The
venoms of scorpions are complex cocktails of
polypeptide toxins that fall into two structural categories: those that contain cysteinyl residues with associated
disulfide bridges and those that do not. As the majority of lethal toxins acting upon
ion channels fall into the first category, most research has been focused there. Here we report the identification and structural characterization of two novel 18-mer
antimicrobial peptides from the
venom of the North African scorpion, Androctonus amoreuxi. Named AamAP1 and AamAP2, both
peptides are C-terminally amidated and differ in primary structure at just two sites:
Leu-->Pro at position 2 and Phe-->Ile at position 17. Synthetic replicates of both
peptides exhibited a broad-spectrum of antimicrobial activity against a Gram-positive bacterium (Staphylococcus aureus), a Gram-negative bacterium (Escherichia coli) and a yeast (Candida albicans), at concentrations ranging between 20 μM and 150 μM. In this concentration range, both
peptides produced significant degrees of
hemolysis. A synthetic replicate of AamAP1 containing a single substitution (His-->Lys) at position 8, generated a
peptide (AamAP-S1) with enhanced antimicrobial potency (3-5 μM) against the three test organisms and within this concentration range, hemolytic effects were negligible. In addition, this His-->Lys variant exhibited potent growth inhibitory activity (ID(50) 25-40 μm) against several human
cancer cell lines and endothelial cells that was absent in both natural
peptides. Natural bioactive
peptide libraries, such as those that occur in
scorpion venoms, thus constitute a unique source of novel lead compounds with drug development potential whose biological properties can be readily manipulated by simple synthetic chemical means.