First isolation and characterization of a novel lectin with potent antitumor activity from a Russula mushroom

To date only a ribonuclease and a protein with anti-HIV-1 reverse transcriptase activity have been isolated from mushrooms of the genus Russula. In this study a novel lectin, with a molecular weight of 32 kDa, and a unique N-terminal sequence different from other lectins, was isolated from the mushroom Russula lepida. It represents the first lectin isolated from Russula mushrooms. The purification scheme involved (NH4)2SO4 precipitation, ion exchange chromatography on diethylaminoethyl DEAE-cellulose and SP-Sepharose, and fast protein liquid chromatography-gel filtration on Superdex 75. The hemagglutinating activity of the lectin (RLL) was inhibited by inulin and O-nitrophenyl-β-D-galacto-pyranoside. The lectin was stable at temperatures up to 70 °C (half of the activity was preserved at 80 °C), and in the presence of NaOH or HCl solutions up to a concentration of 12.5 mM. Its hemagglutinating activity was reduced in the presence of Mn2+, Co2+, and Hg2+ ions, and enhanced by Cu2+ ions. It exhibited antiproliferative activity toward hepatoma Hep G2 cells and human breast cancer MCF-7 cells with an IC50 of 1.6 μM and 0.9 μM, respectively. Daily intraperitoneal injections of RLL (5.0 mg/kg body weight/day for 20 days) brought about 67.6% reduction in the weight of S-180 tumor. RLL was devoid of antifungal, ribonuclease, and HIV-1 reverse transcriptase inhibitory activities.