Meristiella echinocarpa lectin (MEL): a new member of the OAAH-lectin family

A new lectin from the marine red alga Meristiella echinocarpa (MEL) was isolated and biochemically characterized. MEL is a monomeric protein of 28 kDa with specificity for yeast mannan. Hemagglutination activity of MEL was stable between pH 5 and 10, temperatures up to 50 °C, and neither EDTA nor divalent ions affected it. The complete amino acid sequence of MEL was determined through a combination of tandem mass spectrometry and DNA cloning. As a new member of the OAAH-lectin family, the primary structure of MEL consists of 267 amino acid residues distributed in four tandem repeat domains, sharing at least 48% of identity. Theoretical secondary structure of MEL was composed of 3% α-helix, 40% β-sheet, 19% β-turn, and 38% coil. Melting temperatures of the lectin in the absence and presence of mannan were 54 and 61 °C, respectively. Furthermore, MEL was able to recognize and agglutinate pathogenic bacterial strains, such as multidrug-resistant Salmonella and Vibrio alginolyticus.