Methylatable Signaling Helix Coordinated Inhibitory Receiver Domain in Sensor Kinase Modulates Environmental Stress Response in Bacillus Cereus: e0137952

[sigma]B, an alternative transcription factor, controls the response of the cell to a variety of environmental stresses in Bacillus cereus. Previously, we reported that RsbM negatively regulates [sigma]B through the methylation of RsbK, a hybrid sensor kinase, on a signaling helix (S-helix). However, RsbK comprises a C-terminal receiver (REC) domain whose function remains unclear. In this study, deletion of the C-terminal REC domain of RsbK resulted in high constitutive [sigma]B expression independent of environmental stimuli. Thus, the REC domain may serve as an inhibitory element. Mutagenic substitution was employed to modify the putative phospho-acceptor residue D827 in the REC domain of RsbK. The expression of RsbKD827N and RsbKD827E exhibited high constitutive [sigma]B, indicating that D827, if phosphorylatable, possibly participates in [sigma]B regulation. Bacterial two-hybrid analyses demonstrated that RsbK forms a homodimer and the REC domain interacts mainly with the histidine kinase (HK) domain and partly with the S-helix. In particular, co-expression of RsbM strengthens the interaction between the REC domain and the S-helix. Consistently, our structural model predicts a significant interaction between the HK and REC domains of the RsbK intradimer. Here, we demonstrated that coordinated the methylatable S-helix and the REC domain of RsbK is functionally required to modulate [sigma]B-mediated stress response in B. cereus and maybe ubiquitous in microorganisms encoded RsbK-type sensor kinases.