The Cyclic AMP-binding protein CbpB in Brucella melitensis and its role in cell envelope integrity, resistance to detergent and virulence.

Brucella melitensis possesses an operon with two components: the response regulator OtpR and a putative cAMP-dependent protein kinase regulatory subunit encoded by the BMEI0067 gene. In the previous study, the function of OtpR has been studied, while little is known about the function of the BMEI0067 gene. Using a bioinformatics approach, we showed that the BMEI0067 gene encodes an additional putative cAMP-binding protein, which we refer to as CbpB. Structural modeling predicted that CbpB has a cAMP-binding protein (CAP) domain and is structurally similar to eukaryotic protein kinase A regulatory subunits. Here, we report the characterization of CbpB, a cAMP-binding protein in Brucella melitensis, showed to be involved in mouse persistent infections. ∆cbpB::km possessed cell elongation, bubble-like protrusions on cell surface and its resistance to environmental stresses (temperature, osmotic stress and detergent). Interestingly, comparative real-time qPCR assays, the cbpB mutation resulted in significantly different expression of aqpX and several penicillin-binding proteins and cell division proteins in Brucella. Combined, these results demonstrated characterization of CbpB in B. melitensis and its key role for intracellular multiplication.