Ligands for the β-Glucan Receptor, Dectin-1, Assigned Using “Designer” Microarrays of Oligosaccharide Probes (Neoglycolipids) Generated from Glucan Polysaccharides

Abstract

Dectin-1 is a C-type lectin-like receptor on leukocytes that mediates phagocytosis and inflammatory mediator production in innate immunity to fungal pathogens. Dectin-1 lacks residues involved in calcium ligation that mediates carbohydrate-binding by classical C-type lectins; nevertheless, it binds zymosan, a particulate ␤-glucan-rich extract of Saccharomyces cerevisiae, and binding is inhibited by polysaccharides rich in ␤1,3-or both ␤1,3-and ␤1,6-linked glucose. The oligosaccharide ligands on glucans recognized by Dectin-1 have not yet been delineated precisely. It is also not known whether Dectin-1 can interact with other types of carbohydrates. We have investigated this, since Dectin-1 shows glucan-independent binding to a subset of T-lymphocytes and is involved in triggering their proliferation. Here we assign oligosaccharide ligands for Dectin-1 using the neoglycolipid-based oligosaccharide microarray technology, a unique approach for constructing microarrays of lipid-linked oligosaccharide probes from desired sources. We generate "designer" microarrays from three glucan polysaccharides, a neutral soluble glucan isolated from S. cerevisiae and two bacterial glucans, curdlan from Alcaligenes faecalis and pustulan from Umbilicaria papullosa, and use these in conjunction with 187 diverse, sequence-defined, predominantly mammalian-type, oligosaccharide probes. Among these, Dectin-1 binding is detected exclusively to 1,3-linked glucose oligomers, the minimum length required for detectable binding being a 10-or 11-mer. Thus, the ligands assigned so far are exogenous rather than endogenous. We further show that Dectin-1 ligands, 11-13 gluco-oligomers, in clustered form (displayed on liposomes), mimic the macromolecular ␤-glucans and compete with zymosan binding and triggering of tumor necrosis factor-␣ secretion by a Dectin-1-expressing macrophage cell line.Dectin-1 is the main receptor on leukocytes that mediates innate immunity to fungal pathogens (1, 2). It is a germ line-encoded membrane-associated cell surface glycoprotein, first identified on a mouse dendritic cell line and cultured Langerhans cells (3) and on a murine macrophage cell line (4). It is now known to be also expressed at the surface of monocytes and neutrophils and at low levels on a subpopulation of T-cells (5). Studies of the tissue distribution of the murine Dectin-1 by immunohistochemistry have shown it to be expressed in the spleen, thymus, liver, lung, and gut and at low levels in the skin, but it is not detectable in the brain, heart, kidney, or eye (6). The human homologue of Dectin-1 has also been characterized (4, 7-9) and resembles the murine protein but differs in that the transcript is alternatively spliced, resulting in two major and several minor isoforms. The major isoforms appear to serve the same immune function as the murine receptor (10).The deduced amino acid sequence of Dectin-1 is that of a type II transmembrane protein, with an extracellular lectin-like domain at the C terminus followed by a stalk region and a short cyto...

The Pattern Recognition Receptor Dectin-1: From Fungi to Mycobacteria

“…In regard to the Dectin-1 ligand, there are no published reports of mycobacteria expressing β-1,3-glucans, although mycobacteria have been shown to express α-glucans [46,47]. However, biochemical studies do not support a role for α-glucans as Dectin-1 ligands [48]. Nevertheless, as shown with the β-glucans, the molecular weight, branching and tertiary structure of a specific α-glucan may dictate its binding affinity for Dectin-1.…”

Syk‐dependent ERK activation regulates IL‐2 and IL‐10 production by DC stimulated with zymosan

“…In contrast, IL-10 production is largely TLR independent, but requires the spleen tyrosine kinase, Syk, which can be activated by dectin-1 engagement [21]. Dectin-1 is a C-type lectin that binds the b-glucan component of zymosan with high affinity [23][24][25] and couples to Syk activation via a novel "hemITAM" motif [21]. Interestingly, both TLR2/ MyD88 and dectin-1/Syk signalling are required for the induction of maximal IL-2 levels in response to zymosan, indicating that not only can these pathways operate autonomously, but they can also collaborate in eliciting cytokine production from DC [21].…”

Danger, intracellular signaling, and the orchestration of dendritic cell function in skin sensitization

“…However, more recently, CLR that can bind carbohydrates independently of calcium have been identified. One such CLR is the PAMP receptor dectin-1; a receptor that recognizes foreign (fungal) β-1,3-glucans (Palma et al, 2006). Upon ligand binding, the intracellular domain of dectin-1 is phosphorylated by a src family kinase and subsequently Syk is recruited (Diebold, 2009).…”