Figure 4. GSD movements relative to the pore‐forming region.

The α3, β4, β5, and α4 of the pore‐forming region in TcdA at pH 7.5 (olive), TcdA₁₈₃₂ at pH 6.0 (light gray) and TcdB at pH 5.2 (dark gray) are superimposed. The GSD and pore‐forming region are illustrated as a cartoon while the GSD is additionally shown with a transparent surface. The GSD of TcdA₁₈₃₂ and TcdB is rotated relative to the GSD of TcdA (orange) in a progressive manner corresponding to the decreasing pH, and the guard loop (green) goes from a well‐ordered loop interacting with the α1 and α2 helices of the pore‐forming region in TcdA to being disordered and dislocated from α1 to α2 and disordered in TcdA₁₈₃₂ and TcdB.