title: A chemically synthesized version of the insect antibacterial glycopeptide, diptericin, disrupts bacterial membrane integrity.
abstract: Insects protect themselves against bacterial infection by secreting a battery of antimicrobial peptides into the hemolymph. Despite recent progress, important mechanistic questions, such as the precise bacterial targets, the nature of any cooperation that occurs between peptides, and the purpose of multiple peptide isoforms, remain largely unanswered. We report herein the chemical synthesis and preliminary mechanistic investigation of diptericin, an 82 residue glycopeptide that contains regions similar to two different types of antibacterial peptides. A revised, highly practical synthesis of the precursor N(alpha)-Fmoc-Thr(Ac(3)-alpha-D-GalNAc) allowed us to produce sufficient quantities of the glycopeptide for mechanistic assays. The synthetic, full-length polypeptide proved to be active in growth inhibition assays with an IC(50) 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. In all assays, activity appeared 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, suggesting possible mechanisms of action. The ability to access glycopeptides of this type through chemical synthesis will facilitate further mechanistic studies.
authors.affiliation: Department of Chemistry, University of California, Berkeley, California 94720, USA.
authors.forename: K A
authors.initials: KA
authors.lastname: Winans
authors.forename: D S
authors.initials: DS
authors.lastname: King
authors.forename: V R
authors.initials: VR
authors.lastname: Rao
authors.forename: C R
authors.initials: CR
authors.lastname: Bertozzi
mesh_terms: D000595:Amino Acid Sequence; D000818:Animals; D000900:Anti-Bacterial Agents / Q000138:chemical synthesis / Q000737:chemistry / Q000494:pharmacology*; D002463:Cell Membrane Permeability; D002942:Circular Dichroism; D029721:Drosophila Proteins; D004926:Escherichia coli / Q000187:drug effects / Q000254:growth & development; D006020:Glycopeptides; D019476:Insect Proteins / Q000138:chemical synthesis / Q000737:chemistry / Q000494:pharmacology*; D007313:Insecta / Q000737:chemistry*; D009682:Magnetic Resonance Spectroscopy; D008826:Microbial Sensitivity Tests; D008969:Molecular Sequence Data; D011487:Protein Conformation; D017386:Sequence Homology, Amino Acid
chemical_list: D000900:Anti-Bacterial Agents; C054756:DptA protein, Drosophila; D029721:Drosophila Proteins; D006020:Glycopeptides; D019476:Insect Proteins