Assembly of Methyl Coenzyme M Reductase in the Methanogenic Archaeon Methanococcus maripaludis

Methyl coenzyme M reductase (MCR) is a complex enzyme that catalyzes the final step in biological methanogenesis. To better understand its assembly, the recombinant MCR from the thermophileMethanothermococcus okinawensis (rMCRok ) was expressed in the mesophileMethanococcus maripaludis . The rMCRok was posttranslationally modified correctly and contained McrD and the unique nickel tetrapyrrole coenzyme F430 . Subunits of the nativeM. maripaludis (MCRmar ) were largely absent, suggesting that the recombinant enzyme was formed by an assembly of cotranscribed subunits. Strong support for this hypothesis was obtained by expressing a chimeric operon comprising the His-taggedmcrA fromM. maripaludis and themcrBDCG fromM. okinawensis inM. maripaludis . The His-tagged purified rMCR then contained theM. maripaludis McrA and theM. okinawensis McrBDG. The present study prompted us to form a working model for MCR assembly, which can be further tested by the heterologous expression system established here.IMPORTANCE Approximately 1.6% of the net primary production of plants, algae, and cyanobacteria are processed by biological methane production in anoxic environments. This accounts for about 74% of the total global methane production, up to 25% of which is consumed by anaerobic oxidation of methane (AOM). Methyl coenzyme M reductase (MCR) is the key enzyme in both methanogenesis and AOM. MCR is assembled as a dimer of two heterotrimers, where posttranslational modifications and F430 cofactors are embedded in the active sites. However, this complex assembly process remains unknown. Here, we established a heterologous expression system for MCR to learn how MCR is assembled.