NKG2D: Binding Properties for Glycan Ligands, and Mutagenesis Analysis

Killer lectin-like receptor NKG2D, which is found on natural killer cells, recognizes MHC class 1-related ligands and also interacts with glycan ligands, heparin-conjugated bovine serum albumin (heparin-BSA) and sialyl Lewis X (sLeX) on multi-antennary N-glycans on transferrin secreted by HepG2 cells (HepTF). Using the glutathione-S- transferase-fused extracellular domain (AA 73-216) of NKG2D (rGST-NKG2D) and seven site-directed mutants, we ex- plored in detail the binding of NKG2D to sulfate-containing glycan-BSA and HepTF. rGST-NKG2D binds to sulfate- containing glycan-BSA with Kd values of 25 nM ±15 for  -carrageenan-BSA, 66 ±23 nM for fucoidan-BSA, and 1.5±0.5 μM for heparan sulfate-BSA. Of the site-directed rGST-NKG2D mutants, Y152A, Q185A, K197A, Y199A, E201A, and N207A reduced binding to these glycans. These results indicate that NKG2D interacts with highly sulfated- and  2,3- NeuAc-containing glycans and suggest that the glycan-binding sites on NKG2D are shared between sulfate- and  2,3- NeuAc-containing glycans, and might overlap with protein ligand binding sites.