Identification of a novel class of nicotinic receptor antagonists: dimeric conotoxins VxXIIA, VxXIIB, and VxXIIC from Conus vexillum.
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.
Loughnan
Marion
M
Institute for Molecular Bioscience, University of Queensland, Brisbane, Queensland 4072, Australia.
Nicke
Annette
A
Jones
Alun
A
Schroeder
Christina I
CI
Nevin
Simon T
ST
Adams
David J
DJ
Alewood
Paul F
PF
Lewis
Richard J
RJ
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
D020916:Conotoxins; D008024:Ligands; D018733:Nicotinic Antagonists; D011978:Receptors, Nicotinic