Functional desaturase Fads1 (Δ5) and Fads2 (Δ6) orthologues evolved before the origin of jawed vertebrates

Long-chain polyunsaturated fatty acids (LC-PUFAs) such as arachidonic (ARA), eicosapentaenoic (EPA) and docosahexaenoic (DHA) acids are essential components of biomembranes, particularly in neural tissues. Endogenous synthesis of ARA, EPA and DHA occurs from precursor dietary essential fatty acids such as linoleic and α-linolenic acid through elongation and Δ5 and Δ6 desaturations. With respect to desaturation activities some noteworthy differences have been noted in vertebrate classes. In mammals, the Δ5 activity is allocated to the Fads1 gene, while Fads2 is a Δ6 desaturase. In contrast, teleosts show distinct combinations of desaturase activities (e.g. bifunctional or separate Δ5 and Δ6 desaturases) apparently allocated to Fads2-type genes. To determine the timing of Fads1-Δ5 and Fads2-Δ6 evolution in vertebrates we used a combination of comparative and functional genomics with the analysis of key phylogenetic species. Our data show that Fads1 and Fads2 genes with Δ5 and Δ6 activities respectively, evolved before gnathostome radiation, since the catshark Scyliorhinus canicula has functional orthologues of both gene families. Consequently, the loss of Fads1 in teleosts is a secondary episode, while the existence of Δ5 activities in the same group most likely occurred through independent mutations into Fads2 type genes. Unexpectedly, we also establish that events of Fads1 gene expansion have taken place in birds and reptiles. Finally, a fourth Fads gene (Fads4) was found with an exclusive occurrence in mammalian genomes. Our findings enlighten the history of a crucially important gene family in vertebrate fatty acid metabolism and physiology and provide an explanation of how observed lineage-specific gene duplications, losses and diversifications might be linked to habitat-specific food web structures in different environments and over geological timescales.     

Isolation and functional characterisation of the genes encoding Δ(8)-Sphingolipid desaturase from Brassica rapa

△~8-Sphingohpid desaturase is the key enzyme that catalyses desaturation at the C8 position of the long-chain base of sphingolipids in higher plants.There have been no previous studies on the genes encoding△~8-sphingolipid desaturases in Brassica rapa.In this study,four genes encoding A -sphingohpid desaturases from B.rapa were isolated and characterised.Phylogenetic analyses indicated that these genes could be divided into two groups:BrD8A,BrD8C and BrD8D in groupⅠ,and BrD8B in groupⅡ.The two groups of genes diverged before the separation of Arabidopsis and Brassica.Though the four genes shared a high sequence similarity,and their coding desaturases all located in endoplasmic reticulum,they exhibited distinct expression patterns.Heterologous expression in Saccharomyces cerevisiae revealed that BrD8A/B/C/D were functionally diverse A -sphingohpid desaturases that catalyse different ratios of the two products 8(Z)- and 8(E)-C18-phytosphingenine.The aluminium tolerance of transgenic yeasts expressing BrD8A/B/C/D was enhanced compared with that of control cells.Expression of BrD8A in Arabidopsis changed the ratio of 8(Z):8(E)-C18-phytosphingenine in transgenic plants. The information reported here provides new insights into the biochemical functional diversity and evolutionary relationship of△~8-sphingolipid desaturase in plants and lays a foundation for further investigation of the mechanism of 8(Z)- and 8(E)-C18-phytosphingenine biosynthesis.     

Identification of the substrate recognition region in the Δ6-fatty acid and Δ8-sphingolipid desaturase by fusion mutagenesis

Δ⁸-sphingolipid desaturase and Δ⁶-fatty acid desaturase share high protein sequence identity. Thus, it has been hypothesized that Δ⁶-fatty acid desaturase is derived from Δ⁸-sphingolipid desaturase; however, there is no direct proof. The substrate recognition regions of Δ⁶-fatty acid desaturase and Δ⁸-sphingolipid desaturase, which aid in understanding the evolution of these two enzymes, have not been reported. A blackcurrant Δ⁶-fatty acid desaturase and a Δ⁸-sphingolipid desaturase gene, RnD6C and RnD8A, respectively, share more than 80 % identity in their coding protein sequences. In this study, a set of fusion genes of RnD6C and RnD8A were constructed and expressed in yeast. The Δ⁶- and Δ⁸-desaturase activities of the fusion proteins were characterized. Our results indicated that (1) the exchange of the C-terminal 172 amino acid residues can lead to a significant decrease in both desaturase activities; (2) amino acid residues 114–174, 206–257, and 258–276 played important roles in Δ⁶-substrate recognition, and the last two regions were crucial for Δ⁸-substrate recognition; and (3) amino acid residues 114–276 of Δ⁶-fatty acid desaturase contained the substrate recognition site(s) responsible for discrimination between ceramide (a substrate of Δ⁸-sphingolipid desaturase) and acyl-PC (a substrate of Δ⁶-fatty acid desaturase). Substituting the amino acid residues 114-276 of RnD8A with those of RnD6C resulted in a gain of Δ⁶-desaturase activity in the fusion protein but a loss in Δ⁸-sphingolipid desaturase activity. In conclusion, several regions important for the substrate recognition of Δ8-sphingolipid desaturase and Δ⁶-fatty acid desaturase were identified, which provide clues in understanding the relationship between the structure and function in desaturases.     

New Δ8(14)-15-Ketosterols with an Oxygenated Side Chain

New analogues of 3β-hydroxy-5α-cholest-8(14)-en-15-one (15-ketosterol) with modified 17-chains [(22S,23S,24S)- and (22R,23R,24S)-3β-hydroxy-24-methyl-22,23-oxido-5α -cholest-8(14)-en-15- ones and (22RS,23ξ,24S)-24-methyl-5α-cholesta-8(14)-ene-3β, 22,23-triol-15-one] were synthesized from (22E,24S)-3β-acetoxy-24-methyl-5α-cholesta-8(14), 22-dien-15-one. The chiralities of their 22 and 23 centers were determined by NMR spectroscopy. The isomeric 22,23-epoxides effectively inhibited cholesterol biosynthesis in hepatoma Hep G2 cells (IC₅₀ 0.9±0.2 and 0.7±0.2 μM, respectively), and their activities significantly exceeded those of 15-ketosterol (IC₅₀ 4.0±0.5 μM), (22E,24S)-3β-hydroxy-24-methyl-5α-cholesta-8(14),22- dien-15-one (IC₅₀ 3.1±0.4 μM), and the 3β,22,23-triol synthesized (IC₅₀ 6.0±1.0 μM).__________Translated from Bioorganicheskaya Khimiya, Vol. 31, No. 3, 2005, pp. 312–319.Original Russian Text Copyright © 2005 by Flegentov, Piir, Medvedeva, Tkachev, Timofeev, Misharin.     

15-Deoxy-Δ(12,14)-prostaglandin J(2) attenuates the biological activities of monocyte/macrophage cell lines

Monocytes/macrophages link the innate and adaptive immune systems, and in inflammatory disorders their activation leads to tissue damage. 15-Deoxy-Δ(12,14)-prostaglandin J(2) (15d-PGJ(2)), a natural peroxisome proliferator-activated receptor gamma (PPARγ) ligand, has garnered much interest because it possesses anti-inflammatory properties in a number of experimental models. However, whether it regulates monocytes/macrophage pathophysiology is still unknown. This study was designed to examine the effects of 15d-PGJ(2) on the phagocytosis, proliferation and inflammatory cytokines generation in mouse monocyte/macrophage cell line RAW264.7 and J774A.1 cells upon lipopolysaccharide challenge. Our results showed that 15d-PGJ(2) inhibited the phagocytic activity and cell proliferation in a dose-dependent manner, and suppressed proinflammatory cytokines expression, such as tumor necrosis factor-α, transforming growth factor-β1, interleukin-6, and monocyte chemotactic protein-1. These effects were independent of PPARγ, because PPARγ agonist (troglitazone or ciglitazone) and PPARγ antagonist (GW9662) did not affect these activities mentioned above in cells. Treatment of 15d-PGJ(2) also did not modulate expression and distribution of PPARγ. However, these effects of 15d-PGJ(2) were abrogated by antioxidant N-acetylcysteine. Moreover, treatment of 15d-PGJ(2) induced a significant increase in reactive oxygen species production in RAW264.7 and J774A.1 cells. In conclusion, 15d-PGJ(2) attenuates the biological activities of mouse monocyte/macrophage cell line cells involving oxidative stress, independently of PPARγ. These data further underline the anti-inflammation potential of 15d-PGJ(2).     

Newly identified essential amino acid residues affecting Δ8-sphingolipid desaturase activity revealed by site-directed mutagenesis

In order to identify amino acid residues crucial for the enzymatic activity of Δ(8)-sphingolipid desaturases, a sequence comparison was performed among Δ(8)-sphingolipid desaturases and Δ(6)-fatty acid desaturases from various plants. In addition to the known conserved cytb(5) (cytochrome b(5)) HPGG motif and three conserved histidine boxes, they share additional 15 completely conserved residues. A series of site-directed mutants were generated using our previously isolated Δ(8)-sphingolipid desaturase gene from Brassica rapa to evaluate the importance of these residues to the enzyme function. The mutants were functionally characterized by heterologous expression in yeast, allowing the identification of the products of the enzymes. The results revealed that residues H63, N203, D208, D210, and G368 were obligatorily required for the enzymatic activity, and substitution of the residues F59, W190, W345, L369 and Q372 markedly decreased the enzyme activity. Among them, replacement of the residues W190, L369 and Q372 also has significant influence on the ratio of the two enzyme products. Information obtained in this work provides the molecular basis for the Δ(8)-sphingolipid desaturase activity and aids in our understanding of the structure-function relationships of the membrane-bound desaturases.     

Palmitates of Isomeric 15-Oxygenated Δ8(14)-Sterols

3-Hexadecanoyloxy-5-cholest-8(14)-en-15-one, 3-hexadecanoyloxy-5-cholest-8(14)-en-15-one, 15-hexadecanoyloxy-5-cholest-8(14)-en-3-ol, 15-hexadecanoyloxy-5-cholest-8(14)-en-3-ol, 15-hexadecanoyloxy-5-cholest-8(14)-en-3-one, and 15-hexadecanoyloxy-5-cholest-8(14)-en-3-one were synthesized and their chromatographic and ¹H NMR characteristics were determined.     

The effect of potato plant transformation with the gene encoding Δ12-acyl-lipid desaturase on the CO2 exchange and activities of antioxidant enzymes under hypothermia

The effects of potato (Solanum tuberosum L., cv. Desnitsa) plant transformation with the desA gene encoding Δ12-acyl-lipid desaturase from Synechocystis sp. PCC 6803 on the regulation of free-radical processes in relation to plant tolerance to hypothermia are considered. It was shown that the content of polyunsaturated fatty acids (PUFA) in transformed plants was higher than in wild-type ones. In particular, the content of linoleic acid in transformants was higher by 35% and the content of linolenic acid was by 41% higher than in untransformed plants. In addition, transformation induced an increase in the absolute content of C₁₆-PUFA and on the whole resulted in a marked accumulation of membrane lipids. As judged from the values of the damage index and the ratio of photosynthesis to respiration in wild-type and transformed plants under cold treatment, these changes in lipid metabolism favored the protection of coupling membranes, thus preventing plants against free-radical oxidation under low-temperature stress. As a result, the intensity of oxidative stress in transformed plants was much lower than in wild-type ones, whereas antioxidant enzymes (superoxide dismutase, catalase, peroxidase) were not substantially activated under hypothermia.     

Comparison of the Δ~(12) fatty acid desaturase gene between high-oleic and normal-oleic peanut genotypes

Δ12 fatty acid desaturase gene has been targeted as a logical candidate controlling the high oleate trait in peanut seeds.By RT-PCR method,the full-length cDNAs of Δ12 fatty acid desaturase gene were isolated from peanut(Arachis hypogaea L.) genotypes with normal and high ratio of oleic to linoleic acid,which were designated AhFAD2B and AhFAD2B',respectively.Sequence alignment of their coding regions revealed that an extra A was inserted at the position +442 bp of AhFAD2B' sequence of high oleic acid genoty...     

Design and synthesis of pregnenolone/2-cyanoacryloyl conjugates with dual NF-κB inhibitory and anti-proliferative activities

Twenty-five novel pregnenolone/2-cyanoacryloyl conjugates (6–30) were designed and prepared, with the aim of developing novel anticancer drugs with dual NF-κB inhibitory and anti-proliferative activities. Compounds 22 and 27–30 showed inhibition against TNF-α-induced NF-κB activation in luciferase assay, which was confirmed by Western blotting. Among them, compound 30 showed potent NF-κB inhibitory activity (IC₅₀ = 2.5 μM) and anti-proliferative against MCF-7, A549, H157, and HL-60 cell lines (IC₅₀ = 6.5–36.2 μM). The present study indicated that pregnenolone/2-cyanoacryloyl conjugate I can server as a novel scaffold for developing NF-κB inhibitors and anti-proliferative agents in cancer chemotherapy.     

Low linoleic acid may facilitate Δ6 desaturase activity and docosahexaenoic acid accretion in human fetal development

The n-3 and n-6 fatty acids are transferred across the placenta with consistently higher 22:6n-3 and lower 18:2n-6 in fetal than maternal plasma. This study sought to determine whether maternal and fetal cord blood red blood cell (RBC) phospholipid fatty acids show similar saturation with 22:6n-3, and also addressed the relationship between 18:2n-6 and Δ6 desaturase product/precursor ratios for 97 mothers and newborns. Despite higher fetal than maternal plasma phospholipid 22:6n-3, the maternal and fetal RBC phospholipid 22:6n-3 showed similar curvilinear relationships to the plasma phospholipid 22:6n-3. Risk of failure to achieve high RBC phospholipid 22:6n-3 increased sharply below a plasma phospholipid 22:6n-3 of 6.5g/100g fatty acids. Higher maternal and fetal 18:2n-6 was associated with lower RBC phospholipid 22:6n-3/22:5n-3, 22:5n-6/22:4n-6 and 18:3n-6/18:2n-6. These findings suggest low placental transfer of 18:2n-6 may be a specific mechanism to prevent inhibition of fetal Δ6 desaturase and facilitate fetal cellular phospholipid 22:6n-3 accretion.     

Interaction of diet and the masou salmon Δ5-desaturase transgene on Δ6-desaturase and stearoyl-CoA desaturase gene expression and N-3 fatty acid level in common carp (Cyprinus carpio)

The masou salmon Δ5-desaturase-like gene (D5D) driven by the common carp β-actin promoter was transferred into common carp (Cyprinus carpio) that were fed two diets. For P₁ transgenic fish fed a commercial diet, Δ6-desaturase-like gene (D6D) and stearoyl-CoA desaturase (SCD) mRNA levels in muscle were up-regulated (P < 0.05) 12.7- and 17.9-fold, respectively, and the D6D mRNA level in the gonad of transgenic fish was up-regulated 6.9-fold (P < 0.05) compared to that of non-transgenic fish. In contrast, D6D and SCD mRNA levels in transgenic fish were dramatically down-regulated (P < 0.05), 50.2- and 16.7-fold in brain, and 5.4- and 2.4-fold in liver, respectively, in comparison with those of non-transgenic fish. When fed a specially formulated diet, D6D and SCD mRNA levels in muscle of transgenic fish were up-regulated (P < 0.05) 41.5- and 8.9-fold, respectively, and in liver 6.0- and 3.3-fold, respectively, compared to those of non-transgenic fish. In contrast, D6D and SCD mRNA levels in the gonad of transgenic fish were down-regulated (P < 0.05) 5.5- and 12.4-fold, respectively, and D6D and SCD mRNA levels in the brain were down-regulated 14.9- and 1.4-fold (P < 0.05), respectively, compared to those of non-transgenic fish. The transgenic common carp fed the commercial diet had 1.07-fold EPA, 1.12-fold DPA, 1.07-fold DHA, and 1.07-fold higher observed total omega-3 fatty acid levels than non-transgenic common carp. Although these differences were not statistically different (P > 0.05), there were significantly (P < 0.10) higher omega-3 fatty acid levels when considering the differences for all of the individual omega-3 fatty acids. The genotype × diet interactions observed indicated that the potential of desaturase transgenesis cannot be realized without using a well-designed diet with the needed amount of substrates.     

EXAFS and Mössbauer characterization of the Diiron(III) site in stearoyl-acyl carrier protein Δ9– desaturase

Stearoyl-acyl carrier protein (ACP) Δ⁹-desaturase (Δ9D) from the castor plant is the best characterized soluble acyl-ACP desaturase. This enzyme utilizes a diiron center to catalyze the O₂- and NADPH-dependent introduction of a cis double bond between carbons 9 and 10 of stearoyl-ACP, yielding oleoyl-ACP. In the present study, we have used X-ray absorption spectroscopy to provide the first metrical information for the diferric oxidation state. These studies reveal distinct diiron clusters that have Fe-Fe distances of either 3.12 or 3.41?Å. The species having the 3.12?Å Fe-Fe distance also exhibits a 1.8?Å Fe-O bond and is thus proposed to represent Δ9D molecules containing a (μ-oxo)bis(μ-carboxylato)diiron(III) cluster. The species having the 3.41?Å Fe-Fe distance exhibits no short Fe-O bond, and thus likely represents Δ9D molecules containing a (μ-hydroxo)diiron(III) cluster. Mössbauer studies of the extended X-ray absorption fine structure (EXAFS) samples revealed three quadrupole doublets (ΔE _Q(1)=1.53?mm/s, 72%;ΔE _Q(2)=0.72?mm/s, 21%;ΔE _Q(3)=2.20?mm/s, 7%) that originate from three distinct dinuclear clusters. From analysis of spectral intensities and by comparison with previous studies of (μ-oxo)- and (μ-hydroxo)diiron(III) clusters in both model complexes and proteins, doublet 1, the Mössbauer majority species, is likely associated with the EXAFS majority species having a 3.12?Å Fe-Fe separation and a 1.8?Å Fe-μ-oxo bond, while doublet 2 likely results from one iron site (or both) of a cluster associated with the EXAFS species having a 3.41?Å Fe-Fe separation. The presence of multiple diiron center conformations in diferric Δ9D may reflect the necessity for the active site to allow access of the substrate stearoyl-ACP (～9?kDa) during desaturation catalysis.     

Diversification of substrate specificities in teleostei Fads2: characterization of Δ4 and Δ6Δ5 desaturases of Chirostoma estor

Currently existing data show that the capability for long-chain PUFA (LC-PUFA) biosynthesis in teleost fish is more diverse than in other vertebrates. Such diversity has been primarily linked to the subfunctionalization that teleostei fatty acyl desaturase (Fads)2 desaturases have undergone during evolution. We previously showed that Chirostoma estor, one of the few representatives of freshwater atherinopsids, had the ability for LC-PUFA biosynthesis from C₁₈ PUFA precursors, in agreement with this species having unusually high contents of DHA. The particular ancestry and pattern of LC-PUFA biosynthesis activity of C. estor make this species an excellent model for study to gain further insight into LC-PUFA biosynthetic abilities among teleosts. The present study aimed to characterize cDNA sequences encoding fatty acyl elongases and desaturases, key genes involved in the LC-PUFA biosynthesis. Results show that C. estor expresses an elongase of very long-chain FA (Elovl)5 elongase and two Fads2 desaturases displaying Δ4 and Δ6/Δ5 specificities, thus allowing us to conclude that these three genes cover all the enzymatic abilities required for LC-PUFA biosynthesis from C₁₈ PUFA. In addition, the specificities of the C. estor Fads2 enabled us to propose potential evolutionary patterns and mechanisms for subfunctionalization of Fads2 among fish lineages.     

Lithium rescues the impaired autophagy process in CbCln3(Δex7/8/Δex7/8) cerebellar cells and reduces neuronal vulnerability to cell death via IMPase inhibition

Juvenile neuronal ceroid lipofuscinosis (Batten disease) is a neurodegenerative disorder caused by mutation in CLN3. Defective autophagy and concomitant accumulation of autofluorescence enriched with mitochondrial ATP synthase subunit c were previously discovered in Cln3 mutant knock-in mice. In this study, we show that treatment with lithium reduces numbers of LC3-positive autophagosomes and accumulation of LC3-II in Cln3 mutant knock-in cerebellar cells (CbCln3(Δex7/8/Δex7/8) ). Lithium, an inhibitor of GSK3 and IMPase, reduces the accumulation of mitochondrial ATP synthase subunit c and autofluorescence in CbCln3(Δex7/8/Δex7/8) cells, and mitigates the abnormal subcellular distribution of acidic vesicles in the cells. L690,330, an IMPase inhibitor, is as effective as lithium in restoring autophagy in CbCln3(Δex7/8/Δex7/8) cells. Moreover, lithium or down-regulation of IMPase expression protects CbCln3(Δex7/8/Δex7/8) cells from cell death induced by amino acid deprivation. These results suggest that lithium overcomes the autophagic defect in CbCln3(Δex7/8/Δex7/8) cerebellar cells probably through IMPase, thereby reducing their vulnerability to cell death.     

Investigations on the Δ23-, Δ24(28)- and Δ25-Sterols of zea mays

The sterols of Zea mays shoots were isolated and characterized by TLC, HPLC, GC/MS and ¹H NMR techniques. In all, 22 4-demethyl sterols were identified and they included trace amounts of the Δ²³-, Δ²⁴- and Δ²⁵-sterols, 24-methylcholesta-5,E-23-dien-3β-ol, 24-methylcholesta-5,Z-23-dien-3β-ol, 24-methylcholesta-5,25-dien-3β-ol, 24-ethylcholesta-5,25-dien-3β-ol and 24-ethylcholesta-5,24-dien-3β-ol. In the 4,4-dimethyl sterol fraction, cycloartenol and 24-methylenecycloartanol were the major sterol components but small amounts of the Δ²³-compound, cyclosadol, and the Δ²⁵-compound, cyclolaudenol, were recognized. These various Δ²³- and Δ²⁵-sterols may have some importance in alternative biosynthetic routes to the major sterols, particularly the 24β-methylcholest-5-en-3β-ol component of the C₂₈-sterols. Radioactivity from both [2-¹⁴C]MVA and [methyl-¹⁴C]methionine was incorporated by Z. mays shoots into the sterol mixture. Although 24-methylene and 24-ethylidene sterols were relatively highly labelled, the various Δ²³- and Δ²⁵-sterols contained much lower levels of radioactivity, which is possibly indicative of their participation in alternative sterol biosynthetic routes. (24R)-24-Ethylcholest-5-en-3β-ol (sitosterol) had a significantly higher specific activity than the 24-methylcholest-5-en-3β-ol indicating that the former is synthesized at a faster rate.     

A trypsin-like protease with apparent dual function in early Lepeophtheirus salmonis (Kr?yer) development

Background  

Trypsin-like serine proteases are involved in a large number of processes including digestive degradation, regulation of developmental processes, yolk degradation and yolk degradome activation. Trypsin like peptidases considered to be involved in digestion have been characterized in Lepeophtheirus salmonis. During these studies a trypsin-like peptidase which differed in a number of traits were identified.