Anti-viral Activity Of Galectin-1from Flounder Paralichthys Olivaceus

The innate immune system is the first line of defense protecting the host frominvasion by pathogenic microbes. In both vertebrates and invertebrates, the responseto invading pathogens is initiated by the detection of pathogen-associated molecularpatterns (PAMPs) by host pattern recognition receptors (PRRs). Lectins arewell-known PRRs that specifically bind to the carbohydrate molecules on the surfaceof pathogens, and help in their rapid clearance by enhancing opsonization andphagocytosis and also by increasing the oxidative burst activity. Animal lectins areclassified into distinct families characterized by unique sequence motifs and structuralfolds: S-type lectins, C-type lectins, F-type lectins, I-type lectins, P-type lectins,pentraxins, ficolins and cytokine lectins. All of these lectins have at least onecarbohydrate-recognition domain (CRD), conferring the protein itscarbohydrate-binding capacity. Galectins, formerly known as S-type lectin, are afamily of Ca2+-independent soluble lectins characterized by their affinity toβ-galactosides. To date,15galectins have been identified in mammalian species. Inmammals, the roles of galectins in innate host defense against certain bacteria, fungiand viruses have been well documented. Galectins have been isolated from severalfish species, but the immunological functions of galectins in fish remain poorlycharacterized. So, the aim of this paper was to identify the function of galectin-1offlounder in the antiviral response.First, bioinformatics analysis of fGLec-1show that it contained an openingreading frame (ORF) of408bp, and encoded a protein of135amino acids with acalculated molecular weight of about15.4kDa. There was no putative signal peptidein the predicted protein fGLec-1. The3D structure predicted by SWISS-MODELshowed that fGLec-1involved a β sandwich consisting of two anti-parallel β-sheets.Sequence comparison showed that fGLec-1was highly similar to fish counterparts,and less to mammalian. Alignment analysis revealed that the critical residues was present in fGLec-1was highly conserved. The phylogenetic tree constructed usingamino acid sequences of galectin proteins showed that fGLec-1was clustered togetherwith other galectin-1, which reflected the phylogeny of species.Then, the complete ORF of fGLec-1was cloned, expression vertor wasconstructed, and the recombinant fGLec-1protein was expressed in the E.coil. Therecombinant protein was purified and identified. The anti-virus activity of rfGLec-1was performed using the FG cell lines, which results showing that rfGLec-1possesseda virus-neutralizing activity. The expression of galectin-1was decreased in the headkidney in the initial8h after injected with polyI:C, and then increased from24honwards, peaking at48h, suggesting the involvement of fGLec-1in anti-viralresponse in flounder. Intraperitoneal injection of LCDV into flounder resulted in asignification increase in the expression of tnf-ɑ and il-β in the head kidney and the gill,co-injection of LCDV and rfGLec-1remarkably down-regulated the expression oftnf-ɑ and il-β, indicated that rfGLec-1had a potential anti-inflammatory activityagainst viral infection. The rfGLec-1was able to restrain the overexpression ofanti-viral protein gene mx against the virus infection.In conclusion, this study reports that fGLec-1plays an important role in theanti-viral response, and possesses virus-neutralizing activity and anti-inflammatoryactivity. The galectin-1was an important component in the innate immune system.