Characterisation of a novel monomeric lectin (AML) from Astragalus membranaceus with anti-proliferative activity

A novel lectin (AML) was isolated from the roots of a Chinese herb Astragalus membranaceus (Fisch.) Bunge, using a combination of ammonium sulphate fractionation and affinity chromatography. AML was found to be a monomeric protein with a molecular mass of 31.5 kDa. Biochemical characterisation revealed that it is a glycoprotein containing 10.7% neutral sugars. The N-terminus of AML was blocked but amino acid sequences of internal tryptic peptides showed moderate sequence identities with some other known lectins. Amongst the various carbohydrates tested, the lectin was best inhibited by d-galactose and its derivatives with pronounced preference for o-nitrophenyl-β-d-galactopyranoside (8.3 mM). The lectin was stable in the pH range of pH 5.0–12.0 and temperatures up to 55 °C for 30 min. AML inhibited the proliferation of HeLa and K562 cell lines. Thus, the lectin displays a high potential for antitumour activity.