Metal Ion Coordination Essential for Specific Molecular Interactions of Butea monosperma Lectin: ITC and MD Simulation Studies

Crystal structure of Butea monosperma seed lectin (BML) was analyzed and the metal ion geometry identified. In order to understand the role of metal ions for the structural stability and ligand binding, studies of demetallized protein were carried out. Binding of different ligands like GalNAc, lactose, and galactose onto native and demetallized protein was studied by isothermal titration calorimetry as well as molecular simulation methods. Molecular dynamics was applied to the structure after removing the coordinates of metal ions, to identify the effect of demetallization in silico. Docking studies of different sugar molecules as well as the fungal α-amylase was carried out and compared the interactions in the native and apo states. It was found that metal ions are important for the ligand binding with increased affinity. However, their absence did not make any alteration to the secondary structure. Though the metal ions were not coordinated to the loops contacting the α-amylase, the absence of metal ions reduced the protein-protein binding strength due to long-range changes in irregular structures of the lectin.