A Ferredoxin- and F ₄₂₀ H ₂ -Dependent, Electron-Bifurcating, Heterodisulfide Reductase with Homologs in the Domains Bacteria and Archaea

Journal Article · 07 March 2017 · mBio

DOI: https://doi.org/10.1128/mBio.02285-16 · OSTI ID:1786905

Yan, Zhen ^[1]; Wang, Mingyu  ^[1]; Ferry, James G. ^[1]; Ruby, ed., Edward G.; McInerney, Michael; Mukhopadhyay, Biswarup; Leigh, John

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1. Department of Biochemistry and Molecular Biology, Pennsylvania State University, University Park, Pennsylvania, USA

ABSTRACT Heterodisulfide reductases (Hdr) of the HdrABC class are ancient enzymes and a component of the anaerobic core belonging to the prokaryotic common ancestor. The ancient origin is consistent with the widespread occurrence of genes encoding putative HdrABC homologs in metabolically diverse prokaryotes predicting diverse physiological functions; however, only one HdrABC has been characterized and that was from a narrow metabolic group of obligate CO ₂ -reducing methanogenic anaerobes (methanogens) from the domain Archaea . Here we report the biochemical characterization of an HdrABC homolog (HdrA2B2C2) from the acetate-utilizing methanogen Methanosarcina acetivorans with unusual properties structurally and functionally distinct from the only other HdrABC characterized. Homologs of the HdrA2B2C2 archetype are present in phylogenetically and metabolically diverse species from the domains Bacteria and Archaea . The expression of the individual HdrA2, HdrB2, and HdrB2C2 enzymes in Escherichia coli , and reconstitution of an active HdrA2B2C2 complex, revealed an intersubunit electron transport pathway dependent on ferredoxin or coenzyme F ₄₂₀ (F ₄₂₀ H ₂ ) as an electron donor. Remarkably, HdrA2B2C2 couples the previously unknown endergonic oxidation of F ₄₂₀ H ₂ and reduction of ferredoxin with the exergonic oxidation of F ₄₂₀ H ₂ and reduction of the heterodisulfide of coenzyme M and coenzyme B (CoMS-SCoB). The unique electron bifurcation predicts a role for HdrA2B2C2 in Fe(III)-dependent anaerobic methane oxidation (ANME) by M. acetivorans and uncultured species from ANME environments. HdrA2B2C2, ubiquitous in acetotrophic methanogens, was shown to participate in electron transfer during acetotrophic growth of M. acetivorans and proposed to be essential for growth in the environment when acetate is limiting. IMPORTANCE Discovery of the archetype HdrA2B2C2 heterodisulfide reductase with categorically unique properties extends the understanding of this ancient family beyond CO ₂ -reducing methanogens to include diverse prokaryotes from the domains Bacteria and Archaea . The unprecedented coenzyme F ₄₂₀ -dependent electron bifurcation, an emerging fundamental principle of energy conservation, predicts a role for HdrA2B2C2 in diverse metabolisms, including anaerobic CH ₄ -oxidizing pathways. The results document an electron transport role for HdrA2B2C2 in acetate-utilizing methanogens responsible for at least two-thirds of the methane produced in Earth’s biosphere. The previously unavailable heterologous production of individual subunits and the reconstitution of HdrA2B2C2 with activity have provided an understanding of intersubunit electron transfer in the HdrABC class and a platform for investigating the principles of electron bifurcation.

• Sponsoring Organization: USDOE
• OSTI ID: 1786905
• Journal Information: mBio, Journal Name: mBio Journal Issue: 1 Vol. 8; ISSN 2161-2129
• Publisher: American Society for MicrobiologyCopyright Statement
• Country of Publication: United States
• Language: English