Fatty acid desaturases: selecting the dehydrogenation channel

Buist, Peter H.

doi:10.1039/b302094k

Cited by 110 publications

(87 citation statements)

References 152 publications

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“…The model currently used for the active site is that of a compound Q-like oxidant based on the more developed enzymology of soluble methane monooxygenase [115]. Recommended overviews of desaturation systems and the current mechanistic models have been written by Shanklin & Cahoon [116] and Buist [117], respectively.…”

Section: Cloning and Expression Of The Lipid-desaturating Components Ofmentioning

confidence: 99%

Biosynthesis and function of polyacetylenes and allied natural products

Minto

Blacklock

2008

Progress in Lipid Research

291

228

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Polyacetylenic natural products are a substantial class of often unstable compounds containing a unique carbon-carbon triple bond functionality, that are intriguing for their wide variety of biochemical and ecological functions, economic potential, and surprising mode of biosynthesis. Isotopic tracer experiments between 1960 and 1990 demonstrated that the majority of these compounds are derived from fatty acid and polyketide precursors. During the past decade, research into the metabolism of polyacetylenes has swiftly advanced, driven by the cloning of the first genes responsible for polyacetylene biosynthesis in plants, moss, fungi, and actinomycetes, and the initial characterization of the gene products.The current state of knowledge of the biochemistry and molecular genetics of polyacetylenic secondary metabolic pathways will be presented together with an up-to-date survey of new terrestrial and marine natural products, their known biological activities, and a discussion of their likely metabolic origins.

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Section: Cloning and Expression Of The Lipid-desaturating Components Ofmentioning

confidence: 99%

Biosynthesis and function of polyacetylenes and allied natural products

Minto

Blacklock

2008

Progress in Lipid Research

291

228

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“…By analogy to soluble fatty acid desaturases, the presence of conserved His boxes of the formulas HX [3][4] H, HX 2-3 HH, and (H/Q)X 2-3 HH has led to the suggestion that these include the ligands for a diiron cluster at the active site of the enzyme (6) (Figure 2). Amino acid residues that are proposed to contribute to activity tend to cluster around these His boxes (7-10) while hydropathy plots suggest four conserved transmembrane domains (11) (Figure 2).…”

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confidence: 99%

“…These reactions include hydroxylation, epoxidation, conjugated double bond formation, and triple bond formation (3). The acetylenase Crep1, from Crepis alpina, is the first of a number of FAD2-like acetylenases identified in the plant families Asteraceae, Apiaceae, and Araliaceae (4).…”

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Structural Control of Chemoselectivity, Stereoselectivity, and Substrate Specificity in Membrane-Bound Fatty Acid Acetylenases and Desaturases

et al. 2009

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Structural control of chemoselectivity, stereoselectivity, and substrate specificity in membrane-bound fatty acid acetylenases and desaturases Gagné, Steve J.; Reed, Darwin W.; Gray, Gordon R.; Covello, Patrick S. Saskatoon SK S7N 5A8, Canada Received September 14, 2009; Revised Manuscript Received October 26, 2009 ABSTRACT: The FAD2-like desaturases comprise a group of membrane-bound oxygenases involved in the modification of fatty acyl groups in plants and fungi. This group includes typical oleate desaturases which introduce a Δ12 cis double bond and more unusual enzymes such as Crep1, an acetylenase from the plant Crepis alpina, which introduces a triple bond in linoleate at the Δ12 position. In this study, the structure--function relationship between FAD2-like acetylenases and desaturases was examined through site-directed mutagenesis and heterologous expression. Eleven amino acid positions were identified that show complete evolutionary conservation within acetylenases or desaturases but have different amino acids in the other class of enzyme. Point mutants in Crep1 were constructed and expressed in yeast to test the role in fatty acid modification of the amino acids at the 11 positions. Results indicate the importance of five amino acid positions within Crep1 with regard to desaturase and acetylenase chemoselectivity, stereoselectivity, and substrate recognition. For example, relative to wild-type Crep1, the Y150F, F259L, and H266Q mutations all favored desaturation over acetylenation. The data indicate that small changes in primary sequence, particularly in the vicinity of the active site, can have profound changes on chemoselectivity and other aspects of the function of membrane-bound desaturase-like enzymes.The FAD2 1 -like desaturases comprise a group of membranebound oxygenases involved in the modification of fatty acyl groups in plants and fungi. The archetypal plant FAD2 catalyzes the introduction of a cis double bond at the Δ12 position of oleoylphosphatidylcholine in the endoplasmic reticulum (1) (Figure 1). This requires molecular oxygen and reducing equivalents from cytochrome b 5 (2).Interestingly, the FAD2-like enzyme group includes a number of variants which catalyze reactions other than the usual Δ12 cis desaturation. These reactions include hydroxylation, epoxidation, conjugated double bond formation, and triple bond formation (3). The acetylenase Crep1, from Crepis alpina, is the first of a number of FAD2-like acetylenases identified in the plant families Asteraceae, Apiaceae, and Araliaceae (4). Crep1 catalyzes the formation of a triple bond at the 12,13 position of linoleate (18:2-9c,12c) to give crepenynate (18:1-9c,12a) (Figure 1). Crep1 has also been reported to catalyze both cis and trans desaturation of oleate (5) (Figure 1).In general, the membrane-bound desaturases are particularly difficult to work with in vitro.Muchofwhatisknownaboutthe structure and function of these enzymes has been derived from their primary structure and in vivo activities in yeast. By analogy to solub...

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“…Fatty acid acyl carrier protein (ACP) 3 desaturases (EC 1.14.99.6) convert saturated fatty acyl-ACPs into their cis-monounsaturated equivalents in an oxygen-dependent reaction (1)(2)(3)(4)(5)(6). ⌬ 9 -desaturation of 18:0-ACP 4 occurs ubiquitously in the plastids of plants and thus plays an important role in determining the fluidity of cell membranes (7).…”

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confidence: 99%

The Crystal Structure of the Ivy Δ4-16:0-ACP Desaturase Reveals Structural Details of the Oxidized Active Site and Potential Determinants of Regioselectivity

Guy

Whittle

Kumaran

et al. 2007

Journal of Biological Chemistry

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The multifunctional acyl-acyl carrier protein (ACP) desaturase from Hedera helix (English ivy) catalyzes the ⌬ 4 desaturation of 16:0-ACP and the ⌬ 9 desaturation of 18:0-ACP and further desaturates ⌬ 9 -16:1 or ⌬ 9 -18:1 to the corresponding ⌬ 4,9 dienes. The crystal structure of the enzyme has been solved to 1.95 Å resolution, and both the iron-iron distance of ϳ3.2 Å and the presence of a -oxo bridge reveal this to be the only reported structure of a desaturase in the oxidized FeIII-FeIII form. Significant differences are seen between the oxidized active site and the reduced active site of the Ricinus communis (castor) desaturase; His 227 coordination to Fe2 is lost, and the side chain of Glu 224 , which bridges the two iron ions in the reduced structure, does not interact with either iron. Although carboxylate shifts have been observed on oxidation of other diiron proteins, this is the first example of the residue moving beyond the coordination range of both iron ions. Comparison of the ivy and castor structures reveal surface amino acids close to the annulus of the substrate-binding cavity and others lining the lower portion of the cavity that are potential determinants of their distinct substrate specificities. We propose a hypothesis that differences in side chain packing explains the apparent paradox that several residues lining the lower portion of the cavity in the ivy desaturase are bulkier than their equivalents in the castor enzyme despite the necessity for the ivy enzyme to accommodate three more carbons beyond the diiron site. Fatty acid acyl carrier protein (ACP)3 desaturases (EC 1.14.99.6) convert saturated fatty acyl-ACPs into their cis-monounsaturated equivalents in an oxygen-dependent reaction (1-6). ⌬ 9 -desaturation of 18:0-ACP 4 occurs ubiquitously in the plastids of plants and thus plays an important role in determining the fluidity of cell membranes (7). Plants can express distinct acyl ACP desaturases, e.g. Arabidopsis thaliana has a family of seven acyl-ACP desaturases that are differentially expressed in different tissues (8). A structurally related homolog with unknown function from Mycobacterium has also been described (9).Seed oils of various plants accumulate monounsaturated fatty acids with unusual chain lengths and/or double bond positions. Several ⌬ 9 desaturases that recognize 14-, 16-, and 18-carbon chain lengths (4, 10 -12) have been described, and others with ⌬ 6 and ⌬ 9 regiospecificities have also been reported (13,14). The biosynthetic origin of unusual fatty acids is not always straightforward; for instance, Coriandrum sativum L. (coriander) and Hedera helix (English ivy) accumulate petroselinic acid (18:1⌬ 6 ) that originates via a ⌬ 4 desaturation of 16:0-ACP followed by 2-carbon elongation to 18:1⌬ 6 (15). The genes encoding these ⌬ 4 -16:0-ACP desaturase enzymes have been isolated (15,16), and their amino acid sequences are homologous to that of the castor ⌬ 9 -18:0-ACP desaturase for which the crystal structure has been determined (17,18). This implies that ac...

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Fatty acid desaturases: selecting the dehydrogenation channel

Cited by 110 publications

References 152 publications

Biosynthesis and function of polyacetylenes and allied natural products

Biosynthesis and function of polyacetylenes and allied natural products

Structural Control of Chemoselectivity, Stereoselectivity, and Substrate Specificity in Membrane-Bound Fatty Acid Acetylenases and Desaturases

The Crystal Structure of the Ivy Δ4-16:0-ACP Desaturase Reveals Structural Details of the Oxidized Active Site and Potential Determinants of Regioselectivity

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