalool was a poor substrate. Furthermore, the data illustrated that VGT15c is superior to VvGT15a and b. Kinetics of VvGT16 were calculated for geraniol, citronellol and nerol (Table 2). Product formation of VvGT16 (5 μg purified protein) was linear for at least 4 hours. KM and kcat values were obtained for the monoterpenes with a constant UDP-glucose level (512.5 μM) and for UDP-glucose with a fixed geraniol concentration (1.25 mM). VvGT16 exhibited the lowest enzymatic activity towards the substrates of the tested UGTs.
All methods mentioned in this example were carried out as described in Example 1.
To reveal the natural substrates of VvGT14a, VvGT15a-c and VvGT16 (
Initially, the aglycone extracts were incubated with the purified recombinant enzymes (VvGT14a, 15a, and 16) using radiolabeled UDP-[14C] glucose. Formed products were extracted; radioactivity was quantified by liquid scintillation counting and analyzed by radio-TLC (
VvGT14a and VvGT15a-c readily formed radiolabeled products when incubated with an aglycone library obtained from grape skins of Gewurztraminer 11-18 Gm (
The features of the present invention disclosed in the specification, the claims, and/or in the accompanying drawings may, both separately and in any combination thereof, be material for realizing the invention in various forms thereof.
V. vinifera
V. vinifera
V. vinifera
V. vinifera
Sorghum bicolor
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| Number | Date | Country | Kind |
|---|---|---|---|
| 14174722.0 | Jun 2014 | EP | regional |
| Filing Document | Filing Date | Country | Kind |
|---|---|---|---|
| PCT/EP2015/064581 | 6/26/2015 | WO | 00 |
