Novel Functions of frhAGB-Encoded Hydrogenase through Interaction with Formate Dehydrogenase in the Hyperthermophilic Archaeon Thermococcus onnurineus NA1

Abstract

It has been reported that the frhAGB-encoded hydrogenase from Thermococcus onnurineus NA1 is homologous to the F420-reducing hydrogenase from methanogen and can reduce thioredoxin reductase (TrxR) via direct electron transfer from H2 oxidation. In this study, to find other interaction targets of frhAGB-encoded hydrogenase, we searched for structural homologs of TrxR using the PSI-BLAST protein database search program and AlphaFold protein structure database. The strategy using structural homology with the help of structure prediction by AlphaFold was very successful in finding putative targets for the frhAGB-encoded hydrogenase. The interaction potential of the TrxR homolog with the frhAGB-encoded hydrogenase was demonstrated by measuring H2-derived direct electron transfer between the two purified enzymes in vitro. The finding that the hydrogenase can reduce the cofactor through interaction with formate dehydrogenase is significant in that the enzyme can function to supply reducing equivalents, just as F420-reducing hydrogenases in methanogen use coenzyme F420 as an electron carrier. In conclusion, the frhAGB-encoded hydrogenase was identified to transfer electrons directly to formate dehydrogenase without an electron carrier, similar to the mechanism observed for TrxR. These results expand our understanding of the functional role of the frhAGB-encoded hydrogenase in non-methanogenic Thermococcus species.