Biosynthesis of triacylglycerol in the filamentous fungus Mucor circinelloides

Jackson, Frances; Michaelson, Louise V.; Fraser, T.; Stobart, A. K.; Griffiths, Gareth

doi:10.1099/00221287-144-9-2639

Cited by 22 publications

(9 citation statements)

References 38 publications

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“…In addition, a DAGAT without sequence similarity to ACATs was recently discovered in the oleaginous fungus Mortierella ramanniana (21). DAGAT activity of different species was found mainly in microsomes (16,31,33,42) but also in so-called lipid bodies (17,18,19,29), a compartment where neutral lipids such as TAG and steryl esters are stored. A second type of reaction leading to TAG is catalyzed by a phosphatidylcholine:DAGAT.…”

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confidence: 99%

Synthesis of Triacylglycerols by the Acyl-Coenzyme A:Diacyl-Glycerol Acyltransferase Dga1p in Lipid Particles of the Yeast Saccharomyces cerevisiae

2002

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The terminal step of triacylglycerol (TAG) formation in the yeast Saccharomyces cerevisiae is catalyzed by the enzyme acyl-CoA:diacylglycerol acyltransferase (DAGAT). In this study we demonstrate that the gene product of YOR245c, Dga1p, catalyzes a major yeast DAGAT activity which is localized to lipid particles. Enzyme measurements employing a newly established assay containing radioactively labeled diacylglycerol (DAG) as a substrate and unlabeled palmitoyl-CoA as a cosubstrate revealed a 70-to 90-fold enrichment of DAGAT in lipid particles over the homogenate but also a 2-to 3-fold enrichment in endoplasmic reticulum fractions. In a dga1 deletion strain, the DAGAT activity in lipid particles is dramatically reduced, whereas the activity in microsomes is affected only to a minor extent. Thus, we propose the existence of DAGAT isoenzymes in the microsomal fraction. Furthermore, we unveiled an acyl-CoA-independent TAG synthase activity in lipid particles which is distinct from Dga1p and the phosphatidylcholine:DAGAT Lro1p. This acyl-CoA-independent TAG synthase utilizes DAG as an acceptor and free fatty acids as cosubstrates and occurs independently of the acyl-CoA synthases Faa1p to Faa4p. Based on lipid analysis of the respective deletion strains, Lro1p and Dga1p are the major contributors to total cellular TAG synthesis, whereas other TAG synthesizing systems appear to be of minor importance. In conclusion, at least three different pathways are involved in the formation of storage TAG in the yeast.Triacylglycerols (TAGs) are the most important storage form for energy and fatty acids required for membrane biosynthesis in eukaryotic cells. Within the last decade, the formation of TAG in various organisms has been investigated. The most prominent enzyme of this biosynthetic pathway is acyl-coenzyme A (CoA):diacylglycerol acyltransferase (DAGAT; EC 2.3.1.20), which was shown to form TAG from diacylglycerol (DAG) and acyl-CoA as substrates (24). Genes encoding DAGATs homologous to acyl-CoA: cholesterol acyltransferase (ACAT) were identified in plants (14,30,42) and in mice (4). In addition, a DAGAT without sequence similarity to ACATs was recently discovered in the oleaginous fungus Mortierella ramanniana (21). DAGAT activity of different species was found mainly in microsomes (16,31,33,42) but also in so-called lipid bodies (17,18,19,29), a compartment where neutral lipids such as TAG and steryl esters are stored. A second type of reaction leading to TAG is catalyzed by a phosphatidylcholine:DAGAT. This pathway was identified in plants (sunflower, Ricinus communis, and Crepis palaestina) (6) and in the yeast Saccharomyces cerevisiae (6, 28). Finally, an acyl-CoA-independent TAG formation different from phosphatidylcholine:DAGAT was found in rat intestine (25) and mouse (32).TAG synthesis in yeast and fungi has been only poorly studied. DAGAT activity in lipid particles in baker's yeast (S. cerevisiae) was described by Christiansen (5), but the enzyme catalyzing this reaction was not characterized at the molecular...

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Synthesis of Triacylglycerols by the Acyl-Coenzyme A:Diacyl-Glycerol Acyltransferase Dga1p in Lipid Particles of the Yeast Saccharomyces cerevisiae

2002

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“…3 . Although biosynthesis of TAG from PL via DAG is possible in Mucorales fungi 33,36 , the presence of a large amount of exogenous TAG would have suppressed this route of transfer of EPA from PL into TAG. Utilization of oils by microorganisms is accompanied by the production of extracellular lipases that cleave acylglycerol, releasing fatty acids that can either be reincorporated into lipids or used as a source of energy and carbon for biomass synthesis 37,38 .…”

Section: Discussionmentioning

confidence: 99%

“…The Δ 5 and Δ 6 desaturases from several organisms, including M. alpina, are also predominantly specifi c for the sn-2 acyl groups in PC 32 . Moreover, fatty acids generated from endogenous lipids by Δ 9 , Δ 12 , and Δ 6 desaturases appear mainly in PC and phosphatidylethanolamine in Mucor circinelloides 33 . These and other studies 17,34,35 are compatible with our fi nding that a greater proportion of EPA is more rapidly formed in PL than in NL after substantial ALA incorporation into cellular lipids Fig.…”

Section: Discussionmentioning

confidence: 99%

Metabolism and Synthesis of Lipids in the Polyunsaturated Fatty Acid-Producing Fungus Mortierella alliacea

et al. 2011

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“…The third acylation step is catalyzed by transfer of acyl groups to DAG forming TAG. Phosphatidyl choline (PC) is a key intermediate in oil biosynthesis and plays a central role in the production of polyunsaturated fatty acids by serving as a substrate for D-6, D-9, D-12, and D-15 desaturases (Jackson et al 1998). LPAT are known to display specificity for substrates with certain fatty acids and can be important in determining final TAG composition (Franzosi et al 1998).…”

Section: Triacylglcerol Biosynthesismentioning

confidence: 99%