Studies on biological activities, their molecular mechanisms, and structure-function relationships of lectins from marine algae

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The studies were performed aimed at clarifying biological activities, their molecular mechanisms, and structure-function relationships of marine algal lectins, especially those that belong to a high-mannose N-glycan specific lectin family or a multifunctional low-molecular weight polypeptidic lectin family.With respect to a high-mannose N-glycan specific lectin family, first, the detailed carbohydrate-binding specificity and the primary structure of a red alga, Eucheuma serra lectin (ESA-2) were elucidated. Next, it was found that orally administration of ESA-2 suppressed the formation of colon aberrant crypt foci in mice received 1,2-dimethylhydrazine, due to the lower production of active oxygen in the colonic tissues. Relating to this, a receptor for ESA-2 on the cultured cells (HT-29) derived from human colonic cancer was identified using a newly established method for isolation of cell membrane receptors. In addition, the primary structure and the detailed carbohydrate-binding specificity of a cyanobacterium, Oscillatoria agardhii lectin (OAA), that belongs to this family, was elucidated. Furthermore, it was demonstrated that some lectins belonging to this family are very useful as affinity ligands for one-step purification of chicken monoclonal antibody that is usable for diagnosis of bovine spongiform encephalopathy (BSE).With respect to a multifunctional low-molecular weight polypeptidic lectin family, it was found that the lectin (hypnin A) from the red alga, Hypnea japonica is strictly specific for core α1-6 fucose in N-glycans, and would be useful as a reagent to detect cancer marker(s) as well as to prepare medicinal antibodies lacking the core α1-6 fucose that have effective antibody-dependent cellular cytotoxicity (ADCC)