CRUCIAL ROLE OF N-TERMINAL RESIDUE OF BINDING PEPTIDES IN RECOGNITIONOF THE MONOCLONAL-ANTIBODY SPECIFIC FOR THE PEPTIDE-HLA-B5, PEPTIDE-HLA-B35 COMPLEX

The monoclonal antibody (mAb) 4D12 specific for the HLA-BS, -B35 cross -reacting group (CREG) bound to a fraction of HLA-B3501 and HLA-B*510 1 molecules carrying self-peptides. Analysis of the binding of mAb 4D1 2 to HLA-B3501 and -B*5101 molecules pulsed with chemically synthesiz ed peptides revealed that this mAb recognizes a restricted number of p eptides and that P1 of the bound peptides critically influences its bi nding. The 4D12 mAb bound only to HLA-B3501 molecules carrying peptid es with Asn, Asp, Glu, Ser, and Val at P1. Analysis using an HLA-B350 1 crystallographic model suggested that 4D12 may recognize the side ch ain of the P1 residue that is pointing to the solvent. On the other ha nd, 4D12 bound only to HLA-B5101 molecules carrying peptides with Asn or Asp at P1, suggesting that the 4D12 epitope formed by Glu, Ser, or Val at P1 and the A-pocket was changed by the substitution of His for Tyr at residue 171 of HLA-B3501 molecules. This was confirmed by tes ting the binding of mAb 4D12 to HLA-B3501 mutant molecules at residue 171 carrying these peptides. These results together suggest that the conformation of the A-pocket and its hydrogen bound network with the P 1 residue is also critical for the binding of mAb 4D12. The present st udy shows the molecular basis of the specificity of 4D12 for the pepti de-HLA class I complex.