title: Transmembrane movement of the shaker K+ channel S4.
abstract: We have probed internal and external accessibility of S4 residues to the membrane-impermeant thiol reagent methanethiosulfonate-ethyltrimethlammonium (MTSET) in both open and closed, cysteine-substituted Shaker K+ channels. Our results indicate that S4 traverses the membrane with no more than 5 amino acids in the closed state, and that the distribution of buried residues changes when channels open. This change argues for a displacement of S4 through the plane of the membrane in which an initially intracellular residue moves to within 3 amino acids of the extracellular solution. These results demonstrate that the putative voltage-sensing charges of S4 actually reside in the membrane and that they move outward when channels open. We consider constraints placed on channel structure by these results.
authors.affiliation: Department of Molecular and Cell Biology, University of California, Berkeley 94720, USA.
authors.forename: H P
authors.initials: HP
authors.lastname: Larsson
authors.forename: O S
authors.initials: OS
authors.lastname: Baker
authors.forename: D S
authors.initials: DS
authors.lastname: Dhillon
authors.forename: E Y
authors.initials: EY
authors.lastname: Isacoff
mesh_terms: D000818:Animals; D002462:Cell Membrane / Q000378:metabolism; D004330:Drosophila / Q000235:genetics*; D009154:Mutation; D009865:Oocytes / Q000378:metabolism; D018408:Patch-Clamp Techniques; D015221:Potassium Channels / Q000187:drug effects / Q000235:genetics* / Q000502:physiology*; D013439:Sulfhydryl Reagents / Q000494:pharmacology; D014982:Xenopus laevis
chemical_list: D015221:Potassium Channels; D013439:Sulfhydryl Reagents