Steryl ester hydrolases in yeast.
Andrea Wagner, Heidemarie Müllner, Guenter Deutsch, Guenther Daum
Institute of Biochemistry, Graz University of Technology, Petersgasse 12/2, Graz, 8010, Austria
Steryl esters (STE) and triacylglycerols (TAG) are the main storage lipids in eukaryotic cells. In Saccharomyces cerevisiae like in other eukaryotes these storage lipids accumulate in an organelle named lipid particle, lipid body or lipid droplet. Lipid particles of the yeast consist of a highly hydrophobic core of TAG and STE which is surrounded by a phospholipid monolayer with a small amount of proteins embedded. Fatty acids and sterols stored in lipid particles can be utilized for membrane formation under conditions of lipid depletion. For this purpose, storage lipids have to be mobilized which requires catalysis by STE hydrolases and TAG lipases. Recently, a TAG lipase named Tgl3p localized to lipid particles was identified as the first enzyme of this kind in yeast. The aim of this work was to find equivalent enzymes with STE hydrolase activity. Through a combined cell biological and molecular biological approach a number of potential candidate gene products were selected which contain hydrolase motifs and are present on the surface of lipid particles. The respective deletion strains were tested for their ability to hydrolyze STE in vivo and in vitro. This approach identified the two lipid particle proteins Yeh1p und Tgl1p. These enzymes are in addition to the recently identified STE hydrolase Yeh2p responsible for STE mobilization in yeast. (supported by FWF project 15141 to G.D.).