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 t he HLA class I stabilization assay. Of twenty nonamer peptides carrying anc hors 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 the se three HLA-A26 molecules. Analysis using mutants of this peptide at P1, P 2 or P9 showed that acidic amino acids at P1 and five hydrophobic residues (Val, Thr, lie, Leu and Phe) at P2 are anchor residues for the three HLA-A2 6 molecules while with exception of positively charged amino acids, a broad range of amino acids function as P9 anchor residues. These anchors were fu rther evaluated using 38 nonamer peptides carrying anchor residues at P1, P 2 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 carryin g all three anchor residues than for peptides carrying only P2 and P9 ancho r residues. These results indicate that in addition to P2 and P9 anchors, t he P1 anchor plays an important role in peptide binding to three HLA-A26 mo lecules.