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Researchers determined high-resolution structures of the Mtr complex from methanogenic archaea, revealing an unexpected iron-sulfur-carbon metallocluster at its active site that resembles clusters found in nitrogenase enzymes. The cluster is positioned adjacent to both substrate binding sites and a sodium ion binding site, providing structural evidence for how these organisms couple methyl-group transfer reactions to energy generation via sodium ion pumping across membranes. The structures also show that protein binding triggers conformational changes that open a putative ion conduction pathway.
Why it matters
This work reveals a previously unknown mechanism by which methanogens conserve energy during methane production, advancing our understanding of microbial metabolism and chemiosmotic energy conversion. The discovery of a nitrogenase-like cluster in this context may inform biotechnology applications related to methane production or C1 metabolism.
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⚠️ Preprint – Noch nicht peer-reviewed
Dieser Artikel wurde noch nicht von unabhängigen Experten begutachtet. Die Ergebnisse sind vorläufig und sollten mit Vorsicht interpretiert werden.
Methanogenic archaea conserve energy by coupling methyl-group transfer to the generation of a chemiosmotic sodium-ion (Na+) gradient. This central energy-conserving step is catalyzed by the membrane-bound N5-methyl-H4MPT:coenzyme M methyltransferase (Mtr). Here, we present high-resolution cryo-electron microscopy structures of the Mtr complex from Methanosarcina mazei determined under strictly anaerobic conditions. The structures reveal an unexpected, electron-dense metallocluster embedded within the central cavity of the MtrCDE trimer in the membrane plane. Based on the unique topology and density we modeled it as an [FeSC] L-type cluster. It is positioned adjacent to both the coenzyme M substrate and the corrinoid cofactor of MtrA in the MtrA-MtrCDE engaged state, thereby being located right at the catalytic core of the enzyme. We could further show that binding of MtrA to MtrCDE triggers rearrangements within the interface of MtrDE that widen a putative ion-conduction pathway. The proximity of the conserved sodium-binding site to the catalytic center suggests a putative link between methyl-transfer chemistry and Na+ translocation. In a broader context, these findings improve our understanding of how methyl transfer, analogous to redox chemistry, can drive chemiosmotic energy conversion.