Evaluation of antimicrobial activity of a lectin isolated and purified from Indigofera heterantha

Indigofera heterantha commonly called indigo bush is a member of leguminoseae family found in the Himalayan region of Kashmir. A lectin has been isolated from the seeds of Indigofera heterantha by the purification procedure involving anion exchange chromatography on DEAE-cellulose followed by gel filtration chromatography on Sephadex G 100. Molecular characterization of the lectin was done by gel filtration and SDS-PAGE. Activity of the lectin was checked by hemagglutination assay and the sugar specificity by sugar inhibition tests. The antimicrobial activity of the purified lectin was carried out by Agar disc diffusion using appropriate standards. On the ion exchange column, the bound protein when eluted with 0-0.5 M NaCl gradient emerged as three peaks—peak I, peak II and peak III out of which only peak II showed the hemagglutinating activity. The lectin further resolved into two peaks G1 and G2 on gel filtration, with the lectin activity residing in G1, corresponding to a molecular weight of 70 KDa. The purified lectin named as Indigofera heterantha Lectin (IHL) produced a single band on SDS PAGE (18 KDa), revealing the tetrameric nature of the lectin. It agglutinated human erythrocytes (A, B, AB, and O). Hemagglutination was inhibited by D-galactose, Dmannose and D-arabinose. The lectin is reasonably thermostable showing full activity within a temperature range of 30°C to 90°C. pH stability of the lectin falls in the range of 2-9. IHL demonstrated a remarkable antibacterial activity against the pathogenic bacteria Klebsiella pneumoniae, Staphylococcus aureus, Escherichia coli, and Bacillus subtilis. IHL also inhibited the growth of phytopathogenic fungi Aspergillus niger, Aspergillus oryzae and Fusarium oxysporum.