InterPro: IPR012048 Formylmethanofuran dehydrogenase, fused subunit C/D

Formylmethanofuran dehydrogenases (EC:1.2.99.5) is found in methanogenic and sulphate-reducing archaea. The enzyme contains molybdenum or tungsten, a molybdopterin guanine dinuceotide cofactor (MGD) and iron-sulphur clusters [1]. It catalyses the reversible reduction of CO₂ and methanofuran via N-carboxymethanofuran (carbamate) to N-formylmethanofuran, the first and second steps in methanogenesis from CO₂ [2, 3]. This reaction is important for the reduction of CO₂ to methane, in autotrophic CO₂ fixation, and in CO₂ formation from reduced C₁ units [4]. The synthesis of formylmethanofuran is crucial for the energy metabolism of archaea. Methanogenic archaea derives the energy for autrophic growth from the reduction of CO₂ with molecular hydrogen as the electron donor [5]. The process of methanogenesis consists of a series of reduction reactions at which the one-carbon unit derived from CO₂ is bound to C₁ carriers.

There are two isoenzymes of formylmethanofuran dehydrogenase: a tungsten-containing isoenzyme (Fwd) and a molybdenum-containing isoenzyme (Fmd). The tungsten isoenzyme is constitutively transcribed, whereas transcription of the molybdenum operon is induced by molybdate [6]. The archaea Methanobacterium thermoautotrophicum contains a 4-subunit (FwdA, FwdB, FwdC, FwdD) tungsten formylmethanofuran dehydrogenase and a 3-subunit (FmdA, FmdB, FmdC) molybdenum formylmethanofuran dehydrogenase [4].

This entry represents a fusion of subunits C (FmdC) and D (FmdD) of molybdenum-containing formylmethanofuran dehydrogenase. These enzymes consist of five subunits: FmdA (IPR012027), FmdB (IPR016457), FmdC, FmdD and FmdE (IPR012204).