Genomic organization, single nucleotide polymorphism and functional characterization of natural killer enhancing factor (NKEF-A) in Miichthys miiuy.

Peroxiredoxin (Prx) play vital parts in oxidative stress belonging to a cellular antioxidant protein family. Natural killer enhancing factor (NKEF) is a member of the Prx family, which is newly defined. In addition to antioxidant activity, NKEF also can protect DNA from oxidative damage. In order to study immune defense mechanism of NKEF in teleost, NKEF-A gene of miiuy croaker (Miichthys miiuy) was cloned and characterized. The genomic organization containing one non-coding exon, five coding exons and five introns, inclouding one intron located in 5'-terminal untranslated region. The full-length cDNA was 1235 bp, consisting of a 597 bp open reading frame coding for a protein of 198 amino acids. Sequence comparison showed that the deduced amino acid sequence of miiuy croaker NKEF-A had 71.4-90.3 % identity with those of mammal and teleost. Five single nucleotide polymorphisms were detected by direct sequencing of eight samples from three different populations. Phylogenetic analysis revealed that miiuy croaker NKEF-A forms a cluster with other known teleost and mammalian NKEF-As. NKEF-A gene was constitutively expressed in ten examined tissues, and expression level was up-regulated in liver, spleen and kidney after challenge with Vibrio anguillarum. Finally, the NKEF-A was constructed and expressed in Escherichia coli. Then purified recombinant pET-NKEF protein was used to produce the polyclonal antibody and the polyclonal antibody against NKEF-A was tested by Western blot analysis. These results indicate that NKEF may be involved in immune responses as well as homeostatic processes in miiuy croaker.