The identification and characterisation of antimicrobial peptides from snake and scorpion venom.

The need for new antimicrobial agents is becoming one of the most urgent requirements in modem medicine. In the search for new antimicrobial drugs, in recent years, a large amount of research has been undertaken to both identify antimicrobial peptides (AMPs) and elucidate their mechanism of action. AMPs are ubiquitous in nature and have favourable properties that make them attractive for drug development including potent activity, low resistance rates due to their membrane disruptive mechanism of action, and selectivity to prokaryotic membranes.Venoms are an under exploited source of AMPs, in this thesis AMPs have been identified, biologically characterised and their mechanism investigated. From snake venom two novel AMPs (6-7KDa) along with four potential phospholipase A2 (PLA2) proteins have been identified (12-14 KDa). One of these peptides, isolated from black mamba venom (Dendroaspis polylepis) exerts moderate antimicrobial activity and has low cytotoxic properties making it an ideal candidate for future drug development. From scorpion venom, three AMPs (1-4 KDa) have been biologically characterised, one of which, Smp43, is postulated to have a di-helical structure and exhibits good antimicrobial activity especially against Gram positive organisms (4-64 ug/ml) and exhibits negligible haemolytic properties at concentrations up to 512 ug/ml. The mechanism of action of Smp43 and a shorter peptide termed Smp24 has been determined using liposome leakage assays, atomic force microscopy (AFM) and quartz crystal microbalance-dissipation (QCM-D). Smp24 caused pore formation in synthetic prototypical prokaryotic membranes and induced the formation of non lamellar lipid structures and caused lipid segregation in a prototypical eukaryotic membrane whilst Smp43 exerted its effects through a mechanism of diffuse limited aggregation (DLA) which, until now, has not been described as an AMP mechanism of action.In summary, this thesis has identified novel AMPs which can subsequently feed into drug development pipelines, provides further evidence of the membrane disruptive mechanism of AMPs whilst enhancing our understanding of these mechanisms.