Three-dimensional structure of favin: saccharide binding-cyclic permutation in leguminous lectins

Area of Science:

• Biochemistry
• Structural Biology
• Molecular Biology

Background:

• Lectins are proteins that bind carbohydrates.
• Favin is a lectin from Vicia faba (broad bean) that binds glucose and mannose.
• Understanding lectin structure is crucial for deciphering their biological roles.

Purpose of the Study:

• To determine the three-dimensional structure of favin.
• To visualize the specific binding of glucose to favin at high resolution.
• To compare the structure of favin with other known leguminous lectins.

Main Methods:

• X-ray crystallography was used to determine the structure.
• Molecular replacement was employed for structure solution.
• Crystallographic data were collected at a resolution of 2.8 angstroms.

Main Results:

• The three-dimensional structure of favin was determined.
• Specific binding of glucose to favin was observed and visualized.
• Favin exhibits an ellipsoidal dimer structure with extensive beta sheets.
• Each protomer contains binding sites for two divalent metal ions (Mn2+ and Ca2+) and a saccharide.
• The carbohydrate-binding site is located in a cleft and involves interactions with peptide loops and metal ion ligands.

Conclusions:

• The study provides the first high-resolution structural insights into specific saccharide binding in a leguminous lectin.
• Favin's structure is similar to concanavalin A, with minor differences accommodating sequence variations.
• The findings enhance understanding of carbohydrate-protein interactions in lectins.