The Plasticity of Carbohydrate Recognition Domain Dictates the Exquisite Mechanism of Binding of Human Macrophage Galactose-Type Lectin

Human macrophage galactose-type lectin (MGL), expressed on macrophages and dendritic cells (DCs), modulates distinct immune cell responses by recognizing GalNAc-containing structures present on pathogens, self-glycoproteins and tumor cells. Herein, we used NMR spectroscopy and molecular dynamics (MD) simulations to investigate the structural preferences of MGL against different GalNAc-containing structures derived from blood group A antigen, Forssman antigen and the GM2 glycolipid. NMR analyses of the MGL carbohydrate recognition domain (MGL-CRD, C181-H316) in the absence and presence of α-methyl GalNAc, a simple monosaccharide, shows that the MGL-CRD is highly dynamic and its structure is strongly altered upon ligand binding. This plasticity of the MGL-CRD structure explains the ability of MGL to accommodate different GalNAc-containing molecules. However, key differences are observed in the recognition process reliant whether the GalNAc is part of the blood group A antigen, the Forssman antigen or GM2-derived structures. These results are in accordance with molecular dynamics simulations that suggest the existence of a distinct MGL binding mechanism depending on the context of GalNAc moiety presentation. These results afford new perspectives for the rational design of GalNAc modifications able to fine tune MGL immune responses in distinct biological contexts, especially in malignancy.