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Even though more than 90 lectins have been extracted from legumes, few of them bind specifically to sialic acid derivatives. In the present study, a sialic acid-binding protein has been purified from the bark of legume Maackia fauriei using fetuin-affinity chromatography. The eluted fractions from affinity column exhibited hemagglutination activity, thus they are designated as M. fauriei agglutinin (MFA). A typical purification method could produce at least 25.5 mg of pure MFA with a specific activity of 40.2 and a recovery yield of no less than 4.9%. A single N-terminal 20-amino acid sequence of MFA, SDELSFNINNFVPNQADLLF, was determined on an automatic Edman degradation amino acid sequencer, and it exhibits a high homology with lectins from M. amurensis which binds to sialylated oligosaccharide Neu5Aca2-3Galb1-3(Neu5Aca2-6)GalNAc. The hemagglutination activity of MFA with human erythrocytes was specifically inhibited by sialylated trisaccharide Neu5Aca2-3Galb1-4GlcNAc, but it was not inhibited by either Neu5Aca2-6Galb1-4GlcNAc or Neu5Aca2-3Galb1-4Glc/Neu5Aca2-6Galb1-4Glc. This activity of MFA was dependent on divalent cations. Many plant lectins are cytotoxic against cancer cells, with the effect differing with cell type; however, the mechanisms of action remain poorly understood. MFA exerts cytotoxic effects on human breast cancer MCF-7 cells, human melanoma G-361 cells, and human liver cancer SNU-449 cell lines but had no effect on the human colorectal cancer SNU-C1 cell line. It is especially noteworthy that the deleterious effect of MFA on the viability of MCF-7 was greater than that of MAH or wheat germ agglutinin.