Identification and molecular characterization of a natural mutant of the p50.2/KIR2DS2 activating NK receptor that fails to mediate NK cell triggering

P50/KIR2DS molecules represent the activating form of the HLA-C-specific in hibitory NK receptors. They are characterized, in the transmembrane portion , by a charged amino acid that is involved in coupling with signal-transduc ing adaptor polypeptides. In this study we identified a novel p50.2/KIR2DS2 surface molecule, isolated from NK cell clones derived from an otherwise n ormal donor, that was unable to transduce activating signals. Sequence anal ysis of the cDNA encoding this molecule revealed six non-conservative codon mutations in the exon coding for the putative transmembrane portion. Notab ly, one of such mutations involved the charged residue lysine thought to be important for the association with signal-transducing polypeptides. Indeed , co-transfection experiments revealed that this naturally occurring p50.2/ KIR2DS2 mutant, termed Mp50.2, displayed a sharply reduced ability to assoc iate with DAP12 polypeptides. These data provide the first in vivo demonstr ation of the crucial role played by the transmembrane region of p50.2 recep tor molecules in the functional association with DAP12 adaptor molecules an d in the process of activation of NK-mediated cytotoxicity.