Tobe, R. | Search bioRxiv

bioRxiv2025

Multiheme selenoenzyme essential for elemental sulfur respiration

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.

microbiology↗

bioRxiv2021

Group II truncated haemoglobin YjbI prevents reactive oxygen species-induced protein aggregation in Bacillus subtilis

Oxidative stress-mediated formation of protein hydroperoxides can induce irreversible fragmentation of the peptide backbone and accumulation of cross-linked protein aggregates, leading to cellular toxicity, dysfunction, and death. However, how bacteria protect themselves from damages caused by protein hydroperoxidisation is unknown. Here we show that YjbI, a group II truncated haemoglobin from Bacillus subtilis, prevents oxidative aggregation of cell-surface proteins by its biologically unprecedented protein hydroperoxide peroxidase-like activity, which removes hydroperoxide groups from oxidised proteins. Disruption of the yjbI gene in B. subtilis lowered biofilm water repellence and the mechanical stiffness of the cell surface, which associated with the cross-linked aggregation of the biofilm matrix protein TasA. YjbI was localised to the cell surface, and the sensitivity of planktonically grown cells to generators of reactive oxygen species was significantly increased upon yjbI disruption, suggesting that YjbI pleiotropically protects labile cell-surface proteins from oxidative damage. YjbI removed hydroperoxide residues from a model oxidised protein substrate, bovine serum albumin, and prevented its oxidative aggregation in vitro. These findings provide new insights into the role of truncated haemoglobin and the importance of hydroperoxide removal from proteins in the survival of aerobic bacteria.

microbiology↗