Purification, cloning and characterization of egg lectins from the teleost Tribolodon brandti

Three l-rhamnose-binding egg lectins, TBL1, TBL2 and TBL3, were isolated from the eggs of the Far East dace Tribolodon brandti by a combination of affinity chromatography on l-rhamnose-Sepharose 6B gel and reversed-phase HPLC. l-rhamnose is a common inhibitor of the purified lectins and strongly inhibited the hemagglutinating activity of TBL2 and TBL3, but less weakly that of TBL1. l-arabinose, which has the same hydroxyl group orientation at C2 and C4 as l-rhamnose, and d-galactose showed no inhibitory activity against TBL1 but showed weak inhibitory activity against TBL2 and TBL3. The open reading frames of the cDNAs of TBL1, TBL2 and TBL3 encoded for mature proteins of 207, 189, and 293 amino acid residues, respectively. A BLAST homology search showed that the TBLs have about 40% homology to the carbohydrate recognition domains of rhamnose-binding lectins in salmonid eggs. The tandem repeated domains present in TBL1, TBL2 and TBL3 were two, two and three, respectively. TBL2 was exclusively expressed in ovary, while TBL1 and TBL3 were expressed mainly in ovary and weakly in various tissues including gill, heart, kidney, liver, spleen and testis.