Cloning and characterisation of natural resistance associated macrophage protein (Nramp) cDNA from red sea bream (Pagrus major)

Nramp (natural resistance associated macrophage protein) controls aspects of innate resistance to intracellular parasites. Its function is to enhance the ability of macrophages to kill pathogens. However, little is known about the structure and function of Nramp in lower vertebrates such as teleosts. We have recently isolated a cDNA encoding Nramp from spleen of red sea bream (Pagrus major). The full-length cDNA of the Nramp is 4709 bp in length, including 197 bp 5′-terminal untranslated region (UTR), 1662 bp encoding region and 2850 bp 3′-terminal UTR (GenBank accession number: AY485311). The 1662 nt open reading frame was found to code for a protein with 554 amino acid residues. Comparison of the amino acid sequence indicated that red sea bream Nramp consists of 12 transmembrane region (TM) domains. A consensus transport motif (CTM) containing 20 residues was observed between transmembrane domains 8 and 9. The deduced amino acid sequence of red sea bream Nramp had 77.8%, 83.0%, 82.3%, 80.0%, 81.1%, 60.4%, 70.3%, 58.5% and 69.5% identity with that of rainbow trout Nramp α and β, channel catfish Nramp, fathead minnow Nramp, common carp Nramp, mouse Nramp 1 and 2, and human Nramp1 and 2, respectively. Reverse transcription–polymerase chain reaction indicated that levels of Nramp expression were similar among head kidney, spleen, intestine and liver in non-challenged red sea bream, and that challenge of red sea bream with the pathogenic bacterium, Vibrio anguillarum, significantly elevated Nramp mRNA levels in liver and spleen in a time-dependent fashion.