Residue 67 in the DRβ1*0101 and DRβ1*0103 chains strongly influences antigen presentation and DR-peptide molecular complex conformation

Two closely-related molecules, DR(alpha,beta 1*0101) and DR(alpha,beta 1*0103), whose beta chains only differ by three amino acids at positions 67, 70, and 71, and six intermediate molecules obtained by site-directed mutagenesis were used to ascertain the respective roles of the three polymorphic residues. Substitutions at positions 70 (D --> Q), 71 (E --> R) and 67 (I or L --> F) strongly affected HA 306-318-specific T-cell recognition. The consequences of the substitution of residue 67 by a phenylalanine depended on the modified HLA-DR molecule. Although this substitution completely inhibited peptide-specific DR1-restricted T-cell recognition, its manifestations on the DR103S-restricted T cell response were variable (abolishing proliferation of some cell lines and not others), no matter what the peptide presented was (HA 306-319 or HIV P25 peptides). We also observed that inhibition of the proliferation of an alloreactive anti-DR103 T-cell clone, caused by a substitution at position 70, was completely canceled by substitution of residue 67 by a phenylalanine. The observations based on functional experiments, thus, suggest that residue 67 plays an important role in determining conformation of the peptide presented to the T cell. Molecular modeling was used to predict changes induced by amino acid substitutions and highly support-functional data. Substitution of residue 67 by a phenylalanine could have repercussions on the structure of HLA-DR molecule/peptide complexes and affect T-cell recognition.