Storage lipid synthesis is non-essential ..
In the yeast Saccharomyces cerevisiae as in other eukaryotes non-polar lipids are a reservoir of energy and building blocks for membrane lipid synthesis. The yeast non-polar lipids, triacylglycerols (TG) and steryl esters (SE) are stored in so-called lipid particles/droplets (LP) as biologically inert form of fatty acids and sterols. To understand LP structure and function in more detail we investigated the molecular equipment of this compartment making use of mass spectrometric analysis of lipids (TG, SE, phospholipids) and proteins. We addressed the question whether or not lipid and protein composition of LP influence each other and performed analyses of LP from cells grown on two different carbon sources, glucose and oleate. Growth of cells on oleate caused dramatic cellular changes including accumulation of TG at the expense of SE, enhanced the amount of glycerophospholipids and strongly increased the degree of unsaturation in all lipid classes. Most interestingly, oleate as a carbon source led to adaptation of the LP proteome resulting in the appearance of several novel LP proteins. Localization of these new LP proteins was confirmed by cell fractionation. Proteomes of LP variants from cells grown on glucose or oleate, respectively, were compared and are discussed with emphasis on the different groups of proteins detected through this analysis. In summary, we demonstrate flexibility of the yeast LP lipidome and proteome and the ability of LP to adapt to environmental changes.
2002) Storage lipid synthesis is non-essential in ..
Our lipidome analyses led to a number of important observations. First, we found that TG contain large amounts of unsaturated fatty acids, especially C18:1, even when cells were grown on glucose (see ). This effect although not unexpected was dramatically enhanced when oleate served as a carbon source. The reason for this finding appears to be the preference of TG synthesizing enzymes, Dga1p and Lro1p for specific substrates. As a result of this specificity, TG storage molecules have a high degree of fluidity and accumulate as a soft and non-structured core of LP . The second striking observation of the present study was that oleate as a carbon source selectively stimulated formation of TG, whereas SE synthesis was dramatically decreased. Most recently, we showed that inhibition of Are2p, the major SE synthase of S. cerevisiae, by oleate was the reason for this finding. Surprisingly, in Yarrowia lipolytica oleic acid as a carbon source had the opposite effect causing a decrease of TG but an increase of SE . The molecular reason of this effect is not known. Finally, the strong incorporation of C18:1 into TG of S. cerevisiae grown on oleate clearly demonstrated that the exogenous fatty acid was not only used as source of energy and a substrate for β-oxidation in peroxisomes , but also directly incorporated as building block into complex lipids.
All eukaryotes including the yeast contain a lipid storage compartment which is named lipid particle, lipid droplet or oil body. Lipids accumulating in this subcellular fraction serve as a depot of energy and building blocks for membrane lipid synthesis. In the yeast, the major storage lipids are triacylglycerols (TGs) and steryl esters (SEs). An important step in the life cycle of these non-polar lipids is their mobilization from their site of storage and channeling of their degradation components to the appropriate metabolic pathways. A key step in this mobilization process is hydrolysis of TG and SE which is accomplished by lipases and hydrolases. In this review, we describe our recent knowledge of TG lipases from the yeast based on biochemical, molecular biological and cell biological information. We report about recent findings addressing the versatile role of TG lipases in lipid metabolism, and discuss non-polar lipid homeostasis and its newly discovered links to various cell biological processes in the yeast.