Identification, molecular and functional analysis of bioactive peptides from the venom of the scorpion, Tityus serrulatus

Scorpion venoms are rich sources of bioactive polypeptides. They are classified into two major groups: peptides with or without disulfide bridges. Toxins with disulfide bridges are responsible for toxicity of venom by targeting ion channels on cell membranes, while peptides without disulfide bridges are diverse in both structures and bioactivities, rendering them interesting to study. This project aimed to discover novel bioactive peptides from the venom of a South American scorpion, Tityus serrulatus. There are four highlights in this study. Firstly, two putative antimicrobial peptides (TsAP-l and TsAP-2) were identified in scorpion venom, by shotgun molecular cloning and RP-HPLC fractionation of venom. Their synthetic replicates were subjected to a series of bioactivity assays. TsAP- l exhibited low potency against all three test organisms, whereas TsAP-2 exhibited high potency against Gram-positive bacterium, Staphylococcus aureus, and the yeast, Candida albicans. Meanwhile, haemolytic and anti-proliferative activities of TsAP-l were low, while those of TsAP-2 were considerably higher. Secondly, two analogous peptides (TsAP-Sl and TsAP-S2), in which positive net charges and a-helicity increased, were designed by site substitutions in natural antimicrobial peptides. They both exhibited dramatic enhancement in antimicrobial, haemolytic and anti-proliferative activities, indicating the significance of cationicity and a-helical structure in bioactivities of antimicrobial peptides. Thirdly, two putative bradykinin-potentiating peptides (TsHpt-I and QUB 1397) were also identified in venom, and synthesised. In vitro pharmacological assays revealed that they could enhance bradykinin-induced hypotension on rat vascular tissues at micromole levels, although neither of them produced any significant effects on the same tissue. Finally, six cDNAs encoding putative classical disulphide-bridged neurotoxin precursors were also cloned from the same venom-derived cDNA library and were structurally-analysed. These extend knowledge of scorpion venom neurotoxins. All these findings suggest the value of scorpion venom in searching and designing potential drug candidates.EThOS - Electronic Theses Online ServiceGBUnited Kingdo