Eumenitin

Eumenitin, a novel cationic antimicrobial peptide from the venom of solitary wasp Eumenes rubronotatus, was characterized by its effects on black lipid membranes of negatively charged (azolectin) and zwitterionic (1,2-diphytanoyl-sn-glycero-3-phosphocholine (DPhPC) or DPhPC-cholesterol) phospholipids: surface potential changes, single-channel activity, ion selectivity, and pore size were studied. We found that eumenitin binds preferentially to charged lipid membranes as compared with zwitterionic ones. Eumenitin is able to form pores in azolectin (G1=118.00+/-3.67pS or G2=160.00+/-7.07pS) and DPhPC membranes (G=61.13+/-7.57pS). Moreover, cholesterol addition to zwitterionic DPhPC membranes inhibits pore formation activity but does not interfere with the binding of peptide. Open pores presented higher cation (K+) over anion (Cl-) selectivity. The pore diameter was estimated at between 8.5and 9.8 angstroms in azolectin membranes and about 4.3 angstroms in DPhPC membranes. The results are discussed based on the toroidal pore model for membrane pore-forming activity and ion selectivity.

Insect venom peptides (IVPs) eumenitin, lasiocepsin, lycosin1, mastoparanB, panurgine1, and protonectin possess antibacterial properties, and the ubiquitous enzyme ATP synthase has a peptide-binding site. In the present study, we studied the effect of IVPs on binding and inhibition of three Escherichia coli strains (wild type, mutant, and null) and isolated E. coli ATP synthase. IVPs and their C-terminal amide (-NH2) analogs caused variable inhibition of membrane-bound F1Fo ATP synthase. While wild type E. coli growth was substantially hampered, null E. coli growth was near normal in the presence of IVPs and their C-terminal-NH2 analogs. The presence of C-terminal-NH2 groups on IVPs resulted in increased inhibition of ATP synthase and reduced growth of E. coli strains. Insignificant inhibition of the βDELSEED-motif mutant enzyme with the βAAAAAAA-motif confirmed that IVPs interact with the βDELSEED-motif, also known as the peptide-binding site. The higher level of growth loss in E. coli strains by eumenitin, lasiocepsin, lycosin1, mastoparanB, panurgine1, and protonectin and their C-terminal-NH2 analogs suggested the likelihood of additional cellular or molecular targets. IVPs caused inhibition of E. coli strains, which demonstrates an association between antimicrobial traits of IVPs and bacterial ATP synthase.

A novel antimicrobial peptide, eumenitin, was isolated from the venom of the solitary eumenine wasp Eumenes rubronotatus. The sequence of eumenitin, Leu-Asn-Leu-Lys-Gly-Ile-Phe-Lys-Lys-Val-Ala-Ser-Leu-Leu-Thr, was mostly analyzed by mass spectrometry together with Edman degradation, and corroborated by solid-phase synthesis. This peptide has characteristic features of cationic linear alpha-helical antimicrobial peptides, and therefore, can be predicted to adopt an amphipathic alpha-helix secondary structure. In fact, the CD spectra of eumenitin in the presence of TFE or SDS showed a high content of alpha-helical conformation. Eumenitin exhibited inhibitory activity against both Gram-positive and Gram-negative bacteria, and moderately stimulated degranulation from the rat peritoneal mast cells and the RBL-2H3 cells, but showed no hemolytic activity against human erythrocytes. This antimicrobial peptide in the eumenine wasp venom may play a role in preventing potential infection by microorganisms during prey consumption by their larvae.