Purification, characterization and cytotoxicity of malanin, a novel plant toxin from the seeds of Malania oleifera

Malanin, a novel plant toxin with a molecular weight of 61,875 Da and an isoelectric point of 5.5, was isolated from Malania oleifera seeds by homogenization, ammonium sulfate precipitation and hydrophobic interaction chromatography (HIC). It is a glycoprotein with two chains, chain-A and chain-B, which are crosslinked by one or more disulfide bonds. The N-terminal amino-acid sequences of malanin are DETXTDEEFN (X was commonly C) in chain-B, and DYPKLTFTTS in chain-A. Malanin exhibited highly cytotoxic activities against cancer cell lines (HeLa, PC-12, MCF-7, K562) and non-cancer cell lines (Vero and MDCK), producing IC₅₀ values of 0.15 ± 0.08, 7.71 ± 0.24, 11.20 ± 0.02, 15.80 ± 0.09, 2.79 ± 0.05 and 3.92 ± 0.01 nM, respectively. It significantly inhibited the growth of HeLa cells through cell-cycle arrest at S phase and induced an apoptotic response. LD₅₀ values were determined in ICR mice, which were found to be 26.22 μg/kg and 43.11 mg/kg by i.p. and i.g. respectively. Thus, malanin is amongst the most potent toxin of plant origin.