title: Cloning and functional characterisation of a fatty acyl elongase from southern bluefin tuna (Thunnus maccoyii).
abstract: The synthesis of long chain polyunsaturated fatty acids (LCPUFA), such as eicosapentaenoic acid (EPA; 20:5n-3) and docosahexaenoic acid (DHA; 22:6n-3), involves fatty acyl desaturase and elongase enzymes. The marine fish species southern bluefin tuna (SBT) can accumulate large quantities of omega-3 (n-3) LCPUFA in its flesh but their capacity to synthesize EPA and DHA is uncertain. A cDNA, sbtElovl5, encoding a putative fatty acyl elongase was amplified from SBT liver tissue. The cDNA included an open reading frame (ORF) encoding 294 amino acids. Sequence comparisons and phylogenetic analyses revealed a high level of sequence conservation between sbtElovl5 and fatty acyl elongase sequences from other fish species. Heterologous expression of the sbtElovl5 ORF in Saccharomyces cerevisiae confirmed that it encoded a fatty acyl elongase capable of elongating C(18/20) polyunsaturated fatty acid (PUFA) substrates, but not C(22) PUFA substrates. For the first time in an Elovl5, the substrate competition occurring in nature was investigated. Higher activity towards n-3 PUFA substrates than omega-6 (n-6) PUFA substrates was exhibited, regardless of substrate chain length. The sbtElovl5 preferentially elongated 18:4n-3 and 18:3n-6 rather than 20:5n-3 and 20:4n-6. The sbtElovl5 enzyme also elongated saturated and monounsaturated fatty acids.
authors.affiliation: School of Biological Sciences, Flinders University, Adelaide, Australia.
authors.forename: Melissa K
authors.initials: MK
authors.lastname: Gregory
authors.forename: Valene H L
authors.initials: VH
authors.lastname: See
authors.forename: Robert A
authors.initials: RA
authors.lastname: Gibson
authors.forename: Kathryn A
authors.initials: KA
authors.lastname: Schuller
mesh_terms: D000123:Acetyltransferases / Q000737:chemistry / Q000235:genetics* / Q000378:metabolism*; D000595:Amino Acid Sequence; D000818:Animals; D003001:Cloning, Molecular; D000081031:Fatty Acid Elongases; D005231:Fatty Acids, Unsaturated / Q000096:biosynthesis / Q000737:chemistry / Q000378:metabolism; D008099:Liver / Q000378:metabolism; D008969:Molecular Sequence Data; D016366:Open Reading Frames / Q000235:genetics; D010473:Perciformes / Q000235:genetics*; D017422:Sequence Analysis, DNA
chemical_list: D005231:Fatty Acids, Unsaturated; D000123:Acetyltransferases; D000081031:Fatty Acid Elongases