Stereochemically distinct roles for sterol in (original) (raw)
Related papers
Inhibition of sterol biosynthesis by ergosterol and cholesterol in Saccharomyces cerevisiae
Biochimica Et Biophysica Acta (bba) - Lipids and Lipid Metabolism, 1985
When accumulation of squalene was used as a measure of the flow of carbon into the sterol pathway in whole cells of semi-anaerobic Saccharomyces cerevisiae, both ergosterol and cholesterol were found to be inhibitory. However, at equivalent concentrations in the medium ergosterol was substantially the more potent inhibitor. Marked differences found in the absorption and esterification of the two sterols failed to account for the observed difference in their capacities to act as feedback agents. Cholesterol was much more effectively absorbed as well as esterified, but, when the abilities of the two sterols to lower the squalene level were calculated on the basis of free sterol in the cells, ergosterol remained more effective by a factor of four.
FEMS Yeast Research, 2003
Genes of the post-squalene ergosterol biosynthetic pathway in Saccharomyces cerevisiae have been overexpressed in a systematic approach with the aim to construct yeast strains that produce high amounts of sterols from a squalene-accumulating strain. This strain had previously been deregulated by overexpressing a truncated HMG-CoA reductase (tHMG1) in the main bottleneck of the early ergosterol pathway. The overexpression of the gene ERG1 (squalene epoxidase) induced a significant decrease of the direct substrate squalene, a high increase of lanosterol, and a small increase of later sterols. The overexpression of the ERG11 gene encoding the sterol-14K-demethylase resulted in a decrease of lanosterol and an increase of downstream sterols. When these two genes were simultaneously overexpressed, later sterols from zymosterol to ergosterol accumulated and the content of squalene was decreased about threefold , indicating that these steps had limited the transformation of squalene into sterols. The total sterol content in this strain was threefold higher than in a wild-type strain.
Multiple functions for sterols in Saccharomyces cerevisiae
Biochimica et Biophysica Acta (BBA) - Lipids and Lipid Metabolism, 1985
Analyses with a yeast sterol auxotroph indicated that there are at least four different levels of function for sterol which have been designated sparking, critical domain, domain and bulk. Growth of yeast sterol auxotrophs on cholestanol is precluded unless minute amounts of ergosterol are available. We have designated this phenomenon the sparking of growth, in which cholestanol satisfies an overall membrane sterol requirement and ergosterol fulfills a high specificity sparking function. The critical domain role for sterol is observed under conditions of lanosterol supplementation where low levels of ergosterol (lo-times those necessary for sparking on cholestanol) are required for growth. The sterol functions designated domain and bulk are illustrated by assessing cellular free sterol levels and plasma membrane properties of a sterol auxotroph after growth on different concentrations of exogenously supplied sterol. Plasma membranes isolated from auxotrophs grown on domain or bulk levels of sterol underwent no lipid thermotropic transitions, while plasma membranes from cells grown on critical domain levels of sterol underwent a lipid thermotropic transition, when analyzed by steady-state fluorescence anisotropy.
Alternative pathways of sterol synthesis in yeast
Steroids, 2002
Yeast produce traces of aberrant sterols by minor alternative pathways, which can become significant when normal metabolism is blocked by inhibitors or mutations. We studied sterols generated in the absence of the 8 -7 isomerase (Erg2p) or 5 desaturase (Erg3p) by incubating three mutant strains of Saccharomyces cerevisiae with 5␣-cholest-8-en-3-ol, 8-dehydrocholesterol ( 5,8 sterol), or isodehydrocholesterol ( 6,8 sterol), together with the corresponding 3␣-3 H isotopomer. Nine different incubations gave altogether 16 sterol metabolites, including seven 22E sterols formed by action of the yeast C-22 desaturase (Erg5p). These products were separated by silver-ion high performance liquid chromatography (Ag + -HPLC) and identified by gas chromatography-mass spectrometry, nuclear magnetic resonance spectroscopy, and radio-Ag + -HPLC. When 8 -7 isomerization was blocked, exogenous 8 sterol underwent desaturation to 5,8 , 6,8 , and 8,14 sterols. Formation of 5,8 sterol was strongly favored over 6,8 sterol, but both pathways are essentially dormant under normal conditions of sterol synthesis. The 5,8 sterol was metabolically almost inert except for 22 desaturation, whereas the 6,8 sterol was readily converted to 5,7 , 5,7,9(11) , and 7,9(11) sterols. The combined results indicate aberrant metabolic pathways similar to those in mammalian systems. However, 5,7 sterol undergoes only slight isomerization or desaturation in yeast, an observation that accounts for the lower levels of 5,8 and 5,7,9(11) sterols in wild-type yeast compared to Smith-Lemli-Opitz individuals.
Aspects of sterol metabolism in the yeastSaccharomyces cerevisiae and inPhytophthora
Lipids, 1982
Using 5 wild-type strains of yeast, nonequivalence in the isolation of sterol mutants was observed. Experiments are described on the effects of sterol modifications on growth, physical and enzymic properties of Saccharomyces cerevisiae and Phytophthora cactorum. Although discontinuities in Arrhenius kinetics were observed by fluorescence anisotropy and enzymic measurements of mutants (but not wild-types) of yeast, evidence based on membrane permeability and differential scanning calorimetry failed to support bulk lipid phase transitions as the cause for the discontinuities. Lipids 17:187-196, 1982. MATERIALS AND METHODS Organisms The strains ofS. cerevisiae used in this study are shown in Table 1. No ergosterol is synthesized by the nystatin-resistant mutants. Strain 3701B-n3 accumulates ergosta-7,22diene-3~-ol and 8R1 accumulates cholesta-8,24-diene-3~-ol and cholesta-5,7,22,24-tetraene-3~-ol. P. cactorum was obtained from E. Hansen, Oregon State University. Culture Conditions Yeast were routinely cultured on rich medium (1% tryptone, 0.5% yeast extract, 2% carbon source) or Wickerham's synthetic complete media (2,3). For solid media, 1.5% agar (Difco) was added. Cultures of P. cactorum were grown in a
Sterol methylation in Saccharomyces cerevisiae
Journal of bacteriology, 1984
Various nystatin-resistant mutants defective in S-adenosylmethionine: delta 24-sterol-C-methyltransferase (EC 2.1.1.41) were shown to possess alleles of the same gene, erg6. The genetic map location of erg6 was shown to be close to trp1 on chromosome 4. Despite the single locus for erg6, S-adenosylmethionine: delta 24-sterol-C-methyltransferase enzyme activity was found in three separate fractions: mitochondria, microsomes, and the "floating lipid layer." The amount of activity in each fraction could be manipulated by assay conditions. The lipids and lipid synthesis of mutants of Saccharomyces cerevisiae defective in the delta 24-sterol-C-methyltransferase were compared with a C5(6) desaturase mutant and parental wild types. No ergosterol (C28 sterol) could be detected in whole-cell sterol extracts of the erg6 mutants, the limits of detection being less than 10(-11) mol of ergosterol per 10(8) cells. The distribution of accumulated sterols by these mutants varied with grow...
Journal of bacteriology, 1993
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 delta 24-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 stery...
Sterols in erg mutants of Phycomyces: metabolic pathways and physiological effects
Steroids, 2002
Phycomyces is a fungal producer of -carotene and other beneficial metabolites. Several erg mutants of Phycomyces, originally selected to study the effects of membrane alteration on physiological responses, have now been used to gain information about sterol biosynthesis in filamentous fungi. One mutant, H23, and its progeny were found to be blocked at episterol C-5 dehydrogenase and did not produce ergosterol or any other sterol with a conjugated ⌬ 5,7 diene system. This mutant showed abnormal phototropism, which was correlated with the altered sterol composition. Another mutant, H25, seems to be a regulatory mutant. All analyzed mutants synthesized ergosta-7,22,24(28)trien-3-ol, demonstrating for the first time that the sterol C-22 dehydrogenase of Phycomyces is capable of recognizing sterols with a 24(28) unsaturated side chain. New evidence regarding the biogenesis of neoergosterol and phycomysterols, the potential sparking function of cholesterol, as well as the regulation of sterol biosynthesis in this fungus is also reported. Given these results, a pathway for sterol biosynthesis in Phycomyces is proposed.