Methyl coenzyme M reductase (MCR) catalyzes the final step in methanogenesis. MCR is composed of three subunits, alpha (pfam02249), beta (pfam02241) and gamma (pfam02240). Genes encoding the beta (mcrB) and gamma (mcrG) subunits are separated by two open reading frames coding for two proteins C and D. The function of proteins C and D (this family) is unknown. This family nowalso includes family MtrC_related,