Identification of a CyaA region exhibiting high affinity for membranes mimicking the lipid composition of the inner membrane of Bordetella pertussis.

Abstract

The CyaA toxin, a 1706-residue long protein, is one of the major virulence factors produced by Bordetella pertussis. The secretion of CyaA is initiated by its C-terminal extremity through a dedicated Type 1 secretion system (T1SS). We are interested to decipher how CyaA is recognized, uptake and secreted by the T1SS. We have identified a C-terminal membrane-interacting region (MIR), which exhibits high affinity for membranes composed of lipids mimicking the inner leaflet of Bordetella pertussis (ilbp)inner membrane. We show by a combination of approaches that MIR undergoes conformational changes upon interactions with ilbp membranes. We further characterized the parameters tuning MIR/membrane interactions such as pH, ionic strength, and lipid composition. Moreover, key residues of MIR involved in membrane partitioning have been identified. These results allow us to propose a model of MIR/membrane interactions, which may help to recruit CyaA at the surface of the inner membrane, at proximity of the entry gate of the T1SS. These data pave the way to characterize the interaction of the full length CyaA toxin with the inner membrane of Bordetella pertussis prior its secretion from the bacterium.