TABLE I.
Voltage-dependent Gating of K149 Mutants
| Side chain at 149 | V o | z | P min | Volume | pKa | H-bond donors | n |
|---|---|---|---|---|---|---|---|
| mV | Å3 | ||||||
| WT(K) | −95 ± 1.1 | 0.90 ± 0.01 | 0.070 ± 0.008 | 167 | 10.4 | 3 | 25 |
| M | −56 ± 1.7 | 0.66 ± 0.02 | 0.017 ± 0.005 | 167 | 18 | ||
| R | −55 ± 2.1 | 0.71 ± 0.02 | 0.015 ± 0.005 | 194 | ∼12 | 5 | 20 |
| A | −44 ± 0.7 | 0.84 ± 0.01 | 0.014 ± 0.004 | 90 | 13 | ||
| G | −43 ± 1.2 | 0.71 ± 0.02 | 0.009 ± 0.005 | 65 | 20 | ||
| S | −37 ± 1.0 | 0.82 ± 0.01 | 0.031 ± 0.007 | 95 | 1 | 45 | |
| T | −33 ± 1.0 | 0.86 ± 0.01 | 0.014 ± 0.003 | 122 | 1 | 16 | |
| C | −30 ± 1.1 | 0.84 ± 0.02 | 0.017 ± 0.006 | 103 | 9.1–9.5 | 13 | |
| L | −24 ± 1.3 | 0.85 ± 0.02 | 0.028 ± 0.007 | 164 | 13 | ||
| N, Qa | 125, 149 | 2 | |||||
| D, Eb | 117, 142 | ∼4.5 | 0 | ||||
| Wb | 228 | 1 | |||||
| Yb | 197 | 9.6 | 1 |
Plots of apparent open probability (P o) versus voltage were fit as described in Materials and methods to derive the voltage at the midpoint in the voltage-activation curve (V o), the apparent gating charge (z), and the minimum open probability (P min). The mean ± SEM is given for n patches. K149 mutants are listed in order of the severity of their effect along with the corresponding amino acid side-chain volume (V) (from Table 7 of Tsai et al, 1999), side-chain pKa, and number of side-chain hydrogen bond donors.
a
Mutants that expressed but had low current.
b
Mutants that did not give measurable current.