Abstract
The voltage-sensor domain (VSD) is the key module for voltage sensing of transmembrane proteins. Recently, voltage-sensor only protein (VSOP) that contains a single VSD but no pore domain was discovered and functions as the voltage-gated proton channel. The fourth transmembrane segment (S4) of VSOP contains three arginines (R1, R2, R3). We found that VSOP truncated just downstream of R2 retains most channel properties. Two assays, PEGylation-protection assay and membrane insertion assay, showed that S4 inserts into the membrane, even if it is truncated between R2 and R3. These findings provide important clues to the molecular mechanism of voltage-gated proton channel.
