1.C.115 The Membrane-permeabilizing Peptide, Atticin (Atticin) Family 

Insects protect themselves against bacterial infection by secreting a battery of antimicrobial peptides into the hemolymph. The chemical synthesis and preliminary mechanistic investigation of diptericin, an 82 residue glycopeptide that contains regions similar to two different types of antibacterial peptides has been achieved (Winans et al. 1999).The full-length polypeptide was active in growth inhibition assays with an IC₅₀ of approximately 250 nM, a concentration similar to that found in the insect hemolymph. Biological analysis of diptericin fragments indicated that the main determinant of antibacterial activity lay in the C-terminal region that is similar to the attacin peptides, although the N-terminal segment, related to the proline-rich family of antibacterial peptides, augmented that activity by 100-fold.  Activity was glycosylation independent. Circular dichroism of unglycosylated diptericin indicated that the peptide lacked structure both in plain buffer and in the presence of liposomes. Diptericin increased the permeability of the outer and inner membranes of Escherichia coli D22 cells (Winans et al. 1999).