A positive cooperativity binding model between Ly49 natural killer cell receptors and the viral immunoevasin m157: kinetic and thermodynamic studies.

ROMASANTA PN; CURTO LM; URTASUN N; SARRATEA MB; CHIAPPINI S; MIRANDA MV; DELFINO JM; MARIUZZA RA; FERNÁNDEZ MM; MALCHIODI EMILIO L

JOURNAL OF BIOLOGICAL CHEMISTRY

AMER SOC BIOCHEMISTRY MOLECULAR BIOLOGY INC

Año: 2014 vol. 289 p. 5083 - 5096

0021-9258

Natural killer (NK) cells discriminate between healthy and virally infected or transformed cells using receptors that are both activating and inhibitory when interacting with molecules of the Mayor Histocompatibility Complex class I (MHC-I). Among them, the homodimeric Ly49 receptors, which can adopt two distinct conformations (backfolded and extended), are of particular importance for detecting cells infected with mouse cytomegalovirus (MCMV) via recognition of the viral immunoevasin m157. The interactions Ly49H/H-2Dd, Ly49I/H-2Dd and Ly49G/H-2Dk were studied. Thermodynamic and kinetic experiments were carried out to elucidate the Ly49/MHC-I binding mechanism. Combining surface plasmon resonance (SPR), fluorescence anisotropy (FA), and far-UV circular dichroism (CD), an identical and independent binding sites model was determined, where the MHC-I bind to Ly49 with a ~106 M-1 binding constant. There is not a strong positive cooperativity such as seen with the interactions between Ly49 and viral ligand m157. The rate-limiting step of the overall mechanism is the diffusion of the molecules. Using SPR we also studied the Ly49G MHC-I peptide insensitivity, and identified for the first time interactions between activating Ly49 and endogenous ligands in absence of viral ligands.