Sterols in yeast subcellular fractions

Parks, Leo W.; McLean-Bowen, Colleen A.; Taylor, F. R.; Hough, Susan Carol

doi:10.1007/bf02533753

Cited by 26 publications

(10 citation statements)

References 45 publications

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“…Lipid globules in S. cerevisiae contain predominantly steryl esters, triacylglycerol, and phospholipids and are the major storage compartment for steryl esters (19). In electron micrographs, lipid globules appear to be closely associated with the endoplasmic reticulum (6,27).…”

Section: Resultsmentioning

confidence: 99%

Characteristics of sterol uptake in Saccharomyces cerevisiae

Lorenz¹,

Rodríguez²,

Lewis³

et al. 1986

J Bacteriol

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A Saccharomyces cerevisiae sterol auxotroph, FY3 (a hem] erg7 ura), was used to probe the characteristics of sterol uptake in S. cerevisiae. The steady-state cellular concentration of free sterol at the late exponential phase of growth could be adjusted within a 10-fold range by varying the concentration of exogenously supplied sterol. When cultured on 1 ,ug of sterol ml-', the cells contained a minimal cellular free-cholesterol concentration of 0.85 nmol/mg (dry weight) and were termed sterol depleted. When cultured on 11 ,ug of sterol ml-' or more, the cells contained a maximal cellular free-cholesterol concentration of 6.8 nmol/mg (dry weight) and were termed free sterol saturated. Cells with free-sterol concentrations below the maximal level were capable of accumulating free sterol from the medium. The capacity of the cells for cholesterol uptake was inversely proportional to the initial intracellular concentration. The uptake of sterol was shown to be a nonactive process that is independent of cellular energy sources or viability. The intracellular transport of sterol for esterification is not sensitive to anti-microtubule agents.

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Section: Resultsmentioning

confidence: 99%

Characteristics of sterol uptake in Saccharomyces cerevisiae

Lorenz¹,

Rodríguez²,

Lewis³

et al. 1986

J Bacteriol

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“…Alternatively, conversion of zymosterol to fecosterol could occur at contact zones between the endoplasmic reticulum and lipid particles. Close association of lipid particles and the endoplasmic reticulum has been reported before (22,29). Steryl esters produced in the endoplasmic reticulum by steryl ester synthase have to be transferred to lipid particles, where most of the cellular steryl esters are deposited.…”

Section: Discussionmentioning

confidence: 99%

Sterol composition of yeast organelle membranes and subcellular distribution of enzymes involved in sterol metabolism

1993

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Organelles of the yeast Saccharomyces cerevisiae were isolated and analyzed for sterol composition and the activity of three enzymes involved in sterol metabolism. The plasma membrane and secretory vesicles, the fractions with the highest sterol contents, contain ergosterol as the major sterol. In other subcellular membranes, which exhibit lower sterol contents, intermediates of the sterol biosynthetic pathway were found at higher percentages. Lipid particles contain, in addition to ergosterol, large amounts of zymosterol, fecosterol, and episterol. These sterols are present esterified with long-chain fatty acids in this subcellular compartment, which also harbors practically all of the triacylglycerols present in the cell but very little phospholipids and proteins. Sterol A4-methyltransferase, an enzyme that catalyzes one of the late steps in sterol biosynthesis, was localized almost exclusively in lipid particles. Steryl ester formation is a microsomal process, whereas steryl ester hydrolysis occurs in the plasma membrane and in secretory vesicles. The fact that synthesis, storage, and hydrolysis of steryl esters occur in different subcellular compartments gives rise to the view that ergosteryl esters of lipid particles might serve as intermediates for the supply of ergosterol from internal membranes to the plasma membrane.Lipid transport in eukaryotic cells is an essential process, because synthesis of lipids is restricted to certain organelles, whereas lipids are required as constitutive components of all subcellular membranes (3, 37). Lipid migration must be efficiently regulated, because lipids are not randomly distributed among subcellular membranes. In fact, certain lipids are characteristic for specific membranes, e.g., cardiolipin for the inner mitochondrial membrane (6) and sterols (15, 41) and sphingolipids (15, 24) for the plasma membrane. Possible mechanisms of lipid transport are spontaneous or proteincatalyzed transfer of lipid monomers between membranes, vesicle flow, and membrane contact and fusion (3).Sterols are essential components of the eukaryotic plasma membrane. The mechanism of their transport from internal membranes, where they are synthesized, to the periphery of the cell is still obscure. Vesicle flow as a possible mechanism seems very likely, but the vesicles involved need not be identical to protein secretory vesicles (36). Sterol carrier proteins, which have been shown to stimulate translocation of sterols in vitro, have not been proven to catalyze this process in vivo (1).We have chosen the yeast Saccharomyces cerevisiae as a model cell to study intracellular transport of sterols. The yeast-specific sterol ergosterol is structurally and functionally related to sterols found in higher eukaryotes. Under conditions in which yeast cells cannot produce their own ergosterol, e.g., under anaerobiosis, in auxotrophic mutants, or in the presence of inhibitors of sterol biosynthesis, addition of ergosterol to the growth medium and uptake into cells are essential for cellular growth and pro...

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“…Besides plants, UDP-glucose:sterol glucosyltransferase activity was determined by in vitro enzyme assays in Saccharomyces cerevisiae (45)(46)(47)(48), Candida bogoriensis (49), other fungi (50), and Physarum polycephalum (51,11). Although the lipid composition of S. cerevisiae was studied in detail during the last decades, there are only rare reports on the actual isolation of sterol glucoside (SG) 1 from this yeast (8,9).…”

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confidence: 99%

Cloning and Functional Expression of UGT Genes Encoding Sterol Glucosyltransferases from Saccharomyces cerevisiae, Candida albicans, Pichia pastoris, and Dictyostelium discoideum

Warnecke¹,

Erdmann²,

Fahl³

et al. 1999

Journal of Biological Chemistry

122

135

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Sterol glucosides, typical membrane-bound lipids of many eukaryotes, are biosynthesized by a UDP-glucose: sterol glucosyltransferase (EC 2.4.1.173). We cloned genes from three different yeasts and from Dictyostelium discoideum, the deduced amino acid sequences of which all showed similarities with plant sterol glucosyltransferases (Ugt80A1, Ugt80A2). These genes from Saccharomyces cerevisiae (UGT51 ‫؍‬ YLR189C), Pichia pastoris (UGT51B1), Candida albicans (UGT51C1), and Dictyostelium discoideum (ugt52) were expressed in Escherichia coli. In vitro enzyme assays with cell-free extracts of the transgenic E. coli strains showed that the genes encode UDP-glucose:sterol glucosyltransferases which can use different sterols such as cholesterol, sitosterol, and ergosterol as sugar acceptors. An S. cerevisiae null mutant of UGT51 had lost its ability to synthesize sterol glucoside but exhibited normal growth under various culture conditions. Expression of either UGT51 or UGT51B1 in this null mutant under the control of a galactose-induced promoter restored sterol glucoside synthesis in vitro. Lipid extracts of these cells contained a novel glycolipid. This lipid was purified and identified as ergosterol-␤-D-glucopyranoside by nuclear magnetic resonance spectroscopy. These data prove that the cloned genes encode sterol-␤-D-glucosyltransferases and that sterol glucoside synthesis is an inherent feature of eukaryotic microorganisms.Sterol glycosides are widespread membrane lipids, occurring in all plants, several algae (1-3), some fungi (4 -9), slime molds (10 -12), Dictyostelium (13), a few bacteria (14 -19), and even animals (20 -23). The knowledge base for sterol glycosides is rather limited compared with free sterols and sterol esters, where the synthesis, transport, and functions have been studied extensively in animals (24 -29), plants, (30 -35), and yeast (36 -40). The basis for studies on the functions of sterol glycosides is the assumption that free sterols and sterol glycosides differ physiologically. It is obvious that the attachment of a glycosyl moiety to the sterol backbone alters the physical properties of this lipid. As a result, there are changes in the properties of membranes containing different proportions of free sterols and sterol glycosides. Such changes have been studied with artificial membranes in terms of membrane fluidity, permeability, hydration, and phase behavior (41)(42)(43)(44). However, we still do not know how free sterols and sterol glycosides differ physiologically in biological membranes and why many eukaryotic organisms synthesize sterol glycosides. One of the main reasons for our limited knowledge in this field is the lack of a genetic approach. The objective of the present work was the isolation and characterization of sterol glycosyltransferase genes from eukaryotic organisms. We expect that genetic manipulation of these genes will facilitate the elucidation of sterol glycoside functions in these organisms.The predominating sugar moiety in sterol glycosides is glucose. Besides plants...

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Sterols in yeast subcellular fractions

Cited by 26 publications

References 45 publications

Characteristics of sterol uptake in Saccharomyces cerevisiae

Characteristics of sterol uptake in Saccharomyces cerevisiae

Sterol composition of yeast organelle membranes and subcellular distribution of enzymes involved in sterol metabolism

Cloning and Functional Expression of UGT Genes Encoding Sterol Glucosyltransferases from Saccharomyces cerevisiae, Candida albicans, Pichia pastoris, and Dictyostelium discoideum

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