Role of anchor residues in peptide binding to three HLA-A26 molecules

To investigate the role of anchor residues in HLA-A26 binding peptides, we analyzed the binding of various peptides to three HLA-A26 molecules using the HLA class I stabilization assay. Of twenty nonamer peptides carrying anchors at P2 and P9, 3, 6 and 3 peptides bound to HLA-A*2601, HLA-A*2602 and HLA-A*2603, respectively The peptide EV-IPMFSAL bound most strongly to these three HLA-A26 molecules. Analysis using mutants of this peptide at P1, P2 or P9 showed that acidic amino acids at P1 and five hydrophobic residues (Val, Thr, Ile, Leu and Phe) at P2 are anchor residues for the three HLA-A26 molecules while with exception of positively charged amino acids, a broad range of amino acids function as P9 anchor residues. These anchors were further evaluated using 38 nonamer peptides carrying anchor residues at P1, P2 and P9. Nineteen of these peptides bound to at least one HLA-A26 molecule. The frequency of HLA-A26 binding peptides was higher for peptides carrying all three anchor residues than for peptides carrying only P2 and P9 anchor residues. These results indicate that in addition to P2 and P9 anchors, the P1 anchor plays an important role in peptide binding to three HLA-A26 molecules.