De novo venom gland transcriptomics of Calliophis bivirgata flaviceps: uncovering the complexity of toxins from the Malayan blue coral snake

Abstract

Background: The Malayan blue coral snake, Calliophis bivirgata flaviceps , is a medically important venomous snake in Southeast Asia. However, the complexity and diversity of its venom genes remain little explored. Methods: To address this, we applied high-throughput next-generation sequencing to profile the venom gland cDNA libraries of C. bivirgata flaviceps . The transcriptome was de novo assembled, followed by gene annotation, multiple sequence alignment and analyses of the transcripts. Results: A total of 74 non-redundant toxin-encoding genes from 16 protein families were identified, with 31 full-length toxin transcripts. Three-finger toxins (3FTx), primarily delta-neurotoxins and cardiotoxin-like/cytotoxin-like proteins, were the most diverse and abundantly expressed. The major 3FTx (Cb_FTX01 and Cb_FTX02) are highly similar to calliotoxin, a delta-neurotoxin previously reported in the venom of C. bivirgata . This study also revealed a conserved tyrosine residue at position 4 of the cardiotoxin-like/cytotoxin-like protein genes in the species. These variants, proposed as Y-type CTX-like proteins, are similar to the H-type CTX from cobras. The substitution is conservative though, preserving a less toxic form of elapid CTX-like protein, as indicated by the lack of venom cytotoxicity in previous laboratory and clinical findings. The ecological role of these toxins, however, remains unclear. The study also uncovered unique transcripts that belong to phospholipase A 2 of Groups IA and IB, and snake venom metalloproteinases of PIII subclass, which show sequence variations from those of Asiatic elapids. Conclusion: The venom gland transcriptome of C. bivirgata flaviceps from Malaysia was de novo assembled and annotated. The diversity and expression profile of toxin genes provide insights into the biological and medical importance of the species.

De Novo Venom Gland Transcriptome Assembly and Characterization for Calloselasma rhodostoma (Kuhl, 1824), the Malayan Pit Viper from Malaysia: Unravelling Toxin Gene Diversity in a Medically Important Basal Crotaline

“…In contrast, the groups of “non-toxin” (10.39 FPKM/transcript) and “unidentified” (3.81 FPKM/transcript) transcripts have remarkably much lower redundancy gauged by their gene expressions. The same has been observed in a number of snake venom gland transcriptomic studies, which reported >a thousand-fold higher expression of toxin genes in comparison to non-toxin and unidentified genes [ 27 , 28 , 29 , 30 , 31 ]. The high expression of toxin genes is in line with the venom gland’s function in synthesizing secretory proteins into the venom, while the non-toxin genes are mainly house-keeping genes for basic cellular functions.…”

“…The apparently higher abundance of PLA 2 transcripts in the venom gland transcriptome is puzzling, suggesting complex regulation of the mRNA half-life and protein translation that cannot be simplified by a single snapshot of the transcriptomic profile. In fact, the disproportionate expression between PLA 2 transcripts and proteins is not uncommon, as reported in a number of venom gland transcriptomics studies for Naja kaouthia [ 27 , 64 ], Naja sumatrana [ 29 , 65 ], Ophiophagus hannah [ 28 ], Hydrophis curtus [ 31 , 66 ], and Calliophis bivirgata [ 30 , 67 ], when venom glands were harvested 3–4 days post-venom milking.…”

<em>De Novo </em>Venom Gland Transcriptome Assembly and Characterization for <em>Calloselasma rhodostoma</em> (Kuhl, 1824), the Malayan Pit Viper from Malaysia: Unravelling Toxin Gene Diversity in a Medically Important Basal Crotaline

“…In contrast, the groups of "non-toxin" (10.39 FPKM/transcript) and "unidentified" (3.81 FPKM/transcript) transcripts have remarkably much lower redundancy in their gene expression. The same has been observed in a number of snake venom gland transcriptomics, which reported thousand-folds of higher expression of toxins genes in comparison to the non-toxin and unidentified genes [23][24][25][26][27]. The high expression of toxin genes is in line with the venom gland's function in synthesizing secretory proteins into the venom, while the non-toxin genes are mainly house-keeping genes for basic cellular functions.…”

“…The apparently higher abundance of PLA2 transcripts in the venom gland transcriptome is puzzling, suggesting complex regulation of the mRNA half-life and protein translation which cannot be simplified with a single snapshot of the transcriptomic profile. In fact, the disproportionate expression between PLA2 transcripts and their proteins is not uncommon as reported in a number of venom gland transcriptomics for Naja kaouthia [23,60], Naja sumatrana [25,61], Ophiophagus hannah [24], Hydrophis curtus [62] and Calliophis bivirgata [26], when venom glands were harvested 3−4 days post-venom milking.…”

The diversity and conservation status of snakes in the eastern part of PT GAN, Riau Province

“…These venom fangs are located on the upper jaw at the front of the snake's mouth and cannot be folded. C. bivirgatus has fatal and dangerous types of cytotoxins and neurotoxins (Palasuberniam et al 2021). This venom can paralyze nerves and damage cells.…”