Binding of peptides to HLA-DQ molecules: peptide binding properties of the disease-associated HLA-DQ(α1*0501, β1*0201) molecule

Peptide binding to DQ molecules has not previously been described. Here we report a biochemical peptide-binding assay specific for the DQ2 i.e. DQ(alpha 1*0501, beta 1*0201) molecule. This molecule was chosen since it shows a strong association to diseases such as celiac disease and insulin-dependent diabetes mellitus. Initially we radiolabelled some selected peptides and tested them for binding to affinity-purified DQ2 molecules. One of the peptides, a Mycobacterium bovis (MB) 65 kDa 243-255Y peptide, displayed a good signal-to-noise ratio and was thus chosen as an indicator peptide in the DQ2 binding assay. The MB 65 kDa 243-255Y peptide bound to DQ2 in a strictly pH-dependent fashion, with optimal binding around pH 5 and only weak binding at pH 7.4. The association of the MB 65 kDa 243-255Y peptide to DQ2 was slow, but once formed, the peptide-HLA complexes were very stable. The binding of peptides to DQ2 was specific, as shown in inhibition experiments with a panel of 47 peptides, differing in length, sequence, and origin. The binding of peptides to DR3 was tested in a similar assay with a Mycobacterium tuberculosis 65 kDa 3-13 peptide as the binding indicator. DQ2 and DR3 molecules bound to different sets of peptides. However, the peptide binding to DQ2 and DR3 showed, in general, similar characteristics with respect to pH dependence and kinetic parameters, indicating that the overall rules for peptide binding to DQ molecules are the same as those previously shown for human DR and murine I-A and I-E molecules.