Insect immunity. The inducible antibacterial peptide diptericin carries two O-glycans necessary for biological activity.
A bacterial challenge of larvae of the dipteran insect Phormia terranovae induces the rapid synthesis of diptericin, an antibacterial polypeptide, previously characterized at the amino acid level and indirectly by cDNA cloning studies. This 82-residue polypeptide consists of an N-terminal proline-rich domain and a central and C-terminal glycine-rich domain. Using liquid chromatography coupled to electrospray ionization-mass spectrometry, we demonstrate here that this molecule is more complex than anticipated and carries two O-substitutions on threonine residues, one in the proline-rich domain (residue 10) and one in the glycine-rich domain (residue 54). These substitutions consist of identical trisaccharides: glucose-->galactose-->N-acetylgalactosamine-->(threonine). Treatment of diptericin with O-glycosidase, which selectively removes the substitutions without altering the polypeptide proper, abolishes the antibacterial activity, indicating that this posttranslational modification is essential for biological activity of the polypeptide. We also show that diptericin is posttranslationally modified by a C-terminal amidation.
Bulet
P
P
Institut de Biologie Moléculaire et Cellulaire CNRS (UPR 9022, Réponse Immunitaire et Développement chez les Insectes), Strasbourg, France.
Hegy
G
G
Lambert
J
J
van Dorsselaer
A
A
Hoffmann
J A
JA
Hetru
C
C
D000595:Amino Acid Sequence; D000818:Animals; D000900:Anti-Bacterial Agents / Q000737:chemistry*; D002240:Carbohydrate Sequence; D002241:Carbohydrates / Q000737:chemistry; D004175:Diptera / Q000276:immunology / Q000502:physiology*; D029721:Drosophila Proteins; D004926:Escherichia coli / Q000187:drug effects; D006020:Glycopeptides / Q000737:chemistry* / Q000302:isolation & purification / Q000494:pharmacology; D006458:Hemolymph / Q000276:immunology; D007301:Insect Hormones / Q000737:chemistry* / Q000302:isolation & purification* / Q000494:pharmacology; D019476:Insect Proteins; D007814:Larva; D013058:Mass Spectrometry; D008969:Molecular Sequence Data; D010944:Plants / Q000187:drug effects; D014312:Trisaccharides / Q000737:chemistry
D000900:Anti-Bacterial Agents; D002241:Carbohydrates; C054756:DptA protein, Drosophila; D029721:Drosophila Proteins; D006020:Glycopeptides; D007301:Insect Hormones; D019476:Insect Proteins; D014312:Trisaccharides