FIGURE 6.

Electrostatic potential representation of the Type IV mART toxins that ADP-ribosylate Arg-177 in α-actin. A, surface potential of the Ia/C2I subtype members that include ι-toxin (Ia) (magenta ribbon and surface potential models) and VIP2 and C2I (PDB entries 1QS1 and 2J3Z, respectively; surface potential models only). The five regions (1–5) of iota believed to be involved in actin substrate recognition are shown as numbered circles (green). B, surface potentials of the SpvB/VahC subtype toxins are shown, and the iota C-terminal catalytic domain is also shown for comparison. Potential regions that may be involved in actin substrate recognition are also highlighted with green circles. These regions (Regions 2 and 5) correspond to those regions highlighted for Ia/C2I (above) except that Region 6 is unique to the SpvB/VahC subtype. The C/ denotes the catalytic subunit of the toxin only. Molecular surfaces are colored by the relative electrostatic potential (red, negative or acidic; blue, basic or positive). Surface potentials were calculated using PyMOL APBS software (60).