Identification of Conomarphin Variants in the Conus eburneus Venom and the Effect of Sequence and PTM Variations on Conomarphin Conformations

Exploring Diversity of Conopeptides and Revealing Novel Conoinsulins from Conus betulinus by Proteomic Analyses

The venom of cone snails, a potent weapon for predation and defense, contains diverse bioactive peptides (known as conopeptides, or conotoxins) that target various ion channels and receptors, offering potential as pharmacological tools or therapeutics. While transcriptomic studies have expanded conopeptide databases, proteomic validation remains limited. Here, we integrated two high-resolution mass spectrometry platforms to explore conopeptide diversity in Conus betulinus. A total of 283 conopeptides were identified, with 268 classifiable into known gene superfamilies or homology classes, while 15 unclassified conopeptides represent novel superfamilies. There were 46 newly discovered sequences and five new cysteine frameworks. Notably, we report the first proteomic identification of two novel conoinsulins in C. betulinus, Con-ins Be1 and Con-ins Be2. Both of them were predicted to retain insulin's canonical A/B-chain architecture. Structure modeling using the AlphaFold2 multimer suggested that Con-ins Be1 has a four-disulfide-bond arrangement, differing from the three disulfide bonds found in vertebrate insulin. In contrast, Con-ins Be2 was predicted to have three disulfide bonds, consistent with the structure of the vertebrate insulin. In summary, our study not only expanded the conopeptide repository but also provided two novel conoinsulins that may serve as pharmacological tools for insulin system research and merit further investigation.

Variable peptide processing of a Conus (Asprella) neocostatus α-conotoxin generates bioactive toxiforms that are potent against distinct nicotinic acetylcholine receptor subtypes

Conusvenoms are composed of peptides that are commonly post-translationally modified, increasing their chemical diversity beyond what is encoded in the genome and enhancing their potency and selectivity. This study describes how PTMs alter an α-conotoxin's selectivity for specific nAChR subtypes. Venom from the cone snailConus(Asprella)neocostatuswas fractionated using high-performance liquid chromatography and tested using a behavioral intracranial mouse bioassay and a cholinergic calcium imaging assay using SH-SY5Y neuroblastoma cells. Four peptides were isolated from three HPLC fractions and found to have similar amino acid sequences using tandem mass spectrometry; they all containC-terminal amidation. The four peptides appear to be encoded by a single gene as indicated by transcriptomic analysis. One of these, NcIA, contains no additional PTM. NcIB lacked the two glycine residues found in the N-terminus of NcIA and contained two hydroxylated prolines. Analogs of both peptides containing a ɣ-carboxylated glutamic residue (NcIA[E15γ] and NcIB[E13γ]) were also isolated. Functional assays revealed distinct receptor selectivity: NcIA inhibited nicotine-evoked responses by over 70 %, while NcIA[E15γ] did not. Conversely, NcIB[E13γ] was inhibitory (∼60 %), but NcIB was not. Against choline-evoked responses, NcIA was weakly inhibitory (∼40 %), whereas the other three were nearly fully inhibitory. The IC50values for NcIB and NcIB[E13γ] were 91.0 nM and 64.7 nM, respectively. These findings indicate that PTMs andN-terminal modifications influence peptide potency and receptor specificity, suggesting that cone snails use variable peptide processing not only to generate chemical diversity in their venom but also to fine-tune the pharmacology of its components.

Cysteine-free cone snail venom peptides: Classification of precursor proteins and identification of mature peptides

The cysteine-free acyclic peptides present in marine cone snail venom have been much less investigated than their disulfide bonded counterparts. Precursor protein sequences derived from transcriptomic data, together with mass spectrometric fragmentation patterns for peptides present in venom duct tissue extracts, permit the identification of mature peptides. Twelve distinct gene superfamiles have been identified with precursor lengths between 64 and 158 residues. In the case of Conus monile, three distinct mature peptides have been identified, arising from two distinct protein precursors. Mature acyclic peptides are often post-translationally modified, with C-terminus amidation, a feature characteristic of neuropeptides. In the present study, 20 acyclic peptides from Conus monile and Conus betulinus were identified. The common modifications of C-terminus amidation, gamma carboxylation of glutamic acid (E to ϒ), N-terminus conversion of Gln (Q) to a pyroglutamyl residue (Z), and hydroxylation of Pro (P) to Hyp (O) are observed in one or more peptides identified in this study. Proteolytic trimming of sequences by cleavage at the C-terminus of Asn (N) residues is established. The presence of an asparagine endopeptidase is strengthened by the identification of legumain-like sequences in the transcriptome assemblies from diverse Conus species. Such sequences may be expected to have a cleavage specificity at Asn-Xxx peptide bonds.

Synthesis and insecticidal activity of cysteine-free conopeptides from Conus betulinus

The cone snail Conus betulinus is a vermivorous species that is widely distributed in the South China Sea. Its crude venom contains various peptides used to prey on marine worms. In previous studies, a systematic analysis of the peptide toxin sequences from C. betulinus was carried out using a multiomics technique. In this study, 10 cysteine-free peptides that may possess insecticidal activity were selected from a previously constructed conopeptide library of C. betulinus using the CPY-Fe conopeptide as a template. These conopeptides were prepared by solid-phase peptide synthesis (SPPS), then characterized by the reverse-phase high performance liquid chromatography (HPLC) and mass spectrometry. Insect cytotoxicity and injection experiments revealed that these cysteine-free peptides exerted favorable insecticidal effects, and two of them (Bt010 and Bt016) exhibited high insecticidal efficacy with LD50 of 9.07 nM and 10.93 nM, respectively. In addition, the 3D structures of these peptides were predicted by homology modeling, and a phylogenetic tree was constructed based on the nucleotide data of conopeptides to analyze the relationships among structures, functions, and evolution. A preliminary mechanism for the insecticidal activity of the cysteine-free conopeptides was predicted by molecular docking. To the best of our knowledge, this is the first study to report the insecticidal activity of cysteine-free conopeptides derived from Conus betulinus, signaling that they could potentially be developed into bioinsecticides with desirable properties such as easy preparation, low cost, and high potency.

High-Throughput Prediction and Design of Novel Conopeptides for Biomedical Research and Development

Cone snail venoms have been considered a valuable treasure for international scientists and businessmen, mainly due to their pharmacological applications in development of marine drugs for treatment of various human diseases. To date, around 800 Conus species are recorded, and each of them produces over 1,000 venom peptides (termed as conopeptides or conotoxins). This reflects the high diversity and complexity of cone snails, although most of their venoms are still uncharacterized. Advanced multiomics (such as genomics, transcriptomics, and proteomics) approaches have been recently developed to mine diverse Conus venom samples, with the main aim to predict and identify potentially interesting conopeptides in an efficient way. Some bioinformatics techniques have been applied to predict and design novel conopeptide sequences, related targets, and their binding modes. This review provides an overview of current knowledge on the high diversity of conopeptides and multiomics advances in high-throughput prediction of novel conopeptide sequences, as well as molecular modeling and design of potential drugs based on the predicted or validated interactions between these toxins and their molecular targets.