The crystal structure of methanogen McrD, a methyl-coenzyme M reductase-associated protein

Methyl-coenzyme M reductase (MCR) is a multi-subunit (α₂β₂γ₂) enzyme responsible for methane formation via its unique F430 cofactor. The genes responsible for producing MCR (<i>mcrA</i>, <i>mcrB</i> and <i>mcrG</i>) are typically colocated with two other highly conserved genes <i>mcrC</i> and <i>mcrD</i>. We present here the high-resolution crystal structure for McrD from a human gut methanogen <i>Methanomassiliicoccus luminyensis</i> strain B10. The structure reveals that McrD comprises a ferredoxin-like domain assembled into an α + β barrel-like dimer with conformational flexibility exhibited by a functional loop. The description of the <i>M. luminyensis</i> McrD crystal structure contributes to our understanding of this key conserved methanogen protein typically responsible for promoting MCR activity and the production of methane, a greenhouse gas.