ABSTRACT
C-type lectins constitute a superfamily of proteins containing C-type lectin-like domains (CTLDs, Figure 6.1), a large and heterogeneous group of extracellular Metazoan proteins with diverse functions. Evolutionary data suggest that sugar binding is the original function of the superfamily, as it is observed in its most distant members. However, many CTLDs have evolved to recognize ligands other than carbohydrates, including proteins, inorganic substances such as ice and calcium carbonate, and lipids. The unique loop-in-a-loop structure of the domain, in which a large fl exible region is maintained on a stable core (Figure 6.1), can accommodate substantial variation in the shape of the ligand-binding region, and allows specifi c binding of large multivalent ligands such
as complex oligosaccharides. Formation of quaternary complexes further increases both specifi city and affi nity of carbohydrate recognition by C-type lectins, and allows them to function in diverse extracellular contexts, such as innate immune defence, turnover of glycosylated proteins, maintenance of the extracellular matrix structure, and cellular adhesion.
