FINE-TUNING OF PEPTIDE BINDING TO HLA-B-ASTERISK-3501 MOLECULES BY NONANCHOR RESIDUES

The prerequisites of peptide HLA-B3501 interactions have been revisit ed by quantitative peptide binding assays with 190 chemically synthesi zed peptides possessing two anchor residues corresponding to the HLA-B 3501 peptide motif and a statistical residue-position analysis of bin ding and nonbinding peptides. According to the peptide motif of HLA-B 3501, aliphatic hydrophobic (Leu, lie, and Met) or aromatic residues ( Tyr and Phe) specify the main anchor at the C terminus, and position 2 renders an auxiliary anchor for proline. The importance of these resi dues was confirmed as a minimum requirement for peptide binding. Moreo ver, we demonstrated that high affinity peptide binding requires more than one favorable position of positions 3, 4, and 7. Aliphatic hydrop hobic residues and residues that contain -OH or -SH side chains in pos ition 3, 7, and 4 significantly enhance binding. Positions 1 and 5, or 7 may deteriorate peptide binding if these positions are held by prol ine and small residues (Ala and Gly) or basic residues carrying positi vely charged side chains (Arg and Lys), respectively. Positions 6 and 8 were statistically free of constraints. Yet, bulky aromatic residues and basic residues with a positively charged side chain at position 8 decreased the binding affinity. These findings were used to assess th e predictability of binding and nonbinding peptides. Our binding predi ctions of 28 nonamers were verified by experimental data. Taking into account the importance of anchor and nonanchor positions in peptide bi nding and their practical value in peptide binding prediction, the sea rch for peptide epitopes becomes more efficient.