A novel lectin with potent antitumor, mitogenic and HIV-1 reverse transcriptase inhibitory activities from the edible mushroom Pleurotus citrinopileatus

Abstract

The objective of the present study was to isolate a lectin from fresh fruiting bodies of the mushroom Pleurotus citrinopileatus and examine it for various biological activities. The isolation procedure comprised ion exchange chromatography on DEAE-cellulose, CM-celluloses, and Q-Sepharose, and gel filtration on Superdex 75. A homodimeric 32.4 kDa lectin displaying high hemagglutinating activity was isolated with over 110 fold of purification. Its N-terminal amino acid sequence, QYSQMAQVME, has not been reported for other lectins. The lectin was unadsorbed on DEAE-cellulose in 0.001 M NH4HCO3 buffer (pH 9.4), but adsorbed on CM-cellulose in 0.001 M NH4OAc buffer (pH 4.8) and eluted by approximately 0.05 M NaCl in the same buffer. The lectin was subsequently adsorbed on Q-Sepharose and eluted by a linear gradient of 0-0.2 M NaCl in 10 mM NH4HCO3 buffer (pH 8.5). The lectin was obtained in a purified form after gel filtration by fast protein liquid chromatography on Superdex 75. The hemagglutinating activity of the lectin was inhibited by maltose, O-nitrophenyl-beta-d-galactopyranoside, O/P-nitrophenyl-beta-d-glucuronide and insulin. It was stable at temperatures up to 60 degrees C, and in NaOH and HCl solutions up to 0.1 M and 0.006 M concentration, respectively. It was sensitive to inhibition by HgCl2 and potentiation by AlCl3. The lectin exerted potent antitumor activity in mice bearing sarcoma 180, and caused approximately 80% inhibition of tumor growth when administered intraperitonealy at 5 mg/kg daily for 20 days. It elicited a mitogenic response from murine splenocytes in vitro with the maximal response at a lectin concentration of 2 microM. The lectin inhibited HIV-1 reverse transcriptase with an IC50 of 0.93 microM. It was devoid of antifungal activity.