Jandrositz Anita, Petschnigg Julia, Zimmermann Robert, Natter Klaus, Scholze Hubert, Hermetter Albin, Kohlwein Sepp D, Leber Regina
Institute of Molecular Biosciences, SFB Biomembrane Research Center, University of Graz, Schubertstr. 1, A8010 Graz, Austria.
Biochim Biophys Acta. 2005 Jun 15;1735(1):50-8. doi: 10.1016/j.bbalip.2005.04.005.
Based on sequence homology to mammalian acid lipases, yeast reading frame YKL140w was predicted to encode a triacylglycerol (TAG) lipase in yeast and was hence named as TGL1, triglyceride lipase 1. A deletion of TGL1, however, resulted in an increase of the cellular steryl ester content. Fluorescently labeled lipid analogs that become covalently linked to the enzyme active site upon catalysis were used to discriminate between the lipase and esterase activities of Tgl1p. Tgl1p preferred single-chain esterase inhibitors over lipase inhibitors in vitro. Under assay conditions optimal for acid lipases, Tgl1p exhibited steryl esterase activity only and lacked any triglyceride lipase activity. In contrast, at pH 7.4, Tgl1p also exhibited TAG lipase activity; however, steryl ester hydrolase activity was still predominant. Tgl1p localized exclusively to lipid droplets which are the intracellular storage compartment of steryl esters and triacylglycerols in the yeast S. cerevisiae. In a tgl1 deletion mutant, the mobilization of steryl esters in vivo was delayed, but not abolished, suggesting the existence of additional enzymes involved in steryl ester mobilization.
基于与哺乳动物酸性脂肪酶的序列同源性，酵母阅读框YKL140w被预测在酵母中编码一种三酰甘油（TAG）脂肪酶，因此被命名为TGL1，即甘油三酯脂肪酶1。然而，TGL1的缺失导致细胞甾醇酯含量增加。利用在催化作用下与酶活性位点共价连接的荧光标记脂质类似物来区分Tgl1p的脂肪酶和酯酶活性。在体外，Tgl1p更倾向于单链酯酶抑制剂而非脂肪酶抑制剂。在对酸性脂肪酶而言最优的测定条件下，Tgl1p仅表现出甾醇酯酶活性，而缺乏任何甘油三酯脂肪酶活性。相比之下，在pH 7.4时，Tgl1p也表现出TAG脂肪酶活性；然而，甾醇酯水解酶活性仍然占主导。Tgl1p仅定位于脂质滴，脂质滴是酿酒酵母中甾醇酯和三酰甘油的细胞内储存区室。在tgl1缺失突变体中，体内甾醇酯的动员被延迟，但并未被消除，这表明存在参与甾醇酯动员的其他酶。
