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Identification of Chromatophore Membrane Protein Complexes Formed under Different Nitrogen Availability Conditions in Rhodospirillum rubrum
Stockholm University, Faculty of Science, Department of Biochemistry and Biophysics.
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2011 (English)In: Journal of Proteome Research, ISSN 1535-3893, E-ISSN 1535-3907, Vol. 10, no 6, 2703-2714 p.Article in journal (Refereed) Published
Abstract [en]

The chromatophore membrane of the photosynthetic diazotroph Rhodospirillum rubrum is of vital importance for a number of central processes, including nitrogen fixation. Using a novel amphiphile, we have identified protein complexes present under different nitrogen availability conditions by the use of two-dimensional Blue Native/SDS-PAGE and NSI-LC-LTQ-Orbitrap mass spectrometry. We have identified several membrane protein complexes, including components of the ATP synthase, reaction center, light harvesting, and NADH dehydrogenase complexes. Additionally, we have identified differentially expressed proteins, such as subunits of the succinate dehydrogenase complex and other TCA cycle enzymes that are usually found in the cytosol, thus hinting at a possible association to the membrane in response to nitrogen deficiency. We propose a redox sensing mechanism that can influence the membrane subproteome in response to nitrogen availability.

Place, publisher, year, edition, pages
2011. Vol. 10, no 6, 2703-2714 p.
Keyword [en]
Rhodospirillum rubrum, nitrogen metabolism, Blue Native, chromatophore subproteome, amphiphile, Orbitrap
National Category
Biological Sciences
URN: urn:nbn:se:su:diva-67875DOI: 10.1021/pr100838xISI: 000291186100002OAI: diva2:471377
authorCount :8Available from: 2012-01-02 Created: 2012-01-02 Last updated: 2012-10-03Bibliographically approved
In thesis
1. Regulation of nitrogen fixation in Rhodospirillum rubrum: Through proteomics and beyond
Open this publication in new window or tab >>Regulation of nitrogen fixation in Rhodospirillum rubrum: Through proteomics and beyond
2010 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

Adaptability is one of the reasons for the success of bacteria, allowing them to survive in conditions where no other organisms would be able to thrive. Nitrogen deficiency, for example, can be a limiting factor for the growth of micro-organisms, as this element is an essential part of almost all types of biomolecules. As such, some bacteria have evolved specific mechanisms to overcome nitrogen limitation. Nitrogen fixing bacteria, or diazotrophs, use a specific enzyme complex, nitrogenase, in order to harness this element from the enormous reservoir that is the Earth’s atmosphere. However, nitrogen fixation is a demanding process for the cells, requiring vast amounts of energy and tight regulation.

In this thesis we explore the mechanisms regulating nitrogen fixation in Rhodospirillum rubrum, a purple non-sulphur photosynthetic bacterium. Using proteomics tools, we show how the regulation of both the nitrogen and carbon fixation processes is interconnected, possibly in order to maintain the intracellular redox balance. Using a new detergent molecule, we also demonstrate how nitrogen availability affects the chromatophore membrane proteome.

Our studies have revealed the crucial role of the cellular pool of 2-oxoglutarate (2OG) for adequate signaling through the PII proteins and the effects resulting from artificially manipulating this metabolite’s concentration. In R. rubrum nitrogenase is also subjected to post-translational control (the “switch-off” effect) and this work shows for the first time that the enzyme modifying nitrogenase (Dinitrogenase Reductase ADP-ribsosyl Transferase or DRAT) forms a complex with the PII protein GlnB. This complex allows DRAT activation and its formation – and, therefore, DRAT activity – is regulated by binding of ADP:ATP and 2OG to GlnB.

Upon light withdrawal, nitrogenase activity anaerobically in the dark is also here demonstrated to be dependent on the activity of the pathway starting in pyruvate formate-lyase and we show how different nitrogen sources influence the switch-off response. This response can, in some conditions, be modified by addition of pyruvate and we have studied how this metabolite influences nitrogenase activity and switch-off regulation.

This study allows a better understanding of the underlying processes controlling the metabolic routes in R. rubrum and also provides new insights into regulation of enzyme activity, paving the road for the complete establishment of the mechanisms regulating nitrogenase switch-off.

Place, publisher, year, edition, pages
Stockholm: Department of Biochemistry and Biophysics, Stockholm University, 2010. 71 p.
Rhodospirillum rubrum, nitrogen fixation, redox balance, switch-off, DRAT
National Category
Biochemistry and Molecular Biology
Research subject
urn:nbn:se:su:diva-42101 (URN)978-91-7447-125-0 (ISBN)
Public defence
2010-10-08, Magnélisalen, Kemiska övningslaboratoriet, Svante Arrhenius väg 16 B, Stockholm, 10:00 (English)

At the time of the doctoral defense, the following papers were unpublished and had a status as follows: Paper 2: In press. Paper 3: Submitted. Paper 4: Manuscript. Paper 5: Submitted.

Available from: 2010-09-16 Created: 2010-08-16 Last updated: 2012-10-03Bibliographically approved

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Nordlund, StefanNorén, Agneta
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