| Summary: | 碩士 === 國立高雄師範大學 === 生物科技系 === 102 === Bacillus cereus, a Gram-positive bacterium, is a common food pathogen. The alternative sigma σB of B. cereus is response for gene regulation respect to environmental stresses such as heat, acid and osmotic stress. RsbK and RsbY encoded within σB cluster are composed of a two-component system (TCS). Upon environmental stress, RsbK can presumably auto-phosphorylate itself and then transfer the phosphoryl group to D59 of RsbY. D59-phosphorylated RsbY further activated the phosphatase activity of the C-terminal coupled PP2C domain to hydrolyze RsbV-P. To date, the genuine function of the receiver (REC) domain of RsbK remains not clear. The REC domain is supposed to elevate phosphotransfer between RsbK and RsbY, in particular, as D827 in the REC domain is phosphorylated because RsbKD827E (mimicking phosphorylation on D827) led to constitutively high σB. Moreover, the ΔrsbY and ΔrsbKMY strains complemented with the rsbY gene displayed high σB and low σB, respectively, indicating that the stoichiometry of RsbK and RsbY may be associated with σB induction. In addition, an in vitro phosphatase assay showed that RsbY and RsbYD59E and RsbYD59A exhibited distinguishable phosphatase activity toward to RsbV-P. In contrast, the residue substitution on D59 failed to induce σB. The result confirmed an important role of D59 in σB signalling and it also implicated that RsbY may be sequestered by unidentified protein(s) without activation until D59 true phosphorylation can be released to perform RsbV-P dephosphorylation.
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