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Molecular and Cellular Biology, March 2005, p. 1655-1668, Vol. 25, No. 5
0270-7306/05/$08.00+0     doi:10.1128/MCB.25.5.1655-1668.2005
Copyright © 2005, American Society for Microbiology. All Rights Reserved.

The Saccharomyces cerevisiae YLL012/YEH1, YLR020/YEH2, and TGL1 Genes Encode a Novel Family of Membrane-Anchored Lipases That Are Required for Steryl Ester Hydrolysis

René Köffel,1 Rashi Tiwari,1 Laurent Falquet,2 and Roger Schneiter1*

Department of Medicine, Division of Biochemistry, University of Fribourg, Fribourg,1 Swiss Institute of Bioinformatics, Epalinges, Switzerland2

Received 25 July 2004/ Returned for modification 20 September 2004/ Accepted 29 November 2004

Sterol homeostasis in eukaryotic cells relies on the reciprocal interconversion of free sterols and steryl esters. The formation of steryl esters is well characterized, but the mechanisms that control steryl ester mobilization upon cellular demand are less well understood. We have identified a family of three lipases of Saccharomyces cerevisiae that are required for efficient steryl ester mobilization. These lipases, encoded by YLL012/YEH1, YLR020/YEH2, and TGL1, are paralogues of the mammalian acid lipase family, which is composed of the lysosomal acid lipase, the gastric lipase, and four novel as yet uncharacterized human open reading frames. Lipase triple-mutant yeast cells are completely blocked in steryl ester hydrolysis but do not affect the mobilization of triacylglycerols, indicating that the three lipases are required for steryl ester mobilization in vivo. Lipase single mutants mobilize steryl esters to various degrees, indicating partial functional redundancy of the three gene products. Lipase double-mutant cells in which the third lipase is expressed from the inducible GAL1 promoter have greatly reduced steady-state levels of steryl esters, indicating that overexpression of any of the three lipases is sufficient for steryl ester mobilization in vivo. The three yeast enzymes constitute a novel class of membrane-anchored lipases that differ in topology and subcellular localization.

* Corresponding author. Mailing address: University of Fribourg, Department of Medicine, Division of Biochemistry, Chemin du Musée 5, CH-1700 Fribourg, Switzerland. Phone: 41 26 300 8654. Fax: 41 26 300 9735. E-mail: roger.schneiter{at}unifr.ch.

Molecular and Cellular Biology, March 2005, p. 1655-1668, Vol. 25, No. 5
0022-538X/05/$08.00+0     doi:10.1128/MCB.25.5.1655-1668.2005
Copyright © 2005, American Society for Microbiology. All Rights Reserved.



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