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-2Dd. In addition, it binds the polysaccharide fucoidan, consistent with its C-type lectin homology and the hypothesis that Ly-49A interacts with carbohydrates on Dd. Herein, however, we demonstrate that Ly-49A recognizes Dd mutants lacking N-glycosylation. Fucoidan competes for binding with anti-Ly-49A antibodies that inhibit Ly-49A-Dd interaction, and blocks apparent Ly-49A binding to unglycosylated Dd. We confirm that Ly-49A recognizes the alpha1 and amino-terminal alpha2 domains of Dd by analysis of recombinant H-2Kd-H-2Dd molecules. These studies indicate that Ly-49A recognizes carbohydrate-independent epitope(s) on Dd and suggest that Ly-49A has two distinct ligands, carbohydrate and MHC class I.