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

• Two fatty acyl desaturases (Fads) were cloned and the activities were characterized as Δ5.
• Two Δ5 Fads, HdhFad1 and HdhFad2, expressed in all tissues analyzed
• HdhFad1 possessed higher activity but expressed lower level than HdhFad2.

Long chain polyunsaturated fatty acid (LC-PUFA) biosynthesis is limited in many marine species, normally due to lack of Δ5 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 Δ5 Fads in abalone (Haliotis discus hannai Ino). Two Δ5 Fad mRNA transcripts, Hdhfad1 (GQ 470626) and Hdhfad2 (GQ 466197), were found in abalone sharing 96.82% similarity for cDNA sequence and 96.58% similarity for their deduced amino acid sequences. Hdhfad1 cDNA is 1530 bp in length with an opening reading frame (ORF) coding for 438 amino acids. Hdhfad2 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 Hdhfad1 and Hdhfad2 were expressed in tissues of abalone, especially in hepatopancreas and intestine. HdhFad1 possessed higher Δ5 desaturase activity but expressed at a lower level than HdhFad2. 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.