Abstract
In order to determine the regulation mechanisms of ergosterol biosynthesis in yeast, we developed growth conditions leading to high or limiting ergosterol levels in wild type and sterol-auxotrophic mutant strains. An excess of sterol is obtained in anaerobic sterol-supplemented cultures of mutant and wild type strains. A low sterol level is obtained in aerobic growth conditions in mutant strains cultured with optimal sterol supplementation and in wild type strain deprived of pantothenic acid, as well as in anaerobic cultures without sterol supplementation. Measurements of the specific activities of acetoacetyl-CoA thiolase, HMG-CoA (3-hydroxy-3-methylglutaryl-CoA) synthase and HMG-CoA reductase (the first three enzymes of the pathway), show that in cells deprived of ergosterol, acetoacetyl-CoA thiolase and HMG-CoA synthase are generally increased. In an excess of ergosterol, in anaerobiosis, the same enzymes are strongly decreased. A 5-10-fold decrease is observed for acetoacetyl-CoA thiolase and HMG-CoA synthase. In contrast, HMG-CoA reductase is only slightly affected by these conditions. These results show that ergosterol could regulate its own synthesis, at least partially, by repression of the first two enzymes of the pathway. Our results also show that exogenous sterols, even if strongly incorporated by auxotrophic mutant cells, cannot suppress enzyme activities in aerobic growth conditions. Measurement of specific enzyme activities in mutant cells also revealed that farnesyl pyrophosphate thwarts the enhancement of the activities of the two first enzymes.
Full text
PDF
Selected References
These references are in PubMed. This may not be the complete list of references from this article.
- Barton D. H., Corrie J. E., Bard M., Woods R. A. Biosynthesis of terpenes and steroids. IX. The sterols of some mutant yeasts and their relationship to the biosynthesis of ergosterol. J Chem Soc Perkin 1. 1974;11(0):1326–1333. [PubMed] [Google Scholar]
- Boll M., Löwel M., Still J., Berndt J. Sterol biosynthesis in yeast. 3-Hydorxy-3-methylglutaryl-Coenzyme A reductase as a regulatory enzyme. Eur J Biochem. 1975 Jun;54(2):435–444. doi: 10.1111/j.1432-1033.1975.tb04154.x. [DOI] [PubMed] [Google Scholar]
- Brown M. S., Goldstein J. L. Multivalent feedback regulation of HMG CoA reductase, a control mechanism coordinating isoprenoid synthesis and cell growth. J Lipid Res. 1980 Jul;21(5):505–517. [PubMed] [Google Scholar]
- Karst F., Lacroute F. Ertosterol biosynthesis in Saccharomyces cerevisiae: mutants deficient in the early steps of the pathway. Mol Gen Genet. 1977 Sep 9;154(3):269–277. doi: 10.1007/BF00571282. [DOI] [PubMed] [Google Scholar]
- Karst F., Lacroute F. Yeast mutant requiring only a sterol as growth supplement. Biochem Biophys Res Commun. 1974 Jul 10;59(1):370–376. doi: 10.1016/s0006-291x(74)80216-0. [DOI] [PubMed] [Google Scholar]
- Molzahn S. W., Woods R. A. Polyene resistance and the isolation of sterol mutants in Saccharomyces cerevisiae. J Gen Microbiol. 1972 Sep;72(2):339–348. doi: 10.1099/00221287-72-2-339. [DOI] [PubMed] [Google Scholar]
- Pinto W. J., Lozano R., Nes W. R. Inhibition of sterol biosynthesis by ergosterol and cholesterol in Saccharomyces cerevisiae. Biochim Biophys Acta. 1985 Aug 22;836(1):89–95. doi: 10.1016/0005-2760(85)90224-3. [DOI] [PubMed] [Google Scholar]
- Rine J., Hansen W., Hardeman E., Davis R. W. Targeted selection of recombinant clones through gene dosage effects. Proc Natl Acad Sci U S A. 1983 Nov;80(22):6750–6754. doi: 10.1073/pnas.80.22.6750. [DOI] [PMC free article] [PubMed] [Google Scholar]
- Servouse M., Mons N., Baillargeat J. L., Karst F. Isolation and characterization of yeast mutants blocked in mevalonic acid formation. Biochem Biophys Res Commun. 1984 Sep 17;123(2):424–430. doi: 10.1016/0006-291x(84)90247-x. [DOI] [PubMed] [Google Scholar]
- Stewart P. R., Rudney H. The biosynthesis of beta-hydroxy-beta-methylglutaryl coenzyme A in yeast. 3. Purification and properties of the condensing enzyme thiolase system. J Biol Chem. 1966 Mar 10;241(5):1212–1221. [PubMed] [Google Scholar]
- Trocha P. J., Sprinson D. B. Location and regulation of early enzymes of sterol biosynthesis in yeast. Arch Biochem Biophys. 1976 May;174(1):45–51. doi: 10.1016/0003-9861(76)90322-2. [DOI] [PubMed] [Google Scholar]