Characterization of a lectin from Gonatanthus pumilus D. Don having anti-proliferative effect against human cancer cell lines.

A monocot araceous lectin from tubers of Gonatanthus pumilus (GPL) wa earlier purified in our laboratory and reported as T-cell mitogen having homotetrameric structure with subunit molecular mass of 13 kDa. Besides asialofetuin as reported earlier, in the present study it was also inhibited by N-acetyl-D-lactosamine but was non-reactive towards mannose or its derivatives. The lectin is rich in acidic amino acids and cysteine is completely absent. Chemical modification of GPL revealed requirement of tryptophan and tyrosine for lectin sugar interaction. The secondary structure content of GPL, as estimated with CD spectrum in K2D programme, has 73% alpha-helix, 26% beta-sheet and 38% random contributions. Fluorescence spectrum of the lectin solution at 280 nm was typical for tryptophan residues buried inside the protein. Lectin activity decreased when treated with denaturants like guanidine-HCL, urea and thiourea. GPL inhibited the growth of three plant pathogenic fungi namely Colletotrichum lindemuthianum, Fusarium oxysporum and Botrytis cinerea. Out of 11 human cancer cell lines tested, GPL significantly inhibited proliferation of five lines viz. Colo-205, IMR-32, HCT-15, SK-N-SH and HT-29.