A novel mannose-binding lectin from plasma of Labeo rohita

A new mannose-binding lectin was purified from plasma of freshwater fish, rohu (Labeo rohita) by ammonium sulphate precipitation followed by DEAE-cellulose ion-exchange chromatography. The hemagglutinating activity is strong for neuraminidase-treated rabbit erythrocytes. Mannose, glucose and their derivatives inhibit hemagglutination. The apparent molecular weight was determined to be 210 kDa in native PAGE. Analysed on SDS-PAGE under reducing and non-reducing conditions, the protein migrated as a single band of mol.wt. 40,000. The lectin is acidic in nature showing a pI of 4.5. It is a glycoprotein containing complex glycan part as indicated by carbohydrate analysis using high-pressure anion exchange chromatography with a pulsed amperometric detector. The N-terminal sequence (WLNGIGTQIPMKITT) shows no significant homology with known proteins. It appears to be a C-type lectin as Ca2+ is essential for carbohydrate-binding activity. Methyl -α- D-mannopyranoside was found to be the most potent inhibitor among the monosaccharides and disaccharides tested. Purified lectin was found to induce intracellular superoxide production following opsonization of E. coli by its own macrophages.