title: Identification of a novel class of nicotinic receptor antagonists: dimeric conotoxins VxXIIA, VxXIIB, and VxXIIC from Conus vexillum.
abstract: The venoms of predatory marine snails (Conus spp.) contain diverse mixtures of peptide toxins with high potency and selectivity for a variety of voltage-gated and ligand-gated ion channels. Here we describe the chemical and functional characterization of three novel conotoxins, alphaD-VxXIIA, alphaD-VxXIIB, and alphaD-VxXIIC, purified from the venom of Conus vexillum. Each toxin was observed as an approximately 11-kDa protein by LC/MS, size exclusion chromatography, and SDS-PAGE. After reduction, the peptide sequences were determined by Edman degradation chemistry and tandem MS. Combining the sequence data together with LC/MS and NMR data revealed that in solution these toxins are pseudo-homodimers of paired 47-50-residue peptides. The toxin subunits exhibited a novel arrangement of 10 conserved cystine residues, and additional post-translational modifications contributed heterogeneity to the proteins. Binding assays and two-electrode voltage clamp analyses showed that alphaD-VxXIIA, alphaD-VxXIIB, and alphaD-VxXIIC are potent inhibitors of nicotinic acetylcholine receptors (nAChRs) with selectivity for alpha7 and beta2 containing neuronal nAChR subtypes. These dimeric conotoxins represent a fifth and highly divergent structural class of conotoxins targeting nAChRs.
authors.affiliation: Institute for Molecular Bioscience, University of Queensland, Brisbane, Queensland 4072, Australia.
authors.forename: Marion
authors.initials: M
authors.lastname: Loughnan
authors.forename: Annette
authors.initials: A
authors.lastname: Nicke
authors.forename: Alun
authors.initials: A
authors.lastname: Jones
authors.forename: Christina I
authors.initials: CI
authors.lastname: Schroeder
authors.forename: Simon T
authors.initials: ST
authors.lastname: Nevin
authors.forename: David J
authors.initials: DJ
authors.lastname: Adams
authors.forename: Paul F
authors.initials: PF
authors.lastname: Alewood
authors.forename: Richard J
authors.initials: RJ
authors.lastname: Lewis
mesh_terms: D000595:Amino Acid Sequence; D000818:Animals; D020916:Conotoxins / Q000302:isolation & purification / Q000378:metabolism / Q000494:pharmacology; D006801:Humans; D008024:Ligands; D009682:Magnetic Resonance Spectroscopy; D008969:Molecular Sequence Data; D018733:Nicotinic Antagonists / Q000302:isolation & purification / Q000378:metabolism / Q000494:pharmacology; D011485:Protein Binding; D011499:Protein Processing, Post-Translational; D011978:Receptors, Nicotinic / Q000378:metabolism
chemical_list: D020916:Conotoxins; D008024:Ligands; D018733:Nicotinic Antagonists; D011978:Receptors, Nicotinic