Figure 7. Minimum pore radii of the plausible models and gating models of three channels suggested by paths of pore expansion.

(a) The R₀ values of the plausible trimeric models are displayed according to the colour scale at the top. A path connecting the closed P2X4 receptor (PDB 4DW0) to an open model⁹ represents a hypothetical gating mechanism. The first and second branches are plotted with φ shifted by 360° so that the path from the fourth branch to the first branch is connected. The open-state crystal structure (PDB 4DW1) is shown as a grey dot. (b,c) Corresponding results for the tetrameric models and KcsA (path connecting the closed (PDB 1BL8), partially open (PDB 3FB6) and open (PDB 3F5W) states), and for the pentameric models and MscL (path starting from the closed state (PDB 2OAR)), without the shift in φ. (d–f) Illustrations of the gating models for the P2X4 receptor, KcsA and MscL, using conformations shown as black dots in a–c, respectively. Bundles in blue, grey and red represent closed, intermediate and open conformations, respectively, shown in top view (top panels) and side view (bottom panels).