title: Functionality of the voltage-gated proton channel truncated in S4.
abstract: 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.
authors.affiliation: Laboratory of Integrative Physiology, Department of Physiology, Graduate School of Medicine, Osaka University, Suita, Osaka 565-0871, Japan.
authors.forename: Souhei
authors.initials: S
authors.lastname: Sakata
authors.forename: Tatsuki
authors.initials: T
authors.lastname: Kurokawa
authors.forename: Morten H H
authors.initials: MH
authors.lastname: Nørholm
authors.forename: Masahiro
authors.initials: M
authors.lastname: Takagi
authors.forename: Yoshifumi
authors.initials: Y
authors.lastname: Okochi
authors.forename: Gunnar
authors.initials: G
authors.lastname: von Heijne
authors.forename: Yasushi
authors.initials: Y
authors.lastname: Okamura
mesh_terms: D000595:Amino Acid Sequence; D000818:Animals; D001120:Arginine / Q000737:chemistry; D002460:Cell Line; D004285:Dogs; D006801:Humans; D066298:In Vitro Techniques; D015640:Ion Channel Gating; D007473:Ion Channels / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism*; D051379:Mice; D008861:Microsomes / Q000378:metabolism; D008958:Models, Molecular; D008969:Molecular Sequence Data; D018408:Patch-Clamp Techniques; D010446:Peptide Fragments / Q000737:chemistry / Q000235:genetics / Q000378:metabolism; D011522:Protons; D011994:Recombinant Proteins / Q000737:chemistry / Q000235:genetics / Q000378:metabolism; D017386:Sequence Homology, Amino Acid; D014162:Transfection
chemical_list: C510235:HVCN1 protein, human; C540876:Hv1 proton channel, mouse; D007473:Ion Channels; D010446:Peptide Fragments; D011522:Protons; D011994:Recombinant Proteins; D001120:Arginine