Multiplicity, structures, and endocrine and exocrine natures of eel fucose-binding lectins

Lectins, a group of proteins that bind to cell surface carbohydrates and pl ay important roles in innate immunity, are widely used experimentally to di stinguish cell types and to induce cell proliferation. Eel serum lectins ha ve been useful as anti-H hemagglutinins and also in lectin histochemistry a s fucose-binding lectins (fucolectins), but their structures have not been determined. Here we report the primary structures and the sites of synthesi s of eel fucolectins. Eel serum fucolectins were separated by two-dimension al gel electrophoresis and sequenced. cDNA cloning, based on the amino acid sequence information, and Northern blot analysis indicated that 1) the fuc ose-binding lectins are secretory proteins and have unique structures among the lectins, exhibiting only weak similarities to frog pentraxin, horsesho e crab tachylectin-4, and fly fw protein; 2) there are at least seven close ly related members; and 3) their messages are abundantly expressed in the l iver and in significant levels in the gill and intestine. The lectin-produc ing hepatic cells were identified by immunostaining; in the gill, exocrine mucous cells were stained, suggesting that serum fucolectins derive from th e liver. Using primary culture of eel hepatocytes, the message levels were shown to be increased by lipopolysaccharide, suggesting a role for fucolect ins in host defense. SDS-polyacrylamide gel electrophoresis analysis showed that eel fucolectins have a SDS-resistant tetrameric structure consisting of two disulfide-linked dimers.