Integrated study on molecular evolution and biological functions of fish lectins

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The evolutionary process of the conger eel galectins, congerin I and II, was investigated by preparing a probable ancestral form of congerins, Con-ans, on the basis of phylogenetic tree. The comparison among their thermostabilities and sugar specificities showed that congerins have evolved via accelerated evolution under significant selective pressure to improve their functions. The multiple C-type lectins, BRA-1, -2 and -3, from Megabalanus rosa, had characteristic and distinct sugar binding specificities. The lectins also had modulating effects on the crystallization of calcium carbonate, indicating their participation in biomineralization. Multiple L-rhamnose-binding lectins (RBLs) were isolated and characterized from the eggs of various fish species; i.e. steelhead trout, chum salmon, Spanish mackerel, and ayu. RBLs were composed of homologous subunits with 2-3 tandemly repeated domains of about 95 amino acid residues. Each domain could be characterized by highly conserved 8 half-C … More ys residues at homologous positions as well as the conserved peptide motifs. RBLs specifically recognized and bound to globotriaosylceramide (Gb3), and agglutinated Gram-negative and Gram-positive bacteria by recognizing the structures of lipopolysaccharides and lipoteichoic acid on their surfaces, respectively. They also interacted with the spores of a microsporidian parasite. RBLs from chum salmon eggs, CSL1, 2 and 3, induced proinflammatory cytokines by recognizing Gb3 on the surface of the peritoneal macrophage cell line (RTM5 cells) from rainbow trout. In addition, CSLs had an opsonic effect on RTM5 cells by binding to Gb3. CSLs induced the production of reactive oxygen species in dose-dependent manner in RTM5 cells. This activity was not inhibited by L-rhamnose, indicating that the sugar binding site of CSLs was not involved in the activity. Moreover, some RBLs induced apoptosis of human colon cancer cells by recognizing Gb3 on the cells. These properties of RBLs indicate that they may function as biodefence molecules. Less