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bioRxiv · 10.1101/2025.11.18.688581

Multiheme selenoenzyme essential for elemental sulfur respiration

Mihara, H.·Yoshizawa, T.·Izu, Y.·Zhang, W.·Inoue, M.·Shimamoto, N.·Tobe, R.·Aono, R.·Kurihara, T.·Matsumura, H.
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Abstract

Microbial reduction of elemental sulfur is a pivotal process in the global sulfur cycle1. Insoluble elemental sulfur can serve as a terminal electron acceptor during anaerobic respiration, producing sulfide2,3. However, the molecular mechanisms underlying sulfur reduction remain poorly understood. Here we show that an evolutionarily conserved multiheme cytochrome c selenoprotein (MccSep) is essential for elemental sulfur reduction in a sulfur-respiring bacterium. Our biochemical and structural analyses revealed that MccSep comprises four identical subunits, each containing five c-type hemes and one selenocysteine residue (U325). The enzyme catalyzes polysulfide reduction at a unique active site, where C239 coordinates with the heme iron center, while U325 plays a crucial role in the catalytic process. Genetic analysis further revealed the critical roles of U325 and C239 in driving in vivo elemental sulfur respiration. These findings unveiled a selenium-sulfur-dependent catalytic chemistry on a heme center during polysulfide reduction, expanding the scope of biological catalysis and deepening our molecular understanding of bacterial sulfur respiration.

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Mihara, H., Yoshizawa, T., Izu, Y., Zhang, W., Inoue, M., Shimamoto, N., Tobe, R., Aono, R., Kurihara, T., Matsumura, H.. 2025-11-19. Multiheme selenoenzyme essential for elemental sulfur respiration. https://doi.org/10.1101/2025.11.18.688581

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