CRYSTAL-STRUCTURE OF THE HUMAN CLASS-II MHC PROTEIN HLA-DR1 COMPLEXEDWITH AN INFLUENZA-VIRUS PEPTIDE

An influenza virus peptide binds to HLA-DR1 in an extended conformatio n with a pronounced twist. Thirty-five per cent of the peptide surface is accessible to solvent and potentially available for interaction wi th the antigen receptor on T cells. pockets in the peptide-binding sit e accommodate five of the thirteen side chains of the bound peptide, a nd explain the peptide specificity of HLA-DR1. Twelve hydrogen bonds b etween conserved HLA-DR1 residues and the main chain of the peptide pr ovide a universal mode of peptide binding, distinct from the strategy used by class I histocompatibility proteins.