title: KappaM-conotoxin RIIIK, structural and functional novelty in a K+ channel antagonist.
abstract: Venomous organisms have evolved a variety of structurally diverse peptide neurotoxins that target ion channels. Despite the lack of any obvious structural homology, unrelated toxins that interact with voltage-activated K(+) channels share a dyad motif composed of a lysine and a hydrophobic amino acid residue, usually a phenylalanine or a tyrosine. kappaM-Conotoxin RIIIK (kappaM-RIIIK), recently characterized from the cone snail Conus radiatus, blocks Shaker and TSha1 K(+) channels. The functional and structural study presented here reveals that kappaM-conotoxin RIIIK blocks voltage-activated K(+) channels with a novel pharmacophore that does not comprise a dyad motif. Despite the quite different amino acid sequence and no overlap in the pharmacological activity, we found that the NMR solution structure of kappaM-RIIIK in the C-terminal half is highly similar to that of mu-conotoxin GIIIA, a specific blocker of the skeletal muscle Na(+) channel Na(v)1.4. Alanine substitutions of all non-cysteine residues indicated that four amino acids of kappaM-RIIIK (Leu1, Arg10, Lys18, and Arg19) are key determinants for interaction with K(+) channels. Following the hypothesis that Leu1, the major hydrophobic amino acid determinant for binding, serves as the hydrophobic partner of a dyad motif, we investigated the effect of several mutations of Leu1 on the biological function of kappaM-RIIIK. Surprisingly, both the structural and mutational analysis suggested that, uniquely among well-characterized K(+) channel-targeted toxins, kappaM-RIIIK blocks voltage-gated K(+) channels with a pharmacophore that is not organized around a lysine-hydrophobic amino acid dyad motif.
authors.affiliation: Molecular and Cellular Neuropharmacology Group, Max Planck Institute for Experimental Medicine, Hermann-Rein-Strasse 3, D-37075 Göttingen, Germany.
authors.forename: Ahmed
authors.initials: A
authors.lastname: Al-Sabi
authors.forename: Dirk
authors.initials: D
authors.lastname: Lennartz
authors.forename: Michael
authors.initials: M
authors.lastname: Ferber
authors.forename: Jozsef
authors.initials: J
authors.lastname: Gulyas
authors.forename: Jean E F
authors.initials: JE
authors.lastname: Rivier
authors.forename: Baldomero M
authors.initials: BM
authors.lastname: Olivera
authors.forename: Teresa
authors.initials: T
authors.lastname: Carlomagno
authors.forename: Heinrich
authors.initials: H
authors.lastname: Terlau
mesh_terms: D000595:Amino Acid Sequence; D020916:Conotoxins / Q000737:chemistry* / Q000235:genetics / Q000494:pharmacology*; D020128:Inhibitory Concentration 50; D007930:Leucine / Q000235:genetics / Q000378:metabolism; D009682:Magnetic Resonance Spectroscopy; D008958:Models, Molecular; D008969:Molecular Sequence Data; D009154:Mutation / Q000235:genetics; D010446:Peptide Fragments / Q000737:chemistry; D026902:Potassium Channel Blockers / Q000737:chemistry* / Q000494:pharmacology*; D015221:Potassium Channels / Q000378:metabolism*; D017434:Protein Structure, Tertiary; D016415:Sequence Alignment
chemical_list: D020916:Conotoxins; D010446:Peptide Fragments; D026902:Potassium Channel Blockers; D015221:Potassium Channels; C471553:kappaM-conotoxin RIIIK, Conus radiatus; D007930:Leucine