Lunatin, a novel lectin with antifungal and antiproliferative bioactivities from Phaseolus lunatus billb

A novel lectin with a molecular mass of 24.3 kDa, designated Lunatin, was isolated from edible seeds of Phaseolus lunatus billb. The purification scheme consisted of ammonium sulfate precipitation, affinity chromatography, ion exchange chromatography, and gel filtration chromatography. The lectin is a glycoprotein, as determined by staining with periodic acid-Schiff (PAS), and its N-terminal amino acid sequence was determined to be DAVIYRGPGDLHTGS. Lunatin exhibited hemagglutinating activity towards human blood group A erythrocytes, which was mostly preserved up to 50 °C and retained at ambient temperature at pH 2.0–11.0. d-fructose, d-galactose, d-glucose, and mannitol were capable of inhibiting its hemagglutinating activity. Lunatin was found to be a metal-dependent protein, as its activity was inhibited by the metallic compounds K2Cr2O7, SnCl2, and LiCl, though it was unaffected by MgCl2, ZnCl2, BaCl2, CuCl2, FeCl3, or CaCl2. In addition, Lunatin exerted potent antifungal activity toward a variety of fungal species, including Sclerotium rolfsii, Physalospora piricola, Fusarium oxysporum, and Botrytis cinerea. Finally, proliferation of K562 leukemia cells was strongly inhibited by Lunatin, with an IC50 of 13.7 μM, whereas HeLa and HepG2 cells were only weakly affected. These findings further the identification and understanding of functional factors in edible plant seeds.