In human tumors, glycoproteins often exhibit abnormal glycosylation patterns, e.g. certain Lewis structures, TF antigen, Tn antigen and/or their sialylated forms, creating additional binding sites for glycoreceptors. In the present study, we have analyzed the carbohydrate specificity of the C-type lectin CLEC10A using glycan profiling by enzyme-linked immunosorbent assay (ELISA). In addition to the known ligands, we show binding to two tumor-associated antigens, namely Neu5Acα2,6-Tn and Neu5Gcα2,6-Tn, with an affinity of CLEC10A in the micromolar range. Detailed analyses of the glycan-lectin interactions were carried out by surface plasmon resonance (SPR) and saturation transfer difference (STD) NMR. CLEC10A binds Neu5Acα2,6-Tn and Neu5Gcα2,6-Tn with dissociation constants of 297 and 80 µM, respectively, as determined by SPR. Comparison of the STD nuclear magnetic resonance (NMR) binding epitopes of Tn and Neu5Acα2,6-Tn revealed a constant binding mode of the N-acetylgalactosamine moiety. This finding is in good agreement with binding studies of CLEC10A transfectomas, which show a well-defined interaction of transmembrane CLEC10A with 6-sialylated-Tn structures. Since both Neu5Acα2,6-Tn and Neu5Gcα2,6-Tn together with the previously known Tn antigen are expressed in human tumors such as mammary carcinoma, the interaction with CLEC10A expressed by macrophages and dendritic cells could be of major functional significance in tumor progression.

Specialized protein domains bind to posttranslational modifications (PTMs) of proteins, such as phosphorylation or glycosylation. When such PTM-binding protein domains are used as analytical tools, the functional states of cells and tissues can be determined with high precision. Here, we describe the use of recombinant CLEC10A (CD301), a human glycoreceptor of the C-type lectin family, for the detection of ligands in sections from formalin-fixed, paraffin-embedded normal and cancerous mammary tissues. A construct, in which part of the carbohydrate recognition domain (CRD) was deleted, was used as a negative control. In comparison to normal mammary glands, a pronounced staining of tumor tissues was observed. Because the construct with the truncated CRD did not show any tissue staining, the binding of the wild-type glycoreceptor can be attributed to its carbohydrate recognition domain. To distinguish our novel approach from immunohistochemistry, we propose the designation "protein domain histochemistry" (PDH).