Methionine Residues in Exoproteins and Their Recycling by Methionine Sulfoxide Reductase AB Serve as an Antioxidant Strategy in Bacillus cereus
2017
Madeira, Jean-Paul | Alpha-Bazin, Béatrice M. | Armengaud, J. | Duport, Catherine
During aerobic respiratory growth, <em>Bacillus cereus</em> is exposed to continuously reactive oxidant, produced by partially reduced forms of molecular oxygen, known as reactive oxygen species (ROS). The sulfur-containing amino acid, methionine (Met), is particularly susceptible to ROS. The major oxidation products, methionine sulfoxides, can be readily repaired by methionine sulfoxide reductases, which reduce methionine sulfoxides [Met(O)] back to methionine. Here, we show that methionine sulfoxide reductase AB (MsrAB) regulates the Met(O) content of both the cellular proteome and exoproteome of <em>B. cereus</em> in a growth phase-dependent manner. Disruption of <em>msrAB</em> leads to metabolism changes resulting in enhanced export of Met(O) proteins at the late exponential growth phase and enhanced degradation of exoproteins. This suggests that <em>B. cereus</em> can modulate its capacity and specificity for protein export/secretion through the growth phase-dependent expression of <em>msrAB</em>. Our results also show that cytoplasmic <em>MsrAB</em> recycles Met residues in enterotoxins, which are major virulence factors in<em> B. cereus</em>.
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