THE BINDING-AFFINITY AND DISSOCIATION RATES OF PEPTIDES FOR CLASS-I MAJOR HISTOCOMPATIBILITY COMPLEX-MOLECULES

Peptides of various lengths derived from the influenza nucleoprotein (NP) bind to H-2D(b) class I molecules with affinities at 4-degrees-C between approximately 3 x 10(5) - approximately 3 x 10(7) M-1. The peptide with the highest affinity corresponds to the sequence of nine amino acids (NP366-374) recently isolated from cells infected with influenza. This peptide forms stable complexes with half-lives > 110 h at 4-degrees-C, 39 h at 22-degrees-C and 3 h at 37-degrees-C. Small increases in length of the peptide greatly reduce the stability of the complex (t1/2 approximately 1-10 h at 4-degrees-C). These results may explain the homogeneous length of peptides isolated from class I molecules formed in vivo, and suggest that class I and II may differ in their dependence on the length of peptides for the formation of stable complexes.