title: Modulation of peptide binding by HLA-B27 polymorphism in pockets A and B, and peptide specificity of B*2703.
abstract: The results in this study address three aspects of peptide binding to the disease-associated antigen HLA-B27 and its modulation by polymorphism: the contribution of major anchor residues 2 and 9, the role of pocket B polymorphism in modulating peptide specificity, and the binding properties of B*2703, a subtype not found to be associated with spondyloarthropathy. Synthetic analogs of peptides naturally presented by B*2705 were used to demonstrate that residue 2 is essential, since Ala2 analogs bound marginally to B*2705, but the specificity of B*2705 for Arg2 is not absolute, and show that the contribution of basic residue 9 to binding was significant, but less than Arg2. The effect of single mutations in the B pocket was to decrease or--with the Glu > Met-45 mutation--totally shift pocket B specificity for Arg2 towards other residues at this position. This was shown by quantitating the relative binding of Gln2 and Ala2 analogs, and by pool-sequencing of the peptides bound in vivo to these mutants. Peptides naturally presented by B*2705 apparently bound with a lower affinity to pocket A variants with altered hydrogen bonding to the peptide N terminus, including B*2703. Binding of peptide analogs with changes at positions 2 or 9 suggested that in B*2703 pocket A, interactions are weaker and pocket B interactions are stronger than in B*2705. This can be explained by the effect of the unique His59 change in B*2703 in both pockets. Thus, B*2703 is probably the HLA-B27 sub-type with the most stringent specificity for the Arg2 peptide motif.
authors.affiliation: Centro de Biología Molecular, Severo Ochoa (C.S.I.C.-U.A.M.), Universidad Autónoma de Madrid, Facultad de Ciencias, Spain.
authors.forename: J A
authors.initials: JA
authors.lastname: Villadangos
authors.forename: B
authors.initials: B
authors.lastname: Galocha
authors.forename: F
authors.initials: F
authors.lastname: García
authors.forename: J P
authors.initials: JP
authors.lastname: Albar
authors.forename: J A
authors.initials: JA
authors.lastname: López de Castro
mesh_terms: D000595:Amino Acid Sequence; D002460:Cell Line; D004355:Drug Stability; D015796:HLA-B27 Antigen / Q000235:genetics / Q000276:immunology* / Q000378:metabolism*; D006801:Humans; D008969:Molecular Sequence Data; D009154:Mutation / Q000235:genetics; D010452:Peptide Biosynthesis; D011485:Protein Binding / Q000235:genetics; D014162:Transfection
chemical_list: D015796:HLA-B27 Antigen