The crystal structure of a lectin from Butea monosperma: insight into its glycosylation and binding of ligands

Crystal structure of a lectin purified from Butea monosperma seeds was determined by Molecular Replacement method. Its primary structure was determined by Tandem Mass Spectroscopy and electron density maps from X-ray diffraction data. Its quaternary structure was tetrameric, formed of two monomers, α and β, β appearing as truncated α. The occurrence of two tetramers in the asymmetric unit of the crystal might be a consequence of asymmetric contacts due to difference in glycosylation and variable loops structures, to form an 'octamer-structure'. The crystal structure showed binding pockets for γAbu, having a proposed role in plant defense, at the interface of canonical dimer-partners. Hemagglutination studies, enzyme kinetics, isothermal titration calorimetry and molecular dynamics showed that the lectin is specific to N-acetyl d-galactosamine, galactose and lactose in decreasing order, and α-amylase inhibitor.