Galectins
Galectins |
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Structure of human galectin-3 with bound
LacNAc
Beta-strands in one sheet are coloured yellow and those in the opposing sheet, blue. The Gal moiety of LacNAc is shown in yellow and the GlcNAc portion in dark blue. Protein Data Bank structure ID: 1KJL. fDomain organization and dimerization in galectins  |
The galectins consist of globular galectin-type CRDs with relatively minor accessory domains. A galectin-type CRD comprises a/b sandwich similar in overall topology to the L-type CRDs. However, the lack of sequence similarity and the different way in which sugar-binding sites are constructed in these two families of domains suggest that this topological similarity results from convergent evolution. Although mammalian galectins lack conventional signal sequences, they reach the cell surface by a novel mechanism and bind to glycoconjugates on the plasma membrane and in the extracellular matrix. Most galectins contain multiple sugar-binding sites, due to the presence of two galectin-type CRDs in a single polypeptide or as a result of dimerization. A common function of the galectins may be to crosslink N-acetyllactosamine-containing structures found at cell surfaces and in the extracellular matrix. Comparison of all the galectin sequences reveals conservation primarily of inwardly facing hydrophobic residues in beta strands in the beta-sandwich of the galectin fold. Eight residues that form the galactoside-binding site are conserved in most mammalian galectins, although a vertebrate galectin containing only six of the canonical galactose-binding residues interacts with mannose rather than galactose. |
Structure adapted from Bourne Y et al. (1994) Nature Struct. Biol.,1:863.
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