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

 

Praneetha Palasuberniam1,2, Kae Yi Tan3, Choo Hock Tan1

 

1 Venom Research and Toxicology Laboratory, Department of Pharmacology, Faculty of Medicine, University of Malaya. Kuala Lumpur, Malaysia.

2 Department of Biomedical Sciences, University Malaysia Sabah, Faculty of Medicine and Health Sciences, Kota Kinabalu, Sabah, Malaysia.

3 Protein and Interactomics Laboratory, Department of Molecular Medicine, Faculty of Medicine, University of Malaya. Kuala Lumpur, Malaysia.

 

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 CTXlike 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 A2 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.

 

Keywords: Three-finger toxins Delta-elapitoxin-CB1a Calliotoxin Maticotoxin Snakebite Envenomation

 

Correspondence: tanch@um.edu.my

 

Received: 25 February 2021; Accepted: 12 May 2021; Published online: 24 September 2021.