PROBING HLA-B7 CONFORMATIONAL SHIFTS INDUCED BY PEPTIDE-BINDING GROOVE MUTATIONS AND BOUND PEPTIDE WITH ANTI-HLA MONOCLONAL-ANTIBODIES

To determine the influence of peptide-binding groove residues and MHC- bound peptide on HLA-B7 conformation, we investigated the binding site s of nine locus- or allele-specific mAbs using a panel of 82 HLA-B7 va riants, The functional mAb epitopes encircle the HLA-B7 peptide-bindin g groove, Three mAbs are affected by mutations at solvent-accessible p eptide-binding groove mutations, Mutations in peptide-binding groove r esidues 45, 63, and 150 affect multiple nonoverlapping mAb epitopes, p robably by interaction with other MHC residues or bound peptide. Howev er, 18 of 24 peptide-binding groove mutations do not affect mAb bindin g, indicating that the conformation of solvent-accessible HLA-B7 struc tures is largely dissociated from changes in the peptide-binding groov e, To test whether bound peptides alter HLA-BT conformation, we loaded HLA-B7 heavy chains on acid-stripped cells with beta(2)-microgrobulin and 20 individual synthetic peptides, Two of eight mAbs are sensitive to HLA-B7-bound peptides. A likely interpretation of these data is th at the conformational flexibility of HLA-B7 is due to peptide-induced conformational shifts in MHC side chains, rather than major shifts in the MHC main chain, These results suggest that HLA-B7 conformation is largely maintained in the context of different bound peptides and diff erent peptide-binding grooves.