title: Tethered blockers as molecular 'tape measures' for a voltage-gated K+ channel.
abstract: The propagation of electrical signals in excitable cells is orchestrated by a molecular family of voltage-dependent ion channel proteins. These K+, Na+, and Ca++ channels are all composed of four identical or similar units, each containing six transmembrane segments (S1-S6) in a roughly four-fold symmetric structure. The S5-S6 sequences fold into a central pore unit, which is surrounded by a voltage-gating module composed of S1-S4. The recent structure of KcsA, a two-transmembrane bacterial K+ channel, illuminates the physical character of the pore unit, but little is known about the arrangement of the surrounding S1-S4 sequences. To locate regions of this gating module in space, we synthesized a series of compounds of varying length that function as molecular 'tape measures': quaternary ammonium (QA) pore blockers that can be tethered to specific test residues. We show that in a Shaker K+ channel, the extracellular ends of S1 and S3 are approximately 30 ¿ from the tetraethylammonium (TEA) blocking site at the external opening of the pore. A portion of the S3-S4 loop is, at 17-18 ¿, considerably closer.
authors.affiliation: Department of Biochemistry, Howard Hughes Medical Institute Brandeis University, Waltham, Massachusetts 02454, USA.
authors.forename: R O
authors.initials: RO
authors.lastname: Blaustein
authors.forename: P A
authors.initials: PA
authors.lastname: Cole
authors.forename: C
authors.initials: C
authors.lastname: Williams
authors.forename: C
authors.initials: C
authors.lastname: Miller
mesh_terms: D019943:Amino Acid Substitution / Q000235:genetics; D000818:Animals; D001665:Binding Sites; D002138:Calibration; D003545:Cysteine / Q000235:genetics / Q000378:metabolism; D029721:Drosophila Proteins; D004331:Drosophila melanogaster; D004553:Electric Conductivity; D015640:Ion Channel Gating; D008024:Ligands; D008301:Maleimides / Q000737:chemistry / Q000378:metabolism* / Q000494:pharmacology*; D008970:Molecular Weight; D009865:Oocytes; D017354:Point Mutation / Q000235:genetics; D026902:Potassium Channel Blockers; D015221:Potassium Channels / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism; D011487:Protein Conformation; D000644:Quaternary Ammonium Compounds / Q000737:chemistry / Q000378:metabolism* / Q000494:pharmacology*; D051637:Shaker Superfamily of Potassium Channels; D012997:Solvents; D019789:Tetraethylammonium / Q000378:metabolism / Q000494:pharmacology; D014982:Xenopus laevis
chemical_list: D029721:Drosophila Proteins; D008024:Ligands; D008301:Maleimides; D026902:Potassium Channel Blockers; D015221:Potassium Channels; D000644:Quaternary Ammonium Compounds; C496929:Sh protein, Drosophila; D051637:Shaker Superfamily of Potassium Channels; D012997:Solvents; C043592:maleimide; D019789:Tetraethylammonium; D003545:Cysteine