Kinetic and Thermodynamic Studies of the Interaction between Activating and Inhibitory Ly49 Natural Killer Receptors and MHC Class I Molecules

ROMASANTA PABLO; CURTO L; SARRATEA MB; NOLY TRUANT S; ANTONOGLOU B; JULIETA FERNÁNDEZ LYNCH; DELFINO JM; MARIUZZA RA; FERNÁNDEZ MARISA; MALCHIODI EL

BIOCHEMICAL JOURNAL

PORTLAND PRESS LTD

Lugar: Londres; Año: 2016

0264-6021

Natural killer (NK) cells are lymphocytesof the innate immune system that eliminate virallyinfected or malignantly transformed cells. NK cellfunction is regulated by diverse surface receptorsthat are both activating and inhibitory. Amongthem, the homodimeric Ly49 receptors control NKcell cytotoxicity by sensing majorhistocompatibility complex class I (MHC-I)molecules on target cells. Although crystalstructures have been reported for Ly49/MHC-Icomplexes, the underlying binding mechanism hasnot been elucidated. Accordingly, we carried outthermodynamic and kinetic experiments on theinteraction of four Ly49 receptors (Ly49G, Ly49H,Ly49I and Ly49P) with two MHC-I ligands (H-2Dd and H-2Dk). These Ly49s embrace thestructural and functional diversity of the highlypolymorphic Ly49 family. Combining surfaceplasmon resonance, fluorescence anisotropy, andfar-UV circular dichroism (CD), we determinedthat the best model to describe both inhibitory andactivating Ly49/MHC-I interactions is one inwhich the two MHC-I binding sites of the Ly49homodimer are identical and independent, withsimilar binding constants for the two sites (~106M?1) and without far-UV CD observableconformational changes. Furthermore, Ly49/MHCIinteractions are diffusion-controlled andenthalpy-driven. These features stand in markedcontrast to the activation-controlled and entropydriveninteraction of Ly49s with the viralimmunoevasin m157, which is characterized bypositive cooperativity and conformationalselection. These differences are explained by thedistinct structures of Ly49/MHC-I and Ly49/m157complexes. Moreover, they reflect the opposingroles of NK cells to rapidly scan for virallyinfected cells, and of viruses to escape detectionusing immunoevasins such as m157.