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

Abstract

Thioredoxin reductase (TrxR), a dimeric flavin-containing enzyme, plays several important roles in maintaining redox status inside cell by reducing thioredoxin (Trx). Previously, we reported that TrxR in a hyperthermophilic archaeon Thermococcus onnurineus NA1, could be reduced by NAD(P)H and provide reducing power to protein disulfide oxidoreductase (Pdo) and other Trx homologous proteins. In the course of understanding the role of TrxR in T. onnurineus NA1, it was found that a protein co-immunoprecipitated with TrxR using an anti-TrxR antibody. The protein was identified as frhG subunit of the frhAGB-encoding hydrogenase by mass spectrometric analysis. The interaction between TrxR and frhAGB-encoding hydrogenase was confirmed by in vitro pull-down assays. Based on the interaction data, the possibility of electron transfer from frhAGB-encoding hydrogenase to TrxR was investigated. The frhAGB-encoding hydrogenase was capable of reducing TrxR only in the presence of H2. These results indicate that the frhAGB-encoding hydrogenase in the non-methanogenic T. onnurineus NA1 has a distinguished way of electron transfer from those in methanogens employing coenzyme F420. Our findings provide insight into the functionality of the frhAGB-encoding hydrogenase in non-methanogens and the underlying mechanism for the electron transfer in the absence of F420 cofactor.