Mutations throughout the S6 region of the hKv1.5 channel alter the stability of the activation gate.
The S6 segment of voltage-gated K(+) channels is thought to contribute to the gate that opens the central permeation pathway. Here we present evidence that mutations throughout the cytoplasmic end of S6 strongly influence hKv1.5 channel gating characteristics. Modification of hKv1.5 at positions T505, V512, and S515 resulted in large negative shifts in the voltage dependence of activation, whereas modifications at position Y519 resulted in negative (Y519N) and positive (Y519F) shifts. When adjusted for the altered voltage sensitivity, activation kinetics of mutated channels were similar to those of the wild-type (WT) channel; however, deactivation kinetics of mutations T505I, T505V, V512A, and V512M [time constant (tau) = 35, 250, 170, and 420 ms, respectively] were still slower than WT (tau = 8.3 ms). In addition, deactivation of WT channels was highly temperature sensitive. However, deactivation of T505I and V512A channels was largely temperature insensitive. Together, these data suggest that mutations in S6 decouple activation from deactivation by altering the open-state stability and that residues on both sides of the highly conserved Pro-X-Pro sequence influence the movement of S6 during channel gating.
Rich
Thomas C
TC
Department of Biomedical Engineering, Vanderbilt University, Nashville, Tennessee 37232, USA.
Yeola
Sarita W
SW
Tamkun
Michael M
MM
Snyders
Dirk J
DJ
D000818:Animals; D002460:Cell Line; D004594:Electrophysiology; D006801:Humans; D015640:Ion Channel Gating / Q000502:physiology*; D007700:Kinetics; D051666:Kv1.5 Potassium Channel; D008564:Membrane Potentials / Q000502:physiology; D051379:Mice; D008956:Models, Chemical; D016297:Mutagenesis, Site-Directed / Q000502:physiology; D015221:Potassium Channels / Q000737:chemistry* / Q000235:genetics* / Q000378:metabolism; D024642:Potassium Channels, Voltage-Gated; D011392:Proline / Q000235:genetics; D013329:Structure-Activity Relationship; D013696:Temperature
C496981:KCNA5 protein, human; C496982:Kcna5 protein, mouse; D051666:Kv1.5 Potassium Channel; D015221:Potassium Channels; D024642:Potassium Channels, Voltage-Gated; D011392:Proline