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

Abstract

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 hydroperoxidation is unknown. Here we show that YjbI, a group II truncated haemoglobin from Bacillus subtilis, prevents oxidative aggregation of cell-surface proteins by its protein hydroperoxide peroxidase-like activity, which removes hydroperoxide groups from oxidised proteins. Disruption of the yjbI gene in B. subtilis lowered biofilm water repellence, which associated with the cross-linked aggregation of the biofilm matrix protein TasA. YjbI was localised to the cell surface or the biofilm matrix, 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 the model oxidized protein substrate bovine serum albumin and biofilm component TasA, preventing oxidative aggregation in vitro. Furthermore, the replacement of Tyr63 near the haem of YjbI with phenylalanine resulted in the loss of its protein peroxidase-like activity, and the mutant gene failed to rescue biofilm water repellency and resistance to oxidative stress induced by hypochlorous acid in the yjbI-deficient strain. 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.

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“…Among those up-regulated stress response genes, two are involved in protection against oxidative stress: yjbI and ymaD (uniprot.org) (Imai et al, 2021;Prestel et al, 2015). The products of these genes are proteins with peroxidase-like (Imai et al, 2021) and peroxiredoxin-related activity (Prestel et al, 2015), Regulatory cascade of some of the genes involved in spore coat formation (stage V). The spore's coat is organized into four distinct layers: basement layer (pink), inner coat (green), outer coat (blue) and crust (purple) (Liu et al, 2016;McKenney et al, 2010).…”