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

Abstract 

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 32kDa, 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 12.5mM. 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 1.6μM and 0.9μM, respectively. Daily intraperitoneal injections of RLL (5.0mg/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.

Keywords: Antitumor, Lectin, Mushroom, Purification, Russula lepida.