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Poklepovich TJ, Rinaldi MA, Tomazic ML, Favale NO, Turkewitz AP, Nudel CB, Nusblat AD. The cytochrome b5 dependent C-5(6) sterol desaturase DES5A from the endoplasmic reticulum of Tetrahymena thermophila complements ergosterol biosynthesis mutants in Saccharomyces cerevisiae. Steroids 2012; 77:1313-20. [PMID: 22982564 PMCID: PMC3501532 DOI: 10.1016/j.steroids.2012.08.015] [Citation(s) in RCA: 16] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 04/09/2012] [Revised: 08/21/2012] [Accepted: 08/23/2012] [Indexed: 11/23/2022]
Abstract
Tetrahymena thermophila is a free-living ciliate with no exogenous sterol requirement. However, it can perform several modifications on externally added sterols including desaturation at C5(6), C7(8), and C22(23). Sterol desaturases in Tetrahymena are microsomal enzymes that require Cyt b(5), Cyt b(5) reductase, oxygen, and reduced NAD(P)H for their activity, and some of the genes encoding these functions have recently been identified. The DES5A gene encodes a C-5(6) sterol desaturase, as shown by gene knockout in Tetrahymena. To confirm and extend that result, and to develop new approaches to gene characterization in Tetrahymena, we have now, expressed DES5A in Saccharomyces cerevisiae. The DES5A gene was codon optimized and expressed in a yeast mutant, erg3Δ, which is disrupted for the gene encoding the S. cerevisiae C-5(6) sterol desaturase ERG3. The complemented strain was able to accumulate 74% of the wild type level of ergosterol, and also lost the hypersensitivity to cycloheximide associated with the lack of ERG3 function. C-5(6) sterol desaturases are expected to function at the endoplasmic reticulum. Consistent with this, a GFP-tagged copy of Des5Ap was localized to the endoplasmic reticulum in both Tetrahymena and yeast. This work shows for the first time that both function and localization are conserved for a microsomal enzyme between ciliates and fungi, notwithstanding the enormous evolutionary distance between these lineages. The results suggest that heterologous expression of ciliate genes in S. cerevisiae provides a useful tool for the characterization of genes in Tetrahymena, including genes encoding membrane protein complexes.
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Affiliation(s)
- Tomas J. Poklepovich
- Cátedra de Biotecnología y Microbiología Industrial, Facultad de Farmacia y Bioquímica, Universidad de Buenos Aires, Junín 956, (C1113AAD) Buenos Aires, Argentina
| | - Mauro A. Rinaldi
- Cátedra de Biotecnología y Microbiología Industrial, Facultad de Farmacia y Bioquímica, Universidad de Buenos Aires, Junín 956, (C1113AAD) Buenos Aires, Argentina
| | - Mariela L. Tomazic
- Cátedra de Biotecnología y Microbiología Industrial, Facultad de Farmacia y Bioquímica, Universidad de Buenos Aires, Junín 956, (C1113AAD) Buenos Aires, Argentina
| | - Nicolas O. Favale
- Cátedra de Biología Celular, Departamento de Ciencias Biológicas, Facultad de Farmacia y Bioquímica, Universidad de Buenos Aires, Junín 956, (C1113AAD) Buenos Aires, Argentina
| | - Aaron P. Turkewitz
- Department of Molecular Genetics and Cell Biology, The University of Chicago, 920 E. 58th Street, Chicago, IL, USA
| | - Clara B. Nudel
- Cátedra de Biotecnología y Microbiología Industrial, Facultad de Farmacia y Bioquímica, Universidad de Buenos Aires, Junín 956, (C1113AAD) Buenos Aires, Argentina
| | - Alejandro D. Nusblat
- Cátedra de Biotecnología y Microbiología Industrial, Facultad de Farmacia y Bioquímica, Universidad de Buenos Aires, Junín 956, (C1113AAD) Buenos Aires, Argentina
- Corresponding author at all stages of refereeing and publication, also post-publication: * Alejandro D. Nusblat, , Address: Cátedra de Biotecnología y Microbiología Industrial, Facultad de Farmacia y Bioquímica, Universidad de Buenos, Aires, Junín 956, (C1113AAD) Buenos Aires, Argentina. Phone: +54-11-4964-8270, Fax: +54-11-4964-8200
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C-5(6) sterol desaturase from tetrahymena thermophila: Gene identification and knockout, sequence analysis, and comparison to other C-5(6) sterol desaturases. EUKARYOTIC CELL 2009; 8:1287-97. [PMID: 19525418 DOI: 10.1128/ec.00057-09] [Citation(s) in RCA: 12] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 01/23/2023]
Abstract
The gene coding for a C-5(6) sterol desaturase in Tetrahymena thermophila, DES5A, has been identified by the knockout of the TTHERM_01194720 sequence. Macronucleus transformation was achieved by biolistic bombardment and gene replacement through phenotypic assortment, using paromomycin as the selective agent. A knockout cell line (KO270) showed a phenotype consistent with that of the DES5A deletion mutant. KO270 converted only 6% of the added sterol into the C-5 unsaturated derivative, while the wild type accumulated 10-fold larger amounts under similar conditions. The decreased desaturation activity is specific for the C-5(6) position of lathosterol and cholestanol; other desaturations, namely C-7(8) and C-22(23), were not affected. Analysis by reverse transcription-PCR reveals that DES5A is transcribed both in the presence and absence of cholestanol in wild-type cells, whereas the transcribed gene was not detected in KO270. The growth of KO270 was undistinguishable from that of the wild-type strain. Des5Ap resembles known C-5(6) sterol desaturases, displaying the three typical histidine motifs, four hydrophobic transmembrane regions, and two other highly conserved domains of unknown function. A phylogenetic analysis placed T. thermophila's enzyme and Paramecium orthologues in a cluster together with functionally characterized C-5 sterol desaturases from vertebrates, fungi, and plants, although in a different branch.
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Nusblat AD, Muñoz L, Valcarce GA, Nudel CB. Characterization and properties of cholesterol desaturases from the ciliate Tetrahymena thermophila. J Eukaryot Microbiol 2005; 52:61-7. [PMID: 15702982 DOI: 10.1111/j.1550-7408.2005.3279rr.x] [Citation(s) in RCA: 15] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Abstract
Live Tetrahymena thermophila transforms exogenous cholesterol into 7,22-bis, dehydrocholesterol (DHC) by desaturation at positions C7(8) and C22(23) of the cholesterol moiety. In this first report on expression, isolation, characterization, and reconstitution of Tetrahymena's cholesterol desaturases in cell-free extracts, we describe conditions for increasing the expression of both desaturases based on the addition of specific sterols to the culture medium. Reactions performed in vitro, with isolated microsomes, yield only the mono-unsaturated derivatives, 7-DHC and/or 22-DHC. However, selectivity towards one product can be improved with the addition of specific compounds: beta-mercaptoethanol inhibited C22(23) desaturase activity completely, while ethanol selectively increased this activity. Detergent-solubilized microsomes showed no desaturase activity, but partial restoration could be achieved with addition of dilauroyl-phosphatidylcholine liposomes (25%). Both cholesterol desaturases require molecular oxygen and cytochrome b(5). NADH or NADPH can serve as reduced cofactors, albeit with different efficiency, delivered by reductases present in the microsomal fraction. Azide and cyanide, but not azole compounds, inhibited these desaturases, suggesting a key role for cytochrome b(5) in these reactions.
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Affiliation(s)
- Alejandro D Nusblat
- Cátedra de Biotecnología y Microbiología Industrial, Facultad de Farmacia y Bioquímica, Universidad de Buenos Aires, Junin 956, 1113 Buenos Aires, Argentina
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