title: Evidence that the S6 segment of the Shaker voltage-gated K+ channel comprises part of the pore.
abstract: Potassium channels are highly selective and allow the rapid flux of potassium ions through their pore. Several studies have implicated the H5 (P or SS1-SS2) segment as part of the pore in voltage-gated ion channels. The proposal that H5 spans at least 80% of the electric potential drop across the K+ channel pore is based on altered internal tetraethylammonium sensitivity arising from mutations of H5 residues that are 100% conserved among K+ channels having differing sensitivity to tetraethylammonium. Here we report that the S6 segment is also involved in K+ ion permeation and in governing the sensitivity to internal tetraethylammonium and barium. Transplanting the S6 segment of NGK2 into Shaker causes this S6 chimaera to adopt the single-channel conductance and sensitivity to internal tetraethylammonium and barium ions from the NGK2 channel. The differences between NGK2 and Shaker in external tetraethylammonium sensitivity, but not single-channel conductance, can be attributed to the differences in their H5 sequences. Three nonconserved S6 residues have been found to affect either single-channel conductance or internal tetraethylammonium sensitivity.
authors.affiliation: Howard Hughes Medical Institute, University of California at San Francisco 94143-0724.
authors.forename: G A
authors.initials: GA
authors.lastname: Lopez
authors.forename: Y N
authors.initials: YN
authors.lastname: Jan
authors.forename: L Y
authors.initials: LY
authors.lastname: Jan
mesh_terms: D000595:Amino Acid Sequence; D000818:Animals; D001464:Barium / Q000494:pharmacology; D005260:Female; D015640:Ion Channel Gating; D008969:Molecular Sequence Data; D016254:Mutagenesis, Insertional; D009865:Oocytes / Q000502:physiology; D010446:Peptide Fragments / Q000502:physiology; D010455:Peptides / Q000502:physiology; D015221:Potassium Channels / Q000737:chemistry / Q000187:drug effects / Q000502:physiology*; D011993:Recombinant Fusion Proteins; D051637:Shaker Superfamily of Potassium Channels; D019789:Tetraethylammonium; D013757:Tetraethylammonium Compounds / Q000494:pharmacology; D014981:Xenopus
chemical_list: D010446:Peptide Fragments; D010455:Peptides; D015221:Potassium Channels; D011993:Recombinant Fusion Proteins; C076413:Shaker B potassium channel polypeptide; D051637:Shaker Superfamily of Potassium Channels; D013757:Tetraethylammonium Compounds; D001464:Barium; D019789:Tetraethylammonium