STRUCTURAL REQUIREMENTS OF PEPTIDE AND MHC FOR DR(ALPHA,BETA-1-ASTERISK-0401)-RESTRICTED T-CELL ANTIGEN RECOGNITION

We identified functionally important regions of the DR(alpha,beta 104 01) peptide binding site and present a model of bound peptide. DR(alph a,beta 10401)-restricted T cell recognition and peptide binding of My cobacterium leprae (ML) peptide 38-50 and overlapping peptides from th e 18-kDa heat-shock protein were analyzed. ML38-50 is unusual in its r estricted binding pattern, binding to only one of five DR4 subtypes an d no other DR molecules tested. Amino acid substitutions were introduc ed into ML38-50 and the DR(alpha,beta 10401) peptide binding site at positions likely to influence peptide-MHC or peptide- or MHC-TCR inter actions. Peptide binding, T cell proliferation, and computer modeling studies suggest that residues 39F, 42E, and 44D of ML38-50 interact wi th pockets 1, 4, and 6, respectively, of the peptide binding site. Onl y DR(alpha,beta 10401) substitutions at residues in pockets 4 or 7 pr evented binding of ML38-50, while multiple substitutions at other posi tions negatively affected its T cell recognition. In contrast, T cell recognition of some high affinity ML peptides that overlapped ML38-50, and contained N-terminal extensions, was only abolished with pocket 4 substitutions. An inverse correlation of peptide affinity for DR(alph a,beta 10401) with negative effects of MHC substitutions on T cell re cognition of the overlapping ML peptides was observed. Thus, some regi ons, such as pocket 4, dominantly influence T cell recognition of mult iple DR(alpha,beta 10401)-binding peptides. However, each DR(alpha,be ta 10401)-binding peptide appears to have unique properties that dete rmine the outcome of its MHC-peptide interactions and the relative imp ortance of other polymorphic pockets.