Staff Members of the Institute of Biochemistry, TU - Institut für ...

the metabolic flux of long chain fatty acids and very long chain fatty acids required for
sphingolipid and glycerophospholipid synthesis. Moreover, activity and expression levels of
fatty acid elongases, Elo1p and Elo2p, were enhanced as a consequence of reduced TAG
lipolysis emphasizing the link to sphingolipid formation. Finally, the pattern of
phosphatidylcholine (PC), PE and PS molecular species was altered in tgl deletion strain
underlining the important role of TAG turnover in maintenance of the pool size and
remodelling of complex membrane lipids. This study shed new light on the physiological role
of TAG lipases in yeast and in general.
Figure 2: Domains of Tgl3p (from Rajakumari et al., 2010, in press)
Even more surprising evidence was obtained when the enzymology of the three TAG lipases
Tgl3p, Tgl4p and Tgl5p was studied in some detail. Motif search analysis indicated that Tgl3p
and Tgl5p did not only contain the TAG lipase but also an acyltransferase motif (Figure 2).
Interestingly, lipid analysis revealed that deletion of TGL3 resulted in a decrease and
overexpression of TGL3 in an increase of glycerophospholipids. Similar results were obtained
with TGL5. Therefore, we tested purified Tgl3p and Tgl5p for acyltransferase activity. Indeed,
both enzymes did not only exhibit lipase activity but also catalyzed acylation of
lysophosphatidylethanolamine and lysophosphatidic acid, respectively. Experiments using
variants of Tgl3p created by site-directed mutagenesis clearly demonstrated that the two
enzymatic activities act independently of each other. We also showed that Tgl3p is important
for efficient sporulation of yeast cells, but rather through its acyltransferase than lipase
activity. These results demonstrated that yeast Tgl3p and Tgl5p play a dual role in lipid
metabolism contributing to both anabolic and catabolic processes.
In another study, we demonstrated that the yeast TAG lipase Tgl4p, the functional ortholog of
adipose TAG lipase (ATGL), catalyzes multiple functions in lipid metabolism. An extended
domain and motif search analysis revealed that Tgl4p bears not only a lipase consensus
domain but also a conserved motif for calcium independent phospholipases A2 (PLA2). We
showed that Tgl4p exhibits TAG lipase, STE hydrolase and PLA2 activities, but also
catalyzes acyl-CoA dependent acylation of lysophosphatidic acid (LPA) to phosphatidic acid.
Heterologous overexpression of Tgl4p in Pichia pastoris increased total phospholipid and
specifically phosphatidic acid synthesis. Moreover, deletion of TGL4 in Saccharomyces
cerevisiae showed an altered pattern of PC and phosphatidic acid molecular species.
Altogether, our data suggested that yeast Tgl4p functions as hydrolytic enzyme in lipid
degradation, but also contributes to fatty acid channelling and phospholipid remodelling.
Several years ago we identified through a mass spectrometric approach the major lipid
particle proteins of Saccharomyces cerevisiae. This approach was a milestone in the field
because it identified a number of new gene products and their function and provided valuable
hints for processes associated with lipid particles. We realized, however, that this study was
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