Contribution of S4 Charges to Gating Mechanism in Hv Channels

Abstract

Reports on phase coexistence regimes and directions of tie lines of ternary lipid mixtures are often controversial. The origin of these controversies is typically the experimental window of the applied experimental techniques. Additional complications arrive due to putative influences of labels on the phase behavior. Therefore, we combined small-and wide-angle x-ray scattering, differential scanning calorimetry and attenuated total reflection-Fourier transform infrared spectroscopy to probe the stability and physical properties of coexisting domains under label-free conditions. The capabilities of this combination are demonstrated on a model system composed of palmitoyl oleoyl phosphatidylcholine, sphingomyelin and ceramide. This mixture mimics sphingomyelinase activity on biological membranes. We found compositional fluctuations (unstable microscopic domains) in the absence of ceramide and macroscopically separated fluid and gel phases upon the addition of ceramide. Additionally, we observed broad phase transitional regions in the presence of ceramide, where also phase fluctuations occurred. Results are compared to a previously reported phase diagram and discussed in relation to the biological activity of sphingomyelinase. Our study demonstrates the necessity of applying a mix of experimental techniques to probe local/global structural, as well as fast/slow motional properties in complex lipid mixtures.

Voltage-gated proton channel in a dinoflagellate

“…The arginine residues in S4 spaced RxxRxxR are extremely well-conserved, and they are thought to comprise much of the voltage-sensing apparatus of VSD-containing proteins and drive S4 movement during gating of ion channels (32-37), H V 1 (38), and VSPs (39). Despite this conservation, S4 of the H V 1 family contains a different number and/or different arrangement of positive charges compared with other VSD-containing proteins, making several plausible alignments possible (40).…”

Voltage-Gated Proton Channels: Molecular Biology, Physiology, and Pathophysiology of the HVFamily

“…V D2 ). The Larsson group reported that each of the three Arg residues in CiH V 1 contributes measurably to voltage sensing (186). On one hand, this result is not surprising, in view of the analogous function of the outermost four Arg residues in the S4 segment of voltage-gated K + channels.…”

Voltage‐Gated Proton Channels

“…However, a remarkable study of mH V 1 revealed that mutants in which the entire C terminus was truncated along with S4 as far as between the second and third Arg residues in the S4 domain still retained proton channel function (230). Although each of the three S4 Arg residues in H V 1 contributes to voltage sensing (104), their movement must not be as extensive as in K + channels, unless the movement in the C truncated mutant was reduced compared to the WT channel. The charged residues in S4 of the Shaker K + channel VSD are proposed to move through a “gating charge transfer center” (258); the first (R1) is in this center in closed channels, but the fifth (K5) resides there in the open state (157).…”