Enzymology of one-carbon metabolism in methanogenic pathways

Abstract

Methanoarchaea, the largest and most phylogenetically diverse group in the Archaea domain, have evolved energy-yielding pathways marked by one-carbon biochemistry featuring novel cofactors and enzymes. All of the pathways have in common the two-electron reduction of methyl-coenzyme M to methane catalyzed by methyl-coenzyme M reductase but deviate in the source of the methyl group transferred to coenzyme M. Most of the methane produced in nature derives from acetate in a pathway where the activated substrate is cleaved by CO dehydrogenase/acetyl-CoA synthase and the methyl group is transferred to coenzyme M via methyltetrahydromethanopterin or methyltetrahydrosarcinapterin. Electrons for reductive demethylation of the methyl-coenzyme M originate from oxidation of the carbonyl group of acetate to carbon dioxide by the synthase. In the other major pathway, formate or H2 is oxidized to provide electrons for reduction of carbon dioxide to the methyl level and reduction of methyl-coenzyme to methane. Methane is also produced from the methyl groups of methanol and methylamines. In these pathways specialized methyltransferases transfer the methyl groups to coenzyme M. Electrons for reduction of the methyl-coenzyme M are supplied by oxidation of the methyl groups to carbon dioxide by a reversal of the carbon dioxide reduction pathway. Recent progress on the enzymology of one-carbon reactions in these pathways has raised the level of understanding with regard to the physiology and molecular biology of methanogenesis. These advances have also provided a foundation for future studies on the structure/function of these novel enzymes and exploitation of the recently completed sequences for the genomes from the methanoarchaea Methanobacterium thermoautotrophicum and Methanococcus jannaschii.

The Geoglobus acetivorans Genome: Fe(III) Reduction, Acetate Utilization, Autotrophic Growth, and Degradation of Aromatic Compounds in a Hyperthermophilic Archaeon

“…G. acetivorans could also utilize the acetyl-CoA pathway for acetate oxidation to CO 2 (see below), as also described in acetate-oxidizing sulfate-reducing bacteria (45) and acetoclastic methanogens (46).…”

Bio‐Electrocatalytic Application of Microorganisms for Carbon Dioxide Reduction to Methane

“…The proposed mechanism for methanogenic mixed cultures is correlated to the well‐known mechanisms of the conversion of CO 2 and H 2 to CH 4 and water in anaerobic digesters. Deppenmeier et al., Shima et al., and Ferry have discussed not only the detailed enzymological pathways, which include oxidation and reduction reactions for electron transfer within the metabolism, but also the role of metabolic groups for CH 4 production from biomass with such methanogenic mixed cultures 26, 27, 28, 29. The metabolic pathways of these methanogens for the conversion of CO 2 to CH 4 can be summarized in the following overall reaction equation [Eq.…”

Microbial CH4 and N2O Consumption in Acidic Wetlands

“…Microbes that produce CH 4 are methanogenic Archaea, and those that are the main source of N 2 O are denitrifiers in anoxic habitats like wetlands (Conrad, 1996; Ferry, 1999; Drake et al, 2009). CH 4 produced by methanogens is further oxidized by aerobic methanotrophs, which thrive as a significant part of wetland microbial communities and mitigate the net CH 4 flux into the atmosphere (Hanson and Hanson, 1996; Shannon et al, 1996; Whalen, 2005; Knorr et al, 2008; Hornibrook et al, 2009).…”