Prediction of peptide affinity to HLA DRB1*0401.

Hydrogen bonding between conserved amino acids in the HLA DR and the peptide backbone of the ligand both provide the majority of free energy of binding and force the peptide ligands to adopt a similar extended conformation. Consequently the corresponding side chains of all peptides interact with similar pockets in the binding site. For peptides of a common length the contribution of the peptide backbone can be treated as a constant and the differential affinity can be viewed as a simple sum of the side chain interactions. These can be quantified by measuring the effects of each of the naturally occurring amino acids in the context of a simplified polyalanine backbone containing an aromatic amino acid to orient the peptide unequivocally in the binding site. The dataset of the relative contributions can be used to predict quantitatively the affinity of any peptide sequence.