A novel lectin from fresh rhizome of Alisma orientale (Sam.) Juzep

A novel lectin with a molecular mass of 22.5 kDa, designated as AOL, has been isolated from fresh rhizome of Alisma orientale (Sam.) Juzep. The purification procedure involved ammonium sulfate precipitation, affinity chromatography on Affi-gel blue gel and gel filtration chromatography on Sephacryl S200. AOL was a monomer with intrachain disulfide bond; its isoelectric point was estimated to be 5.6. The lectin could be stained in red by periodic acid-Schiff (PAS) reagent, it consisted of 93.7% protein and 6.3% sugar. N-terminal amino acid sequence of AOL was determined to be EAVVDTNGDLIHTGSIH. AOL exhibited hemagglutinating activity in human erythrocytes. The hemagglutinating activity was mostly preserved up to 50 °C and was indiscernible when the temperature above 70 °C. It was stable over the pH range 2–11. Among the carbohydrates tested, l-arabinose, mannitol, d-xylose and l-rhamnose were capable of inhibiting the hemagglutinating activity. AOL was a metal dependent protein, metallic compounds including LiCl, FeCl3, MnCl2 and K2Cr2O7 inhibited the activity whereas MgCl2, ZnCl2, BaCl2, CuCl2 and CaCl2 did not affect its activity, which means all these metallic compounds cannot promote the activity of AOL. Proliferation of tumor cells HeLa cells was inhibited by AOL with an IC50 of 7.3 μM, HepG2 cells and the normal cells MDCK was just slightly affected even at the concentration of 40 μM. AOL did not exhibit antifungal activity.