Structural basis of CD8 coreceptor function revealed by crystallographic analysis of a murine CD8αα ectodomain fragment in complex with H-2K

The crystal structure of the two immunoglobulin variable-like domains of the murine CD8 alpha alpha homodimer complexed to the class I MHC H-2K(b) molecule at 2.8 A resolution shows that CD8 alpha alpha binds to the protruding MHC alpha 3 domain loop in an antibody-like manner. Comparison of mouse CD8 alpha alpha/H-2K(b) and human CD8 alpha alpha/HLA-A2 complexes reveals shared as well as species-specific recognition features. In both species, core-ceptor function apparently involves the participation of CD8 dimer in a bidentate attachment to an MHC class I molecule in conjunction with a T cell receptor without discernable conformational alteration of the peptide or MHC antigen-presenting platform.