MHC/peptide binding studies indicate hierarchy of anchor residues

MHC class I molecules present octa- or nonapeptides derived from cellular proteins. Such peptides adhere to strict rules, which are individual to each MHC allele. Synthetic peptides conforming to these rules or peptides being at variance at critical residues were assayed for binding to MHC class I molecules. The binding assay employed the peptide-induced stabilization of MHC molecules of RMA-S cells. The data indicate that most proline-free peptides conforming to the allele-specific motifs of Kb or Db bind to the respective molecules, whereas peptides missing only one of the two allele-specific anchor residues lost their capacity to stabilize class I molecules on RMA-S cells. The residues allowed at anchor positions of the Kb motif are not equal in their binding efficiency and can be ordered in a hierarchic row. Residues at nonanchor positions may also influence efficiency of peptide binding or may require deviations from the standard peptide length.