Table 2.

The K⁺ ion in the gate: two positions, plus the PVVV mutant: bond length and bond order^a

WT, ion at centerb	WT, ion 0.83 Å displacedc			PVVV mutante		PVPV
Bond lengthd	Bond order	Bond lengthd	Bond order	Bond lengthd	Bond ordere	2nd shell Bond orderf
3.04	0.0184	3.31	0.056	2.98	0.121	–
2.75	0.024	2.81	−0.036	3.03	0.187	–
2.89g	0.157	2.84	0.135	xxxe	xxx	0.133
2.82h	0.117	2.91	0.112	2.71	0.106	0.238
2.81	0.079	2.74	0.077	2.96	0.109	0.303
2.99	0.1349	2.86	0.165	2.77	−0.046	–

Water molecules here are ordered by position, from most extracellular to most intracellular.

^aNBO calculation from optimized structure with 48 waters, B3LYP/6-311G^∗∗; total 693 atoms.

^bCenter is defined as the position at the center of the near planar-square arrangement of the four nitrogens of the proline.

^cThe ion is started at a position 1 Å to the side of the previous position; optimization returns it to 0.83 Å off center.

^dBond length: K⁺ - O distance for the respective water molecules.

^eWater structure split into two separate domains, one above the ion, the other below; the last two water molecules in the table are not in the first shell of solvation.

^fThese three first shell water molecules of the WT structure have a hydrogen with a competing strength hydrogen bond to a second shell water oxygen; those bond orders are shown in this column; bond lengths are in the 2.7 to 2.9 Å range.

^gStrongest bond order of this water with a nonhydrating water: 0.133.

^hStrongest bond order, this water to nonhydrating water, 0.238.