Characterization of β-glucan recognition site on C-type lectin, dectin 1

Dectin I is a mammalian cell surface receptor for (1-->3)-beta-D-glucans. Since (1-->3)-beta-D-glucans are commonly present on fungal cell walls, it has been suggested that dectin I is important for recognizing fungal invasion. In this study we tried to deduce the amino acid residues in dectin I responsible for beta-glucan recognition. HEK293 cells transfected with mouse dectin I cDNA could bind to a gel-forming (1-->3)-beta-D-glucan, schizophyllan (SPG). The binding of SPG to a dectin I transfectant was inhibited by pretreatment with other beta-glucans having a (1-->3)-beta-D-glucosyl linkage but not by pretreatment with alpha-glucans. Dectin 1 has a carbohydrate recognition domain (CRD) consisting of six cysteine residues that are highly conserved in C-type lectins. We prepared 32 point mutants with mutations in the CRD and analyzed their binding to SPG. Mutations at Trp(221) and His(223) resulted in decreased binding to beta-glucan. Monoclonal antibody 4112, a dectin-1 monoclonal antibody which had a blocking effect on the P-glucan interaction, completely failed to bind the dectin-1 mutant W221A. A mutant with mutations in Trp(221) and His(223) did not have a collaborative effect on Toll-like receptor 2-mediated cellular activation in response to zymosan. These amino acid residues are distinct from residues in other sugar-recognizing peptide sequences of typical C-type lectins. These results suggest that the amino acid sequence W221-I222-H223 is critical for formation of a beta-glucan binding site in the CRD of dectin 1.