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

Abstract

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 thermophile (rMCR) was expressed in the mesophile The rMCR was posttranslationally modified correctly and contained McrD and the unique nickel tetrapyrrole coenzyme F Subunits of the native (MCR) 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-tagged from and the from in The His-tagged purified rMCR then contained the McrA and the 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. 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 F 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.

Structure, function, and biosynthesis of nickel‐dependent enzymes

“…(b). Biosynthetic pathway of coenzyme F430 by the Cfb machinery (adapted from Reference ) and proposed working model for MCR assembly (adapted from Reference )…”

“…The mcrBDCGA gene cluster contains two conserved genes, mcrC and mcrD whose function is unknown. A working model has been proposed where McrB would serve as a scaffold for the assembly of the other subunits (Figure b) . The McrBDGA complex would be formed first.…”

Methyl-Coenzyme M Reductase and Its Post-translational Modifications

“…The complex McrBD then associates McrG and McrA when they are translated. The McrD unit is possibly lost or weakly associated after facilitating PTMs in active site and the binding of coenzyme F430 to the modified complex ( Lyu et al, 2018a ). Although this model provided a possible pathway of MCR complex assembly, it was speculative, and more future studies are needed to explore the specific function of the McrD unit and its interactions with the functional part McrABG.…”

“…Cysteine methylation is in a low abundance or absent in many methanogenic archaea, such as M. maripaludis . Glutamine methylation is absent in Methanosarcina barkeri ( Selmer et al, 2000 ; Lyu et al, 2018a ). Didehyroaspartate is absent in Methanothermobacter wolferi ( Wagner et al, 2016 ).…”

“…Previous studies have explored this enzyme from phylogeny to structures, reactions, and functions ( Mansoorabadi et al, 2017 ; Thauer, 2019 ). As one remarkable feature of MCRs, coenzyme F430 located in the active site has been proved to be crucial, and focuses have been put on its reaction mechanism and activation ( Wongnate and Ragsdale, 2015 ; Wongnate et al, 2016 ; Lyu et al, 2018a ). Besides coenzyme F430, unusual post-translational modification (PTM) is identified as another remarkable feature of MCR ( Kahnt et al, 2007 ; Mansoorabadi et al, 2017 ; Nayak et al, 2020 ).…”