Lipid particles/droplets of the yeast Saccharomyces cerevisiae revisited: Lipidome meets Proteome

Abstract

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.

Controlling Lipid Fluxes at Glycerol-3-phosphate Acyltransferase Step in Yeast

“…Induced by Oleic Acid-It is well known that oleate preferentially induces TAG synthesis and its accumulation in LPs in yeast (5,14). Because radiolabeling studies have indicated that Gat1p and Gat2p differentially contribute to TAG synthesis (8), we decided to study their role in response to oleate.…”

“…It is well known that synthesis of lipids is spatially restricted by the localization of biosynthetic systems. Intriguingly, evidence points to Gat1p (but not Gat2p) as an LP resident protein, although this has only been detected during stationary phase in cells cultured in the presence of glucose (5,10,11). In addition, localization studies in actively growing cells showed that both Gat1p and Gat2p are localized to the ER, possibly enriched in distinct ER regions (12).…”

“…Excess availability of fatty acids, like oleate, provides such an experimental condition (5,14). Interestingly, in a recent screening of the haploid yeast deletion collection, cells lacking Gat1p (but not Gat2p) were identified to be sensitive to oleate (15).…”

“…This implies LPs are not just a static storage compartment but a dynamic structure that actively participates in maintaining lipid homeostasis (1)(2)(3). LPs have a signature proteome and lipidome that responds to environmental and nutritional conditions of cells (4,5). Unique LP resident proteins include enzymes catalyzing the degradation of steryl esters and TAG, whereas most anabolic enzymes shuttle between the endoplasmic reticulum (ER) and LPs.…”

The Evolutionary Conserved Oil Body Associated Protein OBAP1 Participates in the Regulation of Oil Body Size

“…Each type of organisms contains a specific set of them, for example, perilipins in mammal cytosolic OBs (Kimmel et al, 2010), 19 proteins in fungi (Grillitsch et al, 2011), and phasins in bacterial OBs (Yang et al, 2012). The most abundant plant proteins associated with OBs are oleosins (Capuano et al, 2007;Huang et al, 2009).…”