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 Hima-layan region of Kashmir. A lectin has been isolated from the seeds of Indigofera heterantha by the purifi-cation procedure involving anion exchange chroma-tography on DEAE-cellulose followed by gel filtration chromatography on Sephadex G 100. Molecular cha- racterization 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 diffu- sion using appropriate standards. On the ion ex- change 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 fur- ther resolved into two peaks G1 and G2 on gel filtra- tion, with the lectin activity residing in G1, corre- sponding to a molecular weight of 70 KDa. The puri- fied 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, D- mannose and D-arabinose. The lectin is reasonably thermostable showing full activity within a tempera- ture range of 30 degree C to 90 degree C. pH stability of the lectin falls in the range of 2 - 9. IHL demonstrated a re- markable antibacterial activity against the pathogenic bacteria Klebsiella pneumoniae, Staphylococcus au- reus, Escherichia coli, and Bacillus subtilis. IHL also inhibited the growth of phytopathogenic fungi Asper- gillus niger, Aspergillus oryzae and Fusarium oxys- porum.