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The aldehyde reductases from the short-chain dehydrogenase/reductase (SDR) family were identified as a series of critical enzymes for the improved tolerance of Saccharomyces cerevisiae to the aldehydes by catalyzing the detoxification reactions of aldehydes. Herein, we report that a novel aldehyde reductase Ykl107wp deduced from YKL107W from S. cerevisiae belongs to the classical SDR group and can catalyze the reduction reactions of acetaldehyde (AA), glycolaldehyde (GA), furfural (FF), formaldehyde (FA), and propionaldehyde (PA) but cannot reduce the six representative ketones. Ykl107wp displayed the best maximum velocity (Vmax), catalytic rate constant (Kcat), catalytic efficiency (Kcat/Km), and highest affinity (Km) to acetaldehyde. The optimum pH of Ykl107wp was 6.0 for the reduction of AA and 7.0 for the reduction of GA and FF, and the optimum temperatures were 40, 35, and 30 °C for the reduction of AA, GA, and FF, respectively. Ykl107wp for the reduction of AA was greatly affected by metal ions, chemical additives, and salts and showed poor thermal and pH stability, but its stability was slightly affected by a substrate. Ykl107wp was localized in endoplasmic reticulum and prevented the yeast cells from damage caused by furfural via the detoxification of furfural to furfural alcohol. This research provides guidelines for the study of uncharacterized classical SDR aldehyde reductases and exploration of their protective mechanisms on the corresponding organelles. [ABSTRACT FROM AUTHOR]

The yeast Saccharomyces cerevisiae able to tolerate lignocellulose-derived inhibitors like furfural. Yeast strain performance tolerance has been measured by the length of the lag phase for cell growth in response to the furfural inhibitor challenge. The aims of this work were to obtain RDS1 yeast tolerant strain against furfural through overexpression using a method of in vivo homologous recombination. Here, we report that the overexpressing RDS1 recovered more rapidly and displayed a lag phase at about 12 h than its parental strain. Overexpressing RDS 1 strain encodes a novel aldehyde reductase with catalytic function for reduction of furfural with NAD(P)H as the co-factor. It displayed the highest specific activity (24.8 U/mg) for furfural reduction using NADH as a cofactor. Fluorescence microscopy revealed improved accumulation of reactive oxygen species resistance to the damaging effects of inhibitor in contrast to the parental. Comparative transcriptomics revealed key genes potentially associated with stress responses to the furfural inhibitor, including specific and multiple functions involving defensive reduction–oxidation reaction process and cell wall response. A significant change in expression level of log2 (fold change >1) was displayed for RDS1 gene in the recombinant strain, which demonstrated that the introduction of RDS1 overexpression promoted the expression level. Such signature expressions differentiated tolerance phenotypes of RDS 1 from the innate stress response of its parental strain. Overexpression of the RDS1 gene involving diversified functional categories is accountable for stress tolerance in yeast S. cerevisiae to survive and adapt the furfural during the lag phase. [ABSTRACT FROM AUTHOR]

Aldehydes are the main inhibitors generated during the pretreatment of lignocellulosic biomass, which can inhibit cell growth and disturb subsequent fermentation. Saccharomyces cerevisiae has the intrinsic ability to in situ detoxify aldehydes to their less toxic or nontoxic alcohols by numerous aldehyde dehydrogenases/reductases during the lag phase. Herein, we report that an uncharacterized open reading frame YMR152W from S. cerevisiae encodes a novel aldehyde reductase with catalytic functions for reduction of at least six aldehydes, including two furan aldehydes (furfural and 5-hydroxymethylfurfural), three aliphatic aldehydes (acetaldehyde, glycolaldehyde, and 3-methylbutanal), and an aromatic aldehyde (benzaldehyde) with NADH or NADPH as the co-factor. Particularly, Ymr152wp displayed the highest specific activity (190.86 U/mg), and the best catalytic rate constant (K cat), catalytic efficiency (K cat /K m), and affinity (K m) when acetaldehyde was used as the substrate with NADH as the co-factor. The optimum pH of Ymr152wp is acidic (pH 5.0–6.0), but this enzyme is more stable in alkaline conditions (pH 8.0). Metal ions, chemical protective additives, salts, and substrates could stimulate or inhibit enzyme activities of Ymr152wp in varying degrees. Ymr152wp was classified into the quinone oxidoreductase (QOR) subfamily of the medium-chain dehydrogenase/reductase (MDR) family based on the results of amino acid sequence analysis and phylogenetic analysis. Although Ymr152wp was grouped into the QOR family, no quinone reductase activity was observed using typical quinones (9,10-phenanthrenequinone, 1,2-naphthoquinone, and p -benzoquinone) as the substrates. This study provides guidelines for exploring more uncharacterized aldehyde reductases in S. cerevisiae for in situ detoxification of aldehyde inhibitors derived from lignocellulosic hydrolysis. • YMR152W from Saccharomyces cerevisiae encodes an aldehyde reductase. • Ymr152wp showed much better specific activity for reduction of acetaldehyde. • Overexpression of YMR152W conferred resistance to aldehyde inhibitors. • Ymr152wp is classified into the QOR subfamily of the MDR family. [ABSTRACT FROM AUTHOR]