Three-megadalton complex of methanogenic electron-bifurcating and CO 2 -fixing enzymes

Abstract

Methanogenesis megacomplex An important first step in methanogenesis is the conversion of carbon dioxide to a reduced one-carbon formyl unit that is a substrate for downstream steps. This reaction is catalyzed by a complex of enzymes, including components for oxidizing hydrogen or formate and splitting two electrons along different energetic paths. Watanabe et al . carefully purified and prepared anaerobic cryo–electron microscopy samples of the enzyme complex responsible, resulting in a three-megadalton hexameric structure at 3- to 3.5-ångström resolution. The arrangement of iron–sulfur cofactors provides an explanation for how electron bifurcation is coupled to large protein motions, which are expected from the multiple conformational states present. —MAF