Methyl coenzyme M reductase (MCR) catalyses the final step in methanogenesis. MCR is composed of three subunits, alpha (Pfam:PF02249), beta (Pfam:PF02241) and gamma (Pfam:PF02240) [1]. Genes encoding the beta (mcrB) and gamma (mcrG) subunits are separated by two open reading frames coding for two proteins C and D [2]. The function of proteins C and D (this family) is unknown. This family nowalso includes family MtrC_related,

1: Phylogeny of Methanopyrus kandleri based on methyl coenzyme M reductase operons. Nolling J, Elfner A, Palmer JR, Steigerwald VJ, Pihl TD, Lake JA, Reeve JN; Int J Syst Bacteriol 1996;46:1170-1173. PMID:8863453

2: Structure and comparative analysis of the genes encoding component C of methyl coenzyme M reductase in the extremely thermophilic archaebacterium Methanothermus fervidus. Weil CF, Cram DS, Sherf BA, Reeve JN; J Bacteriol 1988;170:4718-4726. PMID:3170483