galactose/rhamnose binding lectin domain found in Toxopneustes pileolus rhamnose-binding lectin SUL-I and similar proteins
SUL-I is a galactose/rhamnose-binding lectin with mitogenic, chemotactic, and cytotoxic activity. These activities can be triggered by binding of the lectin to specific carbohydrate chains on target cells. SUL-I may be involved in self-defense against invading microorganisms. SUL-I is composed of three distinctive domains with a folding structure similar to galactose/rhamnose-binding lectin domain found in proteins such as mammalian latrophilins, Oncorhynchus keta L-rhamnose-binding lectins (CSLs), and Silurus asotus rhamnose-binding lectin (SAL). The family also includes Heliocidaris crassispina D-galactoside-specific lectin, also known as sea urchin egg lectin or SUEL, and Echinometra lucunter L-rhamnose-binding lectin ELEL-1, both of which contain only one galactose/rhamnose-binding lectin domain. SUEL binds D-galactoside. It may play an important role in the activation of eggs triggered by fertilization, or in their subsequent differentiation. The dimeric form is essential for hemagglutination activity of SUEL. ELEL-1 is a rhamnose-binding lectin that also binds alpha-D-melibiose, alpha-D-lactose, beta-D-lactose, methyl-alpha-D-galactopyranoside, methyl-beta-D--galactopyranoside and D-galactose, but not D-arabinose, L-fucose, D-glucose, D-mannose, D-maltose, D-sucrose, N-acetyl-D-galactosamine, N-acetyl-D-glucosamine, N-acetyl-D-mannosamine-D-xylose, or by glycoproteins orosomucoid, thyroglobulin, ovomucoid and porcine stomach mucin. It shows cation-independent hemagglutinating activity against rabbit and human erythrocytes. ELEL-1 agglutinates cells of Gram-positive bacterial species S. aureus but not those of Gram-negative E. coli.
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