Abstract/Summary

Snake venom proteins are potential sources for novel drug design both for treatment of snake bites and for human haemostatic disorders. To achieve these, the basic sequence, structure and functional relationships of venom proteins should be understood. Proteolytic enzymes such as metallo and serine proteases are the major components of venom in vipers and are responsible for local and systematic envenomation effects. We have purified, partially sequenced and functionally characterised a serine protease, rhinocerase from the venom of Bitis gabonica rhinoceros. Rhinocerase is a multifunctional enzyme with kininogenase, clotting and defibrase activities. Crystallisation trials have resulted in small crystals. We have also purified, sequenced and functionally characterised a metalloprotease, rhiminopeptidase from the same venom. Crystallisation of this protein yielded slightly larger crystals and their preliminary data has been obtained. Rhiminopeptidase is a zinc dependent aminopeptidase A, with neutral and basic activities. The complete sequence of rhiminopeptidase was obtained via cDNA amplification and a three dimensional structural model was created. 9 further Bitis gabonica rhinoceros serine protease sequences have been obtained. These sequences fall into 2 groups: one with 2 isoforms (high molecular weight serine proteases) and another with 7 isoforms (low molecular weight serine proteases). The latter have substitutions in their catalytic triad residues. To understand more about the sequence, structure and functional relationships of viper venom serine proteases (VVSPs), all complete VVSP sequences have been extracted from sequence database. Sequence analysis of VVSP sequences including our 9 sequences showed that VVSPs have high sequence similarities, share common sequence and structural features, and are predicted to be N-glycosylated. A phylogenetic tree has been generated and analysed in relation to enzyme function. Complete functions and determined structures of most of the VVSPs are unknown and they need to be obtained via experimental studies to understand more about their sequence, structure and functional relationships.