The TGL2 Gene of Saccharomyces cerevisiae Encodes an Active Acylglycerol Lipase Located in the Mitochondria

The Saccharomyces cerevisiae Tgl2 protein shows sequence homology to Pseudomonas triacylglycerol (TAG) lipases, but its role in the yeast lipid metabolism is not known. Using hemagglutinin-tagged Tgl2p purified from yeast, we report that this protein carries a significant lipolytic activity toward long-chain TAG. Importantly, mutant hemagglutinin-Tgl2p(S144A), which contains alanine 144 in place of serine 144 in the lipase consensus sequence (G/A)XSXG exhibits no such activity. Although cellular TAG hydrolysis is reduced in the tgl2 deletion mutant, overproduction of Tgl2p in this mutant leads to an increase in TAG degradation in the presence of fatty acid synthesis inhibitor cerulenin, but that of Tgl2p(S144A) does not. This result demonstrates the lipolytic function of Tgl2p in yeast. Although other yeast TAG lipases are localized to lipid particles, Tgl2p is enriched in the mitochondria. The mitochondrial fraction purified from the TGL2-overexpressing yeast shows a strong lipolytic activity, which was absent in the tgl2 deletion mutant. Therefore, we conclude that Tgl2p is a functional lipase of the yeast mitochondria. By analyzing phenotypic effects of TGL2-deficient yeast, we also find that lipolysis-competent Tgl2p is required for the viability of cells treated with antimitotic drug. The addition of oleic acid, the product of Tgl2p-catalyzed lipolysis, fully complements the antimitotic drug sensitivity of the tgl2 null mutation. Thus, we propose that the mitochondrial Tgl2p-dependent lipolysis is crucial for the survival of cells under antimitotic drug treatment.