Methyl‐Coenzyme M Reductase and its Nickel Corphin Coenzyme F 430 in Methanogenic Archaea

Abstract

Methanogenic archaea contain up to eight different nickel enzymes, one of which is methyl-coenzyme M reductase (MCR). The 300 kDa enzyme catalyses the conversion of methyl-coenzyme M (CH3-S-CoM) and coenzyme B (HS-CoB) to CH4 and CoM-S-S-CoB which is the final step in the energy metabolism of all methanogenic archaea. The nickel enzyme has an α2β2γ2 subunit quarternary structure forming two structurally interlinked active sites, each with a molecule of coenzyme F430 (Figure) in the Ni(I) oxidation state as prosthetic group. Evidence is available that the two active sites are functionally coupled, as in a two-stroke engine, such that the exergonic steps can drive the endergonic steps in the catalytic cycle. MCR is also found in anaerobic archaea that catalyze the anaerobic oxidation of methane and not the formation of methane. The enzyme contains a F430-derived nickel cofactor as prosthetic group. Its structure has recently been elucidated to be 172-methylthio-F430.