N-acetylneuraminic acid specific lectin and antibacterial activity from the red alga Gracilaria canaliculata Sonder

A new lectin from the marine red alga Gracilaria canaliculata (GCL) was isolated by a combination of aqueous ethanol extraction, ethanol precipitation, ion exchange and filtration chromatography. Lectin gave a single band with molecular mass of 22,000 Da in both non-reducing and reducing SDS-PAGE conditions, indicating that GCL is a monomeric protein. The hemagglutination activities of GCL were stable over a wide range of pH from 3 to 10, temperature up 60 oC and not affected by either the presence of EDTA or addition of divalent cations. Lectin GCL had high affinity for N-acetylneuraminic acid through interacting with the acetamido group at equatorial C2 position of these sugar residues, suggesting that GCL is specific for N-acetylneuraminic acid. Furthermore, GCL inhibited the growth of human and shrimp pathogenic bacteria, Staphylococcus aureus and Vibrio alginolyticus, although it did not affect the growth of Escherichia coli, Enterobacter cloace, Vibrio parahaemolyticus and V. harveyi. The red alga G. canaliculata may promise to be a source of valuable lectins for application as antibacterial agents.