Figure 7
Schematic model of CyaA interaction with target membrane. (A) In solution, two conformational isomers of CyaA co-exist in equilibrium that, upon membrane insertion, yield either a translocation precursor competent for subsequent translocation of the AC domain across target membrane, or a pore precursor competent for K+ efflux and involved in formation of oligomeric CyaA pores2, 10, 32,33,34,35. (B) Proposed model for the membrane interaction of the CyaA-A616P, CyaA-A680P, CyaA-A687P and CyaA-V695P mutants. Helix-breaking A616P substitution (A680P, A687P and V695P) within the predicted transmembrane α-helix607-627 as well as three proline substitutions within the predicted transmembrane α-helix678-698 selectively reduced the pore-forming activity of CyaA, but did not affect the capacity of CyaA to translocate the AC domain across the membrane. The putative transmembrane α-helices 607 to 627 and 678 to 698 are marked in gray. (C) Proposed model for the membrane interaction of the CyaA-A609P, CyaA-E622P, CyaA-Y632P, CyaA-Y658P, CyaA-Y725P and CyaA-Y738P mutants. The helix-breaking A609P and E622P substitutions within the predicted transmembrane α-helix607-627 reduced both AC domain translocation and CyaA pore formation similarly as the proline substitutions of the tyrosine residues Y632, Y658, Y725 and Y738, located within long α-helical structures and in the proximity of the putative transmembrane α-helices 607 to 627 and 678 to 698. The putative transmembrane α-helix607-627 is marked in gray. (D) Proposed model for the membrane interaction of the CyaA-Y940A and CyaA-Y940P mutants. The Y940A and Y940P substitutions substantially reduced specific capacity of CyaA to bind target plasma membrane and abolished AC domain translocation and formation of pores.
