A new lectin from the tuberous rhizome of Kaempferia rotunda: isolation, characterization, antibacterial and antiproliferative activities.

A lectin (designated as KRL) was purified from the extracts of Kaempferia rotunda Linn. tuberous rhizome by glucose-sepharose affinity chromatography. KRL was determined to be a 29.0 ± 1.0 kDa polypeptide by SDS-PAGE under both reducing and non-reducing conditions. KRL was a divalent ion dependent glycoprotein with 4% neutral sugar which agglutinated different groups of human blood cells. Methyl-α-D-mannopyranoside, D-mannose and methyl-α-D-glucopyranoside were the most potent inhibitors. N-terminal sequence of KRL showed similarity to some mannose/ glucose specific lectins but the main differences with their molecular masses and sugar content. KRL lost its activity markedly in the presence of denaturants and exhibited high agglutination activity from pH 6.0 to 8.2 and temperature 30 to 60° C. The lectin showed toxicity against brine shrimp nauplii with the LC50 value of 18 ± 6 µg/ml and strong agglutination activity against seven pathogenic bacteria. KRL inhibited the growth of six bacteria partially and did not show antifungal activity. In addition, antiproliferative activity against Ehrlich ascites carcinoma (EAC) cells showed 51% and 67% inhibition in vivo in mice administered 1.25 mg/kg/day and 2.5 mg/kg/day of KRL respectively by injection for five days.