Isolation and characterization of L-rhamnose-binding lectins from chum salmon (Oncorhynchus keta) eggs

Three L-rhamnose-binding lectins, named CSL1, CSL2, and CSL3, were isolated from eggs of chum salmon (Oncorhynchus keta) by affinity chromatography and reversed-phase high-performance liquid chromatography. The yields of CSL1, CSL2, and CSL3 from 2 kg eggs were 2.7, 1.7 and 29.6 mg, respectively. The subunit of CSL1 was composed of 286 amino acid residues with three tandemly repeated domains, while the subunits of both CSL2 and CSL3 were composed of 195 amino acid residues with two tandemly repeated domains. The amino acid sequence homologies among CSL showed 42-52% identities. CSL showed 94-97% sequence identities to three corresponding L-rhamnose-binding lectins, named STL1, STL2 and STL3, from steelhead trout (Oncorhynchus mykiss) eggs. Each CSL showed different hemagglutinating activities against rabbit and human erythrocytes. The lectins also showed different inhibition patterns in the hemagglutination towards rabbit erythrocytes by lipopolysaccharides from Gram-negative bacteria including a fish pathogen, Aeromonas salmonicida. CSL agglutinated Escherichia coli and Bacillus subtilis. These results indicate that CSL could be useful biochemical tools for recognizing specific molecules either in soluble forms or on cell surfaces.