Structure of basic winged-bean lectin and a comparison with its saccharide-bound form

Area of Science:

• Structural biology
• Biochemistry
• Protein crystallography

Background:

• Winged bean agglutinin (WBA) is a lectin known for its carbohydrate-binding properties.
• Understanding the structural basis of WBA's saccharide interaction is crucial for its applications.

Purpose of the Study:

• To elucidate the crystal structure of the saccharide-free form of winged bean agglutinin (WBAI).
• To compare the saccharide-free structure with the WBAI-carbohydrate complex structure.
• To identify structural changes associated with saccharide binding.

Main Methods:

• Molecular replacement method for structure determination.
• X-ray crystallography at 2.3 A resolution.
• Refinement of the crystal structure.

Main Results:

• The saccharide-free WBAI structure was solved, revealing two half-dimers in the asymmetric unit.
• Comparison with the methyl-alpha-D-galactoside complex showed conserved intersubunit interactions.
• The saccharide-binding site in the free form contains ordered water molecules, which are displaced upon ligand binding.

Conclusions:

• The structural data highlights the role of ordered water molecules in the WBAI binding site.
• Saccharide binding involves the expulsion of water and a minor shift in main-chain atoms of the variable loop.
• These findings provide a structural basis for WBA's carbohydrate recognition mechanism.