1afa
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STRUCTURAL BASIS OF GALACTOSE RECOGNITION IN C-TYPE ANIMAL LECTINS
OverviewOverview
The asialoglycoprotein receptors and many other C-type (Ca2+-dependent), animal lectins specifically recognize galactose- or, N-acetylgalactosamine-terminated oligosaccharides. Analogous binding, specificity can be engineered into the homologous rat mannose-binding, protein A by changing three amino acids and inserting a glycine-rich loop, (Iobst, S. T., and Drickamer, K. (1994) J. Biol. Chem. 269, 15512-15519)., Crystal structures of this mutant complexed with beta-methyl galactoside, and N-acetylgalactosamine (GalNAc) reveal that as with wild-type, mannose-binding proteins, the 3- and 4-OH groups of the sugar directly, coordinate Ca2+ and form hydrogen bonds with amino acids that also serve, as Ca2+ ligands. The different stereochemistry of the 3- and 4-OH groups, in mannose and galactose, combined with a fixed Ca2+ coordination, geometry, leads to different pyranose ring locations in the two cases. The, glycine-rich loop provides selectivity against mannose by holding a, critical tryptophan in a position optimal for packing with the apolar face, of galactose but incompatible with mannose binding. The 2-acetamido, substituent of GalNAc is in the vicinity of amino acid positions, identified by site-directed mutagenesis (Iobst, S. T., and Drickamer, K., (1996) J. Biol. Chem. 271, 6686-6693) as being important for the formation, of a GalNAc-selective binding site.
About this StructureAbout this Structure
1AFA is a Single protein structure of sequence from Rattus norvegicus with MBG, CA and CL as ligands. Full crystallographic information is available from OCA.
ReferenceReference
Structural basis of galactose recognition by C-type animal lectins., Kolatkar AR, Weis WI, J Biol Chem. 1996 Mar 22;271(12):6679-85. PMID:8636086
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