Sequence diversity of O-superfamily conopetides from Conus marmoreus native to Hainan

Prospecting for candidate molecules from Conus virgo toxins to develop new biopharmaceuticals

Background

A combination of pharmacological and biomedical assays was applied in this study to examine the bioactivity of Conus virgo crude venom in order to determine the potential pharmacological benefit of this venom, and its in vivo mechanism of action.

Methods

Two doses (1/5 and 1/10 of LC₅₀, 9.14 and 4.57 mg/kg) of the venom were used in pharmacological assays (central and peripheral analgesic, anti-inflammatory and antipyretic), while 1/2 of LC₅₀ (22.85 mg/kg) was used in cytotoxic assays on experimental animals at different time intervals, and then compared with control and reference drug groups.

Results

The tail immersion time was significantly increased in venom-treated mice compared with the control group. Also, a significant reduction in writhing movement was recorded after injection of both venom doses compared with the control group. In addition, only the high venom concentration has a mild anti-inflammatory effect at the late inflammation stage. The induced pyrexia was also decreased significantly after treatment with both venom doses. On the other hand, significant increases were observed in lipid peroxidation (after 4 hours) and reduced glutathione contents and glutathione peroxidase activity, while contents of lipid peroxidation and nitric oxide (after 24 hours) and catalase activity were depleted significantly after venom administration.

Conclusion

These results indicated that the crude venom of Conus virgo probably contain bioactive components that have pharmacological activities with low cytotoxic effects. Therefore, it may comprise a potential lead compound for the development of drugs that would control pain and pyrexia.

Deep venomics reveals the mechanism for expanded peptide diversity in cone snail venom

Cone snails produce highly complex venom comprising mostly small biologically active peptides known as conotoxins or conopeptides. Early estimates that suggested 50-200 venom peptides are produced per species have been recently increased at least 10-fold using advanced mass spectrometry. To uncover the mechanism(s) responsible for generating this impressive diversity, we used an integrated approach combining second-generation transcriptome sequencing with high sensitivity proteomics. From the venom gland transcriptome of Conus marmoreus, a total of 105 conopeptide precursor sequences from 13 gene superfamilies were identified. Over 60% of these precursors belonged to the three gene superfamilies O1, T, and M, consistent with their high levels of expression, which suggests these conotoxins play an important role in prey capture and/or defense. Seven gene superfamilies not previously identified in C. marmoreus, including five novel superfamilies, were also discovered. To confirm the expression of toxins identified at the transcript level, the injected venom of C. marmoreus was comprehensively analyzed by mass spectrometry, revealing 2710 and 3172 peptides using MALDI and ESI-MS, respectively, and 6254 peptides using an ESI-MS TripleTOF 5600 instrument. All conopeptides derived from transcriptomic sequences could be matched to masses obtained on the TripleTOF within 100 ppm accuracy, with 66 (63%) providing MS/MS coverage that unambiguously confirmed these matches. Comprehensive integration of transcriptomic and proteomic data revealed for the first time that the vast majority of the conopeptide diversity arises from a more limited set of genes through a process of variable peptide processing, which generates conopeptides with alternative cleavage sites, heterogeneous post-translational modifications, and highly variable N- and C-terminal truncations. Variable peptide processing is expected to contribute to the evolution of venoms, and explains how a limited set of ∼ 100 gene transcripts can generate thousands of conopeptides in a single species of cone snail.

Probing peptide libraries from Conus achatinus using mass spectrometry and cDNA sequencing: identification of delta and omega-conotoxins

The peptide library present in the venom of the piscivorous marine snail Conus achatinus has been probed using a combination of mass spectrometry and cDNA sequencing methods. Matrix assisted laser desorption ionization mass spectrometry (MALDI-MS) analysis, before and following global reduction/alkylation of peptide mixtures, permits the rapid classification of individual components on the basis of the number of disulfide bonds. Mass fingerprinting and the reverse phase HPLC retention times permit a further deconvolution of the library in terms of peptide size and hydrophobicity. Sequencing of cDNA derived using O-superfamily specific primers yielded five complete conotoxin precursor sequences, ranging in polypeptide length from 75-87 residues containing six Cys residues at the C-terminus. Sequence analysis permits classification of the five putative mature peptides (Ac 6.1 to Ac 6.5) as delta, omega, and omega-like conotoxins. The presence of these predicted peptides in crude venom was established by direct matrix assisted laser desorption ionization tandem mass spectrometry (MALDI-MS/MS) sequencing following trypsin digestion of the peptide mixture after global reduction/alkylation. The determination of partial peptide sequences and comparison with the predicted sequences resulted in the identification of four of the five predicted conotoxins. The characterization of posttranslationally modified analogs, which are hydroxylated at proline or amidated at the C-terminus is also demonstrated. Crude venom analysis should prove powerful in studying both inter- and intra-species variation in peptide libraries.