Two Potent α3/5 Conotoxins from Piscivorous <italic>Conus achatinus</italic>

Abstract

Every cone snail produces a mixture of different conotoxins and secretes them to immobilize their prey and predators. alpha3/5 Conotoxins, isolated from fish-hunting cone snails, target muscle nicotinic acetylcholine receptors. The structure and function of alpha3/5 conotoxin from the piscivorous Conus achatinus have not been studied. We synthesized two pentadecamer peptides, Ac1.1a and Ac1.1b, with appropriate disulfide bonding, based on cDNA sequences of alpha3/5 conotoxins from C. achatinus. Ac1.1a and Ac1.1b differ by only one amino acid residue. They have similar potency on blocking recombinant mouse muscle acetylcholine receptor expressed in Xenopus laevis oocytes, with IC50 values of 36 nM and 26 nM, respectively. For Ac1.1b, deletion of the first three N-terminal amino acids did not change its activity, indicating that the N-terminus is not involved in the interaction with its receptor. Furthermore, our experiments indicate that both toxins strongly prefer the alpha1-delta subunit interface instead of the alpha1-gamma binding site on the mouse muscle nicotinic acetylcholine receptor. These peptides provide additional tools for the study of the structure and function of nicotinic receptor.

Characterization of a novel α4/4-conotoxin, Qc1.2, from vermivorous <italic>Conus quercinus</italic>

“…Previous results suggested that some a3/5-conotoxins also exhibit asymmetric elution peaks on HPLC following oxidation, and have two conformations in aqueous condition [13,[21][22][23], which differ in the second Cys loop and peptide termini region [23]. It would be difficult to determine which conformer is more favorable for peptide activity on nAChRs.…”

“…Oocytes of Xenopus laevis frogs were prepared and injected with capped RNA to elicit expression of mouse fetal skeletal-muscle and various rat neuronal nAChR subtypes as described previously in detail [12][13][14][15][16].…”

Deep Venomics Reveals the Mechanism for Expanded Peptide Diversity in Cone Snail Venom

“…Because these alternatively cleaved forms are always less abundant than the full length mature peptide, their biological relevance is unclear. However, because conopeptides differing by only a few residues at their N-or C termini can have altered biological activity (61)(62)(63), this VPP is expected to have evolutionary significance. Together with the hypermutations seen at the mRNA level, VPP is a new mechanism that contributes to "biological messiness" in venoms, a concept recently developed in the field of enzymology to explain the origins of evolutionary innovation (64).…”

Structural answers and persistent questions about how nicotinic receptors work

“…With an estimated 50 to 200 peptide toxins produced by each Conus species (260), many useful toxins for nAChR research have yet to be characterized. Recently identified conotoxins are specific for different types of nAChRs: muscle-type nAChRs (261)(262)(263), α3β4 nAChRs (264), α3β2 and α7 nAChRs (265), α7-containing nAChRs (266), and α9α10 nAChRs (267). Conotoxin antagonism against α9α10 nAChRs showed both a role of α9α10 nAChRs in neuropathic pain and the potential therapeutic role of conotoxins (268).…”