Publications

• Characterization of human SCD2, an oligomeric desaturase with improved stability and enzyme activity by cross-linking in intact cells.

  Zhang S., Yang Y., Shi Y.

  SCD (stearoyl-CoA desaturase) catalyses the conversion of saturated fatty acids into mono-unsaturated fatty acids, a critical step involved in lipid metabolism and various other biological functions. In the present study, we report the identification and characterization of a human gene that encod ... >> More

  SCD (stearoyl-CoA desaturase) catalyses the conversion of saturated fatty acids into mono-unsaturated fatty acids, a critical step involved in lipid metabolism and various other biological functions. In the present study, we report the identification and characterization of a human gene that encodes a novel SCD enzyme (hSCD2). The hSCD2 gene codes for a 37.5-kDa protein that shares 61% and 57% sequence identity with the human SCD1 and mouse SCD2 enzymes respectively. The recombinant hSCD2 enzyme expressed in mammalian and Sf9 insect cells efficiently catalysed desaturation of both stearoyl- and palmitoyl-CoAs to the corresponding mono-unsaturated fatty acids. In comparison with the hSCD1 gene that is predominantly expressed in liver, hSCD2 is most abundantly expressed in pancreas and brain. Additionally, hSCD2 transcripts from adult and foetal tissues exhibit different sizes because of alternative splicing in the non-coding region, suggesting that hSCD2 expression is developmentally regulated. The recombinant human SCD2 and SCD1 transiently expressed in COS-7 cells exhibited as oligomeric proteins that consist of homodimers and oligomers when resolved by SDS/PAGE. The complex formation was independent of SCD protein expression levels, as supported by a relatively constant ratio of the level of dimers and oligomers to that of the monomers from COS-7 cells transiently transfected with different amounts of SCD expression vectors. Furthermore, treatment of intact COS-7 cells with a cross-linking reagent resulted in dose-dependent increases in the levels of SCD protein and activity, suggesting that oligomerization may play an important role in regulating the stability of SCD enzymes. << Less

  Biochem. J. 388:135-142(2005) [PubMed] [EuropePMC]

  This publication is cited by 2 other entries.

• Electron-transfer mechanism associated with fatty acid desaturation catalyzed by liver microsomes.

  Oshino N., Imai Y., Sato R.

  Biochim Biophys Acta 128:13-27(1966) [PubMed] [EuropePMC]

• Role of fatty acid elongases in determination of de novo synthesized monounsaturated fatty acid species.

  Green C.D., Ozguden-Akkoc C.G., Wang Y., Jump D.B., Olson L.K.

  Enhanced production of monounsaturated fatty acids (FA) derived from carbohydrate-enriched diets has been implicated in the development of obesity and insulin resistance. The FA elongases Elovl-5 and Elovl-6 are regulated by nutrient and hormone status, and have been shown using intact yeast and m ... >> More

  Enhanced production of monounsaturated fatty acids (FA) derived from carbohydrate-enriched diets has been implicated in the development of obesity and insulin resistance. The FA elongases Elovl-5 and Elovl-6 are regulated by nutrient and hormone status, and have been shown using intact yeast and mammalian microsome fractions to be involved in the synthesis of monounsaturated FAs (MUFA). Herein, targeted knockdown and overexpression of Elovl-5 or Elovl-6 was used to determine their roles in de novo synthesis of specific MUFA species in mammalian cells. Treatment of rat insulinoma (INS)-1 cells with elevated glucose increased de novo FA synthesis and the ratio of MUFAs to saturated FAs. Elovl-5 knockdown decreased elongation of 16:1,n-7. Elovl-5 overexpression increased synthesis of 18:1,n-7; however, this increase was dependent on stearoyl-CoA desaturase-driven 16:1,n-7 availability. Knockdown of Elovl-6 decreased elongation of 16:0 and 16:1,n-7, resulting in accumulation of 16:1,n-7. Elovl-6 overexpression preferentially drove synthesis of 16:0 elongation products 18:0 and 18:1,n-9 but not 18:1,n-7. These findings demonstrate that coordinated induction of FA elongase and desaturase activity is required for balanced synthesis of specific n-7 versus n-9 MUFA species. Given the relative abundance of 16:0 to 16:1,n-7 and the specificity of Elovl-6 for 16:0, Elovl-6 is a major elongase for 18:1,n-9 production. << Less

  J. Lipid Res. 51:1871-1877(2010) [PubMed] [EuropePMC]

  This publication is cited by 1 other entry.

• Isolation and functional characterization of two independently-evolved fatty acid Delta12-desaturase genes from insects.

  Zhou X.-R., Horne I., Damcevski K., Haritos V., Green A., Singh S.

  We report the first isolation and characterization of insect fatty acid Delta12-desaturase genes, AdD12Des from house cricket (Acheta domesticus) and TcD12Des from the red flour beetle (Tribolium castaneum), responsible for the production of linoleic acid from oleic acid. Sequence analysis shows t ... >> More

  We report the first isolation and characterization of insect fatty acid Delta12-desaturase genes, AdD12Des from house cricket (Acheta domesticus) and TcD12Des from the red flour beetle (Tribolium castaneum), responsible for the production of linoleic acid from oleic acid. Sequence analysis shows the cricket and flour beetle Delta12-desaturase genes have evolved independently from all previously known Delta12-desaturases and are much more closely related to the archetypal stearoyl-Coenzyme A-acting desaturase from rat than to the phospholipid-acting Delta12-desaturases widely reported in plants. Phylogenetic and functional analysis indicates the cricket AdD12Des gene may have evolved from an ancestral Delta9-desaturase. By contrast, the beetle Delta12-desaturase is distantly related to the cricket genes and beetle Delta9-desaturases suggesting evolution by an independent route. Linoleic acid has key physiological roles in insects and this is the first report of genes capable of producing this essential fatty acid in higher animals. << Less

  Insect Mol. Biol. 17:667-676(2008) [PubMed] [EuropePMC]

  This publication is cited by 3 other entries.

• A function of cytochrome b5 in fatty acid desaturation by rat liver microsomes.

  Oshino N., Imai Y., Sato R.

  J Biochem 69:155-167(1971) [PubMed] [EuropePMC]

• De novo lipogenesis and stearoyl-CoA desaturase are coordinately regulated in the human adipocyte and protect against palmitate-induced cell injury.

  Collins J.M., Neville M.J., Hoppa M.B., Frayn K.N.

  De novo lipogenesis (DNL) is paradoxically up-regulated by its end product, saturated fatty acids (SAFAs). We tested the hypothesis that SAFA-induced up-regulation of DNL reflects coordinate up-regulation of elongation and desaturation pathways for disposal of SAFAs and production of monounsaturat ... >> More

  De novo lipogenesis (DNL) is paradoxically up-regulated by its end product, saturated fatty acids (SAFAs). We tested the hypothesis that SAFA-induced up-regulation of DNL reflects coordinate up-regulation of elongation and desaturation pathways for disposal of SAFAs and production of monounsaturated fatty acids to protect cells from SAFA toxicity. Human preadipocytes were differentiated in vitro for 14 days with [U-(13)C]palmitate (0-200 microM) to distinguish exogenous fatty acids from those synthesized by DNL. Exogenous palmitate up-regulated DNL (p < 0.001) concomitantly with SCD and elongation (each p < 0.001). Adipocytes from some donors were intolerant to high palmitate concentrations (400 microM). Palmitate-intolerant cells showed lower TG accumulation. They had lower expression of SCD mRNA and less monounsaturated fatty acids in TG, emphasizing the importance of desaturation for dealing with exogenous SAFAs. There was greater [U-(13)C]palmitate incorporation in phospholipids. SCD knockdown with small interfering RNA caused down-regulation of DNL and of expression of DNL-related genes, with reduced membrane fluidity (p < 0.02) and insulin sensitivity (p < 0.01), compared with scrambled small interfering RNA controls. There was preferential channeling of DNL-derived versus exogenous palmitate into elongation and of DNL-derived versus exogenous stearate into desaturation. DNL may not act primarily to increase fat stores but may serve as a key regulator, in tandem with elongation and desaturation, to maintain cell membrane fluidity and insulin sensitivity within the human adipocyte. << Less

  J Biol Chem 285:6044-6052(2010) [PubMed] [EuropePMC]

• Mechanistic and structural insights into the regioselectivity of an acyl-CoA fatty acid desaturase via directed molecular evolution.

  Vanhercke T., Shrestha P., Green A.G., Singh S.P.

  Membrane-bound fatty acid desaturases and related enzymes play a pivotal role in the biosynthesis of unsaturated and various unusual fatty acids. Structural insights into the remarkable catalytic diversity and wide range of substrate specificities of this class of enzymes remain limited due to the ... >> More

  Membrane-bound fatty acid desaturases and related enzymes play a pivotal role in the biosynthesis of unsaturated and various unusual fatty acids. Structural insights into the remarkable catalytic diversity and wide range of substrate specificities of this class of enzymes remain limited due to the lack of a crystal structure. To investigate the structural basis of the double bond positioning (regioselectivity) of the desaturation reaction in more detail, we relied on a combination of directed evolution in vitro and a powerful yeast complementation assay to screen for Δx regioselectivity. After two selection rounds, variants of the bifunctional Δ12/Δ9-desaturase from the house cricket (Acheta domesticus) exhibited increased Δ9-desaturation activity on shorter chain fatty acids. This change in specificity was the result of as few as three mutations, some of them near the putative active site. Subsequent analysis of individual substitutions revealed an important role of residue Phe-52 in facilitating Δ9-desaturation of shorter chain acyl substrates and allowed for the redesign of the cricket Δ12/Δ9-desaturase into a 16:0-specific Δ9-desaturase. Our results demonstrate that a minimal number of mutations can have a profound impact on the regioselectivity of acyl-CoA fatty acid desaturases and include the first biochemical data supporting the acyl-CoA acyl carrier specificity of a desaturase able to carry out Δ12-desaturation. << Less

  J. Biol. Chem. 286:12860-12869(2011) [PubMed] [EuropePMC]

• Identification and characterization of murine SCD4, a novel heart-specific stearoyl-CoA desaturase isoform regulated by leptin and dietary factors.

  Miyazaki M., Jacobson M.J., Man W.C., Cohen P., Asilmaz E., Friedman J.M., Ntambi J.M.

  Stearoyl-CoA desaturase (SCD) is the rate-limiting enzyme in the biosynthesis of monounsaturated fatty acids. Thus far, three isoforms of SCD (SCD1, SCD2, and SCD3) have been identified and characterized. Regulation of the SCD1 isoform has been shown to be an important component of the metabolic a ... >> More

  Stearoyl-CoA desaturase (SCD) is the rate-limiting enzyme in the biosynthesis of monounsaturated fatty acids. Thus far, three isoforms of SCD (SCD1, SCD2, and SCD3) have been identified and characterized. Regulation of the SCD1 isoform has been shown to be an important component of the metabolic actions of leptin in liver, but the effects of leptin on SCD isoforms in other tissues have not been investigated. We found that although the mRNA levels of SCD1 and SCD2 were not affected by leptin deficiency in the hearts of ob/ob mice, the SCD activity and levels of monounsaturated fatty acids were increased, implying the existence of another SCD isoform. This observation has led to the cDNA cloning and characterization of a fourth SCD isoform (SCD4) that is expressed exclusively in the heart. SCD4 encodes a 352-amino acid protein that shares 79% sequence identity with the SCD1, SCD2, and SCD3 isoforms. Liver X receptor alpha (LXR alpha) agonists and a high carbohydrate fat-free diet induced SCD4 expression, but unlike SCD1, SCD4 expression was not repressed by dietary polyunsaturated fatty acids. SCD4 mRNA levels were elevated 5-fold in the hearts of leptin-deficient ob/ob mice relative to wild type controls. Treatment of ob/ob mice with leptin decreased mRNA levels of SCD4, whereas levels of SCD1 and SCD2 were not affected. Furthermore, in the hearts of SCD1-deficient mice, SCD4 mRNA levels were induced 3-fold, whereas the levels of SCD2 were not altered. The current studies identify a novel heart-specific SCD isoform that demonstrates tissue-specific regulation by leptin and dietary factors. << Less

  J. Biol. Chem. 278:33904-33911(2003) [PubMed] [EuropePMC]

  This publication is cited by 1 other entry.

• Purification and properties of rat liver microsomal stearyl coenzyme A desaturase.

  Strittmatter P., Spatz L., Corcoran D., Rogers M.J., Setlow B., Redline R.

  The terminal enzyme of the NADH-dependent stearyl coenzyme A desaturase system has been isolated from rat liver microsomes. This desaturase is a single polypeptide of 53,000 daltons containing 62% nonpolar amino-acid residues and one atom of non-heme iron. The purified protein forms high molecular ... >> More

  The terminal enzyme of the NADH-dependent stearyl coenzyme A desaturase system has been isolated from rat liver microsomes. This desaturase is a single polypeptide of 53,000 daltons containing 62% nonpolar amino-acid residues and one atom of non-heme iron. The purified protein forms high molecular weight aggregates that can be dispersed by detergent procedures. Desaturase activity requires NADH, stearyl coenzyme A, oxygen, lipid, and the three enzymes, cytochorme b(5) reductase (EC 1.6.2.2), cytochrome b(5), and desaturase. Cytochrome b(5) is the direct electron donor to the desaturase, which appears to utilize the iron in the oxidation-reduction sequence during desaturation of stearyl coenzyme A. << Less

  Proc Natl Acad Sci U S A 71:4565-4569(1974) [PubMed] [EuropePMC]

• Characterization of HSCD5, a novel human stearoyl-CoA desaturase unique to primates.

  Wang J., Yu L., Schmidt R.E., Su C., Huang X., Gould K., Cao G.

  Stearoyl-CoA desaturase (SCD) is an integral membrane protein of the endoplasmic reticulum (ER) that catalyzes the formation of monounsaturated fatty acids from saturated fatty acids. Recent studies suggest that SCD is a key regulator of energy metabolism and has implications in dislipidemia and o ... >> More

  Stearoyl-CoA desaturase (SCD) is an integral membrane protein of the endoplasmic reticulum (ER) that catalyzes the formation of monounsaturated fatty acids from saturated fatty acids. Recent studies suggest that SCD is a key regulator of energy metabolism and has implications in dislipidemia and obesity. Four SCD isoforms (SCD1-4) have been identified in mouse. In human, only one SCD isoform has been characterized so far. Here we report that the previously reported human ACOD4 gene encodes a distinct stearoyl-CoA desaturase, hSCD5. GenBank database mining revealed orthologues of hSCD5 in the primates, but not in the rodents. In transiently transfected 293 cells, hSCD5 co-localized with calnexin on ER membrane. Microsome fractions prepared from hSCD1 and hSCD5 transfected cells displayed similar delta 9 desaturase activity. Quantitative real-time RT-PCR analysis suggested that hSCD5 was abundantly expressed in adult brain and pancreas. These data suggested that hSCD5 plays a role distinct from that of hSCD1 during development and in normal physiological conditions. << Less

  Biochem. Biophys. Res. Commun. 332:735-742(2005) [PubMed] [EuropePMC]