PURIFICATION AND CHARACTERIZATION OF AN EXTRACELLULAR LECTIN (LECTIN-I) FROM AGROBACTERIUM-RADIOBACTER NCIM-2443

A lectin from culture filtrate of Agrobacterium radiobacter NCIM 2443 is purified to homogeneity by ion exchange chromatography on a DEAE ce llulose column followed by hydrophobic chromatography on phenyl sephar ose and hydroxyapatite column chromatography. The protein (Lectin I) i s a monomer of relative molecular mass 37,000, as determined by denatu ring gel electrophoresis as well as size exclusion chromatography. Lec tin I is stable at pH 5.0 and its isoelectric point is pH 4.0. Amino a cid analysis reveals that acidic amino acids and glycine are predomina nt amino acids and cysteine is absent in the lectin. Chemical modifica tion of tryptophan residues causes more than 80% loss of haemagglutina tion activity of the lectin and 60% loss of activity is caused by modi fication of carboxyl groups. Lectin I agglutinates rabbit erythrocytes but does not agglutinate human A, B and O types of erythrocytes. It i s specific for N-acetyl D-glucosamine, chitobiose, pNP-beta-mannoside as well as high mannose type glycopeptides. The relative inhibition by disaccharides, oligosaccharides and glycoproteins indicates that Lect in I recognizes Man3-GlcNAc-GlcNAc core carbohydrate structure of aspa ragine linked glycopeptides. Tobacco tissue extracts also inhibit the haemagglutination activity of Lectin I.