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.

No abstract

Recent lifestyle changes, such as the Westernization of diets and the rise in the prevalence of obesity, with an associated increase in the number of patients with lifestyle-related diseases, have become a social issue. Fermented food has attracted attention as a solution to problems caused by obesity. Sake lees, a byproduct of sake brewing, represent one such food that is expected to have health benefits. In this study, we investigated the effects of sake lees components on preadipocytes (3T3-L1). We cultured preadipocytes in a medium with indigestible sake lees components (ISLCs) to investigate lipid accumulation, analyzed the glycerol 3-phosphate dehydrogenase (GPDH) and LPL activities of those cells, and performed a real-time PCR analysis of the IL6 expression in the cells. The results show that lipid accumulation and GPDH activity were significantly decreased in adipocytes treated with 1.0 mg/mL ISLCs compared to untreated cells. Furthermore, the expression of IL6 in adipocytes treated with 1.0 mg/mL ISLCs was significantly decreased and the lipase activity was significantly increased in adipocytes treated with ISLCs after differentiation. IL6 is known to have multiple functions in adipose tissue. In conclusion, ISLCs were associated with reduced lipid accumulation in adipocytes, with effects on IL6 expression and LPL activity observed throughout the differentiation period.

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.