Binding of sugar ligands to Ca(2+)-dependent animal lectins. II. Generation of high-affinity galactose binding by site-directed mutagenesis.
Changes have been introduced into the Ca(2+)-dependent carbohydrate-recognition domain (CRD) of rat serum mannose-binding protein by site-directed mutagenesis to model the binding sites of homologous galactose-binding CRDs. Binding assays reveal that galactose-binding activity nearly identical to that of the CRD from the asialoglycoprotein receptor can be introduced into the mannose-binding site by 3 single amino acid changes and insertion of a segment of 5 amino acids. Separate changes are required to establish high-affinity binding to galactose and create high selectivity by exclusion of mannose from the binding site. The mutagenesis studies and NMR analysis of sugar-CRD titrations demonstrate that an important component of high-affinity galactose binding is interaction between the B face of the sugar and tryptophan. The binding properties of the C-type CRD from the cartilage proteoglycan, aggrecan, can also be modeled based on the mannose-binding CRD frame-work. This lower affinity binding site involves stacking of a phenylalanine residue against the sugar ligand.[1]References
- Binding of sugar ligands to Ca(2+)-dependent animal lectins. II. Generation of high-affinity galactose binding by site-directed mutagenesis. Iobst, S.T., Drickamer, K. J. Biol. Chem. (1994) [Pubmed]
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