title: Structural comparison of a 15 residue peptide from the V3 loop of HIV-1IIIb and an O-glycosylated analogue.
abstract: As part of a program to study the effect of glycosylation on the three-dimensional structures of HIV-1IIIB V3 peptide constructs, we have examined the solution structures of a 15 residue peptide (RIQRGPGRAFVTIGK, P18IIIB)- originally mapped as an epitope recognized by CD8+ Dd class I MHC-restricted murine cytotoxic T-lymphocytes (CTL), and an analogue (P18IIIB-g), O-glycosylated with an alpha-galactosamine on Thr-12, using NMR, circular dichroism and molecular modeling methods. Our studies show that the peptides sample mainly random conformations in aqueous solution near 25 degrees C and become more ordered by the addition of trifluoroethanol. Upon decreasing the temperature to 5 degrees C, a reverse turn is formed around the immunodominant tip (G5-R8). Glycosylation on T12 'tightens' the turn slightly as suggested by NOE and CD analysis. In addition, the sugar has a defined conformation with respect to the peptide backbone and influences the local peptide conformation. These data suggest that simple glycosylation may influence the conformational equilibrium of a V3 peptide which contains a domain critical for antibody recognition and virus neutralization. We also show that the ability of cytotoxic T-lymphocytes (CTL) to lyse tumor cells presenting P18IIIB was completely abrogated by threonine glycosylation.
authors.affiliation: Laboratory of Medicinal Chemistry, National Cancer Institute, National Institutes of Health, Bethesda, MD 20892, USA.
authors.forename: X
authors.initials: X
authors.lastname: Huang
authors.forename: M C
authors.initials: MC
authors.lastname: Smith
authors.forename: J A
authors.initials: JA
authors.lastname: Berzofsky
authors.forename: J J
authors.initials: JJ
authors.lastname: Barchi
mesh_terms: D000595:Amino Acid Sequence; D000818:Animals; D002942:Circular Dichroism; D005688:Galactosamine; D006020:Glycopeptides / Q000737:chemistry; D006031:Glycosylation; D015699:HIV Envelope Protein gp120 / Q000737:chemistry* / Q000276:immunology; D015497:HIV-1 / Q000737:chemistry* / Q000276:immunology; D006801:Humans; D009682:Magnetic Resonance Spectroscopy; D051379:Mice; D008958:Models, Molecular; D008969:Molecular Sequence Data; D015394:Molecular Structure; D010446:Peptide Fragments / Q000737:chemistry; D011487:Protein Conformation; D016339:Spectrometry, Mass, Fast Atom Bombardment; D013602:T-Lymphocytes, Cytotoxic / Q000276:immunology; D013912:Threonine
chemical_list: D006020:Glycopeptides; D015699:HIV Envelope Protein gp120; D010446:Peptide Fragments; D013912:Threonine; D005688:Galactosamine