Lectins are the main class of protein which recognize glycans. A member of the C-type lectin family is CLEC10A (h-MGL, CD301), an endocytic receptor located on the surface of immature dendritic cells (DCs) and macrophages. The carbohydrate recognition domain shows exceptional selectivity for α/βGalNAc derivatives, such as Tn antigen and other tumor associated antigens. The binding is calcium dependent and the QPDxW epitope plus the His 284 (full MGL numbering) are indispensable for binding and GalNAc selectivity .
In this work we present the first crystal structure of the carbohydrate recognition domain (CRD) of h-CLEC10A with GalNAc derivatives, including the Tn antigen. The X-ray crystal structure reveals that ligands bind in mode typically defined for lectins as binding mode A.
A previous study in solution  by NMR and molecular dynamics models led to the proposal of mode B being favoured over mode A (4:1 ratio).
The structure shows that binding mode A has interactions of the GalNAc H-3 and H-4, polarized by coordination to a calcium ion, with the indole ring of Trp 271 and also shows hydrogen bonding of the acetamide group to His 286.
The crystal structure packing showed trimerisation of the CRDs. This is independent from the area where the coiled coil neck region would be located, the latter which is believed to induce trimerization. Furthermore, various ligands for the CRD of CLEC10A and the full-length CLEC10A, including glycoculsters, were investigated further by isothermal calorimetry and microscale thermophoresis.
The structural work provides opportunities for structure based ligand or glycocluster design.
- Higashi, N.; Fujioka, K.; Denda-Nagai, K.; Hashimoto, S. I.; Nagai, S.; Sato, T.; Fujita, Y.; Morikawa, A.; Tsuiji, M.; Miyata-Takeuchi, M.; et al. ; J. Biol. Chem. 2002, 277 (23), 20686–20693.
- Marcelo, F.; Garcia-Martin, F.; Matsushita, T.; Sardinha, J.; Coelho, H.; Oude-Vrielink, A.; Koller, C.; André, S.; Cabrita, E. J.; Gabius, H. J.; et al.Chem. ; A Eur. J. 2014, 20 (49), 16147–16155.
- Hudson, K. L.; Bartlett, G. J.; Diehl, R. C.; Agirre, J.; Gallagher, T.; Kiessling, L. L.; Woolfson, D. N. ; J. Am. Chem. Soc. 2015, 137 (48), 15152–15160.