Screening and partial characterization of lectins from Indonesian seaweeds

Lectins are carbohydrate-binding proteins involved in diverse biological processes with potential biotechnological and biomedical applications. Seaweeds are promising sources of novel lectins with unique structures and glycan specificities. This study screened 21 Indonesian seaweed species for lectin occurrence and partially characterized their biochemical properties and glycan-binding specificities. The extraction of the lectins was performed using phosphate-buffered saline, followed by precipitation with 75% (NH4)2SO4. The haemagglutination activity (HA) assay, utilizing both native and enzyme-treated animal and human erythrocytes, revealed that all seaweed samples contained haemagglutinins. This includes 12 species that have not previously been screened for lectins. Lectins from some red and green seaweeds exhibited substantial HA against trypsin-treated chicken erythrocytes. The glycan-binding specificities of the lectin-rich fraction (LF) were determined through a haemagglutination inhibition (HAI) assay, which employed nine monosaccharides and 12 glycoproteins. No inhibition was observed with any of the monosaccharides tested, indicating that the lectins did not recognize or bind to simple sugars. In contrast, most LFs bound to glycoproteins, with the highest inhibition by fetuin, thyroglobulin and mucin, which are glycoproteins bearing N-glycans, O-glycans or complex and high mannose-type N-glycans. The HA of most LFs decreased markedly under acidic conditions and showed a slight reduction in alkaline conditions. A sharp decline in HA was observed at temperatures above 70°C, while the activity was unaffected by the presence or absence of divalent cations. The study identified previously unreported seaweed species as potential sources of lectins, warranting further investigation.