HLA-DR3 MOLECULES CAN BIND PEPTIDES CARRYING 2 ALTERNATIVE SPECIFIC SUBMOTIFS

Three different HLA-DR3-specific peptide binding motifs have been prop osed. These motifs shared a major hydrophobic anchor at the N-terminus , but differed in the C-terminal anchor residues. In the present study , the structural requirements for peptide binding to HLA-DR3 were exam ined in further detail by using quantitative HLA-DR3-specific binding assays and sets of single substitution analogues of DR3 binding peptid es (Lol pollen amino acids 171-190 and sperm whale myoglobin amino aci ds 132-151). We found that the requirements for binding to HLA-DR3 var y among different DR3 binding peptides; the absence of an anchor or th e presence of only a weak anchor residue at either position n or n + 3 can be compensated for by the presence of a strong, positively charge d anchor residue at position n + 5. These results explain several of t he previously reported differences between DR3-specific peptide bindin g motifs. To evaluate the predictive value of the thus-refined motif, the DR3 binding capacity of an overlapping set of peptides, spanning t he entire sequence of the 65-kDa heat shock protein of Mycobacterium t uberculosis was investigated and correlated with the occurence of the different DR3 motifs. A strong correlation was found between the prese nce of the refined DR3 motif and peptide binding to purified HLA-DR3 m olecules.