Structural comparison of a 15 residue peptide from the V3 loop of HIV-1 IIIb and an O-glycosylated analogue

• Published in: FEBS letters 1996-09, Vol.393 (2), p.280-286
• Main Authors: Huang, Xiaolin, Charles Smith, M., Berzofsky, Jay A., Barchi, Joseph J.
• Format: Article
• Language: English
• Subjects: CTL; Glycopeptide; NMR; V3 loop
• ISSN: 0014-5793; 1873-3468
• DOI: 10.1016/0014-5793(96)00912-X

As part of a program to study the effect of glycosylation on the three-dimensional structures of HIV-1 IIIB V3 peptide constructs, we have examined the solution structures of a 15 residue peptide (RIQRGPGRAFVTIGK, P18 IIIB ), originally mapped as an epitope recognized by CD8 + D d class I MHC-restricted murine cytotoxic T-lymphocytes (CTL), and an analogue (P18 IIIB -g), O-glycosylated with an α-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°C and become more ordered by the addition of trifluoroethanol. Upon decreasing the temperature to 5°C, a reverse turn is formed around the immunodominant tip (G 5−R 8). Glycosylation on T 12 ‘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 P18 IIIB was completely abrogated by threonine glycosylation.