Characterisation of novel antimicrobial peptides from Egyptian scorpion and snake venoms.

Scorpion and snake venoms consist of diverse mixtures of peptides and proteins with varying biological activities and offer an attractive source for the development of novel therapeutics. Smp24 (24 aa) and Smp43 (43 aa) are antimicrobial peptides (AMPs) that were identified from the venom gland of the Egyptian scorpion Scorpio maurus palmatus. These alpha-helical peptides showed potent activity against both Gram positive and Gram negative bacteria with MICs ranging from 4 to 128 ug/ml. Four anti-bacterial peptides were purified using HPLC chromatography from the venom of three different species of Egyptian snakes. The molecular masses of the purified proteins were identified by MALDI-TOF/MS and N-terminal sequences suggest that they are members of the three-finger toxin superfamily. Both SEM and TEM were employed to visualise morphological changes and membrane damage of E. coli and S. aureus in response to different concentrations of Smp peptides at different time intervals. Using DNA microarray, we examined the transcriptomic responses of E. coli to sub-inhibitory doses of Smp24 and Smp43 peptides following 5 hours of incubation. Differentially expressed genes in the presence of peptides or a control antibiotic (Polymyxin B) compared with the absence of peptides were predominantly related to siderophore biosynthesis and transport, as well as more generalised cation transport and oxidative stress responses. The antibacterial effects of Smp peptides were inhibited in the presence of calcium and magnesium ions, but not other cations. Smp peptides offer a promising starting point for the development of new antimicrobial agents and transcriptomic analysis can help identify metabolic processes affected by scorpion venom AMPs which may be beneficial in understanding their mechanism of action.