The open reading frame 02797 from Candida tropicalis encodes a novel NADH-dependent aldehyde reductase.

Owing to its high-temperature tolerance, robustness, and wide use of carbon sources, Candida tropicalis is considered a good candidate microorganism for bioconversion of lignocellulose to ethanol. It also has the intrinsic ability to in situ detoxify aldehydes derived from lignocellulosic hydrolysis. However, the aldehyde reductases that catalyze this bioconversion in C. tropicalis remain unknown. Herein, we found that the uncharacterized open reading frame (ORF), CTRG_02797 , from C. tropicalis encodes a novel and broad substrate-specificity aldehyde reductase that reduces at least seven aldehydes. This enzyme strictly depended on NADH rather than NADPH as the co-factor for catalyzing the reduction reaction. Its highest affinity (K m), maximum velocity (V max), catalytic rate constant (K cat), and catalytic efficiency (K cat/ K m) were observed when reducing acetaldehyde (AA) and its enzyme activity was influenced by different concentrations of salts, metal ions, and chemical protective additives. Protein localization assay demonstrated that Ctrg_02797p was localized in the cytoplasm in C. tropicalis cells, which ensures an effective enzymatic reaction. Finally, Ctrg_02797p was grouped into the cinnamyl alcohol dehydrogenase (CADH) subfamily of the medium-chain dehydrogenase/reductase family. This research provides guidelines for exploring more uncharacterized genes with reduction activity for detoxifying aldehydes. • CTRG_02797 from Candida tropicalis encodes a broad-substrate aldehyde reductase. • Ctrg_02797p is strictly NADH dependent for enzymatic conversion of aldehydes to their corresponding alcohols. • Ctrg_02797p is localized to the cytoplasm in C. tropicalis cells. • Ctrg_02797p is a medium-chain dehydrogenase/reductase (MDR) and can be further grouped into the CADH subfamily. [ABSTRACT FROM AUTHOR]

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