Thermodynamic stability of HLA-B*2705 center dot peptide complexes - Effect of peptide and major histocompatibility complex protein mutations

Designing synthetic vaccines from class I major histocompatibility complex (MHC)-binding antigenic peptides requires not only knowledge of the binding affinity of the designed peptide but also predicting the stability of the formed MHC-peptide complex. In order to better investigate structure-stabil ity relationships, we have determined by circular dichroism spectroscopy th e thermal stability of a class I MHC protein, HLA-B*2705, in complex with a set of 39 singly substituted peptide analogues. The influence of two ancho ring side chains (P3 and P9) was studied by peptide mutation and appropriat e site directed mutagenesis of the HLA-B*2705 binding groove. The side chai n at P9 is clearly the one that contributes the most to the thermal stabili ty of the MHC-peptide complexes, as destabilization up to 25 degrees C are obtained after P9 mutation. Interestingly, structure-stability relationship s do not fully mirror structure-binding relationships. ks important as the C-terminal side chain are the terminal ammonium and carboxylate groups. Rem oval of a single II-bond between HLA-B27 and the terminal peptide moieties results in thermal destabilization up to 10 degrees C. Depending on the bou nd peptide and the location of the deleted II-bond, the decrease in the the rmal stability of the corresponding complex is quantitatively different. Th e present study suggests that any peptidic amino acid at positions 3 and 9 promotes refolding of the B27-peptide complex. Once the complex is formed, the C-terminal side chain seems to play an important role for maintaining a stable complex.