Figure 1.

(A) (Above) Schematic representation of CyaA showing adenylate cyclase (AC) domain and hemolysin (Hly) domain which contains the hydrophobic (HP) region, palmitoylation site (Lys⁹⁸³) and the RTX region. Five putative helices in the HP region are indicated by cylinders where α2 and α3, putative membrane-inserting constituents were marked in blue and red, respectively. Each line in the RTX region represents each repeat of (X-U-X-Gly-Gly-X-Gly-X-Asp, X for any amino acid and U for large hydrophobic residues); (B) Left panel: The homology-based model of the CyaA-Hly α2–α3 hairpin. Side chains at pore-lining region of α3 are shown as van der Waals (vdW) spheres and colored according to atoms: cyan, white, red, and blue for C, H, O, and N, respectively. Right panel: Conserved amino acids at pore-lining regions of thirteen related RTX cytolysins, as mentioned earlier in [25]. The side-chains are highlighted in bold letter and the charged residues are colored in red for negative and blue for positive; and (C) Side view of the hairpins of CyaA-Hly and three highly-active RTX cytolysins, i.e., HlyA from E. coli, ApxIA from Actinobacillus pleuropneumoniae and LtxA from Aggregatibacter actinomycetemcomitans, showing three key side chains at Glu⁵⁷⁰/Gln⁵⁷⁴/Glu⁵⁸¹ (for CyaA-Hly) and Glu/Lys/Lys (for HlyA, ApxIA, and LtxA) patches. Inset: Top view of individual hairpins. Amino acids are colored according to their charged/polar properties (red is negatively-charged, blue is positively-charged, and light-blue is N-containing polar uncharged) with H atoms omitted.