Truncation of the voltage-gated proton channel just downstream of the second arginine in the S4 segment retains proton channel activity and inserts into the membrane.
Truncation of the S4 segment in Hv channels downstream of R2 does not prevent membrane insertion or abolish channel properties, providing insights into the molecular mechanisms of voltage sensing and proton permeation.
The voltage sensor domain (VSD) is the key module for voltage sensing in voltage-gated ion channels and voltage-sensing phosphatases. Structurally, both the VSD and the recently discovered voltage-gated proton channels (Hv channels) voltage sensor only protein (VSOP) and Hv1 contain four transmembrane segments. The fourth transmembrane segment (S4) of Hv channels contains three periodically aligned arginines (R1, R2, R3). It remains unknown where protons permeate or how voltage sensing is coupled to ion permeation in Hv channels. Here we report that Hv channels truncated just downstream of R2 in the S4 segment retain most channel properties. Two assays, site-directed cysteine-scanning using accessibility of maleimide-reagent as detected by Western blotting and insertion into dog pancreas microsomes, both showed that S4 inserts into the membrane, even if it is truncated between the R2 and R3 positions. These findings provide important clues to the molecular mechanism underlying voltage sensing and proton permeation in Hv channels.
Sakata et al. (Mon,) reported a other. A206stop mutation in mVSOP vs. Wild-type mVSOP was evaluated on Proton channel current density and gating properties. Truncation of the voltage-gated proton channel just downstream of the second arginine in the S4 segment retains proton channel activity and inserts into the membrane.