UNIQUE PEPTIDE BINDING CHARACTERISTICS OF THE DISEASE-ASSOCIATED DQ(ALPHA-1-ASTERISK-0501, BETA-1-ASTERISK-0201) VS THE NON-DISEASE-ASSOCIATED DQ(ALPHA-1-ASTERISK-0201, BETA-1-ASTERISK-0202) MOLECULE

To understand the dominant association of celiac disease (CD) with the presence of HLA-DQ(alpha 10501, beta 1*0201), the peptide binding ch aracteristics of this molecule were compared with that of the structur ally similar, but non-CD-associated DQ(alpha 10201, beta 1*0202) mole cule. First, naturally processed peptides were acid-extracted from imm uno-affinity-purified DQ molecules of both types. Both molecules conta ined the li-derived CLIP sequence and a particular fragment of the maj or histocompatibility complex (MHC) class I alpha chain. Use of trunca ted analogues of these two peptides in cell-free peptide binding assay s indicated that identical peptide frames are used for binding to the two DQ2 molecules. Detailed substitution analysis of the MHC class I p eptide revealed identical side chain requirements for the anchor resid ues at p6 and p7. At p1, p4, and p9, however, polar substitutions (suc h as N, Q, G, S, and T) were less well tolerated in the case of the DQ (alpha 10201, beta 1*0202) molecule. The most striking difference bet ween the two DQ molecules is the presence of an additional anchor resi due at p3 for the DQ(alpha 10201, beta 1*0202) molecule, whereas this residue was found not to be specifically involved in binding of pepti des to DQ(alpha 10501, beta 1*0201). Similar results were obtained ap plying substitution analysis of the CLIP sequence. Molecular modelling of the DQ2 proteins complexed with the MHC class I and CLIP peptide c orresponds well with the binding data. The results suggest that both C LIP and the MHC class I peptide bind DQ(alpha 10501, beta 1*0201) and DQ(alpha 10201, beta 1*0202) in a DR-like fashion, following highly similar binding criteria. This detailed characterization of unique pep tide binding properties of the CD-associated DQ(alpha 10501, beta 1*0 201) molecule should be helpful in the identification of CD-inducing e pitopes.