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

Abstract

The human macrophage galactose‐type lectin (MGL), expressed on macrophages and dendritic cells (DCs), modulates distinct immune cell responses by recognizing N‐acetylgalactosamine (GalNAc) containing structures present on pathogens, self‐glycoproteins, and tumor cells. Herein, NMR spectroscopy and molecular dynamics (MD) simulations were used to investigate the structural preferences of MGL against different GalNAc‐containing structures derived from the blood group A antigen, the Forssman antigen, and the GM2 glycolipid. NMR spectroscopic analysis of the MGL carbohydrate recognition domain (MGL‐CRD, C181‐H316) in the absence and presence of methyl α‐GalNAc (α‐MeGalNAc), 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 depending on 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 that fine tune MGL immune responses in distinct biological contexts, especially in malignancy.

Activation of the C-Type Lectin MGL by Terminal GalNAc Ligands Reduces the Glycolytic Activity of Human Dendritic Cells

“…This secondary binding site of MGL binds the peptide backbone of Tn-containing glycopeptide ligands, and is essential for the binding of cancer-associated Tn epitopes on tumor cell lines (19). Recent evidence points to ligandspecific conformational changes in the MGL carbohydrate binding domain (11), raising the intriguing possibility that each individual MGL ligand may activate different signaling cascades, and thus a different transcriptional program in the DC. This hypothesis would also explain the differential effects we observed between the two terminal GalNAc structures used in this study.…”

“…To investigate the effect of MGL ligation on moDC biology, we generated control dendrimers and two different glycodendrimers exposing the MGL ligands αGalNAc or GalNAcβ1-4Gal ( Figure 1B). We choose these ligands based on their differential binding to the secondary binding site present in the MGL carbohydrate recognition domain (11,19). To validate the αGalNAc and GalNAcβ1-4Gal glycodendrimers, lectin binding assays were performed using Helix pomatia agglutinin (HPA) and Vicia villosa lectin (VVL).…”

“…Especially, the macrophage galactose-type lectin receptor (MGL, CD301) has a high preference for tumor-associated glycans and can particularly recognize terminal N-acetylgalactosamine (α-or β-linked GalNAc) residues, as found for instance in the truncated O-glycan Tn antigen (αGalNAc-Ser/Thr), which is predominantly expressed on many cancer cells, including, colorectal, cervical and breast cancer cells, and has been associated with metastasis and poor prognosis (2)(3)(4)(5). MGL is the only C-type lectin receptor within the human immune system that interacts with sialylated and non-sialylated Tn antigen, (asialo)GM2 (GalNAcβ1-4Gal), and the LacdiNAc epitope (GalNAcβ1-4GlcNAc) (6)(7)(8)(9)(10)(11). As a consequence, MGL can discriminate between the healthy and tumor-derived glycoforms of the mucin MUC1 (12).…”

“…While the primary binding site engages the GalNAc monosaccharide, this secondary binding site was essential for binding of the peptide backbone of Tn-containing glycopeptide ligands and for the binding of GalNAc epitopes on tumor cell lines (19). Moreover, binding of different terminal αor β-linked GalNAc ligands to MGL induces strong and unique alterations in the MGL molecular conformation, depending on the presentation and context of the GalNAc moiety (11). This suggests that MGL triggering can result in the activation of different signaling pathways, and thereby differentially affect biological processes, depending on the MGL ligand used.…”

ASGR1 and Its Enigmatic Relative, CLEC10A

“…Hepatic ASGR1 contains the analogous His 257 -Phe-Thr 259 sequence (Figure 1), which may prevent the liver from actively ingesting young, sialylated red blood cells. The sequence in ASGR2 is Glu 257 -Val-Gln 259 and the absence of His seems to reduce the specificity for GalNAc [111].…”