A new screening for hemagglutinins from Vietnamese marine macroalgae

Aqueous extracts from 42 species of Vietnamese marine macroalgae, including 17 Chlorophyta, 22 Rhodophyta, and three Phaeophyta species, were examined for hemagglutination activity using native and enzyme-treated different animal and human erythrocytes. All extracts agglutinated at least one type of erythrocytes tested. Strong activity was detected in extracts from four Chlorophyta (Caulerpa serulata var. boryana, Caulerpa sertularioides f. longipes, Halimeda velasquezii, and Halimeda discoidea) and two Rhodophyta species (Gelidiella acerosa and Titanophora pulchra) with enzyme-treated rabbit and horse erythrocytes. The hemagglutinins of some active species were examined for sugar-binding specificity, pH, temperature stability, and divalent cation independency using ammonium sulfate precipitates prepared from their extracts. In a hemagglutination–inhibition test with various monosaccharides and glycoproteins, none of the hemagglutinins had affinity for monosaccharides. The activity of the hemagglutinins was inhibited by some glycoproteins tested. The inhibition profiles with glycoproteins were different depending on hemagglutinin species, suggesting the presence of lectins specific for complex N-glycans, high mannose N-glycans or O-glycans. On the other hand, the activities of almost all algal hemagglutinins were stable over a wide range of pH and temperature, and independent of the presence of divalent cations, except Gelidiopsis scoparia hemagglutinin, its activity was dependent on the presence of divalent cations. These results suggest that Vietnamese marine macroalgae may be good sources of useful lectins for many biological applications.