title: Determination of the allele-specific antigen-binding site on I-Ak and I-Ab molecules.
abstract: Residues 46 and 54 on a pigeon cytochrome c 43-58 analog, 50E, function as major histocompatibility complex class II contact sites. A peptide, 46F50E54A, with phenylalanine (F) at position 46 and alanine (A) at 54 on 50E bound to Ab and a peptide, 46D50E54A, with aspartic acid (D) at 46 and alanine at 54, bound to Ak. To determine the allele-specific peptide contact sites on I-A molecules corresponding to the I-A contact sites of the peptides, we analyzed responses of Ak- and/or Ab-restricted T cell hybridomas to 46F50E54A or 46D50E54A using L cell transfectants expressing recombinant I-A molecules between Ak and Ab or point mutants of Ak as antigen presenting cells. It was shown that the N-terminal half of the alpha helix of the A alpha chain determined the allele-specific T cell responses. Furthermore, with arginine (k type amino acid) or alanine (b type amino acid) at position 56 of the Ak alpha chain, these T cell hybridomas were stimulated predominantly by 46D50E54A (Ak binding peptide) or 46F50E54A (Ab binding peptide), respectively. Thus, the amino acid at position 56 of the A alpha chain determines allele-specific antigen presentation. This postulate was confirmed by direct binding analysis of 50E analogs of various I-A molecules. A single amino acid change (arginine to alanine) at position 56 of the Ak alpha chain altered the peptide binding specificity (46D50E54A to 46F50E54A).
authors.affiliation: Section of Pathology, Institute of Immunological Science, Hokkaido University, Sapporo, Japan.
authors.forename: Y
authors.initials: Y
authors.lastname: Itoh
authors.forename: K
authors.initials: K
authors.lastname: Kajino
authors.forename: K
authors.initials: K
authors.lastname: Ogasawara
authors.forename: M
authors.initials: M
authors.lastname: Katoh
authors.forename: K
authors.initials: K
authors.lastname: Namba
authors.forename: K
authors.initials: K
authors.lastname: Takami
authors.forename: K
authors.initials: K
authors.lastname: Iwabuchi
authors.forename: N S
authors.initials: NS
authors.lastname: Braunstein
authors.forename: K
authors.initials: K
authors.lastname: Onoé
mesh_terms: D000483:Alleles; D000595:Amino Acid Sequence; D000818:Animals; D001665:Binding Sites; D001667:Binding, Competitive; D000949:Histocompatibility Antigens Class II / Q000737:chemistry* / Q000235:genetics; D006825:Hybridomas; D051379:Mice; D008969:Molecular Sequence Data; D010455:Peptides / Q000737:chemistry / Q000276:immunology; D016415:Sequence Alignment; D017386:Sequence Homology, Amino Acid
chemical_list: D000949:Histocompatibility Antigens Class II; D010455:Peptides