Lycotoxins, antimicrobial peptides from venom of the wolf spider Lycosa carolinensis

Two peptide toxins with antimicrobial activity, lycotoxins I and II, were identified from venom of the wolf spider Lycosa carolinensis (Araneae: Lycosidae) by virtue of their abilities to reduce ion and voltage gradients across membranes. Both peptides were purified to homogeneity by reversed-phase liquid chromatography and determined to have the following primary structures by Edman microsequencing: IWLTALKFLGKHAAKHLAKQQLSKL-NH2 for lycotoxin I and KIKWFKTMKSIAKFIAKEQMKKHLGGE-OH for lycotoxin II. The predicted secondary structures of the lycotoxins display amphipathic alpha-helix character typical of antimicrobial pore-forming peptides. Antimicrobial assays showed that both lycotoxins potently inhibit the growth of bacteria (Escherichia coli) and yeast (Candida glabrata) at micromolar concentrations. To verify its hypothesized pore-forming activity, lycotoxin I was synthesized and shown to promote efflux of Ca2+ from synaptosomes, to cause hemolysis of erythrocytes, and to dissipate voltage gradients across muscle membrane. The lycotoxins may play a dual role in spider-prey interaction, functioning both in the prey capture strategy as well as to protect the spider from potentially infectious organisms arising from prey ingestion. Spider venoms may represent a potentially new source of novel antimicrobial agents with important medical implications.