To date, NAD(P)H, ferredoxin, and coenzyme F have been identified as electron donors for thioredoxin reductase (TrxR). In this study, we present a novel electron source for TrxR. In the hyperthermophilic archaeon NA1, the -encoded hydrogenase, a homolog of the F-reducing hydrogenase of methanogens, was demonstrated to interact with TrxR in coimmunoprecipitation experiments and pulldown assays. Electrons derived from H oxidation by the -encoded hydrogenase were transferred to TrxR and reduced Pdo, a redox partner of TrxR. Interaction and electron transfer were observed between TrxR and the heterodimeric hydrogenase complex (FrhAG) as well as the heterotrimeric complex (FrhAGB). Hydrogen-dependent reduction of TrxR was 7-fold less efficient than when NADPH was the electron donor. This study not only presents a different type of electron donor for TrxR but also reveals new functionality of the -encoded hydrogenase utilizing a protein as an electron acceptor. This study has importance in that TrxR can use H as an electron donor with the aid of the -encoded hydrogenase as well as NAD(P)H in NA1. Further studies are needed to explore the physiological significance of this protein. This study also has importance as a significant step toward understanding the functionality of the -encoded hydrogenase in a nonmethanogen; the hydrogenase can transfer electrons derived from oxidation of H to a protein target by direct contact without the involvement of an electron carrier, which is distinct from the mechanism of its homologs, F-reducing hydrogenases of methanogens.

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http://www.ncbi.nlm.nih.gov/pmc/articles/PMC7054103PMC
http://dx.doi.org/10.1128/AEM.02630-19DOI Listing

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