C-type lectins
C-type lectins |
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Mannose binding protein (MBP)
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Ca2+-dependent (C-type) CRDs provide the sugar recognition activity in a variety of cell surface and extracellular lectins. Other modules in these proteins then initiate biological processes such as adhesion, endocytosis and complement fixation. Binding of carbohydrate ligands to the C-type CRD is through a Ca2+ ion that stabilizes the local conformation of the protein and makes coordination bonds to the surface of the protein and to key hydroxyl groups of the sugar ring. Amino acid residues that coordinate the bound Ca2+ also make hydrogen bonds to the sugar hydroxyl groups. Binding of monosaccharide residues in specific orientations is sometimes further stabilized by hydrophobic interactions. Binding of oligosaccharide ligands with high affinity results from extension of this binding site within a single CRD or from multivalent interactions of multi-antennary glycans with clusters of CRDs.
The
C-type CRDs form a subgroup of a large family of protein domains that are
designated C-type lectin-like domains (CTLDs). Many CTLDs bind to protein
ligands rather than to sugars and only some of these binding interactions
are Ca2+ dependent. Part II of this website provides an extensive analysis of CTLDs in mammals and model organisms. |
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