title: Cysteine-scanning mutagenesis study of the sixth transmembrane segment of the Na,K-ATPase alpha subunit.
abstract: The accessibility of the residues of the sixth transmembrane segment (TM) of the Bufo marinus Na,K-ATPase alpha subunit was explored by cysteine scanning mutagenesis. Methanethiosulfonate reagents reached only the two most extracellular positions (T803, D804) in the native conformation of the Na,K-pump. Palytoxin induced a conductance in all mutants, including D811C, T814C and D815C which showed no active electrogenic transport. After palytoxin treatment, four additional positions (V805, L808, D811 and M816) became accessible to the sulfhydryl reagent. We conclude that one side of the sixth TM helix forms a wall of the palytoxin-induced channel pore and, probably, of the cation pathway from the extracellular side to one of their binding sites.
authors.affiliation: Institute of Pharmacology and Toxicology, Bugnon 27, CH-1005, Lausanne, Switzerland.
authors.forename: Saïda
authors.initials: S
authors.lastname: Guennoun
authors.forename: Jean Daniel
authors.initials: JD
authors.lastname: Horisberger
mesh_terms: D000178:Acrylamides / Q000494:pharmacology; D000818:Animals; D002025:Bufonidae / Q000378:metabolism*; D003064:Cnidarian Venoms; D003545:Cysteine / Q000235:genetics / Q000378:metabolism*; D007202:Indicators and Reagents / Q000494:pharmacology; D008565:Membrane Proteins / Q000187:drug effects / Q000235:genetics / Q000378:metabolism*; D008698:Mesylates / Q000494:pharmacology; D008958:Models, Molecular; D016297:Mutagenesis, Site-Directed; D000254:Sodium-Potassium-Exchanging ATPase / Q000187:drug effects / Q000235:genetics / Q000378:metabolism*; D014162:Transfection; D014982:Xenopus laevis; D000095702:Polyether Toxins
chemical_list: D000178:Acrylamides; D003064:Cnidarian Venoms; D003545:Cysteine; D007202:Indicators and Reagents; D008565:Membrane Proteins; D008698:Mesylates; D000254:Sodium-Potassium-Exchanging ATPase; C074502:methanethiosulfonate; C010272:palytoxin; D000095702:Polyether Toxins