Identification, characterization, and functional verification of a novel fish-egg lectin (FEL) from the golden pompano, Trachinotus ovatus.

Lectins play important roles in the innate immune response and therefore are of great interest for immunologists. Although different families of lectins have been increasingly documented in various fish species, our current understanding of fish-egg lectins (FELs) is still in paucity. In this study, a novel FEL (ToFEL) was identified in the commercially important marine fish golden pompano (Trachinotus ovatus) through transcriptomic screening. In addition to bioinformatic characterization, the expression of ToFEL in different tissues and upon pathogenic challenge were profiled. Moreover, the binding capacity of ToFEL to five bacteria and the agglutinating activity of ToFEL against bacteria as well as blood and sperm cells of donor species with and without Ca2+ were assessed using the recombinant T. ovatus FEL (rToFEL). Our results demonstrated that ToFEL had an open reading frame (ORF) of 786 bp, which encodes a putative protein with 261 amino acids including a signal peptide consists of 19 amino acids. In addition to harboring three typical TECPR domains, a Ca2+-binding site was also identified in ToFEL. The ToFEL was shown to be highly homology to FELs of other fish species investigated, especially to its close relatives Seriola dumerili and S. lalandi. The expression of ToFEL was detected in all the ten tissues examined (predominantly in gill, liver, and ovary) under normal condition and was significantly induced upon pathogenic challenge. In addition, in the presence of Ca2+, the rToFEL exhibited strong binding and agglutinating activity against both gram-positive and gram-negative bacteria as well as blood and/or sperm cells of donor species. Collectively, our data indicate that ToFEL is a constitutive and inducible acute-phase immune molecule of T. ovatus in response to a broad-spectrum alien substances.