Unusual Aldehyde Reductase Activity for Production of Full-length Fatty Alcohol by Cyanobacterial Aldehyde Deformylating Oxygenase
Background: Aldehyde-deformylating oxygenase (ADO) is a non-heme di-iron enzyme that catalyzes deformylation of aldehydes to generate alkanes/alkenes. In this study, we report for the first time that under anaerobic or limited oxygen conditions, Prochlorococcus marinus (PmADO) can generate full-length fatty alcohols from fatty aldehydes without eliminating a carbon unit. Results: Unlike the native activity of ADO which requires electrons from the Fd/FNR electron transfer complex, the aldehyde
... lex, the aldehyde reduction activity of ADO requires only NADPH. Our results demonstrated that yield of alcohol products can be affected by oxygen concentration and type of aldehyde. Under O2-scant conditions (10-15%), yields of octanol and dodecanol were around 40-60% and could be increased up to 80% under strict anaerobic conditions (>0.0004%). Unexpectedly, Fe2+ cofactor is not involved in the aldehyde reductase activity of PmADO because yields of alcohols obtained from holo- and apo-enzymes were similar under anaerobic conditions. The direct hydride transfer activity of PmADO is highly specific to substrates; NADPH not NADH can be used as a reductant to reduce medium-chain fatty aldehydes (C6-C10) with decanal as the most preferred substrate (the highest kcat/Km value with 98% bioconversion yield). Molecular dynamics (MD) simulations was used to identify a binding site of NADPH which is located close to the aldehyde binding site. In the metabolic engineered cells containing PmADO, dual activities of alkane and alcohol production could be detected. Conclusion: The findings reported herein highlight a new activity of PmADO which may be applied as a biocatalyst for industrial synthesis of fatty alcohols in the future.