Laboratory of Immunogenetics, National Institute of Allergy and Infectious Diseases, National Institutes of Health, Rockville, MD 20852-1727, USA.
Abstract: The lysis of target cells by human NK cells is inhibited by several kinds of receptors with varying specificities for the MHC class I molecules of target cells. The requirements for complete inhibition of NK cytotoxicity appear to be complex and not well defined. The HLA-C-specific members of the killer cell-inhibitory receptor (KIR) family, carrying two Ig domains (KIR2D), are unusual among Ig superfamily members in their ability to bind zinc. A role for the zinc-binding site in KIR-mediated inhibition was demonstrated in this study using a functional reconstitution system in NK cells. Replacement of six histidines by alanine residues in putative zinc binding sites of a KIR2D ablated zinc binding and markedly impaired its inhibitory function, but left intact its ability to bind HLA-C and to transduce a positive signal through an immunoreceptor tyrosine-based activation motif grafted onto its cytoplasmic tail. Thus, zinc modulates specifically the negative signal transmitted by this KIR molecule. Mutation of an exposed amino-terminal zinc-binding motif alone was sufficient to impair the inhibitory function of KIR. The data suggest that complete inhibition of HLA-C-specific NK cells requires a zinc-dependent protein-protein interaction via the amino-terminal end of KIR2D.