PEPTIDE BINDING CHARACTERISTICS OF THE CELIAC DISEASE-ASSOCIATED DQ(ALPHA-1-ASTERISK-0501, BETA-1-ASTERISK-0201) MOLECULE

Genetic susceptibility to coeliac disease (CD) is strongly associated with the expression of the HLA-DQ2 (alpha 10501, beta 1*0201) allele. Then is evidence that this DQ2 molecule plays a role in the pathogene sis of CD as a restriction element for gliadin-specific T cells in the gut. However, it remains largely unclear which fragments of gliadin c an actually be presented by the disease-associated DQ dimer. With a vi ew to identifying possible CD-inducing antigens, we studied the peptid e binding properties of DQ2. For this purpose, peptides bound to HLA-D Q2 were isolated and characterized. Dominant peptides were found to be derived from two self-proteins: in addition to several size-variants of the invariant chain (li)-derived CLIP peptide, a relatively large a mount of an major histocompatibility complex (MHC) class I-derived pep tide was found. Analogues of this naturally processed epitope (MHCl al pha 46-63) were tested in a cell-free peptide binding competition assa y to investigate the requirements for binding to DQ2. First, a core se quence of 10 amino acids within the MHCl alpha 46-63 peptide was ident ified. By subsequent single amino acid substitution analysis of this c ore sequence, five putative anchor residues were identified at relativ e positions P1, P4, P6, P7, and P9. Replacement by the large, positive ly charged Lys at these positions resulted in a dramatic loss of bindi ng. However, several other non-conservative substitutions had little o r no discernable effect on the binding capacity of the peptides. Subst itutions at P1 and P4 were most critical, suggesting a more prominent role as anchor residues. Structural features of the DQ2 molecule that may relate to the binding motif and to gluten sensitivity are discusse d.