Frontal affinity chromatography analysis of constructs of DC-SIGN, DC-SIGNR and LSECtin extend evidence for affinity to agalactosylated N-glycans

Dendritic cell-specific intracellular adhesion molecule-3-grabbing nonintegrin (DC-SIGN) is a member of the C-type lectin family selectively expressed on immune-related cells. In the present study, we performed a systematic interaction analysis of DC-SIGN and its related receptors, DC-SIGN-related protein (DC-SIGNR) and liver and lymph node sinusoidal endothelial cell C-type lectin (LSECtin) using frontal affinity chromatography (FAC). Carbohydrate-recognition domains of the lectins, expressed as Fc-fusion chimeras, were immobilized to Protein A-Sepharose and subjected to quantitative FAC analysis using 157 pyridylaminated glycans. Both DC-SIGN-Fc and DC-SIGNR-Fc showed similar specificities for glycans containing terminal mannose and fucose, but great difference in affinity under the given experimental conditions. By contrast, LSECtin-Fc showed no affinity to these glycans. As a common feature, the DC-SIGN-related lectin-Fc chimeras, including LSECtin, exhibited binding affinity to mono- and/or bi-antennary agalactosylated N-glycans. The detailed FAC analysis further implied that the presence of terminal GlcNAc at the N-acetylglucosaminyltransferase I position is a key determinant for the binding of these lectins to agalactosylated N-glycans. By contrast, none of the lectins showed significant affinity to highly branched agalactosylated N-glycans. All of the lectins expressed on the cells were able to mediate cellular adhesion to agalactosylated cells and endocytosis of a model glycoprotein, agalactosylated alpha 1-acid glycoprotein. In this context, we also identified three agalactosylated serum glycoproteins recognized by DC-SIGN-Fc (i.e. alpha-2-macroglobulin, serotransferrin and IgG heavy chain), by lectin blotting and MS analysis. Hence, we propose that 'agalactosylated N-glycans' are candidate ligands common to these lectins.