Recognition of an MHC class I-restricted antigenic peptide can be modulated by para-substitution of its buried tyrosine residues in a TCR-specific manner

Conformational dependence of TCR contact residues of the H-2K(b) molecule o n the two buried tyrosine side chains of the vesicular stomatitis virus (VS V)-8 peptide was investigated by systematic substitutions of the tyrosines with phenylalanine, p-fluorophenylalanine (pFF), or p-bromophenylalanine (p BrF), The results of peptide competition CTL assays revealed that all of th e peptide variants, except for the pBrF analogues, had near-native binding to the H-2K(b) molecule. Epitope-mapped anti-H-2K(b) mAbs detected conforma tional differences among H-2K(b) molecules stabilized with these VSV-8 vari ants on RMA-S cells. Selective recognition of the VSV-8 analogues was displ ayed by a panel of three H-2K(b)-restricted, anti-VSV-8 TCRs, Thus, these s ubstitutions result in an antigenically significant conformational change o f the MHC molecular surface structure at both C and D pockets, and the effe ct of this change on cognate T cell recognition is dependent on the TCR str ucture. Our results confirm that the structure of buried peptide side chain s can determine the surface conformation of the MHC molecule and demonstrat e that even a very subtle structural nuance of the buried side chain can be incorporated into the surface conformation of the MHC molecule. The abilit y of buried residues to modulate this molecular surface augments the number of residues on the MHC-peptide complex that can be recognized as "foreign" by the CD8(+) T cell repertoire and allows for a higher level of antigenic discrimination. This may be an important mechanism to expand the total num ber of TCR specificities that can respond to a single peptide determinant.