THE P9 POCKET OF HLA-DQ2 (NON-ASP-BETA-57) HAS NO PARTICULAR PREFERENCE FOR NEGATIVELY CHARGED ANCHOR RESIDUES FOUND IN OTHER TYPE-1 DIABETES-PREDISPOSING NON-ASP-BETA-57 MHC CLASS-II MOLECULES

Susceptibility and resistance to type 1 diabetes are associated with M HC class II alleles that carry non-Asp and Asp at residue 57 of their beta chain respectively. The effect of Asp or non-Asp beta 57 may rela te to a differential ability of distinct class II molecules to bind sp ecific immune-pathogenic peptides, Recent studies in man and mouse hav e revealed that some type 1 diabetes-predisposing non-Asp beta 57 clas s II molecules (i.e. DQ8, DR4Dw15 and I-A(g7)) preferentially bind pep tides with a negatively charged anchor residue at P9, It has been sugg ested that this is a common feature of type 1 diabetes-predisposing cl ass II molecules. The molecular explanation for such a phenomenon coul d be that class II beta chains with Asp beta 57 form a salt bridge bet ween Asp beta 57 and a conserved Arg of the alpha chain, whereas in no n-Asp beta 57 molecules the Arg is unopposed and free to interact with negatively charged P9 peptide anchor residues. We have investigated t he specificity of the P9 pocket of the type 1 diabetes-associated DQ2 molecule and in particular examined for charge effects at this anchor position. Different approaches were undertaken. We analyzed binding of a high-affinity binding ligand and PS-substituted variants of this pe ptide, and we analyzed the binding of a set of synthetic random peptid e libraries. The binding analyses were performed with wild-type DQ2 an d a mutated DQ2 with Ata at beta 57 substituted with Asp. Our results indicate that the wild-type DQ2 (non-Asp beta 57) prefers large hydrop hobic residues at P9 and that there is no particular preference for bi nding peptides with negatively charged residues at this position. The specificity of the P9 pocket in the mutated DQ molecule is altered, in dicating that the beta 57 residue contributes to determining the speci ficity of the P9 pocket. Our data do not lend support to the hypothesi s that all non-Asp beta 57 class II molecules predispose to developmen t of disease by binding peptides with negatively charged P9 anchor res idues.