Cloning and analysis of a ferritin subunit from turbot (Scophthalmus maximus)

Ferritin is an evolutionarily conserved protein that plays an important role in iron storage and detoxification. In this study, the gene encoding a ferritin H subunit homologue (SmFer1) was cloned from turbot (Scophthalmus maximus) and analyzed at the expression and functional levels. The open reading frame of SmFer1 is 534 bp and preceded by a 5'-untranslated region that contains a putative Iron Regulatory Element (IRE). The deduced amino acid sequence of SmFer1 shares extensive sequence identities with the H ferritins of a number of fish species and contains the ferroxidase center that is preserved in ferritin H subunits. Examination of tissue specific expression indicated that SmFer1 expression was most abundant in muscle, liver, and blood. Experimental infection with bacterial pathogens induced significant induction of SmFer1; however, the magnitudes of induction effected by Gram-negative pathogens were much higher than that induced by Gram-positive pathogen. Consistently, lipopolysaccharide (LPS) challenge drastically augmented SmFer1 expression. In addition to bacterial pathogens and LPS, poly(I:C) also induced a strong but transient induction of SmFer1 which differs in profile from those induced by bacterial pathogens. In vitro iron-chelating analysis showed that recombinant SmFer1 purified from Escherichia coli was able to bind ferrous iron in a concentration-dependent manner. To examine whether SmFer1, with its iron-chelating capacity, could have any effect on the infection of bacterial pathogens, purified recombinant SmFer1 was subjected to bacteriostatic analysis and proved to be able to inhibit the growth of the fish pathogen Listonella anguillarum which enhanced SmFer1 expression upon infection. Taken together, these results suggest that SmFer1 is likely to play a role in both iron storage and immune defense against microbial infections.