title: Both alpha and beta chain polymorphisms determine the specificity of the disease-associated HLA-DQ2 molecules, with beta chain residues being most influential.
abstract: We compared the peptide binding specificity of three HLA-DQ molecules; HLA-DQ(alpha1(*)0501, beta1(*)0201), HLA-DQ(alpha1(*)0201, beta1(*)0202), and HLA-DQ(alpha1(*)0501, beta1(*)0301). The first of these molecules confers susceptibility to celiac disease and insulin-dependent diabetes mellitus, while the two latter molecules, which share either the alpha chain or the nearly identical beta chain with HLA-DQ(alpha1(*)0501, beta1(*)0201), do not predispose to these disorders. The binding of peptides was detected in biochemical binding assays as inhibition of binding of radiolabeled indicator peptides to affinity-purified HLA-DQ molecules. Binding experiments with several peptides demonstrated a clear difference in peptide binding specificity between the three HLA-DQ molecules. Further, single amino acid substitution analyses indicated that the HLA-DQ molecules have different peptide binding motifs. The experimental data were corroborated by computer modelling analysis. Our data suggest that the three HLA-DQ molecules prefer large hydrophobic residues in P1 of peptides with subtle differences in side-chain preferences. HLA-DQ(alpha1(*)0501, beta1(*)0201) and HLA-DQ(alpha1(*)0201, beta1(*)0202) both prefer large hydrophobic residues in P9, whereas HLA-DQ(alpha1(*)0501, beta1(*)0301) prefers much smaller residues in this position. HLA-DQ(alpha1(*)0501, beta1(*)0201) and HLA-DQ(alpha1(*)0201, beta1(*)0202), in contrast to HLA-DQ(alpha1(*)0501, beta1(*)0301), prefer negatively charged residues in P4 and P7. A less prominent P6 pocket also appears to differ between the three HLA-DQ molecules. Our results indicate that polymorphic residues of both the alpha and the beta chain determine the peptide binding specificity of HLA-DQ(alpha1(*)0501, beta1(*)0201), but that the beta chain polymorphisms appears to play the most important role. The information on peptide residues which are advantageous and deleterious for binding to these HLA-DQ molecules may make possible the prediction of characteristic features of peptide that bind to HLA-DQ(alpha1(*)0501, beta1(*)0201) and precipitate celiac disease.
authors.affiliation: Institute of Transplantation Immunology, Rikshospitalet, University of Oslo, N-0027 Oslo, Norway.
authors.forename: B H
authors.initials: BH
authors.lastname: Johansen
authors.forename: T
authors.initials: T
authors.lastname: Jensen
authors.forename: C J
authors.initials: CJ
authors.lastname: Thorpe
authors.forename: F
authors.initials: F
authors.lastname: Vartdal
authors.forename: E
authors.initials: E
authors.lastname: Thorsby
authors.forename: L M
authors.initials: LM
authors.lastname: Sollid
mesh_terms: D000595:Amino Acid Sequence; D001402:B-Lymphocytes / Q000378:metabolism; D001665:Binding Sites; D001667:Binding, Competitive; D002446:Celiac Disease / Q000235:genetics / Q000276:immunology*; D002461:Cell Line, Transformed; D005802:Genes, MHC Class II; D006683:HLA-DQ Antigens / Q000235:genetics* / Q000378:metabolism; D006801:Humans; D008958:Models, Molecular; D008969:Molecular Sequence Data; D010047:Ovalbumin / Q000276:immunology / Q000378:metabolism; D010446:Peptide Fragments / Q000378:metabolism; D011110:Polymorphism, Genetic; D055672:Static Electricity; D013499:Surface Properties
chemical_list: D006683:HLA-DQ Antigens; C053186:HLA-DQ2 antigen; D010446:Peptide Fragments; D010047:Ovalbumin