title: Identification of a novel pharmacophore for peptide toxins interacting with K+ channels.
abstract: KappaM-conotoxin RIIIK blocks TSha1 K+ channels from trout with high affinity by interacting with the ion channel pore. As opposed to many other peptides targeting K+ channels, kappaM-RIIIK does not possess a functional dyad. In this study we combine thermodynamic mutant cycle analysis and docking calculations to derive the binding mode of kappaM-conotoxin RIIIK to the TSha1 channel. The final model reveals a novel pharmacophore, where no positively charged side chain occludes the channel pore. Instead the positive-charged residues of the toxin form a basic ring; kappaM-RIIIK is anchored to the K+ channel via electrostatic interactions of this basic ring with the loop and pore helix residues of the channel. The channel amino acid Glu-354 is likely to be a fundamental determinant of the selectivity of kappaM-RIIIK for the TSha1 channel. The Cgamma-OH of Hyp-15 is in contact with the carbonyls of the selectivity filter, disturbing the charge distribution pattern necessary for the coordination of K+ ions. This novel, experimentally based pharmacophore model proves the existence of diverse binding modes of peptidic toxins to K+ channels and underlines the role of intermolecular electrostatic interactions involving channel loop side chains in determining the selectivity of toxins for specific K+ channel types.
authors.affiliation: Department of NMR-based Structural Biology, Max Planck Institute for Biophysical Chemistry, Am Fassberg 11, D-37077 Göttingen, Germany.
authors.forename: Laurent
authors.initials: L
authors.lastname: Verdier
authors.forename: Ahmed
authors.initials: A
authors.lastname: Al-Sabi
authors.forename: Jean E F
authors.initials: JE
authors.lastname: Rivier
authors.forename: Baldomero M
authors.initials: BM
authors.lastname: Olivera
authors.forename: Heinrich
authors.initials: H
authors.lastname: Terlau
authors.forename: Teresa
authors.initials: T
authors.lastname: Carlomagno
mesh_terms: D000595:Amino Acid Sequence; D000818:Animals; D016000:Cluster Analysis; D020916:Conotoxins / Q000737:chemistry* / Q000235:genetics; D004252:DNA Mutational Analysis; D004594:Electrophysiology; D020128:Inhibitory Concentration 50; D007477:Ions; D008958:Models, Molecular; D008969:Molecular Sequence Data; D016297:Mutagenesis, Site-Directed; D009154:Mutation; D009865:Oocytes / Q000378:metabolism; D010455:Peptides / Q000737:chemistry; D017354:Point Mutation; D011188:Potassium / Q000737:chemistry; D015221:Potassium Channels / Q000737:chemistry*; D011485:Protein Binding; D011487:Protein Conformation; D017433:Protein Structure, Secondary; D012984:Software; D055672:Static Electricity; D013816:Thermodynamics; D014337:Trout; D014981:Xenopus
chemical_list: D020916:Conotoxins; D007477:Ions; D010455:Peptides; D015221:Potassium Channels; C471553:kappaM-conotoxin RIIIK, Conus radiatus; D011188:Potassium