Biological functions of rhamnose-binding multiple lectins from fish eggs

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This study focused on the molecular structure, tissue distribution, and biological function of rhamnosebinding lectins (RBLs) isolated from steelhead trout (Oncorhynchus mykiss) eggs. RBLs which were isolated from other Salmonidae such as chum salmon (Oncorhynchus keta) and white-spotted charr (Salvelinus leucomaenis) were characterized for comparison and to know the distribution and evolution of RBLs in fish. Three RBLs, named STL1, STL2, and STL3, were isolated from steelhead trout (Oncorhynchus mykiss) eggs and characterized. These subunits were composed of three (STL1) or two (for STL2 and STL3) tandemly repeated carbohydrate recognition domains (CRDs) in the sequences. Three RBLs named CSL1 CSL2 and CSL3, were isolated from chum salmon eggs and characterized. CSLs are composed of three (for CSL1) or two (for CSL2 and CSLS) tandemly repeated RBL CRDs in the sequences as same as STLs. Two RBLs, named WCL1 and WCL3, were isolated from white-spotted charr eggs. WCL1 and WCL3 showed ap … More proximately 90 % sequence identities to corresponding STL1 and STL3, respectively, and composed of three (for WCL1) or two (for WCL3) tandemly repeated RBL CRDs. STL2-like protein and mRNA were not detected in white-spotted charr. On the basis of the results obtained, the molecular evolution of RBLs and its CRD motif were examined. The CRD motif is not restricted to fishes but is distributed among various other animals, and may have evolved from a common ancestral gene to play their own roles in the biological system. The tissue-specific localization and the changes of STLs proteins and mRNAs during the embryonic development in the steelhead trout were investigated. STL1 has different distribution and expression profiles from those of STL2 and STL3. The interaction between bacteria and STLs was examined. STLs were demonstrated to agglutinate bacteria by recognizing lipopolysacchandes (LPS) and lipoteichoic acid (LTA), which are major integral components of the outer membranes of Gram-negative and Gram-positive bacteria, respectively. This indicates that STLs play important roles in biodefense system. Less