Ligands for the β-glucan receptor, Dectin-1, assigned using designer microarrays of oligosaccharide probes (neoglycolipids) generated from glucan polysaccharides

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 beta- glucan-rich extract of Saccharomyces cerevisiae, and binding is inhibited by polysaccharides rich in beta 1,3- or both beta 1,3- and beta 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 beta- glucans and compete with zymosan binding and triggering of tumor necrosis factor-alpha secretion by a Dectin- 1- expressing macrophage cell line.