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The effects of methylphosphonate, a phosphate analog, on the expression and degradation of the highaffinity phosphate transporter Pho84, in Saccharomyces cerevisiae
Stockholm University, Faculty of Science, Department of Biochemistry and Biophysics.
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2004 (English)In: Biochemistry, ISSN 0006-2960, E-ISSN 1520-4995, Vol. 43, no 45, 14444-14453 p.Article in journal (Refereed) Published
Abstract [en]

In Saccharomyces cerevisiae, the Pho84 high-affinity transport system is the major phosphate transporter activated when the cells experience a limitation in external phosphate. In this study, we have compared the phosphate-responsive mechanism of cells expressing PHO84 with a Δpho84 strain by use of a phosphate analogue, methylphosphonate, which was judged to be suitable for assessment of phosphate homeostasis in the cells. Intracellular levels of the analogue, which in several respects mimicks phosphate, were monitored by 31P NMR spectroscopy. Results show that methylphosphonate is a nonhydrolyzable and nonutilizable analogue that cannot be used to replenish phosphate or polyphosphate in yeast cells grown under conditions of phosphate limitation. However, the presence of methylphosphonate under such conditions represses the Pho5 acidic phosphatase activity of PHO84 cells, a finding that implies a direct role of the analogue in the regulation of phosphate-responsive genes and/or proteins. Likewise, accumulation of the Pho84 protein at the plasma membrane of the same cells is inhibited by methylphosphonate, although the derepressive expression of the PHO84 gene is unperturbed. Thus, a post-transcriptional regulation is suggested. Supportive of this suggestion is the fact that addition of methylphosphonate to cells with abundant and active Pho84 at the plasma membrane causes enhanced internalization of the Pho84 protein. Altogether, these observations suggest that the Pho84 transporter is regulated not only at the transcriptional level but also by a direct molecule-sensing mechanism at the protein level.

Place, publisher, year, edition, pages
2004. Vol. 43, no 45, 14444-14453 p.
National Category
Medical Biotechnology (with a focus on Cell Biology (including Stem Cell Biology), Molecular Biology, Microbiology, Biochemistry or Biopharmacy)
Identifiers
URN: urn:nbn:se:su:diva-23328DOI: 10.1021/bi049327tOAI: oai:DiVA.org:su-23328DiVA: diva2:191379
Note
Part of urn:nbn:se:su:diva-240Available from: 2004-09-16 Created: 2004-09-16 Last updated: 2010-07-07Bibliographically approved
In thesis
1. Regulatory and Structural Properties of the High-Affinity Phosphate Acquisition System in Saccharomyces cerevisiae
Open this publication in new window or tab >>Regulatory and Structural Properties of the High-Affinity Phosphate Acquisition System in Saccharomyces cerevisiae
2004 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

Inorganic phosphate is an essential nutrient required for the synthesis of many cellular components (e.g., nucleic acids, proteins, lipids and sugars), as well as for meeting metabolic needs (e.g., energy production and translocation). In the case of the unicellular yeast Saccharomyces cerevisiae, the presence of both high- and low-affinity phosphate transporters in the plasma membrane provides for adaptation to environmental variations. Of these systems, the high-affinity Pho84 transport system is the major phosphate transporter activated when the cells have limited access to external phosphate.

This integral membrane protein belongs to the major facilitator superfamily (MFS) and possesses 12 predicted transmembrane domains. Activation of this and other proteins (e.g., extracellular phosphatases) involved in maintaining cellular phosphate homeostasis under conditions of limited availability of external phosphate is controlled primarily by transcriptional regulation. However, the presence of proteins indirectly or directly involved in phosphate transport by Pho84, including Gtr1, has been reported. The Gtr1 protein binds guanine nucleotides and probably functions as a molecular switch.

The present thesis describes the regulated intracellular trafficking and degradation of Pho84 in response to phosphate, as well as to its non-hydrolysable and non-utilizable analog methylphosphonate. The involvement of the Gtr1 protein in high-affinity phosphate uptake has also been examined. Moreover, in vitro and in silico analyses of structural and functional aspects of both the Pho84 and Gtr1 proteins are presented and discussed.

Place, publisher, year, edition, pages
Stockholm: Institutionen för biokemi och biofysik, 2004. 63 p.
National Category
Biochemistry and Molecular Biology
Identifiers
urn:nbn:se:su:diva-240 (URN)91-7265-936-X (ISBN)
Public defence
2004-10-07, William-Olssonsalen, Geovetenskapens hus, Svante Arrhenius väg 8 A, Stockholm, 10:00
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Supervisors
Available from: 2004-09-16 Created: 2004-09-16Bibliographically approved

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Biochemistry
Medical Biotechnology (with a focus on Cell Biology (including Stem Cell Biology), Molecular Biology, Microbiology, Biochemistry or Biopharmacy)

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