Direct Electron Transfer between the frhAGB-Encoding Hydrogenase and Thioredoxin Reductase in a Non-Methanogenic Archaeon Thermococcus onnurnieus NA1

Abstract

The thioredoxin reductase (TrxR) of the hyperthermophilic archaeon T. onnurineus NA1 is known to be an NADP-dependent enzyme that uses NAD(P)H as an electron donor. In this study, we demonstrate that electrons generated via hydrogenase-mediated H2 oxidation can be utilized by TrxR directly without the use of other electron carriers. The frhAGB-encoding hydrogenase, a homolog of the F420-reducing hydrogenase of methanogens, that lacks F420-reducing activity, was shown to interact with TrxR in coimmunoprecipitation experiments and in vitro pull-down assays. Furthermore, the transfer of electrons from H2 between the frhAGB-encoding hydrogenase and TrxR was demonstrated by reduction of a redox partner of TrxR, Pdo, identified in the redox cascades of T. onnurineus NA1. Interaction and electron transfer were observed between TrxR and the heterodimeric (FrhAG) hydrogenase complex as well as the heterotrimeric complex (FrhAGB). This study revealed the functionality of the frhAGB-encoding hydrogenase in a non-methanogen and provided insight into the mechanism underlying electron transfer by the hydrogenase to a target in the absence of the F420 cofactor.