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

Availability of snake genome sequences has opened up exciting areas of research on comparative genomics and gene diversity. 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 countries, Government permission is required to handle live snakes, making the process cumbersome and time-consuming. Here, we report comparative sequence analyses of toxin gene homologs from Russells viper (Daboia russelii) using whole-genome sequencing data obtained from the shed skin. When compared with the major venom proteins in Russells viper studied previously, we found 45-100% sequence similarity between the venom proteins and their skin homologs. Additionally, comparative analyses of 20 toxin gene family homologs provided evidence of unique sequence motifs in 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 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 crotalines, viperines and elapids from the in silico structure-based analysis. 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 usefulness of studying venom protein homologs from skin, their unique features and evolution in vipers. Data deposition: Russells viper sequence data is deposited in the NCBI SRA database under the accession number SRR5506741 and sequences for the individual venomassociated gene homologs to GenBank (accession numbers in Table S1). Neeraja M. Krishnan, Ganit Labs, Bio-IT Centre, Institute of Bioinformatics and Applied Biotechnology, Biotech Park, Electronic City Phase I, Bangalore 560100 ∗1Corresponding author: Binay Panda, Ganit Labs, Bio-IT Centre, Institute of Bioinformatics and Applied Biotechnology, Biotech Park, Electronic City Phase I, Bangalore 560100. Email:[email protected]