The lectin-like NK cell receptor Ly-49A recognizes a carbohydrate-independent epitope on its MHC class I ligand

The mouse NK inhibitory Ly-49A receptor specifically interacts with a peptide-induced conformational determinant on its MHC class I ligand, H-2D(d). In addition, it binds the polysaccharide fucoidan, consistent with its C-type lectin homology and the hypothesis that Ly-49A interacts with carbohydrates on D-d. Herein, however, we demonstrate that Ly-49A recognizes D-d mutants lacking N-glycosylation. Fucoidan competes for binding with anti-Ly-49A antibodies that inhibit Ly-49A-D-d interaction, and blocks apparent Ly-49A binding to unglycosylated D-d. We confirm that Ly-49A recognizes the alpha 1 and amino-terminal alpha 2 domains of D-d by analysis of recombinant H-2K(d)-H-2D(d) molecules. These studies indicate that Ly-49A recognizes carbohydrate-independent epitope(s) on D-d and suggest that Ly-49A has two distinct ligands, carbohydrate and MHC class I.