Submitted to: New Biotechnology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: July 2, 2009
Publication Date: December 1, 2009
Citation: Hector, R.E., Bowman, M.J., Skory, C.D., Cotta, M.A. 2009. The Saccharomyces cerevisiae YMR315W gene encodes an NADP(H)-specific Oxidoreductase regulated by the transcription factor Stb5p in response to NADPH limitation. New Biotechnology. 26(3/4):171-180. Interpretive Summary: This research discovered a new method to increase the ability of baker’s yeast to resist certain types of stress. Yeast strains engineered to convert biomass-derived sugars to ethanol require increased amounts of key metabolites to combat numerous cellular stresses that occur due to the high levels of toxic compounds formed during biomass pre-treatment and stresses associated with large scale industrial fermentation processes. Two proteins were identified that, when overexpressed in baker’s yeast, increase a key metabolite needed, allowing the cells to grow under conditions that would normally severely inhibit cell growth. It is anticipated that incorporating these modifications to yeast strains currently used for the production of bio-ethanol will result in increased cell growth and ethanol productivity.
Technical Abstract: Engineered xylose-metabolizing cells grown on xylose show increased expression of YMR315W at both the mRNA and protein levels. Additionally, the YMR315W promoter contains a putative binding site for the transcription factor Stb5p, which has been shown to regulate genes involved in nicotinamide adenine dinucleotide phosphate (NADPH) production. We hypothesized that Ymr315wp, a conserved protein of unknown function, is an additional source of NADPH in wild type cells. In this study, we purified histidine-tagged enzyme and determined that Ymr315wp is an NADP(H) specific oxidoreductase. We also showed that YMR315W transcription is regulated by Stb5p in response to diamide induced NADPH depletion. Overexpression of Ymr315wp resulted in elevated NADPH levels and increased resistance to diamide. However, the presence of Ymr315wp in cells lacking the oxidative branch of the pentose phosphate pathway resulted in decreased NADPH levels and increased diamide sensitivity. These results suggest that in wild type cells Ymr315wp contributes to NADPH production as an alternative source of NADPH.