Nutritional regulation of yeast delta-9 fatty acid desaturase activity

Mitofusin-mediated contacts between mitochondria and peroxisomes regulate mitochondrial fusion

Mitofusins are large GTPases that trigger fusion of mitochondrial outer membranes. Similarly to the human mitofusin Mfn2, which also tethers mitochondria to the endoplasmic reticulum (ER), the yeast mitofusin Fzo1 stimulates contacts between Peroxisomes and Mitochondria when overexpressed. Yet, the physiological significance and function of these "PerMit" contacts remain unknown. Here, we demonstrate that Fzo1 naturally localizes to peroxisomes and promotes PerMit contacts in physiological conditions. These contacts are regulated through co-modulation of Fzo1 levels by the ubiquitin-proteasome system (UPS) and by the desaturation status of fatty acids (FAs). Contacts decrease under low FA desaturation but reach a maximum during high FA desaturation. High-throughput genetic screening combined with high-resolution cellular imaging reveal that Fzo1-mediated PerMit contacts favor the transit of peroxisomal citrate into mitochondria. In turn, citrate enters the TCA cycle to stimulate the mitochondrial membrane potential and maintain efficient mitochondrial fusion upon high FA desaturation. These findings thus unravel a mechanism by which inter-organelle contacts safeguard mitochondrial fusion.

Evaluating oleaginous yeasts for enhanced microbial lipid production using sweetwater as a sustainable feedstock

BACKGROUND

Yeasts exhibit promising potential for the microbial conversion of crude glycerol, owing to their versatility in delivering a wide range of value-added products, particularly lipids. Sweetwater, a methanol-free by-product of the fat splitting process, has emerged as a promising alternative feedstock for the microbial utilization of crude glycerol. To further optimize sweetwater utilization, we compared the growth and lipid production capabilities of 21 oleaginous yeast strains under different conditions with various glycerol concentrations, sweetwater types and pH.

RESULTS

We found that nutrient limitation and the unique carbon composition of sweetwater boosted significant lipid accumulation in several strains, in particular Rhodosporidium toruloides NRRL Y-6987. Subsequently, to decipher the underlying mechanism, the transcriptomic changes of R. toruloides NRRL Y-6987 were further analyzed, indicating potential sugars and oligopeptides in sweetwater supporting growth and lipid accumulation as well as exogenous fatty acid uptake leading to the enhanced lipid accumulation.

CONCLUSION

Our comparative study successfully demonstrated sweetwater as a cost-effective feedstock while identifying R. toluroides NRRL Y-6987 as a highly promising microbial oil producer. Furthermore, we also suggested potential sweetwater type and strain engineering targets that could potentially enhance microbial lipid production.

Exploring engineering strategies that enhance de novo production of exotic cyclopropane fatty acids in Saccharomyces cerevisiae

Cycloalkanes have broad applications as specialty fuels, lubricants, and pharmaceuticals but are not currently available from renewable sources, whereas, production of microbial cycloalkanes such as cyclopropane fatty acids (CFA) has bottlenecks. Here, a systematic investigation was undertaken into the biosynthesis of CFA in Saccharomyces cerevisiae heterologously expressing bacterial CFA synthase. The enzyme catalyzes formation of a 3-membered ring in unsaturated fatty acids. Monounsaturated fatty acids in phospholipids (PL) are the site of CFA synthesis; precursor cis-Δ9 C16 and C18 fatty acids were enhanced through OLE1 and SAM2 overexpression which enhanced CFA in PL. CFA turnover from PL to storage in triacylglycerols (TAG) was achieved by phospholipase PBL2 overexpression and acyl-CoA synthase to increase flux to TAG. Consequently, CFA storage as TAG reached 12 mg g-1 DCW, improved 3-fold over the base strain and >22% of TAG was CFA. Our research improves understanding of cycloalkane biosynthesis in yeast and offers insights into processing of other exotic fatty acids.

Lipid saturation induces degradation of squalene epoxidase for sterol homeostasis and cell survival

A fluid membrane containing a mix of unsaturated and saturated lipids is essential for life. However, it is unclear how lipid saturation might affect lipid homeostasis, membrane-associated proteins, and membrane organelles. Here, we generate temperature-sensitive mutants of the sole fatty acid desaturase gene OLE1 in the budding yeast Saccharomyces cerevisiae Using these mutants, we show that lipid saturation triggers the endoplasmic reticulum-associated degradation (ERAD) of squalene epoxidase Erg1, a rate-limiting enzyme in sterol biosynthesis, via the E3 ligase Doa10-Ubc7 complex. We identify the P469L mutation that abolishes the lipid saturation-induced ERAD of Erg1. Overexpressed WT or stable Erg1 mutants all mislocalize into foci in the ole1 mutant, whereas the stable Erg1 causes aberrant ER and severely compromises the growth of ole1, which are recapitulated by doa10 deletion. The toxicity of the stable Erg1 and doa10 deletion is due to the accumulation of lanosterol and misfolded proteins in ole1 Our study identifies Erg1 as a novel lipid saturation-regulated ERAD target, manifesting a close link between lipid homeostasis and proteostasis that maintains sterol homeostasis under the lipid saturation condition for cell survival.

Desaturases: Structural and mechanistic insights into the biosynthesis of unsaturated fatty acids

This review highlights the key role of fatty acid desaturases in the synthesis of naturally occurring, more common and not unsaturated fatty acids. The three major classes of fatty acid desaturases, such as acyl-lipid, acyl-acyl carrier protein and acyl-coenzyme A, are described in detail, with particular attention to the cellular localisation, the structure, the substrate and product specificity and the expression and regulation of desaturase genes. The review also gives an insight into the biocatalytic reaction of fatty acid desaturation by covering the general and more class-specific mechanistic studies around the synthesis of unsaturated fatty acids Finally, we conclude the review by looking at the numerous novel applications for desaturases in order to meet the very high demand for polyunsaturated fatty acids, taking into account the opportunity for the development of new, more efficient, easily reproducible, sustainable bioengineering advances in the field.

Functional characterization and overexpression of Δ12-desaturase in the oleaginous yeast Rhodotorula toruloides for production of linoleic acid-rich lipids

Linoleic acid (LA) has garnered much attention due to its potential applications in the oleochemical and nutraceutical industries. The oleaginous yeast Rhodotorula toruloides has outstanding lipogenecity, and is considered a potential alternative to the current plant-based platforms for LA production. Δ12-fatty acid desaturases (Δ12-Fads) are involved in LA synthesis in various fungi and yeasts, but their functions in R. toruloides remain poorly understood. To achieve the production of LA-rich lipids in R. toruloides, we investigated the function of the native Δ12-FAD (RtFAD2). First, the overexpression of RtFAD2 and its co-overexpression with RtFAD1 (encoding R. toruloides Δ9-Fad) and their effects on LA production in R. toruloides were investigated. The function of RtFad2 was confirmed by heterologous expression in Saccharomyces cerevisiae. Overexpression of RtFAD2 significantly elevated the LA contents and titers in the wild-type strain R. toruloides DMKU3-TK16 (TK16) and in a thermotolerant derivative of TK16 (L1-1). Additionally, overexpression of RtFAD2 in R. toruloides strains also increased the lipid titer and content. Overexpression of RtFAD1 was down-regulated in the RtFAD1 and RtFAD2 co-overexpressing strains, suggesting that the elevated LA content may function as a key regulator of RtFAD1 expression to control C18 fatty-acid synthesis in R. toruloides. We characterized the function of RtFAD2 and showed that its overexpression in R. toruloides increased the lipid and LA production. These findings may assist in the rational design of metabolic engineering related to LA or polyunsaturated fatty acid production in R. toruloides.

Aspirin Causes Lipid Accumulation and Damage to Cell Membrane by Regulating DCI1/OLE1 in Saccharomyces cerevisiae

Aspirin is one of the most commonly used nonsteroidal anti-inflammatory drugs. Various potential pharmacological effects of aspirin, such as anticancer, antibacterial activity, and prolonging life expectancy have been discovered. However, the mechanism of aspirin is not fully elucidated. Herein, the effects of aspirin on fatty acid metabolism in yeast cell model Saccharomyces cerevisiae were studied. The results showed that aspirin can induce lipid accumulation and reduce the unsaturated fat index in cells. The assessment of cell membrane integrity demonstrated that aspirin caused damage to the cell membrane. These effects of aspirin were attributed to the alterations of the expression of DCI1 and OLE1. Similarly, aspirin was able to cause lipid accumulation and damage to the cell membrane by interfering with the expression of OLE1 in Candida albicans. These findings are expected to improve current understanding of the mode of action of aspirin and provide a novel strategy for antifungal drug design. Graphical abstract [Figure: see text].

A Transcriptional Regulatory System of theS. cerevisiae OLE1Gene Responds to Fatty Acid Species and Intracellular Amount, and not Simply Membrane Status

We examined the effects of unsaturated fatty acid (UFA) species and their concentration on the expression ofOLE1,which encodes the stearoyl CoA desaturase, inSaccharomyces cerevisiae. We controlled the amount of UFA taken up by the cell by varying the concentration of tergitol in the medium. When cultured with 1 mM fatty acid in 0.1% tergitol, cells took up much more fatty acid than when cultured with the same concentration of fatty acid at 1% tergitol, although the amount incorporated was dependent on UFA species. For each fatty acid tested, we found that the higher uptake (0.1% tergitol condition) had a stronger impact onOLE1regulation. A principal product of the desaturase 16:1∆9, and the nonnative UFA 18:2∆9,12, most strongly repressed the reporter constructOLE1-lacZtranscription, while the other major product of the desaturase, 18:1∆9, and the nonnative UFA 17:1∆10 caused a more diminished response. Based on these results, our initial hypothesis was thatOLE1was regulated in response to membrane fluidity; however, subsequent work does not support that idea; we have found that conditions that affect membrane fluidity such as growth temperature and growth with saturated ortransfatty acid supplementation, do not regulateOLE1in the direction predicted by fluidity changes. We conclude that at least one signal that regulatesOLE1transcriptional expression is most likely based on the fatty acids themselves.

The hypoxic transcription factor KlMga2 mediates the response to oxidative stress and influences longevity in the yeast Kluyveromyces lactis

Hypoxia is defined as the decline of oxygen availability, depending on environmental supply and cellular consumption rate. The decrease in O2 results in reduction of available energy in facultative aerobes. The response and/or adaptation to hypoxia and other changing environmental conditions can influence the properties and functions of membranes by modifying lipid composition. In the yeast Kluyveromyces lactis, the KlMga2 gene is a hypoxic regulatory factor for lipid biosynthesis—fatty acids and sterols—and is also involved in glucose signaling, glucose catabolism and is generally important for cellular fitness.

In this work we show that, in addition to the above defects, the absence of the KlMGA2 gene caused increased resistance to oxidative stress and extended lifespan of the yeast, associated with increased expression levels of catalase and SOD genes. We propose that KlMga2 might also act as a mediator of the oxidative stress response/adaptation, thus revealing connections among hypoxia, glucose signaling, fatty acid biosynthesis and ROS metabolism in K. lactis.

Cyanophage-encoded lipid desaturases: oceanic distribution, diversity and function

Cyanobacteria are among the most abundant photosynthetic organisms in the oceans; viruses infecting cyanobacteria (cyanophages) can alter cyanobacterial populations, and therefore affect the local food web and global biochemical cycles. These phages carry auxiliary metabolic genes (AMGs), which rewire various metabolic pathways in the infected host cell, resulting in increased phage fitness. Coping with stress resulting from photodamage appears to be a central necessity of cyanophages, yet the overall mechanism is poorly understood. Here we report a novel, widespread cyanophage AMG, encoding a fatty acid desaturase (FAD), found in two genotypes with distinct geographical distribution. FADs are capable of modulating the fluidity of the host’s membrane, a fundamental stress response in living cells. We show that both viral FAD (vFAD) families are Δ9 lipid desaturases, catalyzing the desaturation at carbon 9 in C16 fatty acid chains. In addition, we present a comprehensive fatty acid profiling for marine cyanobacteria, which suggests a unique desaturation pathway of medium- to long-chain fatty acids no longer than C16, in accordance with the vFAD activity. Our findings suggest that cyanophages are capable of fiddling with the infected host’s membranes, possibly leading to increased photoprotection and potentially enhancing viral-encoded photosynthetic proteins, resulting in a new viral metabolic network.

The trans-10,cis-12 conjugated linoleic acid increases triacylglycerol hydrolysis in yeast Saccharomyces cerevisiae

AIMS

The trans-10,cis-12 conjugated linoleic acid (CLA) is known for its antilipogenic effect but the mechanism is not fully clear. In this study, the potential of yeast (Saccharomyces cerevisiae) metabolism to offer evidence for the mechanism was investigated.

METHODS AND RESULTS

The inhibitory effect of CLA on lipid accumulation was studied by analysing the transcript abundance of selected genes involved in triacylglycerol synthesis (LRO1, DGA1, ARE1 and ARE2) in the presence of the two bioactive CLA isomers: trans-10,cis-12 and the cis-9,trans-11 CLA. None of the enzymes was reduced in transcription but the expression of ARE2 was induced by trans-10,cis-12 CLA. However, the ARE2 overexpression did not contribute to lipid accumulation. The expression of the Δ9 desaturase gene, OLE1, was reduced by the cis-9,trans-11 but not by the trans-10,cis-12 isomer. In the TGL3/TGL4-knockout strain the triacylglycerol content also remained high in the CLA fed cells.

CONCLUSIONS

Triacylglycerol hydrolysis rather than synthesis was the most probable reason for the reduced lipid content in yeast induced by CLA.

SIGNIFICANCE AND IMPACT OF THE STUDY

This study revealed new aspects of the functionality of CLA in eukaryotic lipid metabolism. Yeast was proven to be an applicable model to study further the mechanism of trans-10,cis-12 CLA functionality on lipid metabolism.

Three, two, one yeast fatty acid desaturases: regulation and function

Fatty acid composition of biological membranes functionally adapts to environmental conditions by changing its composition through the activity of lipid biosynthetic enzymes, including the fatty acid desaturases. Three major desaturases are present in yeasts, responsible for the generation of double bonds in position C9-C10, C12-C13 and C15-C16 of the carbon backbone. In this review, we will report data addressed to define the functional role of basidiomycete and ascomycete yeast desaturase enzymes in response to various external signals and the regulation of the expression of their corresponding genes. Many yeast species have the complete set of three desaturases; however, only the Δ9 desaturase seems to be necessary and sufficient to ensure yeast viability. The evolutionary issue of this observation will be discussed.

Genome wide identification of microRNAs involved in fatty acid and lipid metabolism of Brassica napus by small RNA and degradome sequencing

Rapeseed (Brassica napus) is an important cash crop considered as the third largest oil crop worldwide. Rapeseed oil contains various saturation or unsaturation fatty acids, these fatty acids, whose could incorporation with TAG form into lipids stored in seeds play various roles in the metabolic activity. The different fatty acids in B. napus seeds determine oil quality, define if the oil is edible or must be used as industrial material. miRNAs are kind of non-coding sRNAs that could regulate gene expressions through post-transcriptional modification to their target transcripts playing important roles in plant metabolic activities. We employed high-throughput sequencing to identify the miRNAs and their target transcripts involved in fatty acids and lipids metabolism in different development of B. napus seeds. As a result, we identified 826 miRNA sequences, including 523 conserved and 303 newly miRNAs. From the degradome sequencing, we found 589 mRNA could be targeted by 236 miRNAs, it includes 49 novel miRNAs and 187 conserved miRNAs. The miRNA-target couple suggests that bna-5p-163957_18, bna-5p-396192_7, miR9563a-p3, miR9563b-p5, miR838-p3, miR156e-p3, miR159c and miR1134 could target PDP, LACS9, MFPA, ADSL1, ACO32, C0401, GDL73, PlCD6, OLEO3 and WSD1. These target transcripts are involving in acetyl-CoA generate and carbon chain desaturase, regulating the levels of very long chain fatty acids, β-oxidation and lipids transport and metabolism process. At the same, we employed the q-PCR to valid the expression of miRNAs and their target transcripts that involve in fatty acid and lipid metabolism, the result suggested that the miRNA and their transcript expression are negative correlation, which in accord with the expression of miRNA and its target transcript. The study findings suggest that the identified miRNA may play important role in the fatty acids and lipids metabolism in seeds of B. napus.

Control of membrane fluidity: the OLE pathway in focus

The maintenance of a fluid lipid bilayer is key for membrane integrity and cell viability. We are only beginning to understand how eukaryotic cells sense and maintain the characteristic lipid compositions and bulk membrane properties of their organelles. One of the key factors determining membrane fluidity and phase behavior is the proportion of saturated and unsaturated acyl chains in membrane lipids. Saccharomyces cerevisiae is an ideal model organism to study the regulation of the lipid acyl chain composition via the OLE pathway. The OLE pathway comprises all steps involved in the regulated mobilization of the transcription factors Mga2 and Spt23 from the endoplasmic reticulum (ER), which then drive the expression of OLE1 in the nucleus. OLE1 encodes for the essential Δ9-fatty acid desaturase Ole1 and is crucial for de novo biosynthesis of unsaturated fatty acids (UFAs) that are used as lipid building blocks. This review summarizes our current knowledge of the OLE pathway, the best-characterized, eukaryotic sense-and-control system regulating membrane lipid saturation, and identifies open questions to indicate future directions.

Quantitative analysis of proteome and lipidome dynamics reveals functional regulation of global lipid metabolism

Elucidating how and to what extent lipid metabolism is remodeled under changing conditions is essential for understanding cellular physiology. Here, we analyzed proteome and lipidome dynamics to investigate how regulation of lipid metabolism at the global scale supports remodeling of cellular architecture and processes during physiological adaptations in yeast. Our results reveal that activation of cardiolipin synthesis and remodeling supports mitochondrial biogenesis in the transition from fermentative to respiratory metabolism, that down-regulation of de novo sterol synthesis machinery prompts differential turnover of lipid droplet-associated triacylglycerols and sterol esters during respiratory growth, that sphingolipid metabolism is regulated in a previously unrecognized growth stage-specific manner, and that endogenous synthesis of unsaturated fatty acids constitutes an in vivo upstream activator of peroxisomal biogenesis, via the heterodimeric Oaf1/Pip2 transcription factor. Our work demonstrates the pivotal role of lipid metabolism in adaptive processes and provides a resource to investigate its regulation at the cellular level.

Comparative transcriptome profiling of Pyropia yezoensis (Ueda) M.S. Hwang & H.G. Choi in response to temperature stresses

Background

Pyropia yezoensis is a model organism often used to investigate the mechanisms underlying stress tolerance in intertidal zones. The digital gene expression (DGE) approach was used to characterize a genome-wide comparative analysis of differentially expressed genes (DEGs) that influence the physiological, developmental or biochemical processes in samples subjected to 4 treatments: high-temperature stress (HT), chilling stress (CS), freezing stress (FS) and normal temperature (NT).

Results

Equal amounts of total RNAs collected from 8 samples (two biological replicates per treatment) were sequenced using the Illumina/Solexa platform. Compared with NT, a total of 2202, 1334 and 592 differentially expressed unigenes were detected in HT, CS and FS respectively. Clustering analysis suggested P. yezoensis acclimates to low and high-temperature stress condition using different mechanisms: In heat stress, the unigenes related to replication and repair of DNA and protein processing in endoplasmic reticulum were active; however at low temperature stresses, unigenes related to carbohydrate metabolism and energy metabolism were active. Analysis of gene differential expression showed that four categories of DEGs functioning as temperature sensors were found, including heat shock proteins, H2A, histone deacetylase complex and transcription factors. Heat stress caused chloroplast genes down-regulated and unigenes encoding metacaspases up-regulated, which is an important regulator of PCD. Cold stress caused an increase in the expression of FAD to improve the proportion of polyunsaturated fatty acids. An up-regulated unigene encoding farnesyl pyrophosphate synthase was found in cold stress, indicating that the plant hormone ABA also played an important role in responding to temperature stress in P. yezoensis.

Conclusion

The variation of amount of unigenes and different gene expression pattern under different temperature stresses indicated the complicated and diverse regulation mechanism in response to temperature stress in P. yezoensis. Several common metabolism pathways were found both in P. yezoensis and in higher plants, such as FAD in low-temperature stress and HSP in heat stress. Meanwhile, many chloroplast genes and unigene related to the synthesis of abscisic acid were detected, revealing its unique temperature-regulation mechanism in this intertidal species. This sequencing dataset and analysis may serve as a valuable resource to study the mechanisms involved in abiotic stress tolerance in intertidal seaweeds.

Electronic supplementary material

The online version of this article (doi:10.1186/s12864-015-1586-1) contains supplementary material, which is available to authorized users.

Production and analysis of perdeuterated lipids from Pichia pastoris cells

Probing molecules using perdeuteration (i.e deuteration in which all hydrogen atoms are replaced by deuterium) is extremely useful in a wide range of biophysical techniques. In the case of lipids, the synthesis of the biologically relevant unsaturated perdeuterated lipids is challenging and not usually pursued. In this work, perdeuterated phospholipids and sterols from the yeast Pichia pastoris grown in deuterated medium are extracted and analyzed as derivatives by gas chromatography and mass spectrometry respectively. When yeast cells are grown in a deuterated environment, the phospholipid homeostasis is maintained but the fatty acid unsaturation level is modified while the ergosterol synthesis is not affected by the deuterated culture medium. Our results confirm that the production of well defined natural unsaturated perdeuterated lipids is possible and gives also new insights about the process of desaturase enzymes.

The natural diyne-furan fatty acid EV-086 is an inhibitor of fungal delta-9 fatty acid desaturation with efficacy in a model of skin dermatophytosis

Human fungal infections represent a therapeutic challenge. Although effective strategies for treatment are available, resistance is spreading, and many therapies have unacceptable side effects. A clear need for novel antifungal targets and molecules is thus emerging. Here, we present the identification and characterization of the plant-derived diyne-furan fatty acid EV-086 as a novel antifungal compound. EV-086 has potent and broad-spectrum activity in vitro against Candida, Aspergillus, and Trichophyton spp., whereas activities against bacteria and human cell lines are very low. Chemical-genetic profiling of Saccharomyces cerevisiae deletion mutants identified lipid metabolic processes and organelle organization and biogenesis as targets of EV-086. Pathway modeling suggested that EV-086 inhibits delta-9 fatty acid desaturation, an essential process in S. cerevisiae, depending on the delta-9 fatty acid desaturase OLE1. Delta-9 unsaturated fatty acids-but not saturated fatty acids-antagonized the EV-086-mediated growth inhibition, and transcription of the OLE1 gene was strongly upregulated in the presence of EV-086. EV-086 increased the ratio of saturated to unsaturated free fatty acids and phosphatidylethanolamine fatty acyl chains, respectively. Furthermore, EV-086 was rapidly taken up into the lipid fraction of the cell and incorporated into phospholipids. Together, these findings demonstrate that EV-086 is an inhibitor of delta-9 fatty acid desaturation and that the mechanism of inhibition might involve an EV-086-phospholipid. Finally, EV-086 showed efficacy in a guinea pig skin dermatophytosis model of topical Trichophyton infection, which demonstrates that delta-9 fatty acid desaturation is a valid antifungal target, at least for dermatophytoses.

Regulatory role of membrane fluidity in gene expression and physiological functions

Plants, algae, and photosynthetic bacteria experience frequent changes in environment. The ability to survive depends on their capacity to acclimate to such changes. In particular, fluctuations in temperature affect the fluidity of cytoplasmic and thylakoid membranes. The molecular mechanisms responsible for the perception of changes in membrane fluidity have not been fully characterized. However, the understanding of the functions of the individual genes for fatty acid desaturases in cyanobacteria and plants led to the directed mutagenesis of such genes that altered the membrane fluidity of cytoplasmic and thylakoid membranes. Characterization of the photosynthetic properties of the transformed cyanobacteria and higher plants revealed that lipid unsaturation is essential for protection of the photosynthetic machinery against environmental stresses, such as strong light, salt stress, and high and low temperatures. The unsaturation of fatty acids enhances the repair of the damaged photosystem II complex under stress conditions. In this review, we summarize the knowledge on the mechanisms that regulate membrane fluidity, on putative sensors that perceive changes in membrane fluidity, on genes that are involved in acclimation to new sets of environmental conditions, and on the influence of membrane properties on photosynthetic functions.

Expression of yeast acyl-CoA-∆9 desaturase leads to accumulation of unusual monounsaturated fatty acids in soybean seeds

An acyl-CoA-Δ9 desaturase from Saccharomyces cerevisiae was expressed by subcellular-targeting in soybean (Glycine max) seeds with the goal of increasing palmitoleic acid (16:1Δ9), a high-valued fatty acid (FA), and simultaneously decreasing saturated FA in oil. The expression resulted in the conversion of palmitic acid (16:0) to 16:1Δ9 in soybean seeds. 16:1Δ9 and its elongation product cis-vaccenic acid (18:1Δ11) were increased to 17 % of the total fatty acids by plastid-targeted expression of the enzyme. Other lipid changes include the decrease of polyunsaturated FA and saturated FA, suggesting that a mechanism exists downstream in oil biosynthesis to compensate the FA alternation. This is the first time a cytosolic acyl-CoA-∆9 desaturase is functionally expressed in plastid and stronger activity was achieved than its cytosolic expression. The present study provides a new strategy for converting 16:0 to 16:1Δ9 by engineering acyl-CoA-Δ9 desaturase in commercialized oilseeds.

Checks and balances in membrane phospholipid class and acyl chain homeostasis, the yeast perspective

Glycerophospholipids are the most abundant membrane lipid constituents in most eukaryotic cells. As a consequence, phospholipid class and acyl chain homeostasis are crucial for maintaining optimal physical properties of membranes that in turn are crucial for membrane function. The topic of this review is our current understanding of membrane phospholipid homeostasis in the reference eukaryote Saccharomyces cerevisiae. After introducing the physical parameters of the membrane that are kept in optimal range, the properties of the major membrane phospholipids and their contributions to membrane structure and dynamics are summarized. Phospholipid metabolism and known mechanisms of regulation are discussed, including potential sensors for monitoring membrane physical properties. Special attention is paid to processes that maintain the phospholipid class specific molecular species profiles, and to the interplay between phospholipid class and acyl chain composition when yeast membrane lipid homeostasis is challenged. Based on the reviewed studies, molecular species selectivity of the lipid metabolic enzymes, and mass action in acyl-CoA metabolism are put forward as important intrinsic contributors to membrane lipid homeostasis.

Effect of linoleic acids on the release of β-carotene from carotenoid-producing Saccharomyces cerevisiae into sunflower oil

In situ extraction is important for highly productive and cost-efficient processes in industrial biotechnology, but it is difficult to establish for intracellularly accumulating carotenoids like β-carotene. In this study, the organic solvent used in aqueous-organic two-phase media exerted a strong effect on the release of β-carotene from recombinant yeast cells. The carotenoid-synthesizing Saccharomyces cerevisiae strain YB/I/E was cultivated in two-liquid-phase media with 20% dodecane or 20% sunflower oil. Up to 0.6 µg/ml β-carotene was released into sunflower oil, but less than 0.1 µg/ml into dodecane, although biocompatibility and solubility of β-carotene is appropriate for both solvents. Addition of linoleic acid, the main component of sunflower oil, to the dodecane phase increased the amount of β-carotene released, indicating that linoleic acid is the component responsible for the β-carotene release into sunflower oil. These findings demonstrate that the effect of the organic solvent should be taken into consideration for further research on in situ extraction of carotenoids.

Metabolic engineering for enhanced fatty acids synthesis in Saccharomyces cerevisiae

Microbial production of biofuel has attracted significant attention in recent years. The fatty acids are important precursors for the production of fuels and chemicals, and its biosynthesis is initiated by the conversion of acetyl-CoA to malonyl-CoA which requires acetyl-CoA as key substrate. Herein, the yeast Saccharomyces cerevisiae was proposed to be metabolically engineered for cytosol acetyl-CoA enhancement for fatty acid synthesis. By gene disruption strategy, idh1 and idh2 genes involved in citrate turnover in tricarboxylic acid cycle (TCA cycle) were disrupted and the citrate production level was increased to 4- and 5-times in mutant yeast strains. In order to convert accumulated citrate to cytosol acetyl-CoA, a heterologous ATP-citrate lyase (ACL) was overexpressed in yeast wild type and idh1,2 disrupted strains. The wild type strain expressing acl mainly accumulated saturated fatty acids: C14:0, C16:0 and C18:0 at levels about 20%, 14% and 27%, respectively. Additionally, the idh1,2 disrupted strains expressing acl mainly accumulated unsaturated fatty acids. Specifically in Δidh1 strain expressing acl, 80% increase in C16:1 and 60% increase in C18:1 was detected. In Δidh2 strain expressing acl, 60% increase in C16:1 and 45% increase in C18:1 was detected. In Δidh1/2 strain expressing acl, there was 92% increase in C16:1 and 77% increase in C18:1, respectively. The increased fatty acids from our study may well be potential substrates for the production of hydrocarbon molecules as potential biofuels.

Rho signaling participates in membrane fluidity homeostasis

Preservation of both the integrity and fluidity of biological membranes is a critical cellular homeostatic function. Signaling pathways that govern lipid bilayer fluidity have long been known in bacteria, yet no such pathways have been identified in eukaryotes. Here we identify mutants of the yeast Saccharomyces cerevisiae whose growth is differentially influenced by its two principal unsaturated fatty acids, oleic and palmitoleic acid. Strains deficient in the core components of the cell wall integrity (CWI) pathway, a MAP kinase pathway dependent on both Pkc1 (yeast's sole protein kinase C) and Rho1 (the yeast RhoA-like small GTPase), were among those inhibited by palmitoleate yet stimulated by oleate. A single GEF (Tus1) and a single GAP (Sac7) of Rho1 were also identified, neither of which participate in the CWI pathway. In contrast, key components of the CWI pathway, such as Rom2, Bem2 and Rlm1, failed to influence fatty acid sensitivity. The differential influence of palmitoleate and oleate on growth of key mutants correlated with changes in membrane fluidity measured by fluorescence anisotropy of TMA-DPH, a plasma membrane-bound dye. This work provides the first evidence for the existence of a signaling pathway that enables eukaryotic cells to control membrane fluidity, a requirement for division, differentiation and environmental adaptation.

Small amounts of isotope-reinforced polyunsaturated fatty acids suppress lipid autoxidation

Polyunsaturated fatty acids (PUFAs) undergo autoxidation and generate reactive carbonyl compounds that are toxic to cells and associated with apoptotic cell death, age-related neurodegenerative diseases, and atherosclerosis. PUFA autoxidation is initiated by the abstraction of bis-allylic hydrogen atoms. Replacement of the bis-allylic hydrogen atoms with deuterium atoms (termed site-specific isotope-reinforcement) arrests PUFA autoxidation due to the isotope effect. Kinetic competition experiments show that the kinetic isotope effect for the propagation rate constant of Lin autoxidation compared to that of 11,11-D(2)-Lin is 12.8 ± 0.6. We investigate the effects of different isotope-reinforced PUFAs and natural PUFAs on the viability of coenzyme Q-deficient Saccharomyces cerevisiae coq mutants and wild-type yeast subjected to copper stress. Cells treated with a C11-BODIPY fluorescent probe to monitor lipid oxidation products show that lipid peroxidation precedes the loss of viability due to H-PUFA toxicity. We show that replacement of just one bis-allylic hydrogen atom with deuterium is sufficient to arrest lipid autoxidation. In contrast, PUFAs reinforced with two deuterium atoms at mono-allylic sites remain susceptible to autoxidation. Surprisingly, yeast treated with a mixture of approximately 20%:80% isotope-reinforced D-PUFA:natural H-PUFA are protected from lipid autoxidation-mediated cell killing. The findings reported here show that inclusion of only a small fraction of PUFAs deuterated at the bis-allylic sites is sufficient to profoundly inhibit the chain reaction of nondeuterated PUFAs in yeast.

Metabolism and regulation of glycerolipids in the yeast Saccharomyces cerevisiae

Due to its genetic tractability and increasing wealth of accessible data, the yeast Saccharomyces cerevisiae is a model system of choice for the study of the genetics, biochemistry, and cell biology of eukaryotic lipid metabolism. Glycerolipids (e.g., phospholipids and triacylglycerol) and their precursors are synthesized and metabolized by enzymes associated with the cytosol and membranous organelles, including endoplasmic reticulum, mitochondria, and lipid droplets. Genetic and biochemical analyses have revealed that glycerolipids play important roles in cell signaling, membrane trafficking, and anchoring of membrane proteins in addition to membrane structure. The expression of glycerolipid enzymes is controlled by a variety of conditions including growth stage and nutrient availability. Much of this regulation occurs at the transcriptional level and involves the Ino2–Ino4 activation complex and the Opi1 repressor, which interacts with Ino2 to attenuate transcriptional activation of UAS_INO-containing glycerolipid biosynthetic genes. Cellular levels of phosphatidic acid, precursor to all membrane phospholipids and the storage lipid triacylglycerol, regulates transcription of UAS_INO-containing genes by tethering Opi1 to the nuclear/endoplasmic reticulum membrane and controlling its translocation into the nucleus, a mechanism largely controlled by inositol availability. The transcriptional activator Zap1 controls the expression of some phospholipid synthesis genes in response to zinc availability. Regulatory mechanisms also include control of catalytic activity of glycerolipid enzymes by water-soluble precursors, products and lipids, and covalent modification of phosphorylation, while in vivo function of some enzymes is governed by their subcellular location. Genome-wide genetic analysis indicates coordinate regulation between glycerolipid metabolism and a broad spectrum of metabolic pathways.

Comparative Lipidomic Profiling of S. cerevisiae and Four Other Hemiascomycetous Yeasts

Glycerophospholipids (GP) are the building blocks of cellular membranes and play essential roles in cell compartmentation, membrane fluidity or apoptosis. In addition, GPs are sources for multifunctional second messengers. Whereas the genome and proteome of the most intensively studied eukaryotic model organism, the baker’s yeast (Saccharomyces cerevisiae), are well characterized, the analysis of its lipid composition is still at the beginning. Moreover, different yeast species can be distinguished on the DNA, RNA and protein level, but it is currently unknown if they can also be differentiated by determination of their GP pattern. Therefore, the GP compositions of five different yeast strains, grown under identical environmental conditions, were elucidated using high performance liquid chromatography coupled to negative electrospray ionization-hybrid linear ion trap-Fourier transform ion cyclotron resonance mass spectrometry in single and multistage mode. Using this approach, relative quantification of more than 100 molecular species belonging to nine GP classes was achieved. The comparative lipidomic profiling of Saccharomyces cerevisiae, Saccharomyces bayanus, Kluyveromyces thermotolerans, Pichia angusta, and Yarrowia lipolytica revealed characteristic GP profiles for each strain. However, genetically related yeast strains show similarities in their GP compositions, e.g., Saccharomyces cerevisiae and Saccharomyces bayanus.

Oxidative stresses and ageing

Oxidative damage to cellular constituents has frequently been associated with aging in a wide range of organisms. The power of yeast genetics and biochemistry has provided the opportunity to analyse in some detail how reactive oxygen and nitrogen species arise in cells, how cells respond to the damage that these reactive species cause, and to begin to dissect how these species may be involved in the ageing process. This chapter reviews the major sources of reactive oxygen species that occur in yeast cells, the damage they cause and how cells sense and respond to this damage.

Regulation of phospholipid synthesis in the yeast Saccharomyces cerevisiae

The yeast Saccharomyces cerevisiae, with its full complement of organelles, synthesizes membrane phospholipids by pathways that are generally common to those found in higher eukaryotes. Phospholipid synthesis in yeast is regulated in response to a variety of growth conditions (e.g., inositol supplementation, zinc depletion, and growth stage) by a coordination of genetic (e.g., transcriptional activation and repression) and biochemical (e.g., activity modulation and localization) mechanisms. Phosphatidate (PA), whose cellular levels are controlled by the activities of key phospholipid synthesis enzymes, plays a central role in the transcriptional regulation of phospholipid synthesis genes. In addition to the regulation of gene expression, phosphorylation of key phospholipid synthesis catalytic and regulatory proteins controls the metabolism of phospholipid precursors and products.

Phosphatidate phosphatase activity plays key role in protection against fatty acid-induced toxicity in yeast

The PAH1-encoded phosphatidate (PA) phosphatase in Saccharomyces cerevisiae is a pivotal enzyme that produces diacylglycerol for the synthesis of triacylglycerol (TAG) and simultaneously controls the level of PA used for phospholipid synthesis. Quantitative lipid analysis showed that the pah1Δ mutation caused a reduction in TAG mass and an elevation in the mass of phospholipids and free fatty acids, changes that were more pronounced in the stationary phase. The levels of unsaturated fatty acids in the pah1Δ mutant were unaltered, although the ratio of palmitoleic acid to oleic acid was increased with a similar change in the fatty acid composition of phospholipids. The pah1Δ mutant exhibited classic hallmarks of apoptosis in stationary phase and a marked reduction in the quantity of cytoplasmic lipid droplets. Cells lacking PA phosphatase were sensitive to exogenous fatty acids in the order of toxicity palmitoleic acid > oleic acid > palmitic acid. In contrast, the growth of wild type cells was not inhibited by fatty acid supplementation. In addition, wild type cells supplemented with palmitoleic acid exhibited an induction in PA phosphatase activity and an increase in TAG synthesis. Deletion of the DGK1-encoded diacylglycerol kinase, which counteracts PA phosphatase in controlling PA content, suppressed the defect in lipid droplet formation in the pah1Δ mutant. However, the sensitivity of the pah1Δ mutant to palmitoleic acid was not rescued by the dgk1Δ mutation. Overall, these findings indicate a key role of PA phosphatase in TAG synthesis for protection against fatty acid-induced toxicity.

Isotope-reinforced polyunsaturated fatty acids protect yeast cells from oxidative stress

The facile abstraction of bis-allylic hydrogens from polyunsaturated fatty acids (PUFAs) is the hallmark chemistry responsible for initiation and propagation of autoxidation reactions. The products of these autoxidation reactions can form cross-links to other membrane components and damage proteins and nucleic acids. We report that PUFAs deuterated at bis-allylic sites are much more resistant to autoxidation reactions, because of the isotope effect. This is shown using coenzyme Q-deficient Saccharomyces cerevisiae coq mutants with defects in the biosynthesis of coenzyme Q (Q). Q functions in respiratory energy metabolism and also functions as a lipid-soluble antioxidant. Yeast coq mutants incubated in the presence of the PUFA α-linolenic or linoleic acid exhibit 99% loss of colony formation after 4h, demonstrating a profound loss of viability. In contrast, coq mutants treated with monounsaturated oleic acid or with one of the deuterated PUFAs, 11,11-D(2)-linoleic or 11,11,14,14-D(4)-α-linolenic acid, retain viability similar to wild-type yeast. Deuterated PUFAs also confer protection to wild-type yeast subjected to heat stress. These results indicate that isotope-reinforced PUFAs are stabilized compared to standard PUFAs, and they protect coq mutants and wild-type yeast cells against the toxic effects of lipid autoxidation products. These findings suggest new approaches to controlling ROS-inflicted cellular damage and oxidative stress.

Chemical genetic profiling and characterization of small-molecule compounds that affect the biosynthesis of unsaturated fatty acids in Candida albicans

The balance between saturated and unsaturated fatty acids plays a crucial role in determining the membrane fluidity. In the diploid fungal pathogen Candida albicans, the gene for fatty acid Delta9 desaturase, OLE1, is essential for viability. Using a reverse genetic approach, termed the fitness test, we identified a group of structurally related synthetic compounds that induce specific hypersensitivity of the OLE1(+/-) strain. Genetic repression of OLE1 and chemical inhibition by two selected compounds, ECC145 and ECC188, resulted in a marked decrease in the total unsaturated fatty acids and impaired hyphal development. The resulting auxotroph of both was suppressed by the exogenous monounsaturated fatty acids (16:1Delta9 and 18:1Delta9). These correlations suggest that both compounds affect the level of unsaturated fatty acids, likely by impairing Ole1p directly or indirectly. However, the residual levels of monounsaturated fatty acids (MUFAs) resulted from chemical inhibition were significantly higher than OLE1 repression, indicating even partial inhibition of MUFAs is sufficient to stop cellular proliferation. Although the essentiality of OLE1 was suppressed by MUFAs in vitro, we demonstrated that it was required for virulence in a murine model of systemic candidiasis even when the animals were supplemented with a high fat diet. Thus, the fungal fatty acid desaturase is an attractive antifungal drug target. Taking advantage of the inhibitors and the relevant conditional shut-off strains, we validated several chemical genetic interactions observed in the fitness test profiles that reveal novel genetic interactions between OLE1/unsaturated fatty acids and other cellular processes.

Elucidation of the effects of lipoperoxidation on the mitochondrial electron transport chain using yeast mitochondria with manipulated fatty acid content

Lipoperoxidative damage to the respiratory chain proteins may account for disruption in mitochondrial electron transport chain (ETC) function and could lead to an augment in the production of reactive oxygen species (ROS). To test this hypothesis, we investigated the effects of lipoperoxidation on ETC function and cytochromes spectra of Saccharomyces cerevisiae mitochondria. We compared the effects of Fe(2+) treatment on mitochondria isolated from yeast with native (lipoperoxidation-resistant) and modified (lipoperoxidation-sensitive) fatty acid composition. Augmented sensitivity to oxidative stress was observed in the complex III-complex IV segment of the ETC. Lipoperoxidation did not alter the cytochromes content. Under lipoperoxidative conditions, cytochrome c reduction by succinate was almost totally eliminated by superoxide dismutase and stigmatellin. Our results suggest that lipoperoxidation impairs electron transfer mainly at cytochrome b in complex III, which leads to increased resistance to antimycin A and ROS generation due to an electron leak at the level of the Q(O) site of complex III.

Peroxisome proliferator-activated receptor gamma is constitutively activated in yeast

A rapid, simple in vitro test system for high-throughput screening of peroxisome proliferator-activated receptor (PPAR) gamma agonists would be of interest for testing new antidiabetic drugs, alternative medicine, or environmental samples. A yeast two-hybrid assay based on the ligand-dependent recruitment of the coactivator CBP (CREB-binding protein) was constructed. In this system PPARgamma was constitutively activated and the signal was not further increased significantly by adding agonists. In yeast we identified oleic acid as a putative endogenous ligand. Furthermore yeasts seem to lack regulatory mechanisms present in mammalian cells. Mammalian systems are an alternative for screening PPARgamma agonists.

Signalling pathways controlling fatty acid desaturation

Microorganisms, plants and animals regulate the synthesis of unsaturated fatty acids (UFAs) during changing environmental conditions as well as in response to nutrients. Unsaturation of fatty acid chains has important structural roles in cell membranes: a proper ratio of saturated to UFAs contributes to membrane fluidity. Alterations in this ratio have been implicated in various disease states including cardiovascular diseases, immune disorders, cancer and obesity. They are also the major components of triglycerides and intermediates in the synthesis of biologically active molecules such as eicosanoids, which mediates fever, inflammation and neurotransmission. UFAs homeostasis in many organisms is achieved by feedback regulation of fatty acid desaturases gene transcription. Here, we review recently discovered components and mechanisms of the regulatory machinery governing the transcription of fatty acid desaturases in bacteria, yeast and animals.

Identification of Rv3230c as the NADPH oxidoreductase of a two-protein DesA3 acyl-CoA desaturase in Mycobacterium tuberculosis H37Rv

DesA3 is a membrane-bound stearoyl-CoA Delta(9)-desaturase that produces oleic acid, a precursor of mycobacterial membrane phospholipids and triglycerides. The sequence of DesA3 is homologous with those of other membrane desaturases, including the presence of the eight-His motif proposed to bind the diiron center active site. This family of desaturases function as multicomponent complexes and thus require electron transfer proteins for efficient catalytic turnover. Here we present evidence that Rv3230c from Mycobacterium tuberculosis H37Rv is a biologically relevant electron transfer partner for DesA3 from the same pathogen. For these studies, Rv3230c was expressed as a partially soluble protein in Escherichia coli; recombinant DesA3 was expressed in Mycobacterium smegmatis as a catalytically active membrane protein. The addition of E. coli lysates containing Rv3230c to lysates of M. smegmatis expressing DesA3 gave strong conversion of [1-(14)C]-18:0-CoA to [1-(14)C]-cis-Delta(9)-18:1-CoA and of [1-(14)C]-16:0-CoA to [1-(14)C]-cis-Delta(9)-16:1-CoA. Both M. tuberculosis proteins were required for reconstitution of activity, as various combinations of control lysates lacking either Rv3230c or DesA3 gave minimal or no activity. Furthermore, the specificity of interaction between Rv3230c and DesA3 was implied by the inability of other related redox systems to substitute for Rv3230c. The reconstituted activity was dependent upon the presence of NADPH, could be saturated by increasing the amount of Rv3230c added, and was also sensitive to the salt concentration in the buffer. The results are consistent with the formation of a protein-protein complex, possibly with electrostatic character. This work defines a multiprotein, acyl-CoA desaturase complex from M. tuberculosis H37Rv to minimally consist of a soluble Rv3230c reductase and integral membrane DesA3 desaturase. Further implications of this finding relative to the properties of other multiprotein iron-enzyme complexes are discussed.

Fluidization of membrane lipids enhances the tolerance of Saccharomyces cerevisiae to freezing and salt stress

Unsaturated fatty acids play an essential role in the biophysical characteristics of cell membranes and determine the proper function of membrane-attached proteins. Thus, the ability of cells to alter the degree of unsaturation in their membranes is an important factor in cellular acclimatization to environmental conditions. Many eukaryotic organisms can synthesize dienoic fatty acids, but Saccharomyces cerevisiae can introduce only a single double bond at the Delta(9) position. We expressed two sunflower (Helianthus annuus) oleate Delta(12) desaturases encoded by FAD2-1 and FAD2-3 in yeast cells of the wild-type W303-1A strain (trp1) and analyzed their effects on growth and stress tolerance. Production of the heterologous desaturases increased the content of dienoic fatty acids, especially 18:2Delta(9,12), the unsaturation index, and the fluidity of the yeast membrane. The total fatty acid content remained constant, and the level of monounsaturated fatty acids decreased. Growth at 15 degrees C was reduced in the FAD2 strains, probably due to tryptophan auxotrophy, since the trp1 (TRP1) transformants that produced the sunflower desaturases grew as well as the control strain did. Our results suggest that changes in the fluidity of the lipid bilayer affect tryptophan uptake and/or the correct targeting of tryptophan transporters. The expression of the sunflower desaturases, in either Trp(+) or Trp(-) strains, increased NaCl tolerance. Production of dienoic fatty acids increased the tolerance to freezing of wild-type cells preincubated at 30 degrees C or 15 degrees C. Thus, membrane fluidity is an essential determinant of stress resistance in S. cerevisiae, and engineering of membrane lipids has the potential to be a useful tool of increasing the tolerance to freezing in industrial strains.

The sensitivity of yeast mutants to oleic acid implicates the peroxisome and other processes in membrane function

The peroxisome, sole site of beta-oxidation in Saccharomyces cerevisiae, is known to be required for optimal growth in the presence of fatty acid. Screening of the haploid yeast deletion collection identified approximately 130 genes, 23 encoding peroxisomal proteins, necessary for normal growth on oleic acid. Oleate slightly enhances growth of wild-type yeast and inhibits growth of all strains identified by the screen. Nonperoxisomal processes, among them chromatin modification by H2AZ, Pol II mediator function, and cell-wall-associated activities, also prevent oleate toxicity. The most oleate-inhibited strains lack Sap190, a putative adaptor for the PP2A-type protein phosphatase Sit4 (which is also required for normal growth on oleate) and Ilm1, a protein of unknown function. Palmitoleate, the other main unsaturated fatty acid of Saccharomyces, fails to inhibit growth of the sap190delta, sit4delta, and ilm1delta strains. Data that suggest that oleate inhibition of the growth of a peroxisomal mutant is due to an increase in plasma membrane porosity are presented. We propose that yeast deficient in peroxisomal and other functions are sensitive to oleate perhaps because of an inability to effectively control the fatty acid composition of membrane phospholipids.