ABSTRACTMethyl 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 rMCRokwas 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-taggedmcrAfromM. maripaludisand themcrBDCGfromM. okinawensisinM. maripaludis. The His-tagged purified rMCR then contained theM. maripaludisMcrA and theM. okinawensisMcrBDG. 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.IMPORTANCEApproximately 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 F430cofactors 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.
Methyl-coenzyme M reductase A as an indicator to estimate methane production from dairy cows
