title: Conformational studies by NMR of the antimicrobial peptide, drosocin, and its non-glycosylated derivative: effects of glycosylation on solution conformation.
abstract: Drosocin is a cationic 19 amino acid peptide secreted by Drosophila in response to septic injury. The sequence (GKPRPYSPRPTSHPRPIRV) contains six Pro and four Arg residues which are incorporated into three repeated triplet sequences Pro-Arg-Pro. The peptide is glycosylated at Thr11 and has potent antimicrobial activity. This activity is markedly reduced on deglycosylation, but a structural basis for this has not been previously established. In the current study, the solution conformations of drosocin and its non-glycosylated derivative were determined by NMR spectroscopy and structure calculations. The NMR and structure studies showed that the peptides have significant populations of essentially random coil conformations in aqueous solution. Addition of 50% trifluoroethanol causes the development of small populations of folded conformations, mainly in the form of turns. In particular, turn elements occur near residues 4-7, 10-13, 17, and 18. No substantial difference was detected in the predominantly random coil conformation of the glycosylated and non-glycosylated forms, but there are subtle differences in the small populations of folded conformers. In particular, the turn at residues 10-13 tends toward a more extended structure on glycosylation, while there is some tightening of the downstream turn at residues 17 and 18. There are a significant number of nuclear Overhauser enhancement contacts between the sugar moiety and the peptide near the glycosylation site, consistent with a close association between them. Despite this close association, the pKa of H13, which is proximate to the glycosylation site, was found to be unaffected by glycosylation.
authors.affiliation: Centre for Drug Design and Development, University of Queensland, Brisbane, Australia.
authors.forename: A M
authors.initials: AM
authors.lastname: McManus
authors.forename: L
authors.initials: L
authors.lastname: Otvos
authors.forename: R
authors.initials: R
authors.lastname: Hoffmann
authors.forename: D J
authors.initials: DJ
authors.lastname: Craik
mesh_terms: D000595:Amino Acid Sequence; D000818:Animals; D000890:Anti-Infective Agents / Q000737:chemistry* / Q000378:metabolism; D004330:Drosophila; D006020:Glycopeptides / Q000737:chemistry* / Q000378:metabolism; D006031:Glycosylation; D006639:Histidine / Q000737:chemistry; D006860:Hydrogen Bonding; D019476:Insect Proteins / Q000737:chemistry* / Q000378:metabolism; D008969:Molecular Sequence Data; D019906:Nuclear Magnetic Resonance, Biomolecular / Q000379:methods; D009844:Oligosaccharides / Q000737:chemistry; D011487:Protein Conformation; D012996:Solutions; D013696:Temperature
chemical_list: D000890:Anti-Infective Agents; D006020:Glycopeptides; D019476:Insect Proteins; D009844:Oligosaccharides; D012996:Solutions; C082117:drosocin; D006639:Histidine