Lipid storage and mobilization pathways in yeast.

Biochemistry, cell biology and molecular biology of lipids can be properly studied using the yeast Saccharionyces cerevisiae as a model system. We employ this microorganism to investigate pathways of neutral lipid (triacylglycerol, steryl ester) synthesis, storage and mobilization and to identify major gene products involved in these processes. The steryl ester synthases Are1p and Are2p were shown to catalyze steryl ester formation, and Dgalp and Lro1p were identified as major enzymes of triacylglycerol synthesis. Both triacylglycerols and steryl esters are stored in lipid particles, an intracellular compartment that is structurally reminiscent of lipoproteins. Neutral lipid mobilization is initiated by the triacylglycerol lipases Tgl3p, Tgl4p and Tgl5p, and the steryl ester hydrolases Tgl1p, Yeh1p and Yeh2p. The acyltransferases Are1p, Are1p, Lro1p and Dgalp are located in the endoplasmic reticulum, but a substantial amount of Dgalp is also present in lipid particles. The three triacylglycerol lipases as well as Tgl1p and Yeh1p are components of lipid particles, whereas Yeh2p was detected in the plasma membrane. Thus, enzymatic steps of triacylglycerol and steryl ester metabolism are located in different subcellular compartments. Consequently, regulation of neutral lipid metabolism does not only occur at the enzymatic level but also at the organelle level.