Chapter 2 - Glycerolipid Biosynthesis
Publisher Summary
Cellular membranes act as structural components to define the boundaries of the cell and delineate subcellular compartments. Membranes also serve as scaffolds for diverse signaling events, and participate directly in essential metabolic processes. This chapter focuses on the predominant pathways of fatty acid biosynthesis, their modification, and on glycerolipid assembly in Chlamydomonas. It combines these in silico predictions with a thorough review of the experimentally verified pathways to present a comprehensive view of the identities and functions of genes involved in glycerolipid biosynthesis in Chlamydomonas. A distinguishing feature of lipid metabolism in Chlamydomonas is the lack of phosphatidylcholine (PtdCho), whose role appears to be partially assumed by the betaine lipid DGTS. The lack of PtdCho may also explain why chloroplast lipids in Chlamydomonas appear to be almost exclusively synthesized directly in the plastid. Several fatty acid desaturases have been isolated and characterized at the molecular level, and the biochemistry and genetics of fatty acid chain elongation and desaturation in Chlamydomonas are discussed here. Glycerophospholipids are the prevalent lipids in non-photosynthetic organisms. They are characterized by a phosphatidic acid (PtdOH) backbone. In plants, approximately one-third of the organic phosphorus is found in Phosphoglycerolipids and the biosynthesis of glycerolipid covers this.
References (0)
Cited by (32)
Acyl-CoA:diacylglycerol acyltransferase: Properties, physiological roles, metabolic engineering and intentional control
2022, Progress in Lipid ResearchAcyl-CoA:diacylglycerol acyltransferase (DGAT, EC 2.3.1.20) catalyzes the last reaction in the acyl-CoA-dependent biosynthesis of triacylglycerol (TAG). DGAT activity resides mainly in DGAT1 and DGAT2 in eukaryotes and bifunctional wax ester synthase-diacylglycerol acyltransferase (WSD) in bacteria, which are all membrane-bound proteins but exhibit no sequence homology to each other. Recent studies also identified other DGAT enzymes such as the soluble DGAT3 and diacylglycerol acetyltransferase (EaDAcT), as well as enzymes with DGAT activities including defective in cuticular ridges (DCR) and steryl and phytyl ester synthases (PESs). This review comprehensively discusses research advances on DGATs in prokaryotes and eukaryotes with a focus on their biochemical properties, physiological roles, and biotechnological and therapeutic applications. The review begins with a discussion of DGAT assay methods, followed by a systematic discussion of TAG biosynthesis and the properties and physiological role of DGATs. Thereafter, the review discusses the three-dimensional structure and insights into mechanism of action of human DGAT1, and the modeled DGAT1 from Brassica napus. The review then examines metabolic engineering strategies involving manipulation of DGAT, followed by a discussion of its therapeutic applications. DGAT in relation to improvement of traits of farmed animals is also discussed along with DGATs in various other eukaryotic organisms.
The lipid biochemistry of eukaryotic algae
2019, Progress in Lipid ResearchCitation Excerpt :This enzyme is, therefore, capable of synthesising either G3P or glycerol, depending on environmental conditions and/or metabolic demands [264]. Candidate genes for the expression of chloroplast-localised glycerol 3-phosphate acyltransferase (GPAT) in C. reinhardtii were listed by [253] and by [57]. For diatoms, a gene for GPAT was predicted from the Phaeodactylum tricornutum genome [265] and molecular characterisation carried out [266].
Algal lipid metabolism fascinates both scientists and entrepreneurs due to the large diversity of fatty acyl structures that algae produce. Algae have therefore long been studied as sources of genes for novel fatty acids; and, due to their superior biomass productivity, algae are also considered a potential feedstock for biofuels. However, a major issue in a commercially viable “algal oil-to-biofuel” industry is the high production cost, because most algal species only produce large amounts of oils after being exposed to stress conditions. Recent studies have therefore focused on the identification of factors involved in TAG metabolism, on the subcellular organization of lipid pathways, and on interactions between organelles. This has been accompanied by the development of genetic/genomic and synthetic biological tools not only for the reference green alga Chlamydomonas reinhardtii but also for Nannochloropsis spp. and Phaeodactylum tricornutum. Advances in our understanding of enzymes and regulatory proteins of acyl lipid biosynthesis and turnover are described herein with a focus on carbon and energetic aspects. We also summarize how changes in environmental factors can impact lipid metabolism and describe present and potential industrial uses of algal lipids.
Metabolic engineering and molecular biotechnology of microalgae for fuel production
2018, Biomass, Biofuels, Biochemicals: Biofuels from Algae, Second EditionEnergy demand is projected to grow by > 50% by 2025 and the consumption of fossil fuels is affecting global climate stability. Under such circumstances, the development of sustainable and renewable energy is an urgent task to support the continued prosperity and economic growth of the world. Among the environmentally friendly fuel resources, microalgae have shown great potential. Microalgae are single-cell photosynthetic microorganisms that are capable of capturing sunlight and converting CO2 and water into organic matter such as triacylglycerol, a compound that has received considerable attention. As the hydrocarbon of fossil fuels originates from anaerobic decomposition of ancient photosynthetic organisms over hundreds of millions of years, it is not surprising that photosynthetic microalgae possess potential as renewable feedstock for biofuels. The increasing interest in microalgae-based biofuels in recent years has advanced basic understanding of lipid metabolism, photosynthesis, carbon fixation, and related areas. The availability of genomic sequences of several microalgal species and the development of transformation platforms have accelerated forward genetics and allowed for the use of reverse genetics to uncover the molecular mechanisms associated with fuel production. Furthermore, omics approaches such as genomics, transcriptomics, proteomics, and metabolomics studies are providing new insights into gene regulation networks and coordinated cellular activities governing physiological flexibility and metabolic adaptation of microalgae. In this chapter, I focus on biodiesel and summarize recent advances in understanding the molecular mechanism and metabolism of lipids in microalgae with emphasis on the knowledge gained using omics and molecular genetics approaches. The implications and practicality of the molecular wiring of lipid biology and the current challenges of metabolic engineering in microalgal systems are further discussed.
Molecular mechanisms for photosynthetic carbon partitioning into storage neutral lipids in Nannochloropsis oceanica under nitrogen-depletion conditions
2015, Algal ResearchPolysaccharides are a major carbon/energy-reservoir in microalgae, yet their relationship with another form of carbon/energy storage, triacylglycerol (TAG), is poorly understood. Here employing oleaginous microalga Nannochloropsis oceanica as a model, we probed the crosstalk between carbohydrate metabolism and TAG accumulation by tracking the temporal dynamics of lipidomes, monosaccharides and polysaccharides and transcripts of selected genes over 14 days under nitrogen-depleted (N −) and nitrogen-replete (N +) conditions. Glucose, galactose and mannitol were the main monosaccharides in IMET1, and laminarin may be the storage polysaccharide that competes for carbon precursors with TAG. Transcriptional expression analysis revealed that the β-1,3-glucan degradation and pyruvate dehydrogenases pathways were the main regulatory components involved in driving carbon flow to TAG synthesis. Furthermore, temporal changes of lipidomes and transcripts of glycerolipid metabolism genes were indicative of possible conversion of membrane lipids to TAG, especially under an early stage of nitrogen deprivation conditions. A carbon partitioning model for N. oceanica was proposed, in which β-1,3-glucan metabolism, acetyl–CoA synthesis and membrane lipid turnover/degradation, in addition to de novo fatty acid synthesis, all contributed to TAG synthesis.
Edible oils from microalgae: Insights in TAG accumulation
2014, Trends in BiotechnologyMicroalgae are a promising future source for sustainable edible oils. To make microalgal oil a cost-effective alternative for common vegetable oils, increasing TAG productivity and TAG content are of high importance. Fulfilling these targets requires proper understanding of lipid metabolism in microalgae. Here, we provide an overview of our current knowledge on the biology of TAG accumulation as well as the latest developments and future directions for increasing oil production in microalgae, considering both metabolic engineering techniques and cultivation strategies.
Over-expression of Dof-type transcription factor increases lipid production in Chlamydomonas reinhardtii
2014, Journal of BiotechnologyThe high demand for less polluting, newer, and cheaper fuel resources has increased the search of the most innovative options for the production of the so-called biofuels. Chlamydomonas reinhardtii is a photosynthetic unicellular algae with multiple biotechnological advantages such as easy handling in the laboratory, a simple scale-up to industrial levels, as well as a feasible genetic modification at nuclear and chloroplast levels. Besides, its fatty acids can be used to produce biofuels. Previous studies in plants have found that the over expression of DOF-type transcription factor genes increases the synthesis and the accumulation of total lipids in seeds. In this context, the over-expression of a DOF-type transcription factor in C. reinhardtii was applied as approach to increase the amount of lipids. The results indicate higher amounts (around 2-fold) of total lipids, which are mainly fatty acids, in the genetically C. reinhardtii modified strains when compared with the non-genetically modified strain. In order to elucidate the possible function of the introduced Dof-type transcription factor, we performed a transcription profile of 8 genes involved in fatty acid biosynthesis and 6 genes involved in glycerolipid biosynthesis, by quantitative real time (qRT-PCR). Differential expression profile was observed, which can explain the increase in lipid accumulation. However, these strains did not show notable changes in the fatty acid profile. This work represents an early effort in generating a strategy to increase fatty acids production in C. reinhardtii and their use in biofuel synthesis.