ENLARGED SCALE CHEMICAL SYNTHESIS AND RANGE OF ACTIVITY OF DROSOCIN, AN O-GLYCOSYLATED ANTIBACTERIAL PEPTIDE OF DROSOPHILA

Insects respond to a bacterial challenge by rapidly synthesizing a div erse range of antibacterial and antifungal peptides. One of them, dros ocin, a 19-residue proline-rich antibacterial peptide. was isolated fr om Drosophila. This peptide carries a disaccharide moiety attached to a threonine residue in mid-chain position. The present report describe s the enlarged-scale chemical synthesis of drosocin, glycosylated with Gal(beta 1-->3)GalNAc(alpha 1-->O). We have studied the range of acti vity of the synthetic glycopeptide of two truncated glycosylated isofo rms, and of the unglycosylated L and D enantiomers. Both isolated and chemically synthesized drosocins carrying the disaccharide display the same antibacterial activity. Using circular dichroic spectroscopy we demonstrated that the O-linked disaccharidic motif did not affect the backbone conformation of drosocin. The antibacterial activity of the s ynthetic glycopeptide was directed against gram-negative strains with the exception of tile gram-positive bacteria Micrococcus luteus. Delet ion of the first five N-terminal residues completely abolished the act ivity of drosocin, As a first approach to the study of the mode of act ion of drosocin, we have synthesized a non-glycosylated D enantiomer a nd, using this molecule, we have shown that drosocin may act on the gr am-negative bacteria through a stereospecific target.