α-Helical Structural Elements within the Voltage-Sensing Domains of a K+ Channel

Abstract

Voltage-gated K+ channels are tetramers with each subunit containing six (S1–S6) putative membrane spanning segments. The fifth through sixth transmembrane segments (S5–S6) from each of four subunits assemble to form a central pore domain. A growing body of evidence suggests that the first four segments (S1–S4) comprise a domain-like voltage-sensing structure. While the topology of this region is reasonably well defined, the secondary and tertiary structures of these transmembrane segments are not. To explore the secondary structure of the voltage-sensing domains, we used alanine-scanning mutagenesis through the region encompassing the first four transmembrane segments in the drk1 voltage-gated K+ channel. We examined the mutation-induced perturbation in gating free energy for periodicity characteristic of α-helices. Our results are consistent with at least portions of S1, S2, S3, and S4 adopting α-helical secondary structure. In addition, both the S1–S2 and S3–S4 linkers exhibited substantial helical character. The distribution of gating perturbations for S1 and S2 suggest that these two helices interact primarily with two environments. In contrast, the distribution of perturbations for S3 and S4 were more complex, suggesting that the latter two helices make more extensive protein contacts, possibly interfacing directly with the shell of the pore domain.

Structural basis of two-stage voltage-dependent activation in K+channels

“…An additional speculative feature is the kink shown in the S3 helix near a highly conserved proline residue. A break in the secondary structure near this residue is consistent with perturbation analysis of S3 in Kv2.1 and Shaker (11,12). In eag, the proline residue is P325, located just 2 amino acids before D327.…”

Novel sequence variants in theTMC1 gene in Pakistani families with autosomal recessive hearing impairment

“…The first four TM domains of the K + channel α-subunit act as voltage sensors for activation gating (Li-Smerin et al, 2000), whereas the intervening segment between TM5 and TM6 appears to confer channel selectivity (Hanlon and Wallace, 2002). Three highly conserved TMC1 sequence variants in this study -c.830A>G (p.Y277C), c.1114G>A (p.V372M) and c.1334G>A (p.R445H) -lie within the central portion of hydrophobic TM segments.…”

S4-based voltage sensors have three major conformations

“…One way to explore the secondary structure of a transmembrane segment is to scan the entire length of the segment and study the impact of the scanning on the function of the protein (27). A direct way to test the impact of the scan on the voltage sensor function is to measure gating currents as the functional assay of the scan.…”