Changes in the three-dimensional structure of concanavalin A upon demetallization

Area of Science:

• Biochemistry
• Structural Biology
• Protein Science

Background:

• Concanavalin A is a lectin that requires specific metal ions for saccharide binding.
• The native protein contains manganese (Mn2+) and calcium (Ca2+) ions essential for its function.
• Demetallization of concanavalin A leads to a loss of saccharide-binding capability.

Purpose of the Study:

• To investigate the structural consequences of removing essential metal ions from concanavalin A.
• To compare the crystal structures of native (holo-) and demetallized (apo-) concanavalin A.
• To elucidate how structural changes affect the protein's saccharide-binding properties.

Main Methods:

• X-ray crystallography was used to determine the structures of both native and demetallized concanavalin A.
• Automated difference Fourier methods were employed for structure refinement.
• Comparative structural analysis was performed to identify differences between the two forms.

Main Results:

• Significant structural differences were observed primarily in the metal-binding region of the demetallized protein.
• A loop containing metal ligands (residues 7-25) underwent reorganization and became disordered.
• Conformational changes involved residues implicated in saccharide binding, and a cis peptide bond at alanine-207 was altered.

Conclusions:

• The absence of Mn2+ and Ca2+ ions induces substantial structural rearrangements in concanavalin A.
• These conformational changes in the metal-binding site are responsible for the loss of saccharide-binding activity.
• The study highlights the critical role of metal ions in maintaining the functional conformation of concanavalin A.