In APCs, the autologous peptides selected by the diabetogenic I-Ag7 molecule are unique and determined by the amino acid changes in the P9 pocket.
We demonstrate in this study the great degree of specificity in peptides selected by a class II MHC molecule during processing. In this specific case of the diabetogenic I-A(g7) molecule, the P9 pocket of I-A(g7) plays a critical role in determining the final outcome of epitope selection, a conclusion that is important in interpreting the role of this molecule in autoimmunity. Specifically, we examined the display of naturally processed peptides from APCs expressing either I-A(g7) molecules or a mutant I-A(g7) molecule in which the beta57Ser residue was changed to an Asp residue. Using mass spectrometry analysis, we identified over 50 naturally processed peptides selected by I-A(g7)-expressing APCs. Many peptides were selected as families with a core sequence and variable flanks. Peptides selected by I-A(g7) were unusually rich in the presence of acidic residues toward their C termini. Many peptides contained short sequences of two to three acidic residues. In binding analysis, we determined the core sequences of many peptides and the interaction of the acidic residues with the P9 pocket. However, different sets of peptides were isolated from APCs bearing a modified I-A(g7) molecule. These peptides did not favor acidic residues toward the carboxyl terminus.
Suri
Anish
A
Department of Pathology and Immunology, Washington University School of Medicine, 660 South Euclid Avenue, St. Louis, MO 63110, USA.
Vidavsky
Ilan
I
van der Drift
Koen
K
Kanagawa
Osami
O
Gross
Michael L
ML
Unanue
Emil R
ER
D017502:Adenovirus E2 Proteins / Q000378:metabolism; D000595:Amino Acid Sequence; D019943:Amino Acid Substitution / Q000276:immunology*; D000818:Animals; D017951:Antigen Presentation; D000938:Antigen-Presenting Cells / Q000276:immunology* / Q000378:metabolism; D015703:Antigens, CD / Q000378:metabolism; D001324:Autoantigens / Q000276:immunology* / Q000378:metabolism; D003922:Diabetes Mellitus, Type 1 / Q000276:immunology* / Q000378:metabolism; D000949:Histocompatibility Antigens Class II / Q000302:isolation & purification / Q000378:metabolism*; D051907:Lysosomal Membrane Proteins; D008247:Lysosomes / Q000276:immunology / Q000378:metabolism; D008562:Membrane Glycoproteins / Q000378:metabolism; D051379:Mice; D008969:Molecular Sequence Data; D009113:Muramidase / Q000378:metabolism; D010446:Peptide Fragments / Q000276:immunology* / Q000302:isolation & purification / Q000378:metabolism*; D011485:Protein Binding / Q000276:immunology; D022021:Tacrolimus Binding Proteins / Q000378:metabolism; D014407:Tumor Cells, Cultured
D017502:Adenovirus E2 Proteins; D015703:Antigens, CD; D001324:Autoantigens; D000949:Histocompatibility Antigens Class II; C407099:I-A g7 antigen; D051907:Lysosomal Membrane Proteins; D008562:Membrane Glycoproteins; D010446:Peptide Fragments; C421864:hen egg lysozyme; D009113:Muramidase; D022021:Tacrolimus Binding Proteins