Characterization of mannose-binding protein isolated from the African catfish (Clarias gariepinus B.) serum

Lectins are carbohydrate-binding proteins which are involved in many biological functions including cell adhesion, phagocytosis, complement activation and innate immunity. This paper reports the first isolation of mannose-binding protein (MBP), designated as CgMBP or kumpolin1, from the serum of the African catfish, Clarias gariepinus (Burchell, 1822), a robust freshwater fish farmed extensively in Africa and South East Asia. Mannan-agarose affinity column was used to purify the mannose-binding protein from the serum. Molecular weight determination using reducing SDS-PAGE and non-reducing SDS-PAGE analyses revealed a single band close to 35 kDa and 28 kDa protein, respectively. Positive microbial cell agglutination activities of the African catfish mannose-binding protein were observed against Candida albicans, Saccharomyces cerevisiae, Aeromonas hydrophila, Bacillus subtilis, Enterococcus faecalis, Escherichia coli, and Pseudomonas aeruginosa. The functional properties of the MBP were tested under various conditions by using S. cerevisiae as the test organism. Agglutination activity of MBP was found to occur at pH 3–7. It required 0.5 mM calcium and was inhibited by 1 mM EDTA.