title: Unusual topology of an HLA-B27 allospecific T cell epitope lacking peptide specificity.
abstract: Recognition of MHC + peptide complexes by TCRs is thought to involve a large surface formed by exposed residues from the bound peptide and from the alpha-helices of the MHC protein. This interaction appears to be essentially symmetrical in the positioning of the TCR relative to the MHC molecule. In this study the topology of HLA-B27 recognition by an alloreactive TCR, 64.8P, has been analyzed with a panel of site-specific mutants that have changes at multiple positions along the peptide binding site of HLA-B27. Abrogation of transfectant target cell lysis by CTL 64.8P was obtained only with some mutations in the peptide side chain binding pockets A and B, whereas little or no effect was observed with mutations outside these pockets. CTL 64.8P efficiently lysed murine transfectant cells, including HLA-B27+ RMA-S cells. Recognition of this latter transfectant was more efficient upon increased HLA-B27 expression at 26 degrees C. The uneven distribution of mutations affecting HLA-B27 allorecognition by CTL 64.8P strongly suggests an asymmetrical topology in the interaction of this TCR with HLA-B27, in which most of the binding energy is provided by contacts with HLA-B27 and/or peptide residues located close to pockets A and B, with little contribution from other areas of the MHC or peptide molecules. Its conservation in RMA-S cells further suggests that the epitope recognized by CTL 64.8P is either peptide-independent or requires any of a set of peptides having the same amino-terminal residues.
authors.affiliation: Center of Molecular Biology, Autonomous University of Madrid, Cantoblanco, Spain.
authors.forename: J A
authors.initials: JA
authors.lastname: Villadangos
authors.forename: B
authors.initials: B
authors.lastname: Galocha
authors.forename: J A
authors.initials: JA
authors.lastname: López de Castro
mesh_terms: D000818:Animals; D001665:Binding Sites / Q000235:genetics / Q000276:immunology; D002460:Cell Line; D003602:Cytotoxicity, Immunologic; D000939:Epitopes / Q000737:chemistry / Q000235:genetics; D015796:HLA-B27 Antigen / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism; D006801:Humans; D051379:Mice; D016297:Mutagenesis, Site-Directed; D011487:Protein Conformation; D011948:Receptors, Antigen, T-Cell / Q000378:metabolism; D013602:T-Lymphocytes, Cytotoxic / Q000276:immunology; D014162:Transfection
chemical_list: D000939:Epitopes; D015796:HLA-B27 Antigen; D011948:Receptors, Antigen, T-Cell