A disulfide-linked natural killer cell receptor dimer has higher affinity for HLA-C than wild-type monomer

Inhibitory receptors on the surface of natural killer (NK) cells recognize specific MHC class I molecules on target cells and prevent the target cell lysis by NK cells. The killer cell immunoglobulin-related receptors (KIR), KIR2D, found in human, specifically interact with polymorphic HLA-C molecul es. The crystal structure of the inhibitory receptor, KIR2DL1, revealed a r elationship to the hematopoietic receptor family, suggesting that the signa ling mechanism of KIR2D molecules may resemble that of the hematopoietic re ceptors, and involve KIR2D dimerization. We have engineered a disulfide-lin ked dimer of KIR2DL1 by introducing a free cysteine at the C-terminal stem region of the receptor. The disulfide-linked KIR2DL1 dimer binds to HLA-Cw4 at a molar ratio of one dimer to one HLA-Cw4 molecule. Furthermore. the co valently-linked KIR2DL1 dimer binds more tightly to HLA-Cw4 than the wild-t ype monomer, suggesting the occurrence of a second binding event that incre ases the overall affinity of KIR dimer for HLA-C.