On the prosthetic groups of the NiFe sulfhydrogenase from Pyrococcus furiosus: topology, structure, and temperature-dependent redox chemistry

摘要

The sulfhydrogenase complex of Pyrococcus furiosus is an #alpha##beta##gamma##delta# heterotetramer with both hydrogenase activity (borne by the #alpha##delta# subunits) and sulfur reductase activity (carried by the #beta##gamma# subunits). The #beta#-subunit contains at least two [4Fe-4S] cubanes and the #gamma#-subunit contains one [2Fe-2S] cluster and one FAD molecule. The #delta#-subunit contains three [4Fe-4S] cubanes and the #alpha#-subunit carries the NiFe dinuclear center. Only three Fe/S signals are observed in EPR-monitored reduction by dithionite, NADPH, or internal substrate upon heating. All other clusters presumably have reduction potentials well below that of the H~+/H_2 couple. Heat-induced reduction by internal substrate allows, for the first time, EPR monitoring of the NiFe center in a hyperthermophilic hydrogenase, which passes through a number of states, some of which are similar to states previously defined for mesophilic hydrogenases. The complexity of the observed transitions reflects a combination of temperature-dependent activation and temperature-dependent reduction potentials.