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Journal of Bacteriology, January 2002, p. 519-524, Vol. 184, No. 2
0021-9193/02/$04.00+0     DOI: 10.1128/JB.184.2.519-524.2002
Copyright © 2002, American Society for Microbiology. All Rights Reserved.

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

Daniel Sorger and Günther Daum*

Institut für Biochemie, Technische Universität Graz, A-8010 Graz, Austria

Received 19 July 2001/ Accepted 25 October 2001

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.

* Corresponding author. Mailing address: Institut für Biochemie, Technische Universität Graz, Petersgasse 12/2, A-8010 Graz, Austria. Phone: 43-316-873-6462. Fax: 43-316-873-6952. E-mail: guenther.daum{at}tugraz.at.

{dagger} We dedicate this study to Fritz Paltauf on the occasion of his retirement.

Journal of Bacteriology, January 2002, p. 519-524, Vol. 184, No. 2
0021-9193/02/$04.00+0     DOI: 10.1128/JB.184.2.519-524.2002
Copyright © 2002, American Society for Microbiology. All Rights Reserved.



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