T cell receptor (TCR) recognition of MHC class I variants: intermolecular second-site reversion provides evidence for peptide/MHC conformational variation.
We investigated mechanistic differences in antigen presentation between murine MHC class I variants H-2K(b) and H-2K(bm)8. H-2K(bm)8 differs from H-2K(b) by four residues at the floor of the peptide-binding site, affecting its B pocket which interacts with the second (P2) residue of the peptide. The rest of the molecule, including the T cell receptor (TCR)-contacting residues, is identical to H-2K(b). Due to this variation, CTLs that recognize the ovalbumin 257-264 and HSV gB 498-505 peptides on H-2K(b) cannot recognize them on H-2K(bm)8. This could be due to impaired peptide binding or an altered peptide: K(bm)8 conformation. Peptide binding studies ruled out the first explanation. Molecular modeling indicated that the most obvious consequence of amino acid variation between peptide/H-2K(b) and peptide/H-2K(bm)8 complexes would be a loss of the conserved hydrogen bond network in the B pocket of the latter. This could cause conformational variation of bound peptides. Intermolecular second-site reversion was used to test this hypothesis: P2-substituted OVA and HSV peptides, engineered to restore the hydrogen bond network of the B pocket, were the only ones which restored CTL recognition. These results provide a molecular understanding of peptide/MHC conformational variation.
Dyall
R
R
Immunology Program, Sloan-Kettering Institute, New York, USA.
Fremont
D H
DH
Jameson
S C
SC
Nikolić-Zugić
J
J
D000595:Amino Acid Sequence; D000818:Animals; D000938:Antigen-Presenting Cells / Q000276:immunology*; D000956:Antigens, Viral / Q000737:chemistry / Q000276:immunology; D001665:Binding Sites; D006183:H-2 Antigens / Q000737:chemistry / Q000276:immunology*; D051379:Mice; D008810:Mice, Inbred C57BL; D008958:Models, Molecular; D008969:Molecular Sequence Data; D010047:Ovalbumin / Q000737:chemistry / Q000276:immunology; D010455:Peptides / Q000737:chemistry / Q000276:immunology*; D011485:Protein Binding; D011487:Protein Conformation; D011948:Receptors, Antigen, T-Cell / Q000737:chemistry / Q000378:metabolism*; D018139:Simplexvirus / Q000737:chemistry / Q000276:immunology; D013329:Structure-Activity Relationship; D013602:T-Lymphocytes, Cytotoxic / Q000276:immunology*
D000956:Antigens, Viral; D006183:H-2 Antigens; D010455:Peptides; D011948:Receptors, Antigen, T-Cell; D010047:Ovalbumin