Structure and allosteric activity of a single-disulfide conopeptide from Conus zonatus at human α3ß4 and α7 nicotinic acetylcholine receptors.

Conopeptides are neurotoxic peptides in the venom of marine cone snails and have broad therapeutic potential for managing pain and other conditions. Here, we identified the single-disulfide peptides Czon1107 and Cca1669 from the venoms of Conus zonatus and Conus caracteristicus, respectively. We observed that Czon1107 strongly inhibits the human α3ß4 (IC50 15.7 ± 3.0 µm) and α7 (IC50 77.1 ± 0.05 µm) nicotinic acetylcholine receptor (nAChR) subtypes, but the activity of Cca1669 remains to be identified. Czon1107 acted at a site distinct from the orthosteric receptor site. Solution NMR experiments revealed that Czon1107 exists in equilibrium between conformational states that are the result of a key Ser4-Pro5cis-trans isomerization. Moreover, we found that the X-Pro amide bonds in the inter-cysteine loop are rigidly constrained to cis conformations. Structure-activity experiments of Czon1107 and its variants at positions P5 and P7 revealed that the conformation around the X-Pro bonds (cis-trans) plays an important role in receptor subtype selectivity. The cis conformation at the Cys6-Pro7 peptide bond was essential for α3ß4 nAChR subtype allosteric selectivity. In summary, we have identified a unique single-disulfide conopeptide with a noncompetitive, potentially allosteric inhibitory mechanism at the nAChRs. The small size and rigidity of the Czon1107 peptide could provide a scaffold for rational drug design strategies for allosteric nAChR modulation. This new paradigm in the "conotoxinomic" structure-function space provides an impetus to screen venom from other Conus species for similar, short bioactive peptides that allosterically modulate ligand-gated receptor function.

Mass spectrometric identification and denovo sequencing of novel conotoxins from vermivorous cone snail (Conus inscriptus), and preliminary screening of its venom for biological activities in vitro and in vivo.

Venom of Conus inscriptus, a vermivorous cone snail found abundantly in the southern coastal waters was studied to yield conotoxins through proteomic analysis. A total of 37 conotoxins (4 with single disulfide bonds, 20 with two disulfide bonds and 11 three disulfide-bonded peptides) were identified using mass spectrometric analysis. Among them, amino acid sequences of 11 novel conopeptides with one, two and three disulfides belonging to different classes were derived through manual de novo sequencing. Based on the established primary sequence, they were pharmacologically classified into α conotoxins, µ conotoxins and contryphans. Except In1696 all other conopeptides have undergone C-terminal amidation. The natural venom exhibited 50% lethality at 304.82 µg/mL against zebrafish embryo and 130.31 µg/mL against brine shrimp nauplii. The anticonvulsant study of natural venom effectively reduced the locomotor activity against pentylenetetrazole (PTZ) treated zebrafish. This concludes that the venom peptides from Conus inscriptus exhibit potential anticonvulsant function, which leads to the discovery of lead molecules against seizures.