Characterization of two Δ5 fatty acyl desaturases in abalone (Haliotis discus hannai Ino)

Abstract Long chain polyunsaturated fatty acid (LC-PUFA) biosynthesis is limited in many marine species, normally due to lack of Δ 5 fatty acyl desaturase (Fad) activity. Among exceptions, abalone possesses considerable LC-PUFA conversion ability from C18 precursors. However, its characterization and relevant enzyme are not well characterized. Here we successfully cloned and characterized two Δ 5 Fads in abalone ( Haliotis discus hannai Ino). Two Δ 5 Fad mRNA transcripts, Hdh fad1 (GQ 470626) and Hdh fad2 (GQ 466197), were found in abalone sharing 96.82% similarity for cDNA sequence and 96.58% similarity for their deduced amino acid sequences. Hdh fad1 cDNA is 1530 bp in length with an opening reading frame (ORF) coding for 438 amino acids. Hdh fad2 cDNA is 1525 bp in length with an ORF encoding for 439 amino acids. Both have characteristic features of front–end desaturase, including three histidine boxes, an N-terminal cytochrome b5 domain with heme-binding motif and transmembrane regions. Both Hdh fad1 and Hdh fad2 were expressed in tissues of abalone, especially in hepatopancreas and intestine. Hdh Fad1 possessed higher Δ 5 desaturase activity but expressed at a lower level than Hdh Fad2. Both isoforms preferred 20:4n-3 than 20:3n-6 as substrate. These results should provide valuable information on the molecular evolution of Fads and better understanding of LC-PUFA biosynthesis in abalone.