The Journal of Immunology, Vol 157, Issue 6 2470-2478, Copyright © 1996 by American Association of Immunologists

ARTICLES

Probing HLA-B7 conformational shifts induced by peptide-binding groove mutations and bound peptide with anti-HLA monoclonal antibodies

KD Smith, BE Mace, A Valenzuela, JL Vigna, JA McCutcheon, JA Barbosa, E Huczko, VH Engelhard and CT Lutz
Department of Pathology, University of Iowa College of Medicine, Iowa City 52242, USA.

To determine the influence of peptide-binding groove residues and MHC- bound peptide on HLA-B7 conformation, we investigated the binding sites of nine locus- or allele-specific mAbs using a panel of 82 HLA-B7 variants. The functional mAb epitopes encircle the HLA-B7 peptide- binding groove. Three mAbs are affected by mutations at solvent- accessible peptide-binding groove mutations. Mutations in peptide- binding groove residues 45, 63, and 150 affect multiple nonoverlapping mAb epitopes, probably by interaction with other MHC residues or bound peptide. However, 18 of 24 peptide-binding groove mutations do not affect mAb binding, indicating that the conformation of solvent- accessible HLA-B7 structures is largely dissociated from changes in the peptide-binding groove. To test whether bound peptides alter HLA-B7 conformation, we loaded HLA-B7 heavy chains on acid-stripped cells with beta2-microglobulin and 20 individual synthetic peptides. Two of eight mAbs are sensitive to HLA-B7-bound peptides. A likely interpretation of these data is that 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 different peptide-binding grooves.

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