Analysis of Qa-1(b) peptide binding specificity and the capacity of CD94/NKG2A to discriminate between Qa-1-peptide complexes.
The major histocompatibility complex class Ib protein, Qa-1(b), serves as a ligand for murine CD94/NKG2A natural killer (NK) cell inhibitory receptors. The Qa-1(b) peptide-binding site is predominantly occupied by a single nonameric peptide, Qa-1 determinant modifier (Qdm), derived from the leader sequence of H-2D and L molecules. Five anchor residues were identified in this study by measuring the peptide-binding affinities of substituted Qdm peptides in experiments with purified recombinant Qa-1(b). A candidate peptide-binding motif was determined by sequence analysis of peptides eluted from Qa-1 that had been folded in the presence of random peptide libraries or pools of Qdm derivatives randomized at specific anchor positions. The results indicate that Qa-1(b) can bind a diverse repertoire of peptides but that Qdm has an optimal primary structure for binding Qa-1(b). Flow cytometry experiments with Qa-1(b) tetramers and NK target cell lysis assays demonstrated that CD94/NKG2A discriminates between Qa-1(b) complexes containing peptides with substitutions at nonanchor positions P4, P5, or P8. Our findings suggest that it may be difficult for viruses to generate decoy peptides that mimic Qdm and raise the possibility that competitive replacement of Qdm with other peptides may provide a novel mechanism for activation of NK cells.
Kraft
J R
JR
Department of Pathology and Laboratory Medicine, Emory University School of Medicine, Atlanta, Georgia 30322, USA.
Vance
R E
RE
Pohl
J
J
Martin
A M
AM
Raulet
D H
DH
Jensen
P E
PE
D000818:Animals; D015703:Antigens, CD / Q000378:metabolism*; D001665:Binding Sites; D006183:H-2 Antigens / Q000502:physiology; D064532:Histocompatibility Antigen H-2D; D015395:Histocompatibility Antigens Class I / Q000378:metabolism*; D007694:Killer Cells, Natural / Q000276:immunology*; D037181:Lectins, C-Type; D008562:Membrane Glycoproteins / Q000378:metabolism*; D051379:Mice; D008810:Mice, Inbred C57BL; D055654:NK Cell Lectin-Like Receptor Subfamily C; D051920:NK Cell Lectin-Like Receptor Subfamily D; D021382:Protein Sorting Signals / Q000502:physiology; D011971:Receptors, Immunologic / Q000378:metabolism*; D055607:Receptors, Natural Killer Cell
D015703:Antigens, CD; D006183:H-2 Antigens; D064532:Histocompatibility Antigen H-2D; D015395:Histocompatibility Antigens Class I; C527057:Klrc1 protein, mouse; C497870:Klrd1 protein, mouse; D037181:Lectins, C-Type; D008562:Membrane Glycoproteins; D055654:NK Cell Lectin-Like Receptor Subfamily C; D051920:NK Cell Lectin-Like Receptor Subfamily D; D021382:Protein Sorting Signals; C032907:Q surface antigens; D011971:Receptors, Immunologic; D055607:Receptors, Natural Killer Cell