title: Cloning, expression, and fatty acid regulation of the human delta-5 desaturase.
abstract: Arachidonic (20:4(n-6)), eicosapentaenoic (20:5(n-3)), and docosahexaenoic (22:6(n-3)) acids are major components of brain and retina phospholipids, substrates for eicosanoid production, and regulators of nuclear transcription factors. One of the two rate-limiting steps in the production of these polyenoic fatty acids is the desaturation of 20:3(n-6) and 20:4(n-3) by Delta-5 desaturase. This report describes the cloning and expression of the human Delta-5 desaturase, and it compares the structural characteristics and nutritional regulation of the Delta-5 and Delta-6 desaturases. The open reading frame of the human Delta-5 desaturase encodes a 444-amino acid peptide which is identical in size to the Delta-6 desaturase and which shares 61% identity with the human Delta-6 desaturase. The Delta-5 desaturase contains two membrane-spanning domains, three histidine-rich regions, and a cytochrome b(5) domain that all align perfectly with the same domains located in the Delta-6 desaturase. Expression of the open reading frame in Chinese hamster ovary cells instilled the ability to convert 20:3(n-6) to 20:4(n-6). Northern analysis revealed that many human tissues including skeletal muscle, lung, placenta, kidney, and pancreas expressed Delta-5 desaturase mRNA, but Delta-5 desaturase was most abundant in the liver, brain, and heart. However, in all tissues, the abundance of Delta-5 desaturase mRNA was much lower than that observed for the Delta-6 desaturase. When rats were fed a diet containing 10% safflower oil or menhaden fish oil, the level of hepatic mRNA for Delta-5 and Delta-6 desaturase was only 25% of that found in the liver of rats fed a fat-free diet or a diet containing triolein. Finally, a BLAST and Genemap search of the human genome revealed that the Delta-5 and Delta-6 desaturase genes reside in reverse orientation on chromosome 11 and that they are separated by <11,000 base pairs.
authors.affiliation: Program of Nutritional Sciences and the Institute for Cellular and Molecular Biology, The University of Texas-Austin, Austin, Texas 78712, USA.
authors.forename: H P
authors.initials: HP
authors.lastname: Cho
authors.forename: M
authors.initials: M
authors.lastname: Nakamura
authors.forename: S D
authors.initials: SD
authors.lastname: Clarke
mesh_terms: D000595:Amino Acid Sequence; D000818:Animals; D016466:CHO Cells; D003001:Cloning, Molecular; D006224:Cricetinae; D000090943:Delta-5 Fatty Acid Desaturase; D044943:Fatty Acid Desaturases / Q000737:chemistry / Q000235:genetics*; D005227:Fatty Acids / Q000494:pharmacology*; D015971:Gene Expression Regulation, Enzymologic / Q000187:drug effects*; D006801:Humans; D050602:Linoleoyl-CoA Desaturase; D008969:Molecular Sequence Data; D016366:Open Reading Frames; D012333:RNA, Messenger / Q000032:analysis
chemical_list: D000090943:Delta-5 Fatty Acid Desaturase; D005227:Fatty Acids; D012333:RNA, Messenger; D044943:Fatty Acid Desaturases; D050602:Linoleoyl-CoA Desaturase