To date, NAD(P)H, ferredoxin, and coenzyme F₄₂₀ 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 Thermococcus onnurineus NA1, the frhAGB-encoding hydrogenase, a homolog of the F₄₂₀-reducing hydrogenase of methanogens, was demonstrated to interact with TrxR in coimmunoprecipitation experiments and in vitro pull-down assays. Electrons derived from H₂ oxidation by the frhAGB-encoding 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 seven-fold less efficient than when NADPH was electron donor. This study not only presents a different type of electron donor for TrxR but also reveals new functionality of the frhAGB-encoding hydrogenase utilizing a protein as an electron acceptor.

IMPORTANCE This study has importance in that TrxR can use H₂ as an electron donor with the aid of the frhAGB-encoding hydrogenase as well as NAD(P)H in T. onnurineus 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 frhAGB-encoding hydrogenase in a non-methanogen: the hydrogenase can transfer electrons derived from oxidation of H₂ to a protein target by direct contact without the involvement of an electron carrier, which is distinct from the mechanism of its homologs, F₄₂₀-reducing hydrogenases of methanogens.

迄今为止，NAD（P）H，铁氧还蛋白和辅酶F ₄₂₀已被确定为硫氧还蛋白还原酶（TrxR）的电子供体。在这项研究中，我们提出了TrxR的新型电子源。在超嗜热古生菌嗜热球菌NA1中，在共同免疫沉淀实验和体外下拉试验中，证明了frhAGB编码的氢酶（产甲烷酶的F ₄₂₀还原性氢酶的同系物）与TrxR相互作用。frhAGB衍生自H ₂氧化的电子-编码的加氢酶被转移到TrxR和还原的Pdo，Trdo的氧化还原伴侣。TrxR和异二聚体氢化酶复合物（FrhAG）以及异三聚体复合物（FrhAGB）之间观察到相互作用和电子转移。氢依赖的TrxR还原效率比NADPH为电子供体时低7倍。这项研究不仅为TrxR提供了不同类型的电子供体，而且还揭示了利用蛋白质作为电子受体的frhAGB编码加氢酶的新功能。

重要事项这项研究具有重要意义，因为TrxR可以利用frhAGB编码的氢酶以及T. onnurineus NA1中的NAD（P）H来利用H ₂作为电子供体。需要进一步的研究来探索这种蛋白质的生理意义。这项研究对于理解非甲烷源中编码frhAGB的加氢酶的功能性迈出了重要的一步：加氢酶可以通过直接接触将H ₂氧化衍生的电子转移至蛋白质靶标，而无需电子载体的参与与它的同系物F _420还原产甲烷酶的氢酶不同。