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Betaine Lipids in Lower Plants. Biosynthesis of DGTS and DGTA in Ochromonas danica (Chrysophyceae) and the Possible Role of DGTS in Lipid Metabolism
Abstract
Membrane lipids and fatty acids of Ochromonas danica were analyzed. Of the two betaine lipids, the homoserine lipid DGTS mainly contains 14:0 and 18:2 fatty acids, while the alanine lipid DGTA is enriched in 18:0, 18:2 and 22:5 fatty acids. Of the polar moiety of DGTA, improved NMR data are presented. On incubation of cells with [3,4-14C]methionine, DGTS as well as DGTA were labelled. With [1-14C]methionine as a substrate, the label appeared in DGTS only. If double labelled [3H](glycerol)/[14C](polar part)DGTS was used as a precursor, radioactivity was incorporated specifically into DGTA in which the isotope ratio was unchanged compared to the precursor. Thus, the glyceryltrimethylhomoserine part of DGTS acts as the precursor of the polar group of DGTA. Labelling of cells with [1-14C]oleate in a pulse-chase manner and subsequent analysis of the label in the fatty acids and molecular species of different lipids including DGTS and DGTA, suggested a clearly different role of the two betaine lipids: DGTS acts as a i) primary acceptor for exogenous C 18 monoene acid, ii) substrate for the desaturation of 18:1 to 18:2 acid, and iii) donor of mainly 18:2 fatty acid to be distributed among PE and other membrane lipids. Into DGTA, in contrast, fatty acids are introduced only after elongation and desaturation. As a result, the biosynthesis of DGTA from DGTS involves a decarboxylation and recarboxylation of the polar part and a simultaneous deacylation and reacylation of the glycerol moiety.
... The golden-brown microalga Ochromonas danica contains the betaine lipids DGTS and diacylglycerylhydroxymethyltrimethyl-b-alanine (DGTA), and small amounts of PC. When this alga was incubated with 14 C-oleic acid, the majority of the radiolabel was incorporated into DGTS, suggesting that DGTS is the primary acceptor of exogenous oleic acid (Vogel and Eichenberger, 1992). Similar findings were observed in the brown algae Fucus vesiculosus and Ascophyllum nodosum, which contain DGTA and minor quantities of PC. ...
... When 14 C-oleic acid was supplied exogenously to C. reinhardtii, radiolabel first appeared in molecular species of DGTS containing 18:1, and then shifted to species containing 18:2, followed by species containing 18:3D5,9,12, suggesting that C18 fatty acid desaturation occurs on DGTS (Schlapfer and Eichenberger, 1983;Giroud and Eichenberger, 1989). Similar results were obtained in a pulse-chase labeling experiment in the golden-brown microalga O. danica, in which labeling with 14 C-oleic acid resulted in radiolabel being primarily concentrated in DGTS in its 18:1 and 18:2 fatty acids (Vogel and Eichenberger, 1992). During the chase, radiolabel decreased very rapidly in 18:1 while it decreased more slowly in 18:2 fatty acids, and radiolabel increased strongly in 18:3 and 18:4 fatty acids (Vogel and Eichenberger, 1992). ...
... Similar results were obtained in a pulse-chase labeling experiment in the golden-brown microalga O. danica, in which labeling with 14 C-oleic acid resulted in radiolabel being primarily concentrated in DGTS in its 18:1 and 18:2 fatty acids (Vogel and Eichenberger, 1992). During the chase, radiolabel decreased very rapidly in 18:1 while it decreased more slowly in 18:2 fatty acids, and radiolabel increased strongly in 18:3 and 18:4 fatty acids (Vogel and Eichenberger, 1992). This suggested that 18:1 is desaturated on DGTS to produce 18:3 and 18:4 fatty acids. ...
Acyl editing refers to a deacylation and reacylation cycle on a lipid, which allows for fatty acid desaturation and modification prior to being removed and incorporated into other pools. Acyl editing is an important determinant of glycerolipid synthesis and has been well-characterized in land plants, thus this review begins with an overview of acyl editing in plants. Much less is known about acyl editing in algae, including the extent to which acyl editing impacts lipid synthesis and on which lipid substrate(s) it occurs. This review compares what is known about acyl editing on its major hub phosphatidylcholine (PC) in land plants with the evidence for acyl editing of betaine lipids such as diacylglyceryltrimethylhomoserine (DGTS), the structural analog that replaces PC in several species of microalgae. In land plants, PC is also known to be a major source of fatty acids and diacylglycerol (DAG) for synthesis of the neutral lipid triacylglycerol (TAG). We review the evidence that DGTS contributes substantially to TAG accumulation in algae as a source of fatty acids, but not as a precursor to DAG. We conclude with evidence of acyl editing on other membrane lipid substrates in plants and algae apart from PC or DGTS, and discuss future analyses to elucidate the role of DGTS and other betaine lipids in acyl editing in microalgae.
... In addition to DGTS and DGTA being structural isomers, it was shown that DGTS serves as precursor for DGTA biosynthesis. In Ochromonas danica, the biosynthesis of DGTA from DGTS involved decarboxylation and recarboxylation of the polar part and simultaneous deacylation and reacylation of the glycerol moiety [28]. If the synthesis of DGTA in Acanthamoeba followed the same pattern, this could have explained the lack of DGTS esterified with the same FA residues as in the case of DGTA in total lipid preparation from MLBs. ...
Multilamellar bodies (MLBs) are membrane-bound cytoplasmic organelles of lysosomal origin. In some protozoa, they were considered as lipid storage secretory organelles and feasible participants in cell-to-cell communication. However, for Acanthamoeba castellanii, similar vesicles were indicated only as possible transmission vectors of several pathogenic bacteria without attributing them biological roles and activities. Since amoebae belonging to the genus Acanthamoeba are not only of environmental but also of clinical significance, it is of great importance to fully understand their physiology. Thus, determination of MLB lipid composition could partly address these questions. Because MLBs are secreted by amoebae as a result of bacteria digestion, the co-culture technique with the use of “edible” Klebsiella aerogenes was used for their production. Lipids obtained from The MLB fraction, previously purified from bacterial debris, were analyzed by high-performance thin-layer chromatography, gas chromatography coupled with mass spectrometry, and high-resolution mass spectrometry. Lipidomic analysis revealed that in MLBs, a very abundant lipid class was a non-phosphorous, polar glycerolipids, diacylglyceryl-O-(N,N,N)-trimethylhomoserine (DGTS). Since DGTSs are regarded as a source of nitrogen and fatty acids, MLBs can be considered as lipid storage organelles produced in stress conditions. Further, the identification of phytoceramides and possible new betaine derivatives indicates that MLBs might have a distinct bioactive potential.
... La voie de biosynthèse des bétaines lipides est seulement élucidée pour le DGTS, qui se déroule dans le RE catalysée par l'enzyme BTA1 (Riekhof et al., 2005) (Figure 10). Des recherches sont conduites pour déterminer les voies de biosynthèse du DGTA, qui dérive du DGTS (Vogel and Eichenberger, W., 1992), et celles du DGCC (Kato et al., 1996), mais les enzymes responsables de leur synthèse restent inconnues. De même, l'organisation des bétaines lipides dans une membrane n'a pas été étudiée, mais comme leur structure est similaire à celle de la PC, une hypothèse serait que les bétaines lipides s'organisent également en bicouches. ...
Dans le cadre actuel des transitions écologiques et énergétiques, les microalgues sont de plus en plus étudiées pour leur forte teneur en lipides, pouvant être utilisés pour la fabrication de biocarburants. Mais les connaissances sur le métabolisme des microalgues sont encore limitées. Les plantes supérieures et les microalgues, bien qu’habitant dans des endroits distincts, sont soumises à des contraintes environnementales, comme la carence en phosphate (Pi), un macronutriment essentiel pour leur développement. Pour pallier à cette carence, les plantes et les microalgues modifient la composition lipidique de leurs membranes afin de remobiliser le phosphate présent dans les phospholipides. C’est pourquoi, de nombreuses données de la littérature observent une augmentation des lipides non-phosphorés pour remplacer et compenser une diminution des phospholipides. Il est connu que le sulfoquinovosyldiacylglycérol (SQDG) remplace le phosphatidylglycérol (PG), que le digalactosyldiacylglycérol (DGDG) remplace phosphatidylcholine (PC), et chez les microalgues que les bétaines lipides semblent remplacer la PC. Est-ce que le remplacement de chaque phospholipide par un lipide non-phosphoré est lié à leur propriété structurale similaire dans la membrane ? C’est dans ce cadre de recherche fondamentale sur la compréhension des remaniements lipidiques que s’inscrit ce travail de thèse.L’utilisation de la diffraction des neutrons sur des films de lipides est un outil puissant permettant de déterminer de nombreux paramètres structuraux des membranes, comme leur organisation, leur épaisseur et celle de la couche d’eau entre les membranes, ainsi que leur rigidité et leur compressibilité. Dans ce projet, nous avons pu montrer que le PG et le SQDG ont des propriétés biophysiques très similaires expliquant leur interchangeabilité lors de la carence en phosphate. Ensuite, nous avons essayé d’apporter une réponse à la déformation de l’enveloppe du chloroplaste observée chez les plantes en carence, qui semblerait en lien avec l’augmentation du DGDG dans les membranes. Les résultats laissent supposer que le DGDG rend les membranes plus souples et favorise leur juxtaposition, mais les données sont encore insuffisantes pour pouvoir conclure avec certitude. Nous avons ensuite mis en lumière que les propriétés du DGTS (1,2‑diacylglycéryl-3-O-4'-(N,N,N-triméthyl)-homosérine), présents chez les microalgues, sont différentes de celles de la PC, avec notamment une bicouche plus épaisse et une répulsion entre bicouches plus forte, qui pourraient expliquer son absence dans les membranes des plantes à graines. Les plantes n’ayant pas la même composition en acides gras que les microalgues, riches en acides gras en C20 et portant jusqu’à 5 insaturations, ne seraient pas capables de contrebalancer les effets de la tête polaire des bétaines lipides. Un lien étroit entre la composition en acides gras et la présence des bétaines lipides dans l’organisme semble donc se dégager. Enfin, chez certaines microalgues, la présence de l’acyl-SQDG (ASQD) dans les membranes pourrait favoriser l’accolement des membranes et donc l’empilement des thylakoïdes dans le chloroplaste. Mais les données obtenues ne nous permettent pas encore de valider cette hypothèse. Ainsi, l’étude des lipides et membranes par une approche physique nous a permis d’apporter des éléments de réponses à des questions biologiques, permettant d’améliorer notre compréhension des remodelages lipidiques chez les plantes et les microalgues lors de la carence en phosphate.
... The major FA in DGTS composition of endophytes was 18:1. DGTS probably acts as the primary substrate for FA desaturation in the endoplasmic reticulum (ER) [28]. ...
The effect of temperature and light intensity on the polar lipidome of endophytic brown algae Streblonema corymbiferum and Streblonema sp. in vitro was investigated. More than 460 molecular species have been identified in four glycoglycerolipids classes, five phosphoglycerolipids classes and one betaine lipid class. The lipids glucuronosyldiacylglycerol and diacylglyceryl-N,N,N-trimethyl-homoserine were found in the algae of the order Ectocarpales for the first time. A decrease in cultivation temperature led to an increase in the unsaturation level in all classes of polar lipids. Thus, at low temperatures, the content of 18:4/18:4 monogalactosyldiacylglycerol (MGDG), 20:5/18:4 digalactosyldiacylglycerol (DGDG), 18:3/16:0 sulfoquinovosyldiacylglycerol (SQDG), 18:3/18:3 and 18:3/18:4 phosphatidylglycerol (PG), 20:4/20:5 and 20:5/20:5 phosphatidylethanolamine (PE), 14:0/20:5, 16:0/20:5 and 20:5/20:5 phosphatidylcholine (PC), 20:5/20:4 phosphatidylhydroxyethylglycine and 18:1/18:2 DGTS increased. At high temperatures, an increase in the content of chloroplast-derived MGDG, DGDG and PG was observed. Both low and high light intensities caused an increase in 20:5/18:3 MGDG and 18:3/16:1 PG. At low light intensity, the content of DGDG with fatty acid (FA) 18:3 increased, and at high light intensity, it was with FA 20:5. The molecular species composition of extraplastid lipids also showed a dependence on light intensity. Thus, the content of PC and PE species with C20-polyunsaturated FA at both sn-positions, 18:1/18:1 DGTS and 16:0/18:1 phosphatidylinositol increased. Low light intensity induced a significant increase in the content of chloroplast-derived 18:1/16:1 phosphatidylethanolamine.
... Chez les algues la synthèse de DGTS se fait sous l'action de la Bétaïne Lipide Synthase (codée par BTA1) qui assure le transfert de l'homosérine de la SAM sur un DAG puis la triméthylation de la diacylglycéryl homosérine (DGHS) (Figure 22) (Hofmann and Eichenberger, 1996;Riekhof et al., 2005). Le DGTA serait issu de la décarboxylation puis re-carboxylation du DGTS, expliquant la différence de position de la fonction carboxyle des deux isomères (Vogel and Eichenberger, 1992). Le DGCC serait issu d'une voie de biosynthèse visiblement différente et utiliserait la choline comme substrat d'après des expériences de radiomarquage (Kato et al., 2003). ...
Ostreococcus mediterraneus est un phytoplancton (microalgue) picoeucaryote à la base des réseaux trophiques marins côtiers. Ce phytoplancton est soumis à des attaques virales de grands virus nucléocytoplasmiques à ADN du genre Prasinovirus dont la souche Ostreococcus mediterraneus Virus 2 (OmV2) fait partie. Au sein de populations de microalgues sensibles au virus il a été observé l’émergence spontanée de phénotypes immunitaires résistants. Les bases génétiques de cette résistance ont récemment été décrites chez Ostreococcus : elles semblent véhiculées par un chromosome immunitaire atypique appelé SOC (Small Outlier Chromosome). Dans ce contexte nous avons cherché à caractériser les signatures métabolomiques et transcriptomiques de cette immunité au travers d’une approche visant à corréler ces deux niveaux d’expression. Des métabolites lipidiques biomarqueurs (galactolipides, phytostérols, sphingolipides) de chaque profil immunitaire ainsi que les gènes associés à leur métabolisme ont été identifiés. Ces données ont été mis en perspective des résultats de l’analyse métabolomique du virus afin d’identifier des voies métaboliques sollicitées et détournées par le virus lors de l’infection.
A new monoacylglyceryltrimethylhomoserine, 21F121-A (1), was isolated from the culture of Penicillium glaucoroseum (21F00121) by LCMS-guided purification. The structure was elucidated by NMR and mass spectrometries. The absolute configuration of the homoserine moiety was analyzed by the ECD spectrum after acid hydrolysis, and the S-configuration of the glycerol moiety was determined based on the spectrum of the 1,2-dibenzoyl derivative after acid hydrolysis. Although a variety of diacylglyceryltrimethylhomoserine is distributed in lower plants and fungi, a limited number of studies on monoacyl derivatives have been reported. This is the fourth sample of monoacylglyceryltrimethylhomoserine discovered from a natural source, and the second sample isolated from a fungus. Compound 1 contains an unusual branched pentaene chain attached at the sn-1 position of glycerol and weakly inhibited the growth of HCT116 cells.Graphical abstract
Cellular membranes have a remarkable variety of lipids, and different organelles have different lipid compositions. Changes in lipid composition can alter the surface charge, thickness, and fluidity of a membrane—characteristics that affect, for example, photosynthesis efficiency or vesicular trafficking. Therefore, for proper organelle function, these parameters must be kept within an appropriate range and must be regulated. Due to their low mobility, plant and algae are dependent on their environment and face sudden changes such as light, temperature or osmotic variations, that will affect membrane features. This review focus on the physical and structural properties of glycerolipids and their impact on membrane specificities in response to environmental cues. Here, we present an overview of the methods that are currently used to establish biophysical membrane properties. We then describe the common glycerolipids present in plants and algae, with their characteristic and their distribution within cell membranes. In the light of the organelle lipid composition, we illustrate how membranes are able to sense and adapt their architecture to maintain their homeostasis and their properties in response to environmental stresses. Thanks to the improved techniques recently available to study membranes in their native context, we are now discovering that the regulation of membrane properties by lipids is far more complex and entangled than it was originally thought.
