The F420H2 Dehydrogenase fromMethanosarcina mazei Is a Redox-driven Proton Pump Closely Related to NADH Dehydrogenases

Abstract

The F 420 H 2 dehydrogenase is part of the energy conserving electron transport system of the methanogenic archaeon Methanosarcina mazei Gö 1. Here it is shown that cofactor F 420 H 2 -dependent reduction of 2-hydroxyphenazine as catalyzed by the membrane-bound enzyme is coupled to proton translocation across the cytoplasmic membrane, exhibiting a stoichiometry of 0.9 H Methanosarcina mazei strain Gö1 is a strictly anaerobic methanogenic archaeon that converts a limited number of simple substrates (H 2 ϩ CO 2 , methanol, methylamines, and acetate) to methane. 2-methylthioethanesulfonate is the central intermediate in all methanogenic pathways and is reductively demethylated to methane catalyzed by the 2-methylthioethanesulfonate reductase. The two electrons required for the reduction are derived from 7-mercaptoheptanoylthreonine phosphate, resulting in the formation of a heterodisulfide (CoB-S-S-CoM) 1 of 2-mercaptoethanesulfonate (HS-CoM) and 7-mercaptoheptanoylthreonine phosphate (HS-CoB) (1). An energyconserving step in the metabolism of methanogens is the reduction of CoB-S-S-CoM with either molecular hydrogen or reduced coenzyme F 420 . In recent years, the membrane-bound electron transfer of M. mazei Gö1 has been analyzed in detail, resulting in the discovery of two proton translocating systems referred to as H 2 :heterodisulfide oxidoreductase and F 420 H 2 : heterodisulfide oxidoreductase, respectively (2).During growth on methylated substrates, part of the methyl groups of the substrates is oxidized to CO 2 , and reducing equivalents are transferred to F 420 . The reduced cofactor (F 420 H 2 ) is reoxidized by the above-mentioned membrane-bound electron transport system consisting of an F 420 H 2 dehydrogenase and a heterodisulfide reductase. The transfer of electrons between the enzymes is most likely mediated by methanophenazine, a hydrophobic cofactor that has been isolated from the cytoplasmic membrane of M. mazei Gö1. The overall process has been shown to be competent in driving proton translocation across the cytoplasmic membrane (3). The resulting electrochemical proton gradient is the driving force for ATP synthesis from ADP ϩ P i catalyzed by an A 1 A 0 -type ATP synthase (2, 4).The F 420 H 2 dehydrogenase with a molecular mass of 115 kDa has been purified from M. mazei Gö1 and contains iron-sulfur clusters and FAD (5). The isolated enzyme is very similar to the corresponding protein from Methanolobus tindarius (6) and is composed of five different subunits with molecular masses of 40, 37, 22, 20, and 17 kDa. A F 420 H 2 dehydrogenase has also been purified form the sulfate-reducing archaeon Archaeoglobus fulgidus (7).In this report the gene locus encoding the F 420 H 2 dehydrogenase on the M. mazei genome is described. Furthermore, it is shown that the corresponding enzyme is a novel proton pump ¶ To whom correspondence should be addressed. Fax: 49-551-393793; E-mail: udeppen@gwdg.de. 1 The abbreviations used are: CoB-S-S-CoM, heterodisulfide of HSCoM and HS-CoB; HS-CoM, 2-mercaptoethansulfona...

A New Type of Sulfite Reductase, a Novel Coenzyme F420-dependent Enzyme, from the Methanarchaeon Methanocaldococcus jannaschii

“…The N-terminal half of this polypeptide (residues 1-311; called Fsr-N) possessed the sequence features of FqoF and FpoF (Fig. 5A) (31,32) and exhibited a close phylogenetic relationship to FqoF (Fig. 7A).…”

Methylotrophic methanogenesis discovered in the archaeal phylum Verstraetearchaeota

“…Divergent homologues of the genes encoding this electron-bifurcating complex are found co-located in the Verstraetearchaeota (Supplementary Table 3). In addition, homologues of the membrane-bound NADH-ubiquinone oxidoreductase (Nuo), which show high sequence similarity to the F 420 -methanophenazine oxidoreductase (Fpo) found in Methanosarcinales 20 , are present and form an Fpo-like complex capable of re-oxidizing reduced ferredoxin, with concomitant translocation of protons or sodium ions across the cytoplasmic membrane (Fig. 3a).…”

The role of proton and sodium ions in energy transduction by respiratory complex I

“…Considering a membrane potential of 120 mV, in the first situation the H 1 /e cannot exceed 1 whereas in the latter it can be up to 2 (two electrons are involved in NADH:quinone oxidoreduction). In the same way, the observed H 1 /e stoichiometry of 0.9 for the enzyme from M. mazei can be explained (19). This enzyme uses methanophenazine as electron acceptor (E m, 7 2255 mV) and F 420 H 2 as the electron donor (E m,7 2360 mV), being the maximum free energy available 105 mV (this reaction also involves two electrons).…”

“…A H 1 /e 5 1.5 was obtained in studies with dimethyl sulfoxide-respiring E. coli cells (18). Archaeal complex I is also described as a proton pump and a H 1 /e ratio of 0.9 was determined for Methanosarcina mazei inverted vesicles (19).…”