Possible negative regulator of sigma-B activity (By similarity). Phosphorylates and inactivates its specific antagonist protein, BtrV. Upon phosphorylation of BtrV, BtrW is released and binds to an unknown partner(s) that might be sigma-B, thereby blocking its ability to form a complex with its partner (possibly an RNA polymerase holoenzyme (E-sigma-B)). Involved in type III secretion system (TTSS). Phosphorylates BtrV. ATP + L-seryl-[protein] = ADP + H(+) + O-phospho-L-seryl-[protein] ATP + L-threonyl-[protein] = ADP + H(+) + O-phospho-L-threonyl-[protein] Probably able to multimerize; interacts with BtrV. Type III secreted proteins Bsp22 and BopD accumulate intracellularly instead of being secreted in cells expressing the mutagenized BtrV. Belongs to the anti-sigma-factor family.