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Structural basis of galactose recognition by C-type animal lectins
1Department of Structural Biology, Stanford University School of Medicine, Stanford, California 94305, USA.
The Journal of Biological Chemistry
|March 22, 1996
Summary
Researchers engineered a rat mannose-binding protein to recognize galactose and N-acetylgalactosamine. Structural analysis revealed key amino acid changes and a glycine-rich loop conferring specific sugar-binding properties.
Area of Science:
- Biochemistry
- Structural Biology
- Molecular Recognition
Background:
- C-type animal lectins, including asialoglycoprotein receptors, bind galactose- or N-acetylgalactosamine-terminated oligosaccharides.
- Mannose-binding proteins (MBPs) are homologous to these lectins but typically bind mannose.
Purpose of the Study:
- To engineer rat MBP-A to exhibit binding specificity for galactose and N-acetylgalactosamine.
- To elucidate the structural basis for this altered lectin specificity.
Main Methods:
- Site-directed mutagenesis to alter amino acids in rat MBP-A.
- Introduction of a glycine-rich loop into the MBP-A structure.
- X-ray crystallography of the mutant MBP-A complexed with ligands (beta-methyl galactoside and N-acetylgalactosamine).
Main Results:
- The engineered rat MBP-A mutant specifically recognizes galactose and N-acetylgalactosamine.
- Crystal structures show that sugar hydroxyl groups coordinate Ca2+ ions, similar to wild-type MBPs.
- A glycine-rich loop positions a tryptophan residue, favoring galactose binding over mannose.
- The 2-acetamido group of N-acetylgalactosamine interacts with specific amino acid residues crucial for its selective binding.
Conclusions:
- Specific amino acid substitutions and loop insertion can engineer C-type lectin binding specificity.
- The structural mechanisms involve precise coordination of calcium ions and steric interactions driven by the sugar's stereochemistry and substituents.