Specific glycan elements determine differential binding of individual egg glycoproteins of the human parasite Schistosoma mansoni by host C-type lectin receptors

Abstract

During infection with the blood fluke Schistosoma mansoni, glycan motifs present on glycoproteins of the parasite’s eggs mediate immunomodulatory effects on the host. The recognition of these glycan motifs is primarily mediated by C-type lectin receptors on dendritic cells and other cells of the immune system. However, it is not yet known which individual glycoproteins interact with the different C-type lectin receptors, and which structural components are involved. Here we investigated the structural basis of the binding of two abundant egg antigens, kappa-5 and IPSE/α1, by the C-type lectin receptor dendritic cell-specific ICAM3-grabbing non-integrin, macrophage galactose-type lectin and mannose receptor. In the natural soluble form, the secretory egg glycoprotein IPSE/α1 interacts with dendritic cells mainly via mannose receptors. Surprisingly, in plate-based assays mannose receptors preferentially bound to mannose conjugates, while in cell-based assays, IPSE/α1 is bound via the fucosylated Galβ1-4(Fucα1-3)GlcNAc (LeX) motif on diantennary N-glycans. Kappa-5, in contrast, is bound by dendritic cells via all three C-type lectin receptors studied and for a minor part also via other, non-C-type lectin receptors. Kappa-5 interacts with macrophage galactose-type lectins via the GalNAcβ1-4GlcNAc antenna present on its triantennary N-glycans, as well as the GalNAcβ1-4(Fucα1-3)GlcNAc antennae present on a minor N-glycan subset. Dendritic cell-specific ICAM3-grabbing non-integrin binding of kappa-5 was mediated via the GalNAcβ1-4(Fucα1-3)GlcNAc antennae, whereas binding of mannose receptors may involve either GalNAcβ1-4(Fucα1-3)GlcNAc antennae or the fucosylated and xylosylated chitobiose core. This study provides a molecular and structural basis for future studies of the interaction between C-type lectin receptors and other soluble egg antigen glycoproteins and their effects on the host immune response.