Fatty acid desaturase

A fatty acid desaturase is an enzyme that removes two hydrogen atoms from a fatty acid, creating a carbon/carbon double bond. These desaturases are classified as:

  • Delta - indicating that the double bond is created at a fixed position from the carboxyl end of a fatty acid chain. For example, Δ9 desaturase creates a double bond between the ninth and tenth carbon atom from the carboxyl end.
  • Omega - indicating the double bond is created at a fixed position from the methyl end of a fatty acid chain. For instance, ω3 desaturase creates a double bond between the third and fourth carbon atom from the methyl end. In other words, it creates an omega-3 fatty acid.
Fatty acid desaturase, type 1
Identifiers
SymbolFatty_acid_desaturase-1
PfamPF00487
InterProIPR005804
OPM superfamily431
OPM protein4zyo
Fatty acid desaturase, type 2
Identifiers
SymbolFatty_acid_desaturase-2
PfamPF03405
InterProIPR005067

In the biosynthesis of essential fatty acids, an elongase alternates with different desaturases (for example, Δ6desaturase) repeatedly inserting an ethyl group, then forming a double bond.

Function

Maintain structure and function of membranes within cells of the organisms above. This is important when temperatures changes and the membrane is under distress. The enzyme creates the double bond C-Cs which allow the membrane to become more fluid and the temperature is decreased.[1] When temperatures change, a phase transition occurs. In the case of a temperature decrease, the membrane gels and becomes solid which can result in cracks and the imbedded proteins cannot partake in conformational changes, therefore it is important to maintain membrane fluidity.[2]

Role in human metabolism

Fatty acid desaturase appear in all organisms: for example, bacteria fungus plants animals and humans.[1] Four desaturases occur in humans: Δ9 desaturase, Δ6 desaturase, Δ5 desaturase, and Δ4 desaturase.[3]

Δ9 desaturase, also known as stearoyl-CoA desaturase-1, is used to synthesize oleic acid, a monounsaturated, ubiquitous component of all cells in the human body. Δ9 desaturase produces oleic acid by desaturating stearic acid, a saturated fatty acid either synthesized in the body from palmitic acid or ingested directly.

Δ6 and Δ5 desaturases are required for the synthesis of highly unsaturated fatty acids such as eicosopentaenoic and docosahexaenoic acids (synthesized from α-linolenic acid); arachidonic acid and adrenic acid (synthesized from linoleic acid). This is a multi-stage process requiring successive actions by elongase and desaturase enzymes. The genes coding for Δ6 and Δ5 desaturase production have been located on human chromosome 11.[4]

Vertebrates are unable to synthesize polyunsaturated fatty acids because they do not have the necessary fatty acid desaturases to "convert oleic acid (18:1n-9) into linoleic acid (18:2n-6) and α-linolenic acid (18:3n-3)".[4] Linoleic acid and α-linolenic acid are essential for human health and development.

Human fatty acid desaturases include: DEGS1; DEGS2; FADS1; FADS2; FADS3; FADS6; SCD4; SCD5

Classification

Δ-desaturases are represented by two distinct families which do not seem to be evolutionarily related.

Family 1 includes Stearoyl-CoA desaturase-1 (SCD) (EC 1.14.19.1).[5]

Family 2 is composed of:

  • Bacterial fatty acid desaturases.
  • Plant stearoyl-acyl-carrier-protein desaturase (EC 1.14.19.1),[6] an enzyme that catalyzes the introduction of a double bond at the delta-9 position of steraoyl-ACP to produce oleoyl-ACP. This enzyme is responsible for the conversion of saturated fatty acids to unsaturated fatty acids in the synthesis of vegetable oils.
  • Cyanobacterial DesA,[7] an enzyme that can introduce a second cis double bond at the delta-12 position of fatty acid bound to membrane glycerolipids. This enzyme is involved in chilling tolerance; the phase transition temperature of lipids of cellular membranes being dependent on the degree of unsaturation of fatty acids of the membrane lipids.

Acyl-CoA dehydrogenases

Acyl-CoA dehydrogenases are enzymes that catalyze formation of a double bond between C2 (α) and C3 (β) of the acyl-CoA thioester substrates.[8] Flavin adenine dinucleotide (FAD) is a required co-factor.

References
  1. Los DA, Murata N (October 1998). "Structure and expression of fatty acid desaturases". Biochimica et Biophysica Acta (BBA) - Lipids and Lipid Metabolism. 1394 (1): 3–15. doi:10.1016/S0005-2760(98)00091-5. PMID 9767077.
  2. Alberts B, Johnson A, Lewis J, Raff M, Roberts K, Walter P (2002). "The Fluidity of a Lipid Bilayer Depends on Its Composition". Molecular Biology of the Cell (4th ed.). New York: Garland Science. p. 588. ISBN 978-0-8153-3218-3.
  3. Nakamura MT, Nara TY (2004). "Structure, function, and dietary regulation of Δ6, Δ5, and Δ9 desaturases". Annual Review of Nutrition. 24 (1): 345–76. doi:10.1146/annurev.nutr.24.121803.063211. PMID 15189125.
  4. Hastings N, Agaba M, Tocher DR, Leaver MJ, Dick JR, Sargent JR, Teale AJ (December 2001). "A vertebrate fatty acid desaturase with Delta 5 and Delta 6 activities". Proceedings of the National Academy of Sciences of the United States of America. 98 (25): 14304–9. doi:10.1073/pnas.251516598. PMC 64677. PMID 11724940.
  5. Kaestner KH, Ntambi JM, Kelly Jr TJ, Lane MD (September 1989). "Differentiation-induced gene expression in 3T3-L1 preadipocytes. A second differentially expressed gene encoding stearoyl-CoA desaturase" (PDF). The Journal of Biological Chemistry. 264 (25): 14755–61. PMID 2570068.
  6. Shanklin J, Somerville C (March 1991). "Stearoyl-acyl-carrier-protein desaturase from higher plants is structurally unrelated to the animal and fungal homologs". Proceedings of the National Academy of Sciences of the United States of America. 88 (6): 2510–4. Bibcode:1991PNAS...88.2510S. doi:10.1073/pnas.88.6.2510. PMC 51262. PMID 2006187.
  7. Wada H, Gombos Z, Murata N (September 1990). "Enhancement of chilling tolerance of a cyanobacterium by genetic manipulation of fatty acid desaturation". Nature. 347 (6289): 200–3. Bibcode:1990Natur.347..200W. doi:10.1038/347200a0. PMID 2118597. S2CID 4326551.
  8. Thorpe C, Kim JJ (June 1995). "Structure and mechanism of action of the acyl-CoA dehydrogenases". FASEB Journal. 9 (9): 718–25. doi:10.1096/fasebj.9.9.7601336. PMID 7601336. S2CID 42549744.
This article incorporates text from the public domain Pfam and InterPro: IPR005067
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