Lectin from edible seaweed Meristotheca papulosa exhibits a high digestion-resistant property

The physiological impacts of polysaccharides and lipids in seaweed on human health are becoming clearer, but the behavior of the protein components, especially lectins, after ingestion remains poorly understood. In this study, we examined the resistance of edible red algae-derived lectins to digestive enzymes. We found that a lectin extracted from Meristotheca papulosa (MPL-1), belonging to the Jacalin-related lectin family, was relatively stable when subjected to both peptic and tryptic digestion and retained its hemagglutination activity after 24 h of digestion. The activity of MPL-1 was also maintained without a large change for 24 h following exposure to enzymes such as papain, Actinase E, and proteinase K, suggesting that MPL-1 possesses a strong resistant property against proteolytic digestion. We examined the anti-proliferation activity of the MPL fraction from the algal body against HT-29, a human colon cancer-derived cell line, and found that it showed a strong inhibitory activity with a half-maximal inhibitory concentration of 4.5 μg/mL. This activity was nullified in the presence of yeast mannan, an inhibitory sugar compound of lectin, demonstrating that MPL expressed its activity through binding to the glycan moieties on HT-29. This study indicates that this proteinase-resistant lectin could play a vital role after ingestion and is expected to have an inhibitory effect against colorectal cancer.