Second site reversion of T cell recognition of class i variant molecules: Evidence for peptide: MHC conform ational variation

MHC class I variants H-2Kb and H-2Kbltl8 differ from each other at four amino acid residues located on the floor of peptide binding site. Functionally important differences are confined to the B pocket of the groove, One consequence of this variation is that only Kb can present the OVA peptide to cytotoxic T lymphocytes (CTL). We investigated why Kb failed to present this peptide and a related peptide from HSV glycoprotein B. We show that a lack of peptide binding cannot explain a lack of recognition. Molecular modeling indicated that the most obvious change between OVA/K^b and OVA/K^bm8 complexes would be an altered hydrogen bond network in the B pocket. Using second site reversion approach, we provide experimental evidence that this network may be crucial for CTL recognition of the complex. Only OVA and HSV peptide variants which could restore the hydrogen bond network of the B pocket in K1"1, could also restore CTL recognition of the complex. These results provide evidence that in this model, peptide: MHC conformational variation may exert critical influence on TCR recognition.