Figure 5. Distribution of temperature factors around the transmembrane K⁺ binding sites.

(a) A C_α trace of the atomic model at 2.4 Å resolution (PDB ID: 2ZXE) after TLS refinement¹³ with 14 segments determined with TLSMD¹⁶, coloured according to the temperature factors. The colour changes from dark blue (temperature factor of 65 or less), blue (65–75), light blue (75–85), yellow (85–95), orange (95–105), to red (105 or higher). Purple spheres represent bound K⁺. (b) Plots of the temperature factor for the C_α-atoms of the residues in segments that show large thermal movements (M1′-M1 and M4; upper panel) and small movements (lower panel; M6 and M8). M4, M6 and M8 contain residues that coordinate K⁺. E334 in the PEGL motif (small green spheres in a) on M4 is considered to be a gating residue on the cytoplasmic side. Residue names with triangles in a refer to the ends of segments (specified in b) that undergo collective thermal movements.