UT841 purified from sea urchin (Toxopneustes pileolus) venom inhibits time-dependent (45)Ca(2+) uptake in crude synaptosome fraction from chick brain

Functional Diversity of Novel Lectins with Unique Structural Features in Marine Animals

Due to their remarkable structural diversity, glycans play important roles as recognition molecules on cell surfaces of living organisms. Carbohydrates exist in numerous isomeric forms and can adopt diverse structures through various branching patterns. Despite their relatively small molecular weights, they exhibit extensive structural diversity. On the other hand, lectins, also known as carbohydrate-binding proteins, not only recognize and bind to the diverse structures of glycans but also induce various biological reactions based on structural differences. Initially discovered as hemagglutinins in plant seeds, lectins have been found to play significant roles in cell recognition processes in higher vertebrates. However, our understanding of lectins in marine animals, particularly marine invertebrates, remains limited. Recent studies have revealed that marine animals possess novel lectins with unique structures and glycan recognition mechanisms not observed in known lectins. Of particular interest is their role as pattern recognition molecules in the innate immune system, where they recognize the glycan structures of pathogens. Furthermore, lectins serve as toxins for self-defense against foreign enemies. Recent discoveries have identified various pore-forming proteins containing lectin domains in fish venoms and skins. These proteins utilize lectin domains to bind target cells, triggering oligomerization and pore formation in the cell membrane. These findings have spurred research into the new functions of lectins and lectin domains. In this review, we present recent findings on the diverse structures and functions of lectins in marine animals.

Dumbbell-Shaped Ossicles Discovered in Pedicellaria of Flower Sea Urchins

Sea urchins have a globiferous pedicellaria that stands from a test with a stalk on which lies a head made of three movable jaws with venom-injecting teeth. The globiferous pedicellariae of the flower sea urchin Toxopneustes pileolus, one of the most developed among sea urchins, are unique in that the jaws are provided with a jaw membrane that gives the pedicellaria an appearance of a flower when the jaws are open. We observed this membrane in an ionic liquid that does not require processes, such as fixation, dehydration, or coating with conductive materials, for observation with a scanning electron microscope. Using this technique, we discovered dumbbell-shaped ossicles, which consist of two spheres of similar size connected by a cylinder. The diameter of the sphere is 4-8 µm, and the total length of the ossicle is 10-20 µm. The jaw membrane is trimmed with an edge zone. The ossicles were found sparsely in the connective tissue of general part of the membrane, but in the edge zone their density was so high that neighboring ossicles were in close contact with each other. Some neighboring ossicles crossed their cylinders and some inserted one of their spheres to snugly fit in the gap between the spheres of neighboring ossicles. Their structural role is very likely in strengthening the jaw membrane, probably serving as fillers in the general part of the membrane; in the edge zone the interlocking of adjacent ossicles forms a loose network providing a firm frame for the head of the globiferous pedicellaria. When opened, the stiff frame prevents the membrane from sagging. When clasped, it works as a closed door, firmly keeping prey trapped.