Isolation and characterization of a mannan-binding lectin from the freshwater cyanobacterium (blue-green algae) Microcystis viridis

Microcystis viridis NIES-102 strain, a unicellular freshwater bloom-forming cyanobacterium, showed transient hemagglutinating activity in laboratory culture during stationary phase under nonaeration conditions. However, the hemagglutinating activity which was inhibited with yeast mannan could not be observed during culture with aeration. A mannan-binding lectin named MVL was isolated with the assay of the hemagglutinating activity against rabbit erythrocytes from the cyanobacterium by successive hydrophobic and gel filtration chromatography. MVL was composed of a single polypeptide of 13 kDa. The gene (mvl) for MVL was cloned from a genomic DNA of NIES-102 strain as a template, and its sequence was determined. The deduced amino acid sequence showed that MVL consisted of 113 amino acid residues and was composed of two tandemly repeated homologous domains of 54 amino acid residues. MVL showed no sequence homology to any other lectins or proteins.