Patent Application
20230203461
The plant cell wall is composed of cellulose, hemicelluloses, pectic polysaccharides, and lignin, and is collectively termed lignocellulose. Photosynthetically fixed carbon in lignocellulose is produced in vast quantities on the Earth’s surface. Its conversion into liquid transportation fuel represents a potential source of renewable energy with diverse feedstocks, including agricultural residues, municipal waste, and dedicated low-input crops. Effective utilization of lignocellulose, nevertheless, remains a challenge, as the extraction of fermentable sugars for biofuel production requires intensive physico-chemical pretreatments and high loadings of enzyme cocktails. A key factor of this recalcitrance to degradation is the presence of lignin, a heterogeneous, hydrophobic aromatic polymer that encases the cellulose and hemicellulose, blocking enzyme accessibility and impeding cellulase activity.
Lignin is synthesised by plants through the oxidative coupling of three hydroxycinnamyl alcohols: coniferyl alcohol, sinapyl alcohol and p-coumaryl alcohol, generating β—O—4, 4—O—5, β-5, β-1, 5-5 and β-β inter-unit linkages in β-ether, biphenyl ether, phenylcoumaran, spirodienone, biphenyl, and resinol units, respectively. Lignin requires a high redox potential to be oxidatively attacked. Recalcitrance to degradation is further enhanced as lignin has no defined repeat structure. The β—O—4 (or β-aryl) ether linkage is the most abundant linkage in the lignin macromolecule; its cleavage results in substantial lignin depolymerization.
Enzymes for depolymerising lignin are known and disclosed in US2019/048329 and include dehydrogenases, glutathione lyases and β-etherases which attack β—O—4 ether linkages. The β-etherase activity disclosed in US2019/048329 requires the co-substrates NAD+ and glutathione.
Tricin, [5,7-dihydroxy-2-(4-hydroxy-3,5-dimethoxyphenyl)-4H-chromen-4-one], an O-methylated flavone, forms part of the structure of lignin from monocot plants including wheat, rice, sugar cane, and palms. Tricin has only been observed incorporated into the lignin structure via 4—O—β linkages, having arisen from the radical coupling of the flavone at its 4′—O—position with the monolignol at its β-position.
Tricin is recognized as a valuable human health compound due to its antioxidant, anti-aging, anti-cancer, and cardio-protective potential. Tricin may be present as its parent compound that may be released by solvent extraction from a variety of monocotyledons such as wheat (Triticum aestivum), oat bran (Avena sativa), bamboo (Leleba oldhami), sugarcane (Saccharum officinarum), and maize (Zea mays), and has been observed in quantities of up to 3.3% wt of lignin from wheat straw.
This disclosure characterises a copper-containing β-etherase that can cleave the β-aryl ether linkage of lignin and which is secreted from the fungus Parascedosporium when growing on wheat straw. The disclosed β-etherase has no requirement for NAD+ and/or glutathione and was found to readily cleave tricin from wheat straw, also enhancing the saccharification of lignocellulosic biomass when used in combination with cellulolytic enzymes.
According to an aspect of the invention there is provided an isolated nucleic acid molecule encoding a β-etherase polypeptide wherein said polypeptide comprises copper and further wherein the activity of said polypeptide is independent of NAD+ and/or glutathione.
Lignin, the major component of lignocellulosic plant biomass, is an organic heterologous polymer comprising covalently linked phenylpropanoid units and consist essentially of crosslinked methoxylated derivatives of benzene such as p-coumaryl, coniferyl, and sinapyl alcohols. Exemplary phenylpropanoid units derived from the alcohols are p-hydroxyphenyl, guaiacyl, and syringyl units respectively. The phenylpropanoid units can be linked to other phenylpropanoid units through bonds such as β—O—4, 4—O—5, β-5, β-1, 5-5 and β-β inter-unit linkages. β—O—4 ether bonds account for 45-60% of linkages present in lignin. Flavonoid units such as tricin can be incorporated into lignin via 4—O—β ether bonds.
β-etherase activity in the context of this application refers to the capability to cleave β-aryl ether (β—O—4) bonds in lignin that link one phenylpropanoid unit to another phenylpropanoid unit or to flavonoid units such as tricin.
In order to optimize expression levels in recombinant host cells, codon optimisation of the nucleic acid sequence to be expressed may be required to convert a natural sequence to a non-natural sequence that encodes substantially the same polypeptide and would be optimally expressed in a heterologous host cell. Codon optimisation is known in the art and increases translational efficiency in the desired host organism and replace codons of low frequency with codons of high frequency.
In a preferred embodiment of the invention, the said isolated nucleic acid molecule comprises a nucleotide sequence selected from the group consisting of:
Hybridization of a nucleic acid molecule occurs when two complementary nucleic acid molecules undergo an amount of hydrogen bonding to each other. The stringency of hybridization can vary according to the environmental conditions surrounding the nucleic acids, the nature of the hybridization method, and the composition and length of the nucleic acid molecules used. Calculations regarding hybridization conditions required for attaining particular degrees of stringency are discussed in Sambrook et al., Molecular Cloning: A Laboratory Manual (Cold Spring Harbor Laboratory Press, Cold Spring Harbor, NY, 2001); and Tijssen, Laboratory Techniques in Biochemistry and Molecular Biology-Hybridization with Nucleic Acid Probes Part I, Chapter 2 (Elsevier, New York, 1993). The Tm is the temperature at which 50% of a given strand of a nucleic acid molecule is hybridized to its complementary strand. The following is an exemplary set of hybridization conditions and is not limiting:
In a preferred embodiment of the invention said isolated nucleic acid molecule comprises a nucleotide sequence selected from the group consisting of:
In a preferred embodiment of the invention said isolated nucleic acid molecule comprises a nucleotide sequence selected from the group consisting of:
In a preferred embodiment of the invention said isolated nucleic acid molecule comprises a nucleotide sequence selected from the group consisting of:
In a preferred embodiment of the invention said isolated nucleic acid molecule comprises a nucleotide sequence selected from the group consisting of:
In a preferred embodiment of the invention said isolated nucleic acid molecule comprises a nucleotide sequence selected from the group consisting of:
In a preferred embodiment of the invention said isolated nucleic acid molecule comprising a nucleotide sequence selected from the group consisting of:
In a preferred embodiment of the invention said isolated nucleic acid molecule comprises a nucleotide sequence selected from the group consisting of:
In a preferred embodiment of the invention said isolated nucleic acid molecule comprises a nucleotide sequence selected from the group consisting of:
In a preferred embodiment of the invention said isolated nucleic acid molecule comprises a nucleotide sequence selected from the group consisting of:
In a preferred embodiment of the invention said isolated nucleic acid molecule comprises a nucleotide sequence selected from the group consisting of:
In a preferred embodiment of the invention said isolated nucleic acid molecule comprises a nucleotide sequence selected from the group consisting of:
In a preferred embodiment of the invention said isolated nucleic acid molecule comprises a nucleotide sequence selected from the group consisting of:
In a preferred embodiment of the invention said isolated nucleic acid molecule comprises a nucleotide sequence selected from the group consisting of:
In a preferred embodiment of the invention said isolated nucleic acid molecule comprises a nucleotide sequence selected from the group consisting of:
In a preferred embodiment of the invention said isolated nucleic acid molecule comprises a nucleotide sequence selected from the group consisting of:
In a preferred embodiment of the invention said isolated nucleic acid molecule comprises a nucleotide sequence selected from the group consisting of:
The presence of a peptide signal sequence encoded by part of the nucleic acid sequence set forth in SEQ ID NO 1-8 which is located at the N-terminus of the amino acid sequences set forth in SEQ ID NO 9-16, may result in inefficient expression of the protein in an alternative expression host cell. Therefore, typically, the endogenous host specific signal sequence is either replaced with the expression host specific peptide signal sequence or with an ATG codon. The nucleotide sequences set forth in sequence IDs 17-25 represent the nucleotide sequence lacking the signal sequence or an ATG start codon at the 5′-end of the nucleotide sequence and correspondingly, the amino acid sequences set forth in SEQ IDs No 26-33 are lacking the N-terminal signal sequence or a methionine as the first amino acid at the N-terminus of the amino acid sequence. Thus, nucleotide sequences set forth in SEQ ID NO 17-25 comprising an ATG as the first codon at the 5′-end or amino acid sequences set forth in SEQ ID NO 26-33 comprising a methionine as the first amino acid of the N-terminus are also claimed.
In a preferred embodiment of the invention said nucleic acid molecule comprises or consists of a nucleotide sequence as set forth in SEQ ID NO: 1 wherein said nucleic acid molecule encodes a polypeptide with β-etherase activity.
In a preferred embodiment of the invention said nucleic acid molecule comprises or consists of a nucleotide sequence as set forth in SEQ ID NO: 2 wherein said nucleic acid molecule encodes a polypeptide with β-etherase activity.
In a preferred embodiment of the invention said nucleic acid molecule comprises or consists of a nucleotide sequence as set forth in SEQ ID NO: 3 wherein said nucleic acid molecule encodes a polypeptide with β-etherase activity.
In a preferred embodiment of the invention said nucleic acid molecule comprises or consists of a nucleotide sequence as set forth in SEQ ID NO: 4 wherein said nucleic acid molecule encodes a polypeptide with β-etherase activity
In a preferred embodiment of the invention said nucleic acid molecule comprises or consists of a nucleotide sequence as set forth in SEQ ID NO: 5 wherein said nucleic acid molecule encodes a polypeptide with β-etherase activity.
In a preferred embodiment of the invention said nucleic acid molecule comprises or consists of a nucleotide sequence as set forth in SEQ ID NO: 6 wherein said nucleic acid molecule encodes a polypeptide with β-etherase activity.
In a preferred embodiment of the invention said nucleic acid molecule comprises or consists of a nucleotide sequence as set forth in SEQ ID NO: 7 wherein said nucleic acid molecule encodes a polypeptide with β-etherase activity.
In a preferred embodiment of the invention said nucleic acid molecule comprises or consists of a nucleotide sequence as set forth in SEQ ID NO: 8 wherein said nucleic acid molecule encodes a polypeptide with β-etherase activity.
In a preferred embodiment of the invention said nucleic acid molecule comprises or consists of a nucleotide sequence as set forth in SEQ ID NO: 17 wherein said nucleic acid molecule encodes a polypeptide with β-etherase activity.
In a preferred embodiment of the invention said nucleic acid molecule comprises or consists of a nucleotide sequence as set forth in SEQ ID NO: 18 wherein said nucleic acid molecule encodes a polypeptide with β-etherase activity.
In a preferred embodiment of the invention said nucleic acid molecule comprises or consists of a nucleotide sequence as set forth in SEQ ID NO: 19 wherein said nucleic acid molecule encodes a polypeptide with β-etherase activity.
In a preferred embodiment of the invention said nucleic acid molecule comprises or consists of a nucleotide sequence as set forth in SEQ ID NO: 20 wherein said nucleic acid molecule encodes a polypeptide with β-etherase activity.
In a preferred embodiment of the invention said nucleic acid molecule comprises or consists of a nucleotide sequence as set forth in SEQ ID NO: 21 wherein said nucleic acid molecule encodes a polypeptide with β-etherase activity.
In a preferred embodiment of the invention said nucleic acid molecule comprises or consists of a nucleotide sequence as set forth in SEQ ID NO: 22 wherein said nucleic acid molecule encodes a polypeptide with β-etherase activity.
In a preferred embodiment of the invention said nucleic acid molecule comprises or consists of a nucleotide sequence as set forth in SEQ ID NO: 23 wherein said nucleic acid molecule encodes a polypeptide with β-etherase activity.
In a preferred embodiment of the invention said nucleic acid molecule comprises or consists of a nucleotide sequence as set forth in SEQ ID NO: 24 wherein said nucleic acid molecule encodes a polypeptide with β-etherase activity.
In a preferred embodiment of the invention said nucleic acid molecule comprises or consists of a nucleotide sequence as set forth in SEQ ID NO: 25 wherein said nucleic acid molecule encodes a polypeptide with β-etherase activity.
According to a further aspect of the invention there is provided an isolated β-etherase polypeptide wherein said polypeptide comprises copper and further wherein the activity of said polypeptide is independent of NAD+ and/or glutathione.
In a preferred embodiment of the invention said β-etherase polypeptide comprises two copper binding sites comprising the motif:
In a preferred embodiment of the invention said polypeptide has β-etherase activity in the absence of NAD+ and glutathione.
In a further preferred embodiment of the invention said isolated β-etherase polypeptides share at least 23% sequence identity over the full-length sequence set forth in SEQ ID NO 9 or 26
In a further preferred embodiment of the invention said isolated β-etherase polypeptides share between 23-45% sequence identity over the full-length sequence set forth in SEQ ID NO 9 or 26.
In a further preferred embodiment of the invention said isolated β-etherase polypeptides share at least 23%, 24%, 25%, 30%, 35%, 37%, 38%, 39%, 40%, 41%, 44% and 45% sequence identity over the full-length sequence set forth in SEQ ID NO 9 or 26.
In an alternative further preferred embodiment of the invention said isolated β-etherase polypeptides share at least 50% sequence identity over the full-length sequence set forth in SEQ ID NO 9 or 26.
In an alternative further preferred embodiment of the invention said isolated β-etherase polypeptides share between 50-88% sequence identity over the full-length sequence set forth in SEQ ID NO 9 or 26.
In an alternative further preferred embodiment of the invention said isolated β-etherase polypeptides share at least 50%, 55%, 60%, 65%, 70%, 75%, 80%, 85%, 86%, 87%, 88%, 89%, 90%, 91%, 92%, 93%, 94%, 95%, 96%, 97%, 98% and 99% sequence identity over the full-length sequence set forth in SEQ ID NO 9 or 26.
In a preferred embodiment of the invention said isolated polypeptide is selected from the group consisting of:
In a preferred embodiment of the invention said isolated polypeptide is selected from the group consisting of:
According to an aspect of the invention there is provided an isolated polypeptide selected from the group consisting of:
In a preferred embodiment of the invention said isolated polypeptide is selected from the group consisting of:
In a preferred embodiment of the invention said isolated polypeptide is selected from the group consisting of:
In a preferred embodiment of the invention said isolated polypeptide is selected from the group consisting of:
In a preferred embodiment of the invention said isolated polypeptide is selected from the group consisting of:
In a preferred embodiment of the invention said isolated polypeptide is selected from the group consisting of:
A modified polypeptide as herein disclosed may differ in amino acid sequence by one or more substitutions, additions, deletions, truncations that may be present in any combination. Among preferred variants are those that vary from a reference polypeptide by conservative amino acid substitutions. Such substitutions are those that substitute a given amino acid by another amino acid of like characteristics. The following non-limiting list of amino acids are considered conservative replacements (similar): a) alanine, serine, and threonine; b) glutamic acid and aspartic acid; c) asparagine and glutamine d) arginine and lysine; e) isoleucine, leucine, methionine and valine and f) phenylalanine, tyrosine and tryptophan. Most highly preferred are variants that retain the same biological function and activity as the reference polypeptide from which it varies.
In a preferred embodiment of the invention the modified polypeptides have at least 23%, 24%, 25%, 30%, 35%, 40%, 45%, 50%, 55%, 60%, 65%, 70%, 75%, 80%, 81%, 82%, 83%, 84%, 85%, 86%, 87%, 88%, 89%, 90%, 91%, 92%, 93%, 94%, 95%, 96%, 97%, 98% identity, and at least 99% identity with the full-length amino acid sequence illustrated herein.
In a preferred embodiment of the invention the modified polypeptides have at least 23% identity with the full-length amino acid sequence illustrated herein.
In a preferred embodiment of the invention the modified polypeptides have at least 88% identity with the full-length amino acid sequence illustrated herein.
According to a further aspect of the invention there is provided a vector comprising a nucleic acid molecule according to the invention.
In a preferred embodiment of the invention the vector is an expression vector adapted for expression in a microbial host cell as herein disclosed.
Preferably the nucleic acid molecule in the vector is under the control of, and operably linked to, an appropriate promoter or other regulatory elements for transcription in a host cell such as a microbial, (e.g., bacterial, yeast), or plant cell. The vector may be a bi-functional expression vector which functions in multiple hosts.
According to a further aspect of the invention there is provided a host cell transformed or transfected with a nucleic acid molecule or vector according to the invention. In a preferred embodiment of the invention said cell is a heterologous host cell wherein said heterologous host cell does not naturally express a nucleic acid molecule according to the invention or vector comprising a nucleic acid molecule according to the invention.
In a further preferred embodiment of the invention said cell transformed or transfected with a nucleic acid molecule or vector according to the invention is a recombinant cell.
In the context of this application a recombinant cell defines a host organism cell comprising DNA from a different species e.g. expression of a nucleotide sequence from Parascedosporium species in an Aspergillus spp cell. In a preferred embodiment of the invention said cell is a microbial cell.
In a preferred embodiment said cell is selected from the group consisting of bacterial cell, yeast cell, fungal cell, insect cell and plant cell.
In a preferred embodiment said cell is a bacterial cell.
In a preferred embodiment of the invention said bacterial cell is an Escherichia coli cell.
In a preferred embodiment said transgenic is a fungal or yeast cell.
In a further preferred embodiment of the invention said fungal cell is an Aspergillus sp. cell
In a further preferred embodiment of the invention said fungal cell is an Aspergillus niger cell.
In a further preferred embodiment of the invention said fungal cell is not a Parascedosporium sp cell.
In a preferred embodiment of the invention said yeast cell is selected from the group consisting of Saccharomyces cerevisae, Schizosaccharomyces pombe or Pichia pastoris.
If microbial cells are used as organisms and in the process according to the invention they are grown or cultured in the manner with which the skilled worker is familiar, depending on the host organism. As a rule, microorganisms are grown in a liquid medium comprising a carbon source, usually in the form of sugars, a nitrogen source, usually in the form of organic nitrogen sources such as yeast extract or salts such as ammonium sulphate, trace elements such as salts of iron, copper, manganese and magnesium and, if appropriate, vitamins, at temperatures of between 0° C. and 100° C., preferably between 10° C. and 60° C., while gassing in oxygen.
The pH of the liquid medium can either be kept constant and regulated during the culturing period, or not. The cultures can be grown batchwise, semi-batchwise or continuously. Nutrients can be provided at the beginning of the fermentation or fed in semi-continuously or continuously. To this end, the organisms can advantageously be disrupted beforehand. In this process, the pH value is advantageously kept between pH 4 and 12, preferably between pH 6 and 9, especially preferably between pH 7 and 8.
The culture medium to be used must suitably meet the requirements of the strains in question. Descriptions of culture media for various microorganisms can be found in the textbook “Manual of Methods for General Bacteriology” of the American Society for Bacteriology (Washington D.C., USA, 1981).
As described above, these media which can be employed in accordance with the invention usually comprise one or more carbon sources, nitrogen sources, inorganic salts, vitamins and/or trace elements.
Preferred carbon sources are sugars, such as mono-, di- or polysaccharides. Examples of carbon sources are glucose, fructose, mannose, galactose, ribose, sorbose, ribulose, lactose, maltose, sucrose, raffinose, starch or cellulose. Sugars can also be added to the media via complex compounds such as molasses or other by-products from sugar refining. The addition of mixtures of a variety of carbon sources may also be advantageous. Other possible carbon sources are oils and fats such as, for example, soya oil, sunflower oil, peanut oil and/or coconut fat, fatty acids such as, for example, palmitic acid, stearic acid and/or linoleic acid, alcohols and/or polyalcohols such as, for example, glycerol, methanol and/or ethanol, and/or organic acids such as, for example, acetic acid and/or lactic acid.
Nitrogen sources are usually organic or inorganic nitrogen compounds or materials comprising these compounds. Examples of nitrogen sources comprise ammonia in liquid or gaseous form or ammonium salts such as ammonium sulphate, ammonium chloride, ammonium phosphate, ammonium carbonate or ammonium nitrate, nitrates, urea, amino acids, or complex nitrogen sources such as cornsteep liquor, soya meal, soya protein, yeast extract, meat extract, and others. The nitrogen sources can be used individually or as a mixture.
Inorganic salt compounds which may be present in the media comprise the chloride, phosphorus and sulphate salts of calcium, magnesium, sodium, cobalt, molybdenum, potassium, manganese, zinc, copper, and iron.
Inorganic sulphur-containing compounds such as, for example, sulphates, sulphites, dithionites, tetrathionates, thiosulfates, sulphides, or else organic sulphur compounds such as mercaptans and thiols may be used as sources of sulphur for the production of sulphur-containing fine chemicals and pathway intermediates, in particular of methionine.
Phosphoric acid, potassium dihydrogenphosphate or dipotassium hydrogenphosphate or the corresponding sodium-containing salts may be used as sources of phosphorus.
Chelating agents may be added to the medium in order to keep the metal ions in solution. Particularly suitable chelating agents comprise dihydroxyphenols such as catechol or protocatechuate and organic acids such as citric acid.
The fermentation media used according to the invention for culturing microorganisms usually also comprise other growth factors such as vitamins or growth promoters, which include, for example, biotin, riboflavin, thiamine, folic acid, nicotinic acid, panthothenate, and pyridoxine. Growth factors and salts are frequently derived from complex media components such as yeast extract, molasses, cornsteep liquor and the like. It is moreover possible to add suitable precursors to the culture medium. The exact composition of the media compounds heavily depends on the particular experiment and is decided upon individually for each specific case. Information on the optimization of media can be found in the textbook “Applied Microbiol. Physiology, A Practical Approach” (Editors P.M. Rhodes, P.F. Stanbury, IRL Press (1997) pp. 53-73, ISBN 0 19 963577 3). Growth media can also be obtained from commercial suppliers, for example Standard 1 (Merck) or BHI (brain heart infusion, DIFCO) and the like.
All media components are sterilized, either by heat (20 min at 1.5 bar and 121° C.) or by filter sterilization. The components may be sterilized either together or, if required, separately. All media components may be present at the start of the cultivation or added continuously or batchwise, as desired.
The culture temperature is normally between 15° C. and 45° C., preferably at from 25° C. to 40° C. and may be kept constant or may be altered during the experiment. The pH of the medium should be in the range from 5 to 8.5, preferably around 7.0. The pH for cultivation can be controlled during cultivation by adding basic compounds such as sodium hydroxide, potassium hydroxide, ammonia and aqueous ammonia or acidic compounds such as phosphoric acid or sulfuric acid. Foaming can be controlled by employing antifoams such as, for example, fatty acid polyglycol esters. To maintain the stability of plasmids it is possible to add to the medium suitable substances having a selective effect, for example antibiotics. Aerobic conditions are maintained by introducing oxygen or oxygen-containing gas mixtures such as, for example, ambient air into the culture. The temperature of the culture is normally 20° C. to 45° C. and preferably 25° C. to 40° C. The culture is continued until formation of the desired product is at a maximum. This aim is normally achieved within 10 to 160 hours.
The fermentation broth can then be processed further. The biomass may, according to requirement, be removed completely or partially from the fermentation broth by separation methods such as, for example, centrifugation, filtration, decanting or a combination of these methods or be left completely in said broth. It is advantageous to process the biomass after its separation.
According to an aspect of the invention there is provided a method for the manufacture of a β-etherase polypeptide comprising the following steps:
In a preferred method of the invention said cell is a microbial cell.
Preferably, said microbial cell is a bacterial or fungal host cell.
Protocols for the manufacture of recombinantly expressed proteins are known to the skilled person. Isolating proteins under denaturing conditions can result in a higher yield of the protein of interest when compared to non-denaturing protein purification methods. The purified denatured proteins are subsequently allowed to re-fold into their native structure.
In a further method said polypeptide isolation is under denaturing conditions.
According to an aspect of the invention there is provided a composition comprising or consisting of one or more polypeptides according to the invention.
In a preferred embodiment of the invention said composition comprises at least the polypeptide is set forth in SEQ ID NO:9 or 26
In a further preferred embodiment of the invention said one more polypeptide is set forth in SEQ ID NO: 9, 10, 11, 12, 13, 14, 15 and 16.
In a further preferred embodiment of the invention said one more polypeptide is set forth in SEQ ID NO: 26, 27, 28, 29, 30, 31, 32 and 33.
In a further preferred embodiment of the invention said composition further comprises one or more polypeptides for the saccharification of lignocellulose selected from the group consisting of cellulases, lytic polysaccharide monooxygenases, carbohydrate esterases, hemicellulases, glycosylhydrolases, endoglucanases, cellobiohydrolases, beta-glucosidases, xylanases, mannases, cellobiose dehydrogenases, and beta-xylosidases.
Saccharification is the process of breaking down complex carbohydrates such as cellulose into polysaccharides, disaccharides, and monosaccharides.
In a further preferred embodiment of the invention said composition comprises a buffer.
In a preferred embodiment of the invention said composition has a pH between 5 and 12, more preferably between 6 and 11, even more preferably between 7 and 10.
In a preferred embodiment of the invention said composition has a pH of 10.
In a preferred embodiment of the invention said composition has a pH of 7.
According to an aspect of the invention there is provided a method for the modification of plant biomass comprising the following steps:
Plant biomass in the context of this application comprises or consist of lignin and/or lignocellulose.
In a preferred method of the invention said method comprises further step iii) extracting said depolymerised lignin units from the reaction mixture.
In a preferred method of the invention said depolymerised lignin units are selected from the group consisting of flavones, p-coumaric acid, and ferulic acid.
In a further preferred method of the invention said depolymerised lignin units are selected from the group consisting of flavones and p-coumaric acid.
In a further preferred method of the invention said depolymerised lignin units are selected from the group consisting of flavones, monomeric guaiacyl phenylpropanoid units, monomeric syringyl phenylpropanoid units, and monomeric p-hydroxyphenyl phenylpropanoid units.
In a further preferred method of the invention said flavones are tricin.
In a further preferred method of the invention said depolymerised lignin units are tricin and/or p-coumaric acid.
In a further preferred method of the invention said plant biomass is selected from hardwood and softwood or woody biomass.
In the context of this application woody biomass defines saw mill or paper mill discards.
In a further preferred method of the invention said plant biomass is selected from grasses, corn stover, corncob, corn fiber, wheat straw, sugarcane bagasse, wood pulp, rice straw, and municipal solid waste.
In a further preferred method of the invention said plant biomass is wheat straw or sugarcane bagasse.
In a further preferred method of the invention said method comprises further step of contacting the reaction mixture of iii) with a saccharification composition comprising one or more polypeptides for the saccharification of depolymerised lignin units.
In a preferred further method of the invention said saccharification composition comprises or consist of one or more polypeptides selected from the group consisting of cellulases, lytic polysaccharide monooxygenases, carbohydrate esterases, hemicellulases, glycosylhydrolases, endoglucanases, cellobiohydrolases, beta-glucosidases, xylanases, mannases, cellobiose dehydrogenases, and beta-xylosidases
In an alternative preferred method of the invention said saccharification composition is provided during step i).
In a preferred method of the invention said method comprises extracting di- and/or monosaccharides.
In a preferred method of the invention said monosaccharides are selected from the group consisting of glucose, xylose, and arabinose
According to an aspect of the invention there is provided the use of the polypeptides, cells or composition according to the invention in the hydrolysis of lignocellulose.
According to a further aspect of the invention there is provided a bioreactor comprising a cell or composition according to the invention.
In a preferred embodiment of the invention said bioreactor is a fermenter.
Throughout the description and claims of this specification, the words “comprise” and “contain” and variations of the words, for example “comprising” and “comprises”, means “including but not limited to”, and is not intended to (and does not) exclude other moieties, additives, components, integers or steps. “Consisting essentially” means having the essential integers but including integers which do not materially affect the function of the essential integers.
Throughout the description and claims of this specification, the singular encompasses the plural unless the context otherwise requires. In particular, where the indefinite article is used, the specification is to be understood as contemplating plurality as well as singularity, unless the context requires otherwise.
Features, integers, characteristics, compounds, chemical moieties or groups described in conjunction with an aspect, embodiment or example of the invention are to be understood to be applicable to any other aspect, embodiment or example described herein unless incompatible therewith.
An embodiment of the invention will now be described by example only and with reference to the following figures:
The quantification values shown in the table are for relative comparisons of the lignin components determined from NMR contour volume-integrals based on S + G + H = 100%. The pCA and T units are lignin appendages; their levels were estimated and expressed based on the total lignin (S + G + H). Assignments are from papers noted in the Experimental Section, along with the newly Aβ-T assignment (80). Note that, to allow the crucial lignin side-chain contours to be more clearly seen, the boxed lignin side-chain region was vertically scaled by ~1.75×.
Two-liter shake flasks, containing 1 L minimal media and 5% (w/v) milled wheat straw, were inoculated with 1% (w/v) compost. The inoculum was collected from composting wheat straw that had been developed over the period of a year and watered at regular intervals. The inoculum was prepared by blending until homogenized and used on the day of preparation. The minimal media was based on Aspergillus niger minimal media and contained KCI 0.52 g/L, KH2PO4 0.815 g/L, K2HPO4 1.045 g/L, MgSO4 1.35 g/L, NaNO3 1.75 g/L, Hutner’s trace elements (Na2EDTA·2H2O 50 g/L, ZnSO4·7H2O 22 g/L, H3BO3 11.4 g/L, MnCl2·4H2O 0.506 g/L, FeSO4·7H2O 0.4499 g/L, CoCl2·6H2O 0.161 g/L, CuSO4-5H2O 0.157 g/L, (NH4)6Mo7O24·4H2O 0.110 g/L). These flasks were incubated at 30° C. and shaken at 150 rpm. Aliquots (10 mL) containing both the solid and liquid fractions were aseptically collected weekly for eight weeks. The samples were then serially diluted with x1 phosphate-buffered saline to concentrations ranging between 10-1 and 10-7. From these dilutions 100 µL samples were used to create spread plates on both nutrient agar (NA) and potato dextrose agar (PDA), in order to culture strains from the composting environment.
Genomic DNA was harvested from the compost cultures using a modified CTAB protocol adapted for use on materials with high phenolic contents. From the composting shake flask, 20 mL aliquots were harvested weekly. The biomass was separated from the liquid fraction by centrifugation performed at 4000 g at 4° C., and 0.5 g of biomass removed to a 2 mL screw-cap tube. To this 500 µL of cetyltrimethylammonium bromide (CTAB) buffer (2% (w/v) CTAB 100 mM Tris-HCI (pH 8.0), 20 mM EDTA (pH 8.0), 2 M NaCl, 2% (w/v) polyvinylpyrrolidone (Mr 40.000), 5% 2-mercaptoethanol (v/v), 10 mM ammonium acetate, was added along with 0.5 g of zirconia beads and 0.5 mL of phenol: chloroform: isoamyl alcohol (25: 24: 1, pH 8.0), before briefly vortexing. The material was then bead-beaten using a TissueLyser II (Qiagen) for 5 min at speed 28/s. A modified phenol-chloroform method was used to extract DNA after cell lysis. The sample was spun for 5 min at max speed to achieve separation of the phases before the aqueous layer was removed to a fresh 2 mL Eppendorf tube. To the aqueous phase chloroform: isoamyl alcohol (21:1) was added, and this was spun and the aqueous phase transferred to a fresh tube, to remove any remaining phenolics. To precipitate the DNA within the sample, an equal volume of ice-cold 100% isopropanol was added and incubated for 1 h. DNA was pelleted by centrifugation at 13,000 rpm for 10 min, and supernatant was removed without disturbing the pellet. The pellet was then washed with 80% ethanol, before being resuspended in DNAse-free water.
Regions for amplicon sequencing were amplified using Phusion® High-Fidelity DNA Polymerase (Finnzymes OY, Finland) as per manufactures instructions before being purified with Agencourt AMPure XP (Beckman Coulter), and sequenced at the Biorenewables Development Centre (BDC), York, U.K. using an Ion Torrent platform. The primers pairs, for ITS and 16S sequencing, were as follows; ITS1 Fw - TCCGTAGGTGAACCTGCGG (SEQ ID NO 34), Rv - CGCTGCGTTCTTCATCG (SEQ ID NO 35), 16S Fw -AYTGGGYDTAAAGNG (SEQ ID NO 36), Rv-TACNVGGGTATCTAATCC(SEQ ID NO 37). Ribosomal DNA sequence data generated via targeted amplicon sequencing was analyzed using the open-access software Qiime on the University of York’s Technology Facilities linux server. 57 Each fastq file generated from the IonTorrent platform was first demultiplexed and then converted into both fasta and qual file types using Qiimes python script convert_fastaqual_fastq.py. To remove the primer sequences from the reads, the script split_libraries.py was used along with a mapping file generated as per Qiimes instructions. Low-quality reads were removed by filtering out reads under 180 bp long and those without recognizable primers. The orientation of the sequences was then corrected based on the primer location. Operational taxonomic units (OTUs) were then created from the fasta files. These files were picked using the open-reference OTU picking process. To perform this, the script pick_open_reference_otus.py was used. This step also includes taxonomy assignment, sequence alignment, and tree building steps. For the taxonomy assignments of bacterial sequences the default reference database was used, (greengenes gg_13_8 97_otus database),58,59 and for the fungal ITS sequences the UNITE (alpha release 12_11) database was used.60
Media was optimized using a central composite design with rotation.61 It was optimized for the production of both cellulase and xylanase enzymes after seven days on 1.5% wheat straw and minimal media, as assessed by measuring reducing sugar release after incubation on CMC and xylan. The concentrations of both sodium nitrate and yeast extract were varied as part of the optimization. The sodium nitrate concentration was varied between 0 g/L and 3.5 g/L, and yeast extract was varied between 0% and 1% (w/v). Statistica 6.0 software was used to create the experimental design and analyze the results.
The optimized media for P. putredinis NO1 growth consisted of yeast extract 8.55 g/L, KCI 0.52 g/L, KH2PO4 0.815 g/L, K2HPO4 1.045 g/L, MgSO4 1.35 g/L, NaNO3 1.75 g/L and Hutner’s trace elements.
Growth of P. putredinis NO1 was assessed using the dried weight of the biomass present within the culture. Cultures were transferred to pre-weighed and freeze-dried falcon tubes and chilled for 5 min. They were then centrifuged at 4,500 rpm, and the supernatant removed. The biomass was gently rinsed with x1 PBS and tubes were flash-frozen in liquid nitrogen and lyophilized. Each tube was then re-weighed to calculate the dry weight of the biomass present. The total protein content of the cultures was used as an indicator of growth on insoluble materials such as wheat straw. Total protein was extracted by boiling 100 µg of freeze-dried biomass in 1 mL of 0.2% (w/v) sodium dodecyl sulfate, for 5 min to lyse all cells present. Protein was then collected by centrifugation at 14,000 rpm and the supernatant collected into a fresh 50 mL falcon tube. This was repeated three times, without heating, and with vigorous vortexing between each centrifuge step to wash the biomass of any remaining protein. Extracted protein was precipitated with five volumes of ice-cold acetone overnight at -20° C., before being centrifuged at 4500 rpm and the resulting pellet washed with 80% (v/v) ice-cold ethanol. The ethanol-protein mix was then centrifuged again, and the supernatant removed and the pellet air-dried. The protein was then solubilized in 3 mL of H2O and quantified using the Bradford assay. The ability of an enzyme to cleave polysaccharides and produce products with reducing ends was assessed at each timepoint by incubating 10 µL of cultural supernatant with the 2% (w/v) of either carboxymethylcellulose (CMC) or xylan (beechwood) in 200 µL of 50 mM sodium phosphate at 6.8 and 30° C. Before and after incubation 10 µL aliquots mixed with p-hydroxybenzoic acid hydrazide (PAHBAH), heated to 70° C. for 10 min, and color change detected at 415 nm using a microtitre Tecan Safire2 plate reader.62 A stock solution of the appropriate monosaccharide was assayed to obtain a standard curve for quantification of sugar release.
Cultures of P. putredinis NO1 were established in 200 mL shake flasks, containing 20 mL of the optimized growth media and either 1.5% wheat straw or 0.5% glucose. These were incubated at 30° C. with shaking at 180 rpm. To control for varying amounts of cell growth, aliquots of either 0.5 g, 0.3 g and 0.1 g of biomass from the wheat straw cultures were weighed into 2 mL screw-cap tubes that contained 3×3 mm tungsten carbide beads and 1 mL Trizol (Life Technologies). The cells were then disrupted in a TissueLyser II (Qiagen) for either 2×2 min or 2×5 min at 28/s, dependent on the stage of growth. Total RNA was then extracted with the standard Trizol method as per manufacturer’s instructions and extracted RNA was resuspended in 50 µL of nuclease-free water. The quality of RNA was assessed by visualization on agarose gels. To obtain enough RNA for processing six technical replicates were performed for each biological replicate. These were stored at -80° C. after being flash-frozen in liquid nitrogen before further processing could occur. The RNA samples were treated for DNA contamination with RTS DNase kits (Mobio) using standard methods described by the manufacturers. The samples were then cleaned with ZymoResearch RNA Clean &
Concentrator™ 5 kits, using the manufacturer’s protocol to separate small and large RNA fragments into different fractions. RNA fragments greater than 200 nt were elution into 50 µL of RNase-free water before RNA concentration, and quality was evaluated with the 2200 TapeStation (Aligent). Once total RNA of a suitable quantity and quality was obtained, samples could be enriched for messenger RNA (mRNA). This was performed using Ribo-Zero™ Magnetic Epidemiology rRNA removal kit (RZE1224/MRZ11124C; Illumina) according to the manufacturer’s protocol.
The Genome Analysis Centre (TGAC), Norwich, U.K, performed the RNA sequencing on an Illumina HiSeq platform. As per the requirements of the sequencing service, 100 ng of enriched mRNA was provided for each sample. From the proved mRNA, cDNA libraries were constructed using the adapted TruSeq RNA v2 protocol (Illumina 15026495 Rev.B). Libraries were then normalized using elution buffer (Qiagen) and pooled in equimolar amounts into one final 12 nM pool. These were then diluted to a final concentration of 10 pM, spiked with 1% PhiX and loaded onto the Illumina cBotTemplate, for hybridization and first extension, using the TruSeq Rapid PE Cluster Kit v1 before the flow cell was transferred onto the Illumina HiSeq2500. Here, the remainder of the clustering process was conducted, and the library pool was run in a single lane for 100 cycles of each paired-end read before samples were demultiplexed. One base-pair mismatch per library was allowed, and reads were converted to FASTq. The raw data was subject to rRNA removal by catching the remaining paired reads after mapping to a modified rRNA_115_tax_silva_v1.0 ribosomal set, using BOWTIE2. The reads were further trimmed to remove adaptor sequences with the ngsShoRT_2.1 method, and libraries were pooled before being assembled by Trinity Software to obtain 37,720 contigs. Then, using this assembly as a reference, the original (unprocessed) individual libraries were mapped and the number of reads counted for each contig. Counts per million (CPM) were converted to reads per kilobase of exon per million reads mapped (RPKM) to normalize for both the depth of sequencing achieved in each sample and length of the contig.
Emboss GETORF (http://www.bioinformatics.nl/cgi-bin/emboss/getorf) was used to generate putative protein-coding sequences by translating all regions over 300 bp between potential start and stop codons. Putative open reading frames (ORFs) were searched against the NCBI non-redundant protein database and KOG database using BLASTp, and Pfam and dbCAN databases using HMMER3.(45, 81, 82) Local BLAST searches using unique were performed using BLAST+ 2.3.0.(65, 64) Signal peptides were predicted from ORFs using SignalP 4.0.(66, 67)
Supernatant proteins were harvested by collecting samples (20 mL) from the culture supernatant of P. putredinis NO1 and precipitated in five volumes of ice-cold acetone. The acetone fractions were incubated overnight at -20° C., before being centrifuged at 10,000 xg. The resulting pellet was washed with 80% ice-cold acetone, air-dried and resuspended in 0.5x PBS with 0.1% sodium dodecyl sulfate (SDS). To selectively extract biomass bound proteins, two grams of biomass collected from the fungal cultures was washed twice with ice-cold 0.5x PBS, before being resuspended and mixed for 1 h at 4° C., in 0.5x PBS with 10 mM EZ-linked biotin (Thermo Scientific). The reaction was then quenched for 30 min with 50 mM Tris-HCL, pH 8, and excess biotin was removed by washing twice with ice-cold 0.5 × PBS. Warmed SDS (2% w/v, at 60° C.) was used to extract the proteins. The mixture was incubated at room temperature for 1 h, centrifuged and precipitated with ice-cold acetone as described above. The resulting pellets were solubilized in 1x PBS containing 0.1% SDS then loaded onto streptavidin columns (Thermo Scientific) that had been pre-washed (0.1% SDS 1× PBS). The proteins were then incubated for 1 h on the column at 4° C., and washed with three column volumes of 0.1% SDS 1x PBS, before being incubated overnight with elution buffer (50 mM DTT in 1 × PBS) at 4° C. Proteins were eluted the following day by the addition of 1 mL elution buffer and the resulting fraction collected. The column was incubated for one hour before this was repeated. In total the elution was performed four times. These fractions were then flash-frozen in liquid nitrogen, freeze-dried, resuspended in 2 mL distilled water and desalted using Zeba, 7 K MWCO columns (Thermo Scientific) following manufacturer’s instructions. Both the supernatant and biotin-tagged proteins were stored in 4-12% (w/v) Bis-Tris acrylamide gels. Protein samples were loaded into the gel, separated electrophoresis for 20 min and stained with InstantBlue (Sigma-Aldrich).
LC-MS/MS was performed to identify proteins within both the supernatant and biotin-labelled fractions. Proteins contained within gel slices were washed with 50% (v/v) aqueous acetonitrile containing 25 mM ammonium bicarbonate, then reduced with 10 mM DTE and S-carbamidomethylated with 50 mM iodoacetamide. Gels were then dehydrated with acetonitrile and digested with 0.2 µg trypsin (Promega) in 25 mM ammonium bicarbonate. The digestion was performed overnight at 37° C. Peptides were extracted with 50% (v/v) aqueous acetonitrile, dried in a vacuum concentrate and resuspended in 0.1% (v/v) aqueous trifluoroacetic acid. Peptides were loaded onto a nanoAcquity UPLC system (Waters) equipped with a nanoAcquity Symmetry C18, 5 µm trap (180 µm × 20 mm Waters) and a nanoAcquity HSS T3 1.8 µm C18 capillary column (75 mm × 250 mm, Waters). The trap was washed with 0.1% (v/v) aqueous formic acid at a flow rate of 10 µL min-1, before switching to the capillary column. Peptides were separated using a gradient elution of two solvents, 0.1% (v/v) aqueous formic acid (solvent A) and acetonitrile containing 0.1% (v/v) formic acid (solvent B). The flow rate used was 300 nL min-1, and the column temperature was 60° C. The gradient proceeded linearly from 2% solvent B to 30% over 125 min, then 30-50% over 5 min, before being washed with 95% solvent B for 2.5 min. The column was then re-equilibrated at the initial conditions for 25 min before subsequent injections. The nanoLC system was interfaced with a maXis HD LC-MS/MS System (Bruker Daltonics) with a CaptiveSpray ionization source (Bruker Daltonics). Positive ESI- MS & MS/MS spectra were acquired using AutoMSMS mode. Instrument control, data acquisition and processing were performed using Compass 1.7 software (microTOF control, Hystar and DataAnalysis, Bruker Daltonics). Instrument settings were as follows: ion spray voltage: 1,450 V; dry gas: 3 L min-1; dry gas temperature 150° C.; collision RF: 1,400 Vpp; transfer time: 120 ms; ion acquisition range: m/z 150-2,000. AutoMSMS settings specified: absolute threshold 200 counts, preferred charge states: 2-4 , singly charged ions excluded. Cycle time: 1 s, MS spectra rate: 5 Hz, MS/MS spectra rate: 5 Hz at 2,500 cts increasing to 20 Hz at 250,000 cts or above. Collision energy and isolation width settings were automatically calculated using the AutoMSMS fragmentation table. A single MS/MS spectrum was acquired for each precursor, with dynamic exclusion for 0.8 min unless the precursor intensity increased fourfold.
The raw data was subject to rRNA removal by catching the remaining paired reads after mapping to a modified rRNA_115_tax_silva_v1.0 ribosomal set, using BOWTIE2. The reads were further trimmed to remove adaptor sequences with the ngsShoRT_2.1 method, and libraries were pooled before being assembled by Trinity Software to obtain 37,720 contigs. Then, using this assembly as a reference, the original (unprocessed) individual libraries were mapped and the number of reads counted for each contig. Counts per million (CPM) were converted to reads per kilobase of exon per Million reads mapped (RPKM) to normalize for both the depth of sequencing achieved in each sample and length of the contig. Emboss GETORF (http://www.bioinformatics.nl/cgi-bin/emboss/getorf) was used to generate putative protein-coding sequences in all six reading frames from the transcriptomic libraries by translating regions over 300 bp long between potential start and stop codons. These putative open reading frames (ORFs) were searched against the NCBI non-redundant protein database and KOG database using BLASTp, the Pfam and dbCAN databases using HMMER3.45,63 Annotations were subsequently mapped back to the contig from which the ORF originated. Local BLAST searches using unique were performed using BLAST+ 2.3.0.64,65 Signal peptides were predicted from ORFs using SignalP 4.0.66,67
Spectra obtained from the LC-MS/MS analysis were searched against all potential opening reads frames generated from the P. putredinis NO1 transcriptomic library, using Mascot (Matrix Science Ltd., version 2.4). This was locally run through the Bruker ProteinScape interface (version 2.1). Search criteria were specified as follows; the instrument was selected as ESI-QUAD-TOF, trypsin was stated as the digestion enzyme, fixed modifications as carbamidomethyl (C), and variable modifications as oxidation (M). Peptide tolerance was 10 ppm, and MS/MS tolerance 0.1 Da. Results were filtered through ‘Mascot Percolator’ to achieve a global false discovery rate of 1%, as assessed against a decoy database and further adjusted to accept only individual peptides with an expect score of 0.05 or lower. An estimation of relative protein abundance was performed as described by Ishihama,68 whereby an exponentially modified Protein Abundance Index (emPAI) is used to estimate the relative abundance of proteins in LC-MS/MS experiments. From this index the molar percentage values could be calculated by normalising individual protein Mascot emPAI values against the sum of all emPAI values for each sample. Protein sequences were retrieved using the R package BioStrings.69
The synthetic substrate GGβ4MU was synthesized in 6 steps according to the protocol reported by Weinstein and Gold starting from acetovanillone.44 The pure substrate GGβ4MU was obtained as a white solid following purification using plate chromatography on silica-gel (10% v/v MeOH in CH2Cl2). The NMR data were in excellent agreement with those previously reported.44
P. putredinis NO1 was cultivated in medium containing 1.5% wheat straw. The supernatant was filtered, and the protein of interest purified by different purification steps, including ammonium sulfate precipitation (ASP), gel filtration using a superdex 200 (GF) on two different columns and anion-exchange chromatography (AE). Briefly, filtered culture supernatant with 0.1% Tween20 was concentrated in a 50 mL stirred Ultracentrifugation Cell (Millipore Corporation, USA) with a Biomax 30 kDa Ultrafiltration Membrane (Millipore Corporation, USA). Ammonium sulfate was slowly added to the filtered culture supernatant to a concentration of 20% while stirring at 4° C. The solution was centrifuged at 10.000 g for 15 min. The pellet was then resuspended in 2 mL buffer A (50 mM Tris-HCI, 100 mM NaCl, 0.1% Tween 20, pH 8.5). Additional ammonium sulfate was added to the supernatant, following the same procedure as described above, to obtain fractions with 30, 40 and 50% ammonium sulfate. After assessing the fractions with the GGβ4MU assay, samples were purified via gel-filtration on a Superdex-200 (GE Healthcare, US), using the ÄKTA system and 50 mM Tris-HCl, 100 mM NaCl, 0.1% Tween 20, pH 8.5. The most active sample was further purified using anion-exchange chromatography. Anion-exchange chromatography was conducted on a DEAE FF column (GE Healthcare, US) with an increasing salt concentration from 0 to 1 M NaCl in 20 min (5 mL/min). A running buffer of 30 mM Tris-HCI, 0.1% Tween 20, at various pH (7.0/7.4/8.5) was used. The Elution buffer was 30 mM Tris-HCI, 1 M NaCl, 0.1% Tween 20.
The c2092 gene was codon-optimized for expression in E. coli and synthesized into pET151 vector with N-terminal His-tag by Invitrogen. The expression plasmid was transformed into Arctic Express (DE3) competent cells, and successful transformants were selected on LB media containing ampicillin (100 mg L-1) and gentamycin (10 mg L-1). Auto-induction media was used for protein production. Inoculated cultures were incubated at 30° C. with shaking at 180 rpm until an optical density of 0.6 at 600 nm was reached. Once a suitable cell density was reached flasks, the temperature was reduced to 11° C. for 48 h before harvesting.
Cell pellets were collected by centrifugation at 7000 rpm and 4° C. for 15 min, then suspended in 50 mL (50 mM Tris, 1 mm DTT, pH 8.5). Suspended pellets were then sonicated on ice for using a Misonix S-4000 sonicator at 70 kHz for 4 min, using a program of 3 s off followed by 7 s on. After centrifugation at 17,000 rpm for 45 min to remove cell debris, the protein was purified by anion-exchange chromatography facilitated by an ÄKTA purifier UPC10 with UNICORN 5.31 workstation. Briefly, clear supernatant was loaded onto a mono-Q anion-exchange chromatography HP column (5 mL, GE Healthcare) that had previously been equilibrated with 50 mm Tris, 100 mm NaCl, 10% glycerol pH 8. The protein was then eluted with an increasing NaCl gradient (0 to 1 M) for 100 min at a rate of 1 mL/min. Eluted fractions containing the protein of interest were pooled and concentrated using Millipore Vivaspin20 10 kDa (Sartorius). These were then injected into a superdex 75 (16/60) gel-filtration column (GE Healthcare) that had been equilibrated with 50 mM Tris, 150 mM NaCl, 10% glycerol pH 8.5. Fractions were assessed with SDS-PAGE to determine purity, and the protein concentration was calculated spectroscopically using the extinction coefficient at 280 nm.
Cell cultures were pelleted through centrifugation. Supernatant was discarded, and pellets were suspended in 5 mL per 100 mL of starting culture 20 mM (4-(2-hydroxyethyl)-1-piperazineethanesulfonic acid) (HEPES) pH 8, before sonicated on ice (70 V, 4 s on, 7 s off for a total of 4 min on). Centrifugation at 10 000 xg was again used to pellet cell debris and inclusion bodies. The pellet was washed with 20 mM HEPES, 2 M Urea, 0.5 M NaCl, 2% TritonTM X-100, pH 8, using the same volume as before, and sonicated and centrifuged as before. The resultant pellet was then resuspended in 20 mM HEPES, 0.5 M NaCl, 5 mM imidazole, 6 M guanidine hydrochloride, 1 mM dithiothreitol (DTT) pH 8, using 10 mL per 100 mL of original cell culture, to solubilise inclusion bodies. After pelleting through centrifugation for a final time, the supernatant was applied to a HisTrap column equilibrated with 20 mM HEPES, 0.5 M NaCl, 5 mM imidazole, 6 M guanidine hydrochloride, 1 mM DTT pH 8. The equilibration buffer was then used to wash the column for a total of 5 CV followed by the same volume of 20 mM HEPES, 0.5 M NaCl, 20 mM imidazole, 6 M urea, 1 mM DTT pH 8. A linear gradient from the final wash buffer to 20 mM HEPES, 0.5 M NaCl, 20 mM imidazole, 0.1 mM CuSO4, 1 mM DTT pH 8 was then used to refold the tagged protein on the column. This was applied over 30 mL using a flow rate of 0.5 ml/min. To elute refolded protein another linear gradient was applied over 20 mL, starting with 20 mM HEPES, 0.3 M MgCl2, 20 mM imidazole, 1 mM DTT, pH 8 and ending with the same buffer with the addition of 500 mM imidazole and 10% glycerol. Apart from when otherwise mentioned, the flow rate was kept at 1 mL/ min when using a 1 mL capacity column and 3 mL/min when using a 5 mL capacity column. Fractions of 1.5 mL were collected throughout the elution step, and UV absorbance was used to determine protein content. Fractions with high protein contents were visualised using SDS-polyacrylamide gel electrophoresis (SDS-PAGE) and the presence of the recombinant protein confirmed through western blot analysis. Protein activity was confirmed through the measurement of 4MU from the GGβ4MU assay after removal of imidazole and DTT using Zeba™ Spin Desalting Columns, 7K MWCO (ThermoFisher) or Slide-A-Lyzer™ Dialysis Cassettes 10 K MWCO (ThermoFisher).
Enzyme activity was measured in 1 mL reaction containing 10 µL 4MU/GGβ4MU (synthetic fluorescent substrate 10 mM) and appropriate concentration of pure protein in 50 mM Tris-HCI, 100 mM NaCl, pH 8.5, 5 mM CuSO4. The reaction was incubated at 30° C. for 1 h. Formation of 4-methylumbelliferone (4MU) was monitored using an RF-1500 fluorometric analyzer. After 0 h and 1 h of incubation 100 µL of the reaction mixture was taken and added to 50 µL of 100 mM glycine-NaOH buffer (pH 10.0). One unit of the enzyme was defined as the amount that released 1 nmol of 4 MU/h from the substrate. Five replicate were taken for each sample, and control reactions of boiled enzyme and wheat straw treated with buffer only were also performed.
The effect of pH and temperature on enzyme activity was investigated by varying the pH of the reaction mixtures using 50 mM Tris-HCI buffer from pH 7.0 to 9.5, 50 mM glycine-NaOH buffer at pH range 9.0 to 10.5 and 50 mM Na2HPO4-NaOH buffer at pH range 10.5 to 12. The optimum temperature of enzyme activity was determined at various temperatures ranging from 20° C. to 70° C. Assays were performed as described in the previous section.
Specificity was investigated by incubating 1 mM of each substrate of interest with the enzyme in 100 µL Tris pH 8.5 buffer at room temperature. Activity was determined by monitoring the change in Ultraviolet-Visible absorbance spectra (220 - 750 nm) of aliquots using a NanoDrop 8000 Microvolume UV-Vis spectrophotometer (Thermo Scientific). Scans were performed at regular intervals over 2 h.
Wheat straw was ground to <1 mm using a cyclone mill (Retsch) and washed several times with 50 mM Tris pH 8 to remove residual surface sugars. In 1 mL reactions, 100 mg of washed wheat straw was incubated with an appropriate concentration of pure enzyme in 50 mM Tris buffer at pH 8 with 5 mM CuSO4. Reactions were incubated overnight at 30° C. with shaking. Control reactions were performed using wheat straw incubated with boiled β-etherase or with buffer only. Tricin was extracted based upon Karambelkar.70 Briefly, 1 mL of ethyl acetate was added to 100 µL of the reaction supernatant. This was homogenized before being centrifuged for 5 min at 13,000 rpm. The ethyl acetate layer was transferred into new tubes and evaporated using a centrifugal evaporator at 55° C. before being resuspended in 100 µL 50% H2O, 50% acetonitrile. This was analyzed with a Waters 2996 photodiode array detector Separations Module HPLC system, column used was C18-5 µM preparative column (4.6 × 250 mm, Waters, X-Bridge, Made in Ireland). The mobile phase was 0.1% acetic acid in water (A), and methanol (B) and a linear gradient was used; 95% A (5 min), 70% A (25 min), 0% A (30 min), 95% A (5 min), the flow rate was 1.0 mL/min. After identification through comparisons with authentic standards, based on retention time and UV spectrum, peaks were manually collected and the mass confirmed with mass spectroscopy.
For saccharification reactions, biomass pretreated with β-etherase was incubated with 1.2 µg/mL enzyme cocktail (4:1 Celluclast: novo 188 (Novozymes)) in 50 mM sodium acetate at pH 4.5 and incubated overnight at 37-40° C. with shaking. This was performed alongside a control reaction with buffer only. Solids were removed by centrifugation, and residual protein was precipitated with 80% ethanol. The supernatant, containing mono- and oligosaccharides, was dried with a centrifugal evaporator before samples were resuspended in ultra-pure water and filtered through a 0.2 µm polytetrafluoroethylene (PTFE) filter. Five replicates from each sample were investigated, and carbohydrate composition was analyzed by high-performance anion-exchange chromatography (HPAEC).
High-performance anion-exchange chromatography was used to analyze monosaccharide release after saccharification. Briefly, 5 µL of samples or standards were injected on a CarboPac PA20 3 × 150 mm analytical column via a CarboPac PA20 3×0 mm guard column using Chromeleon 6.8 Chromatography Data Systems software (Dionex). Sugars were separated at a flow rate of 0.4-0.5 mL min-1 at a temperature of 25° C. as follows: after equilibration of the column with 100% H2O, samples were separated in a linear gradient of 100% H2O to 99%-1% of H2O-0.2 M NaOH for 5 min, then constant for 10 min, followed by a linear gradient to 47.5%-22.5%-30% of H2O-0.2 M NaOH-0.5 M NaOAc/0.1 M NaOH in 7 min and then kept constant for 15 min. After washing the column with 0.2 M NaOH for 8 min it was re-equilibrated with 100% H2O for 10 min before the injection of the next sample. Carbohydrates were detected by ICS-3000 PAD system with an electrochemical gold electrode, identified by comparison with retention times of external standards (arabinose, fucose, galactose, glucose, glucuronic acid, mannose, rhamnose, and xylose) and quantified through the integration of these known standards.
Enzyme lignins, representing essentially all of the lignin in the sample, were prepared following ball-milling of the cell wall isolate as previously described.(75-77, 78)
2D NMR of enzyme lignins (EL) in 4:1 v/v DMSO-d6:pyridine-d5 were acquired on a Bruker Biospin (Billerica, MA) Avance 700 MHz spectrometer equipped with a 5-mm QCI 1H/31P/13 C/15 N QCI cryoprobe with inverse geometry (proton coils closest to the sample), as described previously.(76,77) Volume-integration of contours in HSQC plots used TopSpin 4.07 (Mac version) software, and no correction factors were used. The data represent volume-integrals only, and data are presented on an S + G + H = 100% basis (
Where mentioned two tail ANOVAs were performed using R core package “stats”.(83)
We inoculated liquid cultures containing wheat straw as the sole carbon source with samples of wheat straw-enriched compost and tracked the dynamics of the resulting microbial community using targeted amplicon sequencing during cultivation. Sequencing of 16S ribosomal RNA genes generated over three million reads from the prokaryotic community over the whole time course, which clustered together to form 25,304 operational taxonomic units (OTUs) (
We confirmed that P. putredinis NO1 could grow on wheat straw as a sole carbon source and optimized the composition of growth media for cellulase and xylanase production using a central composite design (
As the macromolecular structure of lignocellulose prohibits intracellular degradation, many enzymes for its deconstruction must be secreted. We therefore performed LC-MS/MS analysis on protein samples collected directly from the culture supernatant, and separately from those bound to insoluble components of the culture using a biotin-labelling method designed to enrich for proteins tightly bound to the residual biomass.26 We identified 3,671 proteins across all samples, including 1,037 proteins present in only wheat straw conditions (
The most abundant CAZy protein family, accounting for 3.7% and 3.6% of the respective supernatant and biotin-labelled fractions on the fourth day, were GH6s, which may be endoglucanases or processive cellobiohydrolases. These, along with GH7s, often constitute the major cellulases in filamentous fungi.27 The GH6 family, is represented by four distinct proteins within the proteome, included the most abundant single protein - c7229_g3_i1_1, a putative cellobiohydrolase with an 85.89% sequence identity to a cellulase (XP_016646396.1) from Scedosporium apiospermum. Other abundant GHs likely active on cellulose include GH7 (typically cellobiohydrolases or endoglucanases), GH5 and GH45 (often endoglucanases) and GH1 and 3 (typically glucosidases).28
Efficient lignocellulose deconstruction demands a combination of cellulolytic and hemicellulolytic enzymes that work cooperatively. Enzymes related to the depolymerization of arabinoxylan (major hemicellulose of wheat straw), were well represented within the exoproteome. Nine proteins were identified with homology to endo β-1-4-xylanases (GH10 and GH11), which hydrolyse the arabinoxylan backbone, and five proteins were identified as putative β-1,4-xylosidases that act on the resultant fragments to produce xylose monomers (GH3, GH31, GH43_1, GH43_11, GH43_36). Also of note were the GH43 subfamilies GH43_1, GH43_21, GH43_22, GH43_26 and GH43_36 that were abundant within the secretome, including putative β-D-xylosidases, α-L-arabinofuranosidase, and β-1,3-galactosidase activities. Fifteen GH43 subfamily members were identified, with nine proteins showing closest homology to known arabinofuranosidases.
Three proteins, belonging to the CE1 family, showed significant sequence homology to feruloyl esterases. Ferulic acid is esterified to the arabinose side chain of arabinoxylans, and through the formation of diferulate bridges and ester-ether linkages allows the respective formation of covalent interactions between arabinoxylan chains and lignin. Feruloyl esterases, therefore, are thought to aid the solubilization of plant cell wall polysaccharides by the hydrolysis of the ester link that exists between ferulic acid residues and arabinose, thereby disrupting the crosslinking of cell wall components.29 Putative acetyl xylan esterases (3 in CAZy family CE1 and 3 in CE5) were also observed and are known to facilitate the degradation of xylan through the removal of acetyl substitutions.30
The CAZy auxiliary activity (AA) class is classified as containing enzymes that act in conjunction with carbohydrate-active enzymes through redox activities. Interestingly, 69 putative proteins from the AA class were detected in the exosecretome, more than many lignocellulose-degrading fungi contain in their total genome,31 suggesting an important role for the oxidative degradation of lignocellulose in P. putredinis NO1. The AA9 family, which along with the AA10, AA11, AA13, AA14 and AA15 families constitute the lytic polysaccharide monooxygenases (LPMOs) - a class of copper metalloenzymes that catalyse the oxidative cleavage of glycosidic bonds in multiple polysaccharide substrates including chitin, cellulose, and xylan,32.33 were highly represented within the exosecretome. In total, we identified nineteen putative LPMOs (16 AA9s; 2 AA11s; 1 AA13), fifteen of which were upregulated tenfold or more between glucose and wheat straw conditions. Fittingly, 16 AA3s (glucose-methanol-choline (GMC) oxidoreductase) and 9 AA7s (glucooligosaccharide oxidase), which have been shown to facilitate the activity of the LPMOs through electron shuttling,34,35 were also present within wheat straw cultures.
Five putative multicopper oxidase proteins were also observed - two from the AA1_3 subfamily (Laccase-like multicopper oxidase) and one from the AA1_2 subfamily (Ferroxidase). Laccase-like multicopper oxidases are of unknown function but have been implicated in lignin degradation, as well as other diverse functions (iron homeostasis, offense/defence),36 whereas ferroxidases have been reported to be involved in lignocellulose degradation in Ascomycetes, in which they generate hydroxyl radicals via the Fenton reaction.37 Established lignin depolymerizing enzymes associated with the white-rot fungal decay of lignin, including laccases from the AA1_1 subfamily or peroxidases from the AA2 family, were not present within the libraries, perhaps not surprising given the P. putredinis NO1 sits within the Ascomycota phylum, and as such is closer in relation to the soft-rots.
Despite the apparent lack of known ligninases in P. putredinis NO1, a putative AA6 (1,4-benzoquinone reductase) associated with the intracellular biodegradation of aromatic compounds was present within the supernatant and may have a role in the metabolism of lignin breakdown products.31,38
Of key interest to us was the potential of P. putredinis NO1 to produce novel lignocellulolytic activities, particularly those able to boost lignocellulose deconstruction via the modification and solubilization of lignin. An unknown protein, c2092, identified in the exosecretome was subsequently found to have β-etherase activity and no CAZy identification.
The β-ether motif with its characteristic β—O—4 inter-unit linkage is the most abundant in lignin, estimated at representing over 50% of the total inter-unit linkages.39 Enzymes employing β-ether cleavage mechanisms can deconstruct synthetic and extracted lignin;40,41,42 these bacterial etherases that have been characterized to date, however, are intracellular proteins, and are glutathione- or NAD+- dependent, suggesting that in nature they are not directly involved in the breakdown of the lignin macromolecule, but rather its smaller, membrane-transportable oligomers. An extracellular fungal protein displaying β-etherase activity was previously purified from the supernatant of the Chaetomium sp. 2BW- 1, although its identity remains unknown.43
Using a synthetic lignin model compound GGβ4MU (7-[2-hydroxy-2-(4-hydroxy-3-methoxyphenyl)-1-(hydroxymethyl)ethoxy]-4-methyl-2/7-1-benzopyran-2-one) containing a β-methylumbelliferyl ether, guaiacylglycerol-β-(4-methylumbelliferyl) ether (
The putative β-etherase was initially purified by ammonium sulfate precipitation of the proteins in the culture supernatant to decrease sample pigmentation and reduce protein-protein interactions. This treatment facilitated further purification by size-exclusion and anion-exchange chromatography. Using shotgun proteomics, we identified c2092, a 44.5 kDa protein present in the purified fraction that contained a predicted signal peptide. Analysis of the transcriptomic and proteomic data revealed this protein was strongly upregulated in the presence of wheat straw and present in both the supernatant and biotin-labelled proteomic libraries throughout the growth of P. putredinis NO1 on wheat straw (
To determine if c2092 was responsible for the observed β-etherase activity, we heterologously expressed the codon-optimized sequence in Escherichia coli. The recombinant protein was purified (Table 3), and the β-etherase activity of the protein was confirmed by determining the level of fluorescence released after incubation with GGβ4MU (
Tricin has recently been described as a subunit in the lignin of monocot species, incorporated through a 4—O—β linkage.11 As wheat straw contains relatively high concentrations of tricin compared to other agriculturally relevant feedstocks,8 we assessed the ability of the β-etherase to release tricin from wheat straw. The β-etherase was incubated with wheat straw for sixteen hours under physiological conditions (pH 8.5 and 30° C.). Reaction products were monitored by High-Performance Liquid-Chromatography (HPLC), and a peak corresponding to tricin was identified by reference to an authentic standard and confirmed by mass spectrometry. Under the growth conditions used for P. putredinis NO1, a significantly higher concentration of tricin was present in the reaction supernatant of wheat straw with the β-etherase compared to incubations with buffer alone (ANOVA, F(2,12)=44.67, p<0.05) (
NMR (
We further tested the activity of the β-etherase on alternative feedstocks, including sugarcane bagasse and rice straw. A smaller amount of tricin was released from sugarcane bagasse compared to wheat straw; however, in contrast to assays with wheat straw, p-coumaric acid was significantly enriched (ANOVA, F(2,12)=44.67, p<0.05) (
As mushroom tyrosinase has been reported to cleave β-ether linkages promiscuously,50 we tested its β-etherase activity on these lignocellulosic substrates under equivalent conditions. We observed less tricin, p-coumaric acid, and p-hydroxybenzaldehyde production in the reaction mixtures containing mushroom tyrosinase compared to the P. putredinis NO1 β-etherase treatments. Tricin is a known tyrosinase inhibitor that binds non-competitively to the hydrophobic pocket of the protein,53 and p-coumaric acid has been characterized as having a mixed-type inhibition effect.54 This inhibition, through the non-reversible binding of the reaction products, could go some way to explaining why mushroom tyrosinase displays little activity towards the lignin macromolecule.
The recalcitrance of lignocellulose to degradation requires that feedstocks are pretreated in order to disrupt lignin, before efficient saccharification can be achieved using current commercial enzymatic cocktails. These pretreatments are typically physico-chemical, using a combination of heat and pressure with acid, alkali or organic solvents. As these industrial processes are energy-intensive and environmentally damaging, the use of biological treatments, performed under relatively mild conditions, are desirable. To investigate if the application of the β-etherase would improve saccharification rates, we treated sugarcane bagasse, wheat straw, and rice straw with β-etherase for sixteen hours before the addition of commercial cellulases. Sugarcane bagasse demonstrated a major improvement in digestibility after pretreatment with β-etherase resulting in a significant increase in glucose, xylose, and arabinose compared to the untreated control (2-fold, 5-fold and 23-fold, respectively) after saccharification (
P. putredinis NO1 is able to dominate cultures in the latter stages of wheat straw degradation in a mixed microbial community, in liquid culture, when easily accessible polysaccharides have been exhausted. Using a combination of omics approaches, we have identified a diverse range of potentially industrially relevant carbohydrate-active enzymes, including a large number of enzymes associated with the oxidative attack on lignocellulose. In particular, we have identified a new extracellular β-etherase that is preferentially expressed in the presence of wheat straw and demonstrated that this enzyme can boost enzymatic hydrolysis by cellulases as well as selectively release the pharmaceutically relevant flavonoid tricin from monocot lignin. The cleavage of β-ether bonds most likely aids the breakdown of lignocellulose in natural environments. We contend that this ability to deconstruct and modify lignin is important for P. putredinis NO1 to be able to out-compete other microbial species during the latter stage of plant biomass degradation. Preferential removal of tricin subunits has been described by the white-rot fungi, Pleurotus eryngii, during the selective delignification of wheat straw and has been proposed to be key to lignocellulose degradation, although the enzyme activity that facilitated tricin release was not identified.56 When the publicly available genome of P. eryngii was examined for the presence of proteins with homology to the β-etherase from P. putredinis NO1 no significant hits were detected. As the protein described as being responsible for β-etherase activity from Chaetomium sp. 2BW-1 was not identified to sequence level, it is unclear whether it shares homology to the enzyme described here; however, the proteins appear to be distinct as the reported sizes differ by 20 kDa.43 Taken together, these observations suggest that multiple, structurally dissimilar, enzymes in the natural environment may mediate ether linkage disruption in lignocellulose-degrading microbes. To the best of our knowledge, this is the first identification and characterization of an extracellular β-etherase that has no cofactor requirement for activity capable of selectively releasing tricin from lignin and could have potential biotechnological applications.
| Number | Date | Country | Kind |
|---|---|---|---|
| 2000378.6 | Jan 2020 | GB | national |
The present application relates to nucleic acids encoding polypeptides with β-etherase activity; polypeptides with β-etherase activity; vectors comprising said nucleic acids for the production of recombinant β-etherase; cells, for example microbial cells, transformed with nucleic acids encoding β-etherase activity and vectors including nucleic acids encoding β-etherases; a composition comprising β-etherases suitable for processing lignocellulose; and a method that uses β-etherases or compositions comprising β-etherases in the processing of lignocellulose and related polysaccharides. This invention was made with government support under DE-SC0018409 awarded by the US Department of Energy. The government has certain rights in the invention.
| Filing Document | Filing Date | Country | Kind |
|---|---|---|---|
| PCT/EP2021/050317 | 1/9/2021 | WO |
