TABLE 1.

Simulations performed

Simulation	Model	Waters	Duration (ns)	Core Cα RMSD(nm)	P + F region Cα RMSD (nm)
WT0	Wild-type	0	2*	0.18	0.16
WT1	Wild-type	1	2	0.16	0.13
WT3	Wild-type	3	2	0.16	0.15
VT0	V127T	0	2	0.24	0.17
VT1	V127T	1	2	0.17	0.18
VT3	V127T	3	2	0.28	0.24
GF0	G135F	0	2	0.21	0.17
GF1	G135F	1	2	0.24	0.15
GF3	G135F	3	2	0.24	0.15
MC0	M137C	0	2	0.19	0.13
MC1	M137C	1	2	0.18	0.15
MC3	M137C	3	2	0.24	0.18

^*The WT0 simulation was extended to 5 ns to check for any further significant structural drift after 2 ns. We therefore report RMSDs for the last 0.5 ns of the 2-ns and of the 5-ns simulation period.

Summary of simulations performed, defining the nomenclature used in the text. The number of waters per subunit positioned behind the selectivity filter in the initial setup of the systems was: 0 = no waters behind filter; 1 = a single water per subunit behind filter, as in the high [K⁺] structure of KcsA (PDB code 1K4C); and 3 = three waters per subunit behind the filter, as in the low [K⁺] structure of KcsA (PDB code 1K4D). RMSD values are calculated over the final 500 ps of each simulation for the Cα atoms of the core TM region (i.e., M1 and M2 helices plus P + F region (the latter defined as residues T116 to G135).