The F420H2 dehydrogenase from Methanosarcina mazei is a redox-driven proton pump closely related to NADH dehydrogenases

The F420H2 dehydrogenase is part of the energy conserving electron transpor t system of the methanogenic archaeon Methanosarcina mazei Gal, Here it is shown that cofactor F420H2-dependent reduction of 2-hydroxy-phenazine as ca talyzed by the membrane-bound enzyme is coupled to proton translocation acr oss the cytoplasmic membrane, exhibiting a stoichiometry of 0.9 H+ transloc ated per two electrons transferred. The electrochemical proton gradient the reby generated was shown to drive ATP synthesis from ADP + Pi. The gene clu ster encoding the F420H2 dehydrogenase of M. mazei Gol comprises 12 genes t hat are referred to as fpoA, B, C, D, H, I, J, K, L, M, N, and O. Analysis of the deduced amino acid sequences revealed that the enzyme is closely rel ated to proton translocating NADH dehydrogenases of respiratory chains from bacteria (NDH-1) and eukarya (complex I). Like the NADH-dependent enzymes, the F420H2 dehydrogenase is composed of three subcomplexes. The gene produ cts FpoA, EF, J, K, L, M, and N are highly hydrophobic and are homologous t o subunits that form the membrane integral module of NDH-1. FpoB, C, D, and I have their counterparts in the amphipathic membrane-associated module of NDH-1. Homologues to the hydrophilic NADH-oxidizing input module are not p resent in M. mazei Gill, Instead, the gene product FpoF maS be responsible for F420H2 oxidation and may function as the electron input part, Thus, the F420H2 dehydrogenase from M. mazei Gol resembles eukaryotic and bacterial proton transiocating NADH dehydrogenases in many ways. The enzyme from the methanogenic archaeon functions as a NDB-1/complex I homologue and is equip ped with an alternative electron input unit for the oxidation of reduced co factor F-420 and a modified output module adopted to the reduction of metha nophenazine.