Purification and characterization of an Anti-proliferative and mitogenic plant lectin from tubers of Arisaema speciosum

A novel lectin having specificity for N-acetyllactosamine was purified from the tubers of Arisaema speciosum Martius (family: Araceae) by affinity chromatography on asialofetuin-linked amino activated silica beads. The lectin have four identical subunits of 13.5 kDa each and native molecular mass of 51.2 kDa. ASL agglutinated rabbit, rat, sheep and guinea pig erythrocytes but human ABO blood group erythrocytes were not even after neuraminidase treatment. ASL gave as single band on native PAGE, pH 4.5 and multiple bands in isoelectric focusing and at PAGE 8.3. ASL is a glycoprotein with 0.7% carbohydrate content, stable up to 50°C and at pH 2 to 10. The lectin had no requirement for divalent cations and was stable up to 4M Urea, 3M thiourea and 3M Guanidine-HCl. ASL was rich in acidic amino acids but cysteine was completely absent. Amino acid modification revealed the involvement of tryptophan and tyrosine residues in lectin sugar interaction. The secondary structure estimated in far UV CD spectrum was 38% α-helix, 27% β-sheet and 35% random contributions. ASL showed mitogenic potential towards human peripheral blood mononuclear cell. ASL produced more that 50% growth inhibition of seven human cancer cell lines viz. SW-620, IMR-32, PC-3, SK-N-SH, Colo-205, HCT-15 and HT-29 at 100 μg/ml out of eleven cell lines used.