Purification and characterization of a Ca2+-dependent novel lectin from Nymphaea nouchali tuber with antiproliferative activities

A lectin (termed NNTL) was purified from the extracts of Nymphaea nouchali tuber followed by anion-exchange
chromatography on DEAE-cellulose, hydrophobic chromatography on HiTrap Phenyl HP and by repeated anion-exchange
chromatography on HiTrap Q FF column. The molecular mass of the purified lectin was 27.0 +−1.0 kDa, as estimated
by SDS/PAGE both in the presence and in the absence of 2-mercaptoethanol. NNTL was an o-nitrophenyl β-Dgalactopyranoside
sugar-specific lectin that agglutinated rat, chicken and different groups of human blood cells and
exhibited high agglutination activity over the pH range 5–9 and temperatures of 30–60◦C. The N-terminal sequence
of NNTL did not show sequence similarity with any other lectin and the amino acid analysis revealed that NNTL was
rich in leucine, methionine and glycine residues. NNTL was a glycoprotein containing 8% neutral sugar and showed
toxicity against brine shrimp nauplii with an LC50 value of 120 +−
29 μg/ml and exerted strong agglutination activity
against four pathogenic bacteria (Bacillus subtilis, Sarcina lutea, Shigella shiga and Shigella sonnei). In addition,
antiproliferative activity of this lectin against EAC (Ehrlich ascites carcinoma) cells showed 56% and 76% inhibition in
vivo in mice at 1.5 and 3 mg·kg−1·day−1 respectively. NNTL was a divalent ion-dependent glycoprotein, which lost its
activity markedly in the presence of denaturants. Furthermore, measurement of fluorescence spectra in the presence
and absence of urea and CaCl2 indicated the requirement of Ca2+ for the stability of NNTL.