Purification and characterization of Microcystis aeruginosa (freshwater cyanobacterium) lectin

Microcystis aeruginosa, strain M228, a laboratory culture of freshwater cyanobacterium, showed hemagglutinating activity against rabbit, horse and human ABO erthrocytes. Crossed absorption tests revealed the presence of a single type of lectin in the extract of M228 strain cells. The lectin, termed MAL, was purified in combination with the affinity chromatography on acid-treated agarose gel and the gel permeation chromatography in an electrophoretically pure form. MAL was a glycoprotein containing 7.8% neutral sugars and was composed of a single polypeptide having a molecular weight of 57 kDa. Isoelectric point was estimated to be pH 6.4. Hemagglutinating activity of the lectin was inhibited effectively by N-acetyl-D-galactosamine and by glycoproteins. D-galactose and lactose also showed moderate inhibitory activity. The destruction of the hemagglutinating activity by a 2-mercaptoethanol treatment suggests the presence of intra-chain disulfide bond(s) essential for the activity in the molecule. The sequence of the amino-terminal region of MAL was determined as Val-Leu-Ala-Ser-Leu-Val-Ser-Thr-Ser-Gln-Ala-Gly-Ser-Leu-Glu-Leu-Leu- Ala [corrected].