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

Abstract

As part of continuing studies of the identification of gene organization and cloning of novel a-conotoxins, the first a4/4-conotoxin identified in a vermivorous Conus species, designated Qc1.2, was originally obtained by cDNA and genomic DNA cloning from Conus quercinus collected in the South China Sea. The predicted mature toxin of Qc1.2 contains 14 amino acid residues with two disulfide bonds (I-III, II-IV connectivity) in a native globular configuration. The mature peptide of Qc1.2 is supposed to contain an N-terminal post-translationally processed pyroglutamate residue and a free carboxyl C-terminus. This peptide was chemically synthesized and refolded for further characterization of its functional properties. The synthetic Qc1.2 has two interconvertible conformations in aqueous solution, which may be due to the cis-trans isomerization of the two successive Pro residues in its first Cys loop. Using the Xenopus oocyte heterologous expression system, Qc1.2 was shown to selectively inhibit both rat neuronal a3b2 and a3b4 subtypes of nicotinic acetylcholine receptors with low potency. A block of 63% and 37% of the ACh-evoked currents was observed, respectively, and the toxin dissociated rapidly from the receptors. Compared with other characterized a-conotoxin members, the unusual structural features in Qc1.2 that confer to its receptor recognition profile are addressed.

High Throughput Identification of Novel Conotoxins from the Vermivorous Oak Cone Snail (Conus quercinus) by Transcriptome Sequencing

“…They have at least one aa difference between each other in the mature regions. The 41 conotoxins previously identified by traditional methods in C. quercinus [26,27,28] were classified into six superfamilies, including A, M, T, Q, O 1 and K (Figure 1A; Supplementary Table S9); 14 of these conotoxins belong to the A-superfamily, six belong to the M-superfamily and four belong to the T-superfamily, which account for 33.33%, 14.29% and 9.52%, respectively.…”

“…To date, only 41 conotoxins have been previously identified in the Oak cone snail ( C. quercinus ) using traditional methods, and they were classified into 6 superfamilies (A, M, T, Q, O 1 and K) [26,27,28]. To further contribute to the cataloguing of conotoxin diversity in the main lineages of cone snails, we employed the high-throughput transcriptome sequencing approach to explore additional conotoxins from the transcriptomes of different organs, including the venom duct, venom bulb and salivary gland in C. quercinus .…”

Marine natural products

“…732 Two I-superfamily peptides, ca11a (38 residues) and ca11b (34 residues) of unknown function, were purified from the venom of South China Sea collections of C. caracteristicus. [738][739][740] Given the potency of binding of conotoxins to their respective biological targets, it is of no surprise that they continue to act as highly specific molecular probes of receptors and ion channels. Using a cDNA probe of the signal peptide sequence, a number of new conotoxin peptide sequences were identified, including two Osuperfamily toxins, suggesting a close evolutionary link between I-and O-superfamily toxins.…”

A novel α4/7‐conotoxin LvIA from Conus lividus that selectively blocks α3β2 vs. α6/α3β2β3 nicotinic acetylcholine receptors

“…The presence of additional conformations of CTxs appears to be quite common, but tends to go unreported if the major conformation is readily assignable and similar to a previously published structure and the minor form is less well defined. However, there are now several reports of CTxs showing 2 (or more) conformations in solution (52)(53)(54), where it has been possible to modulate the relative populations of the conformers by the addition of cosolvents to help define them. For example, Nielsen et al (54) noted that for CTx PIIIA, Figure 4.…”