WO2011027796A1 - 五炭糖輸送体 - Google Patents
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- WO2011027796A1 WO2011027796A1 PCT/JP2010/064962 JP2010064962W WO2011027796A1 WO 2011027796 A1 WO2011027796 A1 WO 2011027796A1 JP 2010064962 W JP2010064962 W JP 2010064962W WO 2011027796 A1 WO2011027796 A1 WO 2011027796A1
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- C12P—FERMENTATION OR ENZYME-USING PROCESSES TO SYNTHESISE A DESIRED CHEMICAL COMPOUND OR COMPOSITION OR TO SEPARATE OPTICAL ISOMERS FROM A RACEMIC MIXTURE
- C12P7/00—Preparation of oxygen-containing organic compounds
- C12P7/02—Preparation of oxygen-containing organic compounds containing a hydroxy group
- C12P7/04—Preparation of oxygen-containing organic compounds containing a hydroxy group acyclic
- C12P7/06—Ethanol, i.e. non-beverage
- C12P7/08—Ethanol, i.e. non-beverage produced as by-product or from waste or cellulosic material substrate
- C12P7/10—Ethanol, i.e. non-beverage produced as by-product or from waste or cellulosic material substrate substrate containing cellulosic material
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- C07K—PEPTIDES
- C07K14/00—Peptides having more than 20 amino acids; Gastrins; Somatostatins; Melanotropins; Derivatives thereof
- C07K14/37—Peptides having more than 20 amino acids; Gastrins; Somatostatins; Melanotropins; Derivatives thereof from fungi
- C07K14/39—Peptides having more than 20 amino acids; Gastrins; Somatostatins; Melanotropins; Derivatives thereof from fungi from yeasts
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- Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
- Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
- Y02E—REDUCTION OF GREENHOUSE GAS [GHG] EMISSIONS, RELATED TO ENERGY GENERATION, TRANSMISSION OR DISTRIBUTION
- Y02E50/00—Technologies for the production of fuel of non-fossil origin
- Y02E50/10—Biofuels, e.g. bio-diesel
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- the present invention relates to a membrane transport protein (transporter) that promotes uptake of arabinose and / or xylose.
- the woody biomass that makes up the bulk of the world's biomass is made up of lignocellulose.
- lignocellulose In typical lignocellulosic biomass, 35-45% cellulose, 25-40% hemicellulose, 15-30% Consists of lignin.
- cellulose and lignin have been actively studied for their energy utilization, such as a technique for converting to glucose in a short time using supercritical water.
- Hemicellulose can be easily broken down into monosaccharides such as xylose by acid hydrolysis or enzymatic degradation.
- xylose is converted to xylulose by xylose isomerase (XI) in one step without depending on a coenzyme.
- XR xylose reductase
- XDH xylitol dehydrogenase
- XI is a xylose metabolic pathway mainly found in bacteria.
- bacteria such as Streptomyces sp. And Actinoplanes ⁇ ⁇ ⁇ sp.
- Can convert xylose to xylulose by XI and then convert it to ethanol through a pentose-phosphate circuit Non-patent Document 1, 2.
- its efficiency is very low. This is thought to be caused by the formation of organic acids as by-products. For these reasons, it has not been industrially utilized.
- KO11 strain has been developed in the United States in which two types of pyruvate decarboxylase and alcohol dehydrogenase of zymomonas bacteria used for tequila production are expressed in E. coli (Patent Documents 1 and 2).
- This recombinant Escherichia coli can convert all monosaccharides contained in lignocellulose biomass to ethanol.
- by-products such as lactic acid, succinic acid, fumaric acid, and acetic acid are produced during fermentation and the low resistance to fermentation inhibitors produced when saccharifying lignocellulose biomass is still not completely solved.
- XI exists in several types of eukaryotic rumen fungi.
- the XR-XDH pathway is a pathway mainly found in eukaryotic microorganisms, and Pichia stipitis, Candida C shehatae, Pachysolen tannophilus and the like are known to have this pathway (Non-patent Documents 3 and 4). These eukaryotic microorganisms have been used mainly to optimize fermentation conditions, but it is difficult to control anaerobic conditions, etc., and the resistance to saccharification degradation products of alcohol and lignocellulose biomass However, because it is inferior, it is not mainstream now. Instead, S. cerevisiae is a eukaryotic microorganism that has been studied the most because of its potential alcohol fermentability and alcohol resistance.
- XR-XDH-XK which constitutively expresses three types of genes, mainly XR and XDH genes derived from P. stipitis, and now XK of S. cerevisiae. Genetically modified yeast is mainly used.
- XI was not able to be expressed functionally in yeast cells at the beginning, research has not progressed, but recently it was successfully expressed in a rumen fungus-derived gene, and xylose fermentation was also successful. However, it has been found that the efficiency is lower than that of the XR-XDH system.
- Another problem is that the fermentation rate of pentose is very slow compared to hexose.
- One of the causes is metabolic delay after intracellular conversion from xylose ⁇ xylitol ⁇ xylulose ⁇ xylulose 5-phosphate.
- Transketolase (TKL) and transaldolase (TKL) and transaldolase (PK) other than XK Improvements such as enhancing the expression of (TAL) have been made (Non-patent Document 9).
- the second cause is the weaker ability to transport pentose sugars into cells than hexose sugars.
- Non-patent Document 12 an Arabidopsis thaliana xylose transporter gene (accession No. # BT015354 / # BT015128) into S. cerevisiae into which the XR-XDH-XK gene was chromosomally integrated. It has been confirmed that the introduced gene is expressed accurately and membrane localization is normal by immunofluorescence using a histidine tag added to the amino acid terminal. The effect on xylose fermentation is that xylose transport capacity, consumption rate, and ethanol productivity improved by 46%, 40%, and 70%, respectively.
- Non-patent Document 13 An attempt to directly identify the xylose transporter of the filamentous fungus Trichoderma reesei has been made by Ruohonen et al. (Non-patent Document 13).
- a library was constructed to express the cDNA of T. reesei in S. evicerevisiae, and the above strain was integrated into the S. cerevisiae mutant KY73 lacking the major hexose transporter in the XR-XDH-XK gene.
- a library was introduced, and colonies capable of growing using xylose as a carbon source were selected. Only one colony was isolated and Xlt1 was identified as a xylose transporter (accession No. AY818402).
- GXF1 (accession No. AJ937350) uses a method that complements the phenotype of the S. cerevisiae hexose-deficient mutant, while GXS1 (accession No. AJ 875406) is a cell membrane of C. intermedia grown on xylose.
- the protein was directly purified from the cDNA and cDNA was isolated from the determined partial amino acid sequence (Non-patent Document 14). Both GXF1 and GXS1 showed glucose and xylose transport capacity.
- SUT1 gene was first isolated (accession No. U77382), and then SUT2 and SUT3 having very similar nucleotide sequences were isolated by genomic Southern hybridization using SUT1 as a probe (accession). No. AF0728080 / U77581).
- SUT1-3 is known to be able to transport xylose in addition to hexoses, and SUT1 is the best kinetics.
- Kondo et al. Introduced this SUT1 in the form of a plasmid into Saccharomyces yeast into which the XR-XDH-XK gene was chromosomally integrated (Non-patent Document 18). This improved the xylose consumption rate during xylose fermentation, but the final ethanol production was the same. This study is the only example that has achieved some success in the field using a technique called sugar transport gene transfer.
- L-arabinose is a pentose that occupies 15% of the constituents in corn stover (stem), though not so much in woody biomass, and is positioned as the main pentose of lignocellulose biomass along with xylose It has been.
- Bacteria have a metabolic pathway by L-arabinose isomerase (AraA), librokinase (AraB) and ribulose 5-phosphate 4 isomerase (AraD), so L-arabinose fermentation can be achieved by adding fermentative ability like E. coli KO11. ( Figure 2).
- the metabolic pathways of eukaryotic microorganisms have not been elucidated, and attempts to ferment L-arabinose by S.
- Non-patent Document 19 the pathway of this bacterium (mainly Escherichia coli and Bacillus subtilis). was hardly expressed at the beginning (Non-patent Document 19). By optimizing the codons of the introduced gene for yeast, it became possible to secure a certain level of expression (Non-patent Document 20). In addition, since GAL2 of S. cerevisiae can transport L-arabinose, it was also expressed in large quantities under the control of a constant expression promoter. Although these improvements have made it possible to ferment L-arabinose, it is always acclimatized by long-term subculture.
- L-arabinose metabolic genes of eukaryotic microorganisms were identified through a series of studies by Penttila et al. (Non-patent Documents 21 and 22). According to this, L-arabinose is converted into L-arabinitol ⁇ L-xylulose ⁇ xylitol ⁇ xylulose ⁇ xylulose pentaphosphate (FIG. 2). Since the first and last two enzymes are XR, XDH, and XK, the new enzymes compared to the xylose metabolic pathway are L-arabinitol 4-dehydrogenase (LADH) and L-xylulose reductase (LXR).
- LADH L-arabinitol 4-dehydrogenase
- LXR L-xylulose reductase
- Non-patent Document 23 the LADH / LXR gene was expressed in XR-XDH-XK transgenic S. cerevisiae (Non-patent Document 23). In contrast to bacterial genes, expression in yeast cells was not a problem, but little ethanol was produced and L-arabinitol was accumulated as a by-product.
- KmLAT1 and PgLAT2 which are thought to be L-arabinose transporters, were identified from each yeast, and introduced as a plasmid into recombinant Saccharomyces yeast that expressed a large amount of bacterial AraA, AraB, and AraD.
- GAL2 and PgLAT2 of S. cerevisiae were co-expressed, the Doubling time of growth when L-arabinose was used as a carbon source was accelerated. It appears that ethanol is not produced.
- Hahn-Hagerdal et al. Identified an L-arabinose transporter gene from Candida arabinofermentas, an L-arabinose-metabolizing yeast (Patent Document 4). Fermentation experiments using S. cerevisiae were not conducted.
- SUT4 there is another similar homolog in addition to SUT2 and SUT3 on the genome of P. stipitis, which is named SUT4.
- SUT1-4 are shown in the molecular phylogenetic tree created using amino acid sequences of known sugar transporters of eukaryotic microorganisms (Fig. 3), and less than 40 (presumed) sugar transporters of P. stipitis. Since it is closest to the hexose transporter HXT of Saccharomyces yeast, it is possible to predict to some extent that these can transport glucose and xylose.
- the object of the present invention is to solve the energy problem by converting monosaccharides that can be easily obtained by hydrolyzing hemicellulose occupying about 30% or more of woody and other biomass resources into ethanol with high efficiency. Is to provide one means to do.
- the present inventor first constructed a system that expresses all (presumed) sugar transporter genes of P. stipitis in Saccharomyces yeast, and comprehensively analyzed the substrate specificity of each gene for bioethanol production. An attempt was made to clarify the pentose transporter important for yeast breeding development. As a result, it was found that a specific gene functions as a pentose transport protein in yeast.
- the present invention provides the following genes or pentose transporters such as xylose and arabinose of the expressed proteins or their use, or use thereof, and a method for producing bioethanol.
- Item 1 Use of HGT2 gene or an expressed protein thereof as a xylose transporter.
- Item 2 Xylose and / or L-arabinose transporter, which is an expressed protein of a gene selected from the group consisting of HGT2 gene, XUT1 gene and HXT2.4 gene.
- Item 3 Use of a gene selected from the group consisting of HGT2 gene, XUT1 gene and HXT2.4 gene as a xylose and / or L-arabinose transporter.
- Item 4 At least one gene selected from the group consisting of HGT2 gene, XUT1 gene and HXT2.4 gene is introduced into yeast and cultured in the presence of biomass containing xylose and / or L-arabinose.
- Item 5. The method for producing bioethanol according to Item 4, wherein the biomass containing xylose and / or L-arabinose is lignocellulose.
- the uptake ability of pentose can be remarkably improved and the use of pentose can be promoted.
- ethanol can be efficiently produced from lignocellulosic woody biomass by simultaneously introducing pentose metabolism-related enzymes into microorganisms such as yeast.
- Non-patent document 18 shows that S. ⁇ ⁇ ⁇ cerevisiae MT8-1 into which XR-XDH-XK is integrated as a host is used as a host, and even though SUT1 is introduced, bioethanol production is not improved. It was shown that ethanol production was improved by introducing the SUT1 gene into the same host.
- Kondo et al. In Non-Patent Document 18 are cultivated by adding all the missing amino acids directly into the medium, whereas in the present invention, auxotrophy other than adenine is complemented by inserting a plasmid. is doing. While not wishing to be bound by theory, this suggests that auxotrophy is preferably complemented by the inclusion of a plasmid.
- Xylose metabolic pathway L-arabinose metabolic pathway of bacteria (A) and eukaryotic microorganisms (B).
- the boldface of the molecular phylogenetic tree of the sugar transporter of eukaryotic microorganisms is that of P. stipitis that we analyzed this time. All other organisms have been subjected to functional analysis.
- Sc Saccharomyces cerevisiae; Kl, Kluyveromyces lactis; Td, Torulaspora delbrueckii; Ci, Candida intermedia; Dh, Debaryomyces hansenii; Bc, Botrytis cinerea; Tr, Trichoderma reesei; Ca, Candida albicans.
- cDNAs for intron-containing genes are synthesized by PCR twice. For e in the figure, the internal HindIII site (double underlined) is crushed. Subcloning of (putative) sugar transporter gene of P. stipitis. Confirmed by PCR using cDNA incorporated into pPGK plasmid as a template. The number in parentheses indicates the length of the gene base. Strains and plasmids used in this study. Substrate specificity of the (presumed) sugar transporter gene of P. stipitis. Each gene was transformed into S.
- evicerevisiae are both expressed by the PGK promoter and are within the aureobasidin resistance gene AUR1-C when homologously recombined on the chromosome of S. cerevisiae Cut and transform at the restriction enzyme site of BsiWI.
- Each gene was introduced as a plasmid into the S. cerevisiae KY73-XYL strain having xylose-metabolizing enzyme but not transporting ability.
- the vertical axis represents the component concentration g / L
- the horizontal axis represents the fermentation time h.
- stipitis is cultured in the minimum medium containing a specific carbon source.
- A) is glucose
- B) is mannose
- C) is fructose
- D is galactose
- E is xylose
- F is an experimental result in a medium containing L-arabinose as a carbon source.
- each series component in (A) to (F) is RGT2, SNF3, SUT1, SUT2 / 3/4, HXT2.1, HXT2.2, HXT2.3, HXT2.4 from the left as shown in (G).
- each series component in (A) to (F) consists of glucose, mannose, fructose, galactose, xylose, L-arabinose, D-arabinose, L-rhamnose, maltose, cellobiose, sucrose from the left.
- the results of experiments in a medium containing lactose and glycerol are shown. The result which shows the sugar transport ability of HGT2 and XUT1.
- (A) shows the result of xylose transport ability.
- (B) shows the ability to transport L-arabinose.
- (circle) in a figure shows the transport ability of saccharide
- ⁇ indicates the sugar transport ability when only HGT2 is expressed in the presence of xylose and L-arabinose.
- ⁇ indicates the sugar transport ability when HGT2 and XUT1 are expressed in the presence of xylose and L-arabinose.
- the HGT2 gene or an expressed protein thereof is preferably exemplified by those derived from P. tipstipitis (NCBI accession No. XM_001382718).
- xylose transporters derived from other eukaryotic cells or prokaryotic cells and The HGT2 gene or its expressed protein including a variant thereof having a function as an L-arabinose transporter is widely included.
- the SUT1 gene or an expressed protein thereof is preferably exemplified by those derived from P. stipitis (NCBI accession No. ⁇ U77382).
- xylose transporters derived from other eukaryotic cells or prokaryotic cells and The SUT1 gene or its expressed protein including a variant thereof having a function as an L-arabinose transporter is widely included.
- the XUT1 gene or its expressed protein is preferably exemplified by those derived from P. stipitis (NCBI accession No. XM_001385546).
- xylose transporters derived from other eukaryotic cells or prokaryotic cells and The XUT1 gene or its expressed protein containing a variant thereof having a function as an L-arabinose transporter is widely included.
- the HXT2.4 gene or an expressed protein thereof is preferably exemplified by those derived from P. stipitis (NCBI accession No. XM_001387720), but xylose transport derived from other eukaryotic cells or prokaryotic cells. And the HXT2.4 gene or its expressed protein including a variant thereof having a function as an L-arabinose transporter.
- the HGT2 gene, the XUT1 gene, the SUT1 gene, the HXT2.4 gene and the like are incorporated into a host capable of expressing the gene, alone or in combination, and a protein having an amino acid sequence encoded by the gene is xylose. Used as transporter and / or L-arabinose transporter.
- the expression conditions may be known conditions generally used when a foreign gene is incorporated into a host cell for expression.
- the HGT2 gene, the XUT1 gene, the SUT1 gene, the HXT2.4 gene, etc. are incorporated into an ethanol-fermentable host alone or in combination, and are incorporated in the presence of biomass containing xylose and / or L-arabinose.
- Bioethanol can be produced by fermentation. Fermentation conditions are the same as the fermentation conditions of the host not incorporating these genes, and known conditions may be used as they are.
- Biomass used for ethanol fermentation is not particularly limited as long as it contains xylose and / or arabinose, and known biomass is widely used. As such biomass, wood, rice straw, aquatic plants and the like containing lignocellulose are used.
- Example 1 Protein-Blast search was performed on the P. stipitis genome sequence using the Saccharomyces yeast hexose transporter (HXT) as a probe, and 38 homologous genes were selected with about 30% as the lower limit. Oligonucleotide primers were designed so that appropriate restriction enzyme sites were added to the 5 ′ and 3 ′ ends of each gene (FIG. 4). The cDNA treated with the restriction enzyme was subcloned into a pPGK plasmid containing a Phosphoglycerate kinase (PGK) promoter / terminator cassette, which is a constitutive expression promoter of Saccharomyces yeast, and URA3 as a marker gene. The results of PCR experiments using each plasmid as a template are shown in FIG.
- PGK Phosphoglycerate kinase
- KY73 a saccharomyces yeast mutant lacking all of the major hexose transporters HXT1-7 and GAL2, was used to examine the transport ability for the hexoses glucose, D-mannose, D-fructose, and D-galactose. This strain cannot grow on carbon sources other than maltose, and uracil is the only auxotroph that can be used.
- the KY73 strain was transformed with a pPGK plasmid containing a P. stipitis sugar transporter gene and selected on a YNB medium plate using maltose as a carbon source.
- a single colony was selected, and the presence or absence of growth was observed in a YNB liquid medium containing glucose, D-mannose, D-fructose, and D-galactose as carbon sources.
- a YNB liquid medium containing glucose, D-mannose, D-fructose, and D-galactose as carbon sources.
- Glucose SUT1, HGT2, SUT3, SUT2, XUT3, SUT4, XUT1, HXT2.2 D-Mannose: SUT1, SUT2, SUT3, SUT4, HGT2, RGT2, XUT3, XUT1 D-fructose: SUT1, SUT2, XUT3, SUT3, SUT4, HGT2 D-galactose, SUT1, SUT3
- the growth curve is shown in FIG. As an overall trend, it can be seen that only a small part of the selected sugar transporter inheritance has the ability to transport hexose, which can simultaneously transport glucose, D-mannose and D-fructose except D-galactose. Weierstall et al. Introduced a genomic library of P.
- SUT1 stipitis into a mutant strain Y of Saccharomyces yeast that is different from KY73 but has the same mutation to identify SUT1. Furthermore, SUT2 and SUT3 have been identified as homologs. Also in this experiment, SUT1-3 showed the strongest complementation of KY73's ability to transport hexose, which is in good agreement with this result.
- Example 2 “D-xylose transporter” (1) Screening for xylose transporter gene The following experiment was conducted to identify a transporter for D-xylose, which is the main pentose sugar of lignocellulosic biomass.
- the KY73 strain carrying the pPGK plasmid containing the P. stipitis sugar transporter gene was cultured in 10 mL of YNBMal (minimum medium containing maltose as a carbon source) for 30 ° C. for 3 days. Thereby, all the maltose in a culture medium is consumed. Next, 400 ⁇ L of 50% D-xylose solution is added (final concentration 2%).
- the yeast cells are collected by centrifugation and washed twice with 30 mL of ice-cold sterile water. Next, the collected yeast cells are suspended in 400 ⁇ L of sterilized water and shaken at 37 ° C./200 rpm for 1 hour. Thereby, D-xylose transported into the cell by the introduced gene is discharged out of the cell.
- the concentration of D-xylose in the supernatant was identified by a differential refraction system (RI) with an HPLC system connected to an AminexHPX-87H column.
- this plasmid carries the aureobasidin resistance gene AUR1-C, which exhibits antibacterial activity against eukaryotic microorganisms, and homologous recombination occurs with the allele AUR on the Saccharomyces yeast chromosome.
- the XR-XDH-XK gene can be stably introduced onto the chromosome using shidin resistance as a marker.
- the strain prepared in this way is named KY73-XYL.
- pPGK plasmids carrying HGT2, SUT1, SUT2, and SUT3, respectively, were transformed into KY73-XYL.
- xylose taken up into cells by each gene is metabolized to ethanol.
- the KY73-XYL strain can grow using xylose as the sole carbon source, and a fermentation experiment was conducted at a rotational speed of 150 rpm using a 200 mL baffle flask using 20 g / L xylose as the carbon source (FIG. 11). From the xylose consumption rate and the ethanol concentration produced, it can be seen that SUT1 and HGT2 are sufficient for xylose fermentation.
- xylose fermentation was performed using Saccharomyces yeast not deficient in the hexose transporter, not the KY73 strain.
- the pAUR-XR-XDH-XK plasmid was introduced into the MT8-1 strain (MATa ade his3 leu2 trp1 ura3) which is a host yeast (named MT8-1XYL). Genomic PCR and enzyme activity in the cell-free extract confirmed that the XR / XDH gene was normally incorporated and that the XK gene activity was increased.
- MT8-1XYL strain is coated with pPGK, pPGK-SUT1, pPGK-SUT2, pPGK-HGT2 (all ura3 + ) plasmids and YEpM4 (leu2 + ), pHV1 (his3 + ), pTV3 (trp1 + ), respectively.
- the YNB plate was transformed (strain name is the same as the plasmid).
- Each transformed yeast was cultured in a YNB minimal medium containing adenine using glucose as a carbon source, and then a fermentation experiment was performed at a rotational speed of 150 rpm using a 20 mL / L xylose containing adenine as a carbon source in a 200 mL baffle flask. The results are shown in FIG.
- Example 3 "L-arabinose transporter"
- L-arabinose transporter In order to identify a transporter for L-arabinose, which is another major pentose of lignocellulosic biomass along with D-xylose, the following experiment was conducted. Measurement of the ability of the P. stipitis sugar transporter gene to be incorporated into cells using the KY73 strain was performed according to D-xylose.
- Fig. 13 shows the results of measurement of intracellular L-arabinose concentration by HPLC.
- the L-arabinose peak appears around 10.8 minutes, but the identified peak is around 11.2 minutes, which corresponds to L-arabinitol. This is thought to be because GRE3 possessed by Saccharomyces yeast acts as L-arabinose reductase and converts L-arabinose incorporated into cells into L-arabinitol.
- the sugar transporter genes of P. stipitis in which the peak of L-arabinitol was confirmed were XUT1, HGT2, SUT3, SUT2, SUT1, and XUT3.
- the time course of L-arabinose transport was measured for the above seven genes (FIG. 14). The highest L-arabinose transport was confirmed in HGT2 and XUT1.
- Example 4 “Gene expression analysis by real-time PCR” So far, the analysis of sugar transport ability of sugar transporter gene translation products using mainly Saccharomyces yeast mutant KY73 has been described. On the other hand, for example, the ability of the sugar transporter gene A to transport sugar B does not necessarily coincide with the function of the gene in the metabolism of sugar B in P. stipitis. Strictly speaking, it is necessary to create a mutant strain in which each sugar transporter gene is individually disrupted and to examine the phenotype. However, here, "the expression of a transporter gene using a certain sugar as a substrate is based on that sugar as a carbon source. Based on the general knowledge that it is induced under growth, P. stipitis is cultured in various minimal media containing various sugars as carbon sources, and the amount of mRNA of the sugar transporter gene is estimated by real-time PCR. The correlation between gene function and gene expression was compared.
- the amplification primer used for real-time PCR was designed using the Primer3 program (http://frodo.wi.mit.edu/primer3/input.htm), so that amplification of 100 to 150 bp was performed from the gene to be analyzed.
- the specific primer sequences used in this example are shown in FIG. P.
- stipitis contains glucose, mannose, fructose, galactose, xylose, L-arabinose D-arabinose, L-rhamnose, maltose, cellobiose, sucrose, lactose, and glycerol as carbon sources at a concentration of 2% (w / v).
- FIGS. 16 show the results of the average value of the experiment performed twice.
- the results shown in FIG. 16 show the expression levels of various genes for each saccharide contained in the minimal medium.
- the vertical axis of the graph in the figure represents the expression level of each gene relative to the expression level of the actin gene which is a housekeeping gene used as a control.
- FIG. 17 summarizes the data shown in FIG. 16 for each expression gene. Based on the expression level when glucose is contained in the minimum medium at a concentration of 2% (w / v), The expression levels of various genes when cultured in a minimal medium containing the same concentration of sugar are shown.
- the above-mentioned screening was not the most commonly expressed SUT gene group known as the hexose transporter.
- Newly identified HGT2 gene since the expression product of the HGT2 gene is sufficiently expressed even when grown in a minimal medium containing galactose that cannot be transported, the HGT2 gene is not induced by a specific sugar but is constitutively expressed. It is thought that it is a gene. SUT1-4 and RGT2 are expressed next to HGT2, and this result is in good agreement with the complementary growth experiment using the above-mentioned KY73 strain.
- Non-Patent Document 17 shows that expression of SUT1 is not induced in the presence of xylose, and SUT2 or SUT3 is expressed only under aerobic conditions. ing. Also in this example, the expression level of SUT2-4 was sufficiently lower than that of SUT1 in aerobic culture, which is in good agreement with conventional knowledge. On the other hand, HGT2 is more than twice as expressed as SUT2-4, suggesting that it is the most important xylose transporter of P. stipitis together with the results of protein function analysis.
- HXT2.4 which was 670 times more induced than the experimental result with the minimum medium containing glucose.
- this protein has not been confirmed to transport L-arabinose (at least in Saccharomyces yeast) and may have a problem in functional expression in Saccharomyces yeast.
- XUT1 which shows the highest expression level after HXT2.4, shows sufficient L-arabinose transport ability from the above examples, suggesting that it is the most important L-arabinose transporter of P. stipitis . Therefore, HXT2.4 is also considered to be involved as an L-arabinose transporter.
- Example 5 “Transportability of xylose in the presence of xylose and L-arabinose” Looking at the transport ability of the KY73 strain expressing HGT2 by the method according to Example 2 or 3 in the presence of xylose and L-arabinose (both at 2% (w / v) concentration), L-arabinose The xylose uptake ability is improved about 3 times compared to the absence (FIG. 18: A). However, this effect does not change even when XUT1 is expressed together with HGT2, and the additive effect of L-arabinose incorporation of HGT2 and XUT1 is maintained (FIG. 18: B).
- yeast cells expressing HGT2, XUT1, etc. under conditions where xylose, L-arabinose, etc. are mixed shows a cooperative effect in the uptake of xylose and L-arabinose is very favorable. .
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Abstract
Description
項1 HGT2遺伝子またはその発現タンパク質のキシロース輸送体としての使用。
項2 HGT2遺伝子、XUT1遺伝子およびHXT2.4遺伝子からなる群から選ばれる遺伝子の発現タンパク質であるキシロースおよび/またはL-アラビノース輸送体。
項3 HGT2遺伝子、XUT1遺伝子およびHXT2.4遺伝子からなる群から選ばれる遺伝子のキシロースおよび/またはL-アラビノース輸送体としての使用。
項4 HGT2遺伝子、XUT1遺伝子およびHXT2.4遺伝子からなる群から選ばれる少なくとも1種の遺伝子を酵母に導入し、キシロースおよび/またはL-アラビノースを含有するバイオマスの存在下で培養することを特徴とするバイオエタノールの製造方法。
項5 キシロースおよび/またはL-アラビノースを含有するバイオマスが、リグノセルロースである上記項4に記載のバイオエタノールの製造方法。
P. stipitisのゲノム配列に対して、サッカロミセス酵母のヘキソース輸送体(HXT)をプローブとしてProtein-Blastサーチを行い、約30%を下限として相同性のある遺伝子38個を選抜した。それぞれの遺伝子の5’および3’末端に適切な制限酵素部位が付加されるようにオリゴヌクレオチドプライマーを設計した(図4)。制限酵素処理したcDNAは、サッカロミセス酵母の構成的発現プロモーターであるPhosphoglycerate kinase(PGK)プロモーター・ターミネーターカセットおよびマーカー遺伝子としてURA3を含むpPGKプラスミドにサブクローニングした。各プラスミドを鋳型としたPCR実験結果を図5に示す。
D-マンノース:SUT1・SUT2・SUT3・SUT4・HGT2・RGT2・XUT3・XUT1
D-フルクトース:SUT1・SUT2・XUT3・SUT3・SUT4・HGT2
D-ガラクトース・SUT1・SUT3
生育曲線を図7に示す。全体の傾向として、選抜した糖輸送体遺伝のごく一部のもののみに六炭糖輸送能があり、それはD-ガラクトースを除くグルコース・D-マンノース・D-フルクトースを同時に輸送できることが分かる。Weierstallらは、P. stipitisのグルコース輸送体遺伝子を同定する目的で、P. stipitisのゲノムライブラリをKY73とは異なるが同様の変異を有するサッカロミセス酵母の変異株Yに導入しSUT1を同定。さらにそのホモログとしてSUT2・SUT3を同定している。本実験でも、SUT1-3で最も強くKY73のヘキソース輸送能の補完が見られており、この結果とよく一致している。
(1)キシロース輸送体遺伝子のスクリーニング
リグノセルロース系バイオマスの主要五炭糖であるD-キシロースに対する輸送体を同定するために以下のような実験を行った。P. stipitisの糖輸送体遺伝子を含むpPGKプラスミドを保持するKY73株を、10mLのYNBMal(マルトースを炭素源とする最小培地)で30oC・3日間培養した。これにより、培地中のマルトースは全て消費される。次に、400μLの50%D-キシロース溶液を加える(最終濃度2%)。2時間の振騰後、酵母細胞を遠心で集め氷冷した滅菌水30mLで二度洗浄する。次に、集めた酵母細胞を400μLの滅菌水に懸濁し、37oC・200rpmで1時間振騰する。これにより、導入した遺伝子によって細胞内に輸送されたD-キシロースは細胞外に排出される。上清中のD-キシロース濃度は、AminexHPX-87HカラムをつないだHPLCシステムによる示差屈折系(RI)によって同定した。
主要なキシロース輸送体であるHGT2・SUT1・SUT2・SUT3についてキシロース発酵の際の性質を調べるために以下のような実験を行った。まず、KY73株に、P. stipitis由来のXRおよびXDH遺伝子、さらにサッカロミセス酵母由来のXK遺伝子をそれぞれPGKプロモーターにつないだカセットを有する酵母染色体組み込み型プラスミドpAUR-XR-XDH-XKを導入した(図10)。本プラスミドは同時に真核微生物に対して抗菌作用を示すオーレオバシジンの耐性遺伝子AUR1-Cを保持しており、サッカロミセス酵母染色体上にある対立遺伝子AURとの間で相同組み換えが起こることによってオーレオバシジン耐性をマーカーとしてXR-XDH-XK遺伝子を染色体上に安定して導入することができる。このようにして作製した株をKY73-XYLと名付ける。
D-キシロースと並びリグノセルロース系バイオマスのもう1つの主要五炭糖であるL-アラビノースに対する輸送体を同定するために以下のような実験を行った。P. stipitisの糖輸送体遺伝子のKY73株を用いた細胞内への取り込み能の測定は、D-キシロースに準じて行った。
これまでは、主にサッカロミセス酵母変異株KY73を用いた糖輸送体遺伝子翻訳産物の糖輸送能解析について記載してきた。一方、例えば糖輸送体遺伝子Aが糖Bを輸送する能力があることとその遺伝子がP. stipitisにおける糖Bの代謝において機能していることは必ずしも一致しない。厳密に言えば各糖輸送体遺伝子を個別に破壊した変異株を作製し表現型を調べる必要があるが、ここでは「ある糖を基質とする輸送体遺伝子の発現はその糖を炭素源とした生育下で誘導される」という一般的知見に基づいて、各種糖を炭素源として含む各種最小培地においてP. stipitisを培養し、糖輸送体遺伝子のmRNAの量をリアルタイムPCRによって見積もることで、タンパク質としての機能と遺伝子発現の相関について比較検討した。
実施例2または3に準じた方法にてHGT2を発現させたKY73株のキシロース・L-アラビノース共存下(共に2% (w/v)濃度)での輸送能を見てみると、L-アラビノース非存在下に比べてキシロースの取り込み能が約3倍に向上する(図18:A)。但し、この効果はHGT2と共にXUT1を発現させても変わらず、またHGT2及びXUT1のL-アラビノース取り込みの加算的効果も維持される(図18:B)。
Claims (5)
- HGT2遺伝子またはその発現タンパク質のキシロース輸送体としての使用。
- HGT2遺伝子、XUT1遺伝子およびHXT2.4遺伝子からなる群から選ばれる遺伝子の発現タンパク質であるキシロースおよび/またはL-アラビノース輸送体。
- HGT2遺伝子、XUT1遺伝子およびHXT2.4遺伝子からなる群から選ばれる遺伝子のキシロースおよび/またはL-アラビノース輸送体としての使用。
- HGT2遺伝子、XUT1遺伝子およびHXT2.4遺伝子からなる群から選ばれる少なくとも1種の遺伝子を酵母に導入し、キシロースおよび/またはL-アラビノースを含有するバイオマスの存在下で培養することを特徴とするバイオエタノールの製造方法。
- キシロースおよび/またはL-アラビノースを含有するバイオマスが、リグノセルロースである請求項4に記載のバイオエタノールの製造方法。
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US13/393,664 US20120270290A1 (en) | 2009-09-03 | 2010-09-01 | Pentose transporter |
BR112012004828A BR112012004828A2 (pt) | 2009-09-03 | 2010-09-01 | transportador de pentose |
JP2011529923A JP5689062B2 (ja) | 2009-09-03 | 2010-09-01 | 五炭糖輸送体 |
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WO2008080505A1 (de) * | 2006-12-20 | 2008-07-10 | Johann Wolfgang Goethe-Universität Frankfurt am Main | Neuer spezifischer arabinose-transporter aus der hefe pichia stipitis und dessen verwendungen |
US20090325241A1 (en) * | 2008-06-13 | 2009-12-31 | Thomas William Jeffries | Sugar transport sequences, yeast strains having improved sugar uptake, and methods of use |
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WO2008080505A1 (de) * | 2006-12-20 | 2008-07-10 | Johann Wolfgang Goethe-Universität Frankfurt am Main | Neuer spezifischer arabinose-transporter aus der hefe pichia stipitis und dessen verwendungen |
US20090325241A1 (en) * | 2008-06-13 | 2009-12-31 | Thomas William Jeffries | Sugar transport sequences, yeast strains having improved sugar uptake, and methods of use |
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BAE, JU YUN: "Identification and characterization of xylose transporters, Xutl and Sut4, of Pichia stipitis.", DISSERTATION ABSTRACTS INTERNATIONAL, vol. 70, no. 2, 2009 * |
DATABASE DDBJ/EMBL/GENBANK [online] 23 February 2007 (2007-02-23), retrieved from http://www.ncbi.nlm.nih.gov/ nuccore/126132459?sat=NCBI&satkey=16581899 Database accession no. XM_001382718 * |
DATABASE DDBJ/EMBL/GENBANK [online] 23 February 2007 (2007-02-23), retrieved from http://www.ncbi.nlm.nih.gov/ nuccore/126138119?sat=NCBI&satkey=16584737 Database accession no. XM_001385546 * |
JEFFRIES T.W. ET AL.: "Genome sequence of the lignocellulose-bioconverting and xylose- fermenting yeast Pichia stipitis.", NATURE BIOTECHNOLOGY, vol. 25, no. 3, 2007, pages 319 - 326 * |
KATAHIRA S. ET AL.: "Improvement of ethanol productivity during xylose and glucose co- fermentation by xylose-assimilating S. cerevisiae via expression of glucose transporter Sutl.", ENZYME AND MICROBIAL TECHNOLOGY, vol. 43, 2008, pages 115 - 119 * |
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US20120270290A1 (en) | 2012-10-25 |
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