title: Improving the performance of industrial ethanol-producing yeast by expressing the aspartyl protease on the cell surface.
abstract: The yeasts used in fuel ethanol manufacture are unable to metabolize soluble proteins. The PEP4 gene, encoding a vacuolar aspartyl protease in Saccharomyces cerevisiae, was either secretively or cell-surface anchored expressed in industrial ethanol-producing S. cerevisiae. The obtained recombinant strains APA (expressing the protease secretively) and APB (expressing the protease on the cell wall) were studied under ethanol fermentation conditions in feed barley cultures. The effects of expression of the protease on product formation, growth and cell protein content were measured. The biomass yield of the wild-type was clearly lower than that of the recombinant strains (0.578 ± 0.12 g biomass/g glucose for APA and 0.582 ± 0.08 g biomass/g glucose for APB). In addition, nearly 98-99% of the theoretical maximum level of ethanol yield was achieved (relative to the amount of substrate consumed) for the recombinant strains, while limiting the nitrogen source resulted in dissatisfactory fermentation for the wild-type and more than 30 g/l residual sugar was detected at the end of fermentation. In addition, higher growth rate, viability and lower yields of byproducts such as glycerol and pyruvic acid for recombinant strains were observed. Expressing acid protease can be expected to lead to a significant increase in ethanol productivity.
authors.affiliation: The Key Laboratory of Industrial Biotechnology, Ministry of Education, Center for Bioresources and Bioenergy, School of Biotechnology, Jiangnan University, Wuxi 214122, People's Republic of China.
authors.forename: Zhong-peng
authors.initials: ZP
authors.lastname: Guo
authors.forename: Liang
authors.initials: L
authors.lastname: Zhang
authors.forename: Zhong-yang
authors.initials: ZY
authors.lastname: Ding
authors.forename: Zheng-Xiang
authors.initials: ZX
authors.lastname: Wang
authors.forename: Gui-Yang
authors.initials: GY
authors.lastname: Shi
mesh_terms: D016282:Aspartic Acid Endopeptidases / Q000235:genetics* / Q000378:metabolism*; D002473:Cell Wall / Q000201:enzymology* / Q000235:genetics; D000431:Ethanol / Q000378:metabolism*; D005110:Extracellular Space / Q000201:enzymology / Q000235:genetics; D005285:Fermentation; D015870:Gene Expression; D007218:Industrial Microbiology; D015202:Protein Engineering; D021381:Protein Transport; D012441:Saccharomyces cerevisiae / Q000201:enzymology / Q000235:genetics / Q000378:metabolism*; D029701:Saccharomyces cerevisiae Proteins / Q000235:genetics* / Q000378:metabolism*
chemical_list: D029701:Saccharomyces cerevisiae Proteins; D000431:Ethanol; C499267:PEP4 protein, S cerevisiae; D016282:Aspartic Acid Endopeptidases