Cobalt-mediated dimerization of the human natural killer cell inhibitory receptor

Upon engagement of specific class I major histocompatibility complex (MHC) molecules on target cells, inhibitory receptors on natural killer (NK) cell s deliver a negative signal that prevents the target cell lysis by NK cells . In humans, killer cell immunoglobulin-related receptors (KIR) with two im munoglobulin-like domains (KIR2D) modulate the lysis of target cells bearin g specific HLA-C alleles (Moretta, A., Vitale, M., Bottino, C., Orengo, A. M., Morelli, L., Augugliaro, R., Barbaresi, M., Ciccone, E., and Moretta, L . (1993) J. Exp. Med. 178, 597-604). The transduction of inhibitory signals by KIR2D molecules is impaired by the zinc chelator, 1,10-phenanthroline, and mutation of a putative zinc-binding site (Rajagopalan, S., and Long, E. O. (1998) J. Immunol. 161, 1299-1305), but the mechanism by which zinc may affect the function of KIR remains unknown. In this study, the inhibitory NK receptor KIR2DL1 was discovered to dimerize in the presence of Co2+ as o bserved on native gel electrophoresis and by gel filtration column chromato graphy. Furthermore, Co2+-mediated KIR2DL1 dimer binds to HLA-Cw4 with high er affinity than the wild type KIR2DL1 monomer. Replacement of the amino-te rminal His residue by Ala abolishes the ability of KIR2DL1 to bind Co2+, in dicating that Co2+-mediated KIR2DL1 dimerization involves pairing of the D1 domain. Although not observed on native gels, the inhibitory receptor KIR2 DL1 can be chemically cross-linked into dimers in the presence of Zn2+ and its related divalent metal ions, suggesting that Co2+-mediated dimerization of KIR2DL1 may mimic a weaker interaction between KIR2DL1 and zinc in vivo .