title: Conformation of MHC class II I-A(g7) is sensitive to the P9 anchor amino acid in bound peptide.
abstract: Type I diabetes is a chronic autoimmune disease resulting in the destruction of insulin-producing beta cells in the pancreas. In humans, disease incidence is linked to expression of specific MHC class II alleles and in mice type I diabetes is associated with the class II allele I-A(g7). I-A(g7) contains a polymorphism that is shared by human class II alleles associated with the disease, at position 57 in the beta chain, in which aspartic acid is changed to a serine. The P9 pocket in the peptide-binding groove is in part shaped by beta57, and therefore the structure of this pocket is modified in I-A(g7). Using mAbs, we have previously determined that alternative conformations of I-A(g7) form in response to peptide binding. In this study, we have extended these findings by examining how peptides induce I-A(g7) molecules to adopt different conformations. By mutating the amino acid in the P9 position of either class II-associated invariant chain peptide (CLIP) or glutamic acid decarboxylase (GAD) 65 (207-220), we have determined that the chemical nature of the P9 anchor amino acid, either acidic or small hydrophobic, affects the overall conformation of the I-A(g7) class II molecule. T cell hybridomas specific for GAD 65 (207-220) in the context of I-A(g7) were also examined for recognition of I-A(g7) bound to GAD 65 (207-220), in which Glu(217) in the P9 position was changed to alanine. We found that although some TCRs were able to recognize both peptides in the context of I-A(g7), and thus both class II conformations, approximately one-third of the T cells tested were not able to recognize the alternate class II conformation formed with the mutated peptide. These results indicate that the I-A(g7) conformations may affect functional activation of T cells, and thus may play a role in autoimmunity.
authors.affiliation: Department of Biology, American University, 4400 Massachusetts Avenue NW Washington, DC 20016, USA.
authors.forename: Amy
authors.initials: A
authors.lastname: Gardiner
authors.forename: Katherine A
authors.initials: KA
authors.lastname: Richards
authors.forename: Andrea J
authors.initials: AJ
authors.lastname: Sant
authors.forename: Lynne S
authors.initials: LS
authors.lastname: Arneson
mesh_terms: D000595:Amino Acid Sequence; D000596:Amino Acids / Q000737:chemistry* / Q000276:immunology; D000818:Animals; D001665:Binding Sites; D002460:Cell Line; D000949:Histocompatibility Antigens Class II / Q000737:chemistry* / Q000235:genetics / Q000276:immunology; D051379:Mice; D008969:Molecular Sequence Data; D010446:Peptide Fragments / Q000737:chemistry* / Q000276:immunology; D011487:Protein Conformation; D012680:Sensitivity and Specificity; D013601:T-Lymphocytes / Q000276:immunology
chemical_list: D000596:Amino Acids; D000949:Histocompatibility Antigens Class II; C407099:I-A g7 antigen; D010446:Peptide Fragments