The complementarity-determining region-like loops of CD8 alpha interact differently with beta 2-microglobulin of the class I molecules H-2Kb and thymic leukemia antigen, while similarly with their alpha 3 domains.
The murine CD8 glycoprotein interacts with both classical MHC class I molecules and some nonclassical molecules, including the thymic leukemia Ag (TL). TL binds preferentially to CD8alphaalpha homodimers with a 10-fold higher affinity than H-2K(b) class I molecules. To understand the molecular basis for this difference, we created a panel of CD8alpha mutants and tested the ability of the CD8alphaalpha homodimers to bind to H-2K(b) tetramers and TL tetramers. Mutations in three CD8 residues located on the complementarity-determining region-like loops contacting the negatively charged loop in the alpha3 domain of MHC class I greatly reduced binding to both tetramers. Because TL and H-2K(b) class I sequences are highly conserved in the alpha3 domain of MHC class I, this suggests that CD8 contacts the alpha3 domain of TL and H-2K(b) in a similar manner. In contrast, mutations in residues on the A and B beta strands of CD8 that are involved in contact with beta(2)-microglobulin affected interaction with the H-2K(b) tetramer, but not the TL tetramer. Therefore, the orientation of interaction of TL with CD8 appears to be different from that of H-2K(b). The unique high affinity binding of TL with CD8alphaalpha is most likely a result of amino acid differences in the alpha3 domain between TL and H-2K(b), particularly at positions 198 (K to D) and 228 (M to T), which are contact residues in the CD8alphaalpha-H-2K(b) cocrystal.
Devine
Lesley
L
Department of Laboratory Medicine and Section of Immunobiology, Yale University School of Medicine, New Haven, CT 06520, USA.
Rogozinski
Linda
L
Naidenko
Olga V
OV
Cheroutre
Hilde
H
Kavathas
Paula B
PB
D000595:Amino Acid Sequence; D019943:Amino Acid Substitution / Q000235:genetics / Q000276:immunology; D000818:Animals; D000951:Antigens, Neoplasm / Q000378:metabolism*; D016827:CD8 Antigens / Q000235:genetics / Q000276:immunology / Q000378:metabolism*; D019556:COS Cells; D022801:Complementarity Determining Regions / Q000378:metabolism; D019281:Dimerization; D006183:H-2 Antigens / Q000378:metabolism*; D007106:Immune Sera / Q000378:metabolism; D008562:Membrane Glycoproteins / Q000378:metabolism*; D051379:Mice; D008969:Molecular Sequence Data; D016297:Mutagenesis, Site-Directed; D010446:Peptide Fragments / Q000276:immunology / Q000378:metabolism; D011485:Protein Binding / Q000235:genetics / Q000276:immunology; D017433:Protein Structure, Secondary / Q000235:genetics; D017434:Protein Structure, Tertiary / Q000235:genetics; D013950:Thymus Gland / Q000276:immunology / Q000378:metabolism; D014162:Transfection; D001613:beta 2-Microglobulin / Q000378:metabolism*
D000951:Antigens, Neoplasm; D016827:CD8 Antigens; C409469:CD8 antigen, alpha chain; C433839:CD8alphabeta antigen; D022801:Complementarity Determining Regions; D006183:H-2 Antigens; C032876:H-2Kb protein, mouse; D007106:Immune Sera; D008562:Membrane Glycoproteins; D010446:Peptide Fragments; D001613:beta 2-Microglobulin; C028388:thymus-leukemia antigens