Binding Affinities of NKG2D and CD94 to Sialyl Lewis X-Expressing N-Glycans and Heparin

Abstract

Lectin-like receptors natural killer group 2D (NKG2D) and CD94 on natural killer (NK) cells bind to α2,3-NeuAc-containing N-glycans and heparin/heparan sulfate (HS). Using recombinant glutathione S-transferase-fused extracellular lectin-like domains of NKG2D (rGST-NKG2Dlec) and CD94 (rGST-CD94lec), we evaluated their binding affinities (K_d) to high sialyl Lewis X (sLeX)-expressing transferrin secreted by HepG2 cells (HepTf) and heparin-conjugated bovine serum albumin (Heparin-BSA), using quartz crystal microbalance (QCM) and enzyme immunoassay (EIA) microplate methods. K_d values obtained by linear reciprocal plots revealed good coincidence between the two methods. K_d values of rGST-NKG2Dlec obtained by QCM and EIA, respectively, were 1.19 and 1.11 μM for heparin-BSA >0.30 and 0.20 μM for HepTf, while those of rGST-CD94lec were 1.31 and 1.45 μM for HepTf >0.37 and 0.36 μM for heparin-BSA. These results suggested that these glycans can interact with NKG2D and CD94 to modulate NK cell-dependent cytotoxicity.