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 transport system of the methanogenic archaeon Methanosarcina mazei Gal, Here it is shown that cofactor F420H2-dependent reduction of 2-hydroxy-phenazine as catalyzed by the membrane-bound enzyme is coupled to proton translocation across the cytoplasmic membrane, exhibiting a stoichiometry of 0.9 H+ translocated per two electrons transferred. The electrochemical proton gradient thereby generated was shown to drive ATP synthesis from ADP + Pi. The gene cluster encoding the F420H2 dehydrogenase of M. mazei Gol comprises 12 genes that 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 related 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 products FpoA, EF, J, K, L, M, and N are highly hydrophobic and are homologous to 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 present 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 equipped with an alternative electron input unit for the oxidation of reduced cofactor F-420 and a modified output module adopted to the reduction of methanophenazine.