Figure 3.

The two adjacent PC-binding pockets on monomeric α-toxin^H35A. A, 2F_o − F_c electron density map (green mesh) for the two PCho moieties contoured at 1.2σ (site 1) and 1.0σ (site 2). B, surface representation of the C₁₄PC-α-toxin^H35A complex viewed parallel to the membrane, with the PCho moieties shown in stick format with transparent CPK spheres. The two binding sites are labeled. The locations of key binding site residues are indicated. C, close-up view of the two adjacent PCho-binding pockets, with the PCho moieties displayed in stick format with transparent CPK spheres. Residues that make direct side chain contacts with the PCho moieties are shown in ball-and-stick format. The Ω1 and Ω2 loops are labeled. Cation-π interactions are represented as green dotted lines. Hydrogen bonds are shown as pink dotted lines. D, close-up view of the interface between the two independent α-toxin^H35A monomers (blue and green, respectively) in the asymmetric unit. Hydrogen bonds and salt bridges near the His³⁵→Ala mutation site are depicted as pink dotted lines.