T-CELL RECEPTOR AND PEPTIDE-CONTACTING RESIDUES IN THE HLA-DR17(3) BETA-1 CHAIN

Previously, we have proposed that the beta 1 residues 9-13, 26, 28 and 86 in HLA-DR17, the most common subtype of DR3, might be critical for the binding of an immunodominant, mycobacterial epitope (peptide 3-13 of the 65-kDa heat shock protein). In order to examine directly (i) w hich DR17 residues are involved in peptide binding, (ii) whether the s ame or other DR17 residues are involved in the binding of different pe ptides, and (iii) whether subtle differences in the made of peptide bi nding can influence T cell stimulation, we have now systematically mut ated 15 highly polymorphic DR17 beta 1 residues, located in the propos ed peptide binding groove of DR17, and examined the effect thereof on binding and presentation of two peptides, hsp65 p3-13 and p56-65 of th e 30/31-kDa secreted mycobacterial protein. Mutations in residues 28 ( D --> H) and 86 (V --> G) completely eliminated binding of p3-13 and s ignificantly reduced binding of p56-65. A mutation in residue 26 (Y -- > F) decreased binding of p3-13 but did not affect binding of p56-65. Substitutions of amino acid residues 28, 67, 71 and 86 in the DR17 bet a 1 chain abrogated peptide-specific stimulation of both the p3-13- an d the p56-65-specific T cell clones, while specific stimulation by onl y one peptide was eliminated by substitution at positions 26 and 74 (p 3-13) and by substitution of residues 11 and 37 (p56-65). The observat ion that substitution of several other peptide-contacting DR17 beta 1 chain residues does not significantly affect peptide binding but does affect T cell stimulation, suggests that these substitutions alter the conformation of the bound peptide.