Purification and characterization of three galactose specific lectins from sajna (Moringa oleifera L.) leaves

Three lectins designated as SLL-1, SLL-2 and SLL-3 were purified from small sized Sajna (Moringa oleifera L.) leaves by gel filtration of 100% ammonium sulfate saturated crude protein extract on Sephadex G-75 followed by ion-exchange chromatography on DEAE and affinity chromatography on Sepharose-4B. The molecular weight of the lectins SLL-1, SLL-2 and SLL-3 were 1,55,000, 1,15,000 and 85,000, respectively, as determined by gel filtration on Sephadex G-150 and 1,60,000; 1,20,000 and 85,500, respectively, by SDS-polyacrylamide slab gel electrophoresis. SLL-1 and SLL-2 are dimer in nature held together by disulfide bond (s), while SLL-3 is a monomer. The lectins agglutinated specifically rat red blood cells and the agglutination was inhibited specifically by methyl-a-D-galactopyranoside, methyl-β-D-galactopyranoside and D-galactose. The lectins SLL-1, SLL-2 and SLL-3 contain 3.9, 3.4 and 2.8% neutral sugar, respectively, and the sugar compositions were glucose for SLL-1, mannose for SLL-2 and SLL-3 contained either N-acetyl-D-glucosamine or N-acetyl-D-galactosamine or both. The lectins exhibited cytotoxicity in brine shrimp lethality bioassay.