Comparative analyses of toxin-associated gene homologs from an Old World viper, Daboia russelii.

Abstract

Molecular basis of toxin gene diversity among snakes is poorly understood. Lack of whole genome sequence information for most snakes makes studies on toxin genes and their orthologous counterparts difficult. One of the challenges in studying snake genomes is the acquisition of biological material from live animals, especially from the venomous ones. Additionally, in certain geographies, Government permission is required to handle live snakes making the process cumbersome and time-consuming. Here, we report comparative sequence analyses of toxin genes from Russells viper (Daboia russelii) using whole-genome sequencing data obtained from the skin exuviate. In addition to the comparative analyses of 46 toxin-associated proteins, we present evidence of unique sequence motifs in five key toxin-associated protein domains; nerve growth factor (NGF), platelet derived growth factor (PDGF), Kunitz/Bovine pancreatic trypsin inhibitor (Kunitz BPTI), cysteine-rich secretory proteins, antigen 5, and pathogenesis-related 1 proteins (CAP) and cysteine-rich secretory protein (CRISP). We compared the venom-associated domains from Russells viper with those from both venomous and non-venomous vertebrates and invertebrates. The in silico study on structures identified V11 and T35 in the NGF domain; F23 and A29 in the PDGF domain; N69, K2 and A5 in the CAP domain; and Q17 in the CRISP domain to be responsible for differences in the largest pockets across the protein domain structures in New World vipers, Old World vipers and elapids. Similarly, residues F10, Y11 and E20 appear to play an important role in the protein structures across the kunitz protein domain of viperids and elapids. Our study sheds light on the uniqueness of these key toxin-associated proteins and their evolution in vipers.\n\nData deposition: Russells viper sequence data is deposited in the NCBI SRA database under the accession number SRR5506741 and the GenBank accession numbers for the individual venom-associated genes is provided in Table S1.