| 1. |
- Jonsson, Anders, et al.
(författare)
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A novel peroxiredoxin activity is located within the C-terminal end of Rhodospirillum rubrum adenylyltransferase.
- 2008
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Ingår i: Journal of Bacteriology. - 0021-9193 .- 1098-5530. ; 190:1, s. 434-7
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Tidskriftsartikel (refereegranskat)abstract
- Adenylyltransferase (GlnE) catalyzes the reversible adenylylation of glutamine synthetase. In this report we present, for the first time, evidence for a peroxiredoxin activity of Rhodospirillum rubrum GlnE, through the carboxyl-terminal AhpC/thiol-specific antioxidant (TSA) domain. The combination of GlnE and AhpC/TSA domains within the same polypeptide constitutes a unique domain architecture that has not previously been identified among proteobacteria.
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| 2. |
- Jonsson, Anders, et al.
(författare)
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Reduced activity of glutamine synthetase in Rhodospirillum rubrum mutants lacking the adenylyltransferase GlnE
- 2009
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Ingår i: Research in Microbiology. - : Elsevier BV. - 0923-2508 .- 1769-7123. ; 160:8, s. 581-4
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Tidskriftsartikel (refereegranskat)abstract
- In the nitrogen-fixing bacterium Rhodospirillum rubrum, the GlnE adenylyltransferase (encoded by glnE) catalyzes reversible adenylylation of glutamine synthetase, thereby regulating nitrogen assimilation. We have generated glnE mutant strains that are unable to adenylylate glutamine synthetase (GS). Surprisingly, the activity of GS was lower in the mutants than in the wild type, even when grown in nitrogen-fixing conditions. Our results support the proposal that R. rubrum can only cope with the absence of an adenylylation system in the presence of lowered GS expression or activity. In general terms, this report also provides further support for the central role of GS in bacterial metabolism.
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| 3. |
- Jonsson, Anders, et al.
(författare)
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The activity of adenylyltransferase in Rhodospirillum rubrum is only affected by alpha-ketoglutarate and unmodified PII proteins, but not by glutamine, in vitro
- 2007
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Ingår i: The FBS Journal. - : Wiley. - 1742-464X. ; 274:10, s. 2449-2460
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Tidskriftsartikel (refereegranskat)abstract
- Ammonium assimilation is tightly regulated in nitrogen-fixing bacteria; the target of regulation is primarily the activity of the key enzyme glutamine synthetase that is regulated by reversible covalent modification by AMP groups in reactions catalysed by the bifunctional adenylyltransferase (ATase). The properties and regulation of ATase from Escherichia coli have been studied in great detail. We have investigated the regulation of ATase from Rhodospirillum rubrum, a photosynthetic nitrogen-fixing bacterium. In this diazotroph, nitrogenase is regulated at the metabolic level in addition to the transcriptional regulation operating in all diazotrophic bacteria, which makes understanding the regulatory features of nitrogen assimilation even more interesting. We show that in R. rubrum, in contrast to the E. coli system, ATase is primarily regulated by α-ketoglutarate and that glutamine has no effect on neither the adenylylation nor the deadenylylation of glutamine synthetase. Furthermore, the role of the regulatory PII proteins is only to stimulate the adenylylation reaction, as there is no effect on the reverse reaction. We propose that in R. rubrum and possibly other diazotrophs α-ketoglutarate plays the central role in the regulation of ATase and thus glutamine synthetase activity.
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| 4. |
- Teixeira, Pedro Filipe, et al.
(författare)
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Interaction of the signal transduction protein GlnJ with the cellular targets AmtB1, GlnE and GlnD in Rhodospirillum rubrum: dependence on manganese, 2-oxoglutarate and the ADP/ATP ratio
- 2008
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Ingår i: Microbiology. - : Microbiology Society. - 1350-0872 .- 1465-2080. ; 154:8, s. 2336-2347
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Tidskriftsartikel (refereegranskat)abstract
- The PII family of signal transduction proteins is widespread amongst the three domains of life, and its members have fundamental roles in the general control of nitrogen metabolism. These proteins exert their regulatory role by direct protein-protein interaction with a multitude of cellular targets. The interactions are dependent on the binding of metabolites such as ATP, ADP and 2-oxoglutarate (2-OG), and on whether or not the PII protein is modified. In the photosynthetic nitrogen-fixing bacterium Rhodospirillum rubrum three PII paralogues have been identified and termed GlnB, GlnJ and GlnK. In this report we analysed the interaction of GlnJ with known cellular targets such as the ammonium transporter AmtB1, the adenylyltransferase GlnE and the uridylyltransferase GlnD. Our results show that the interaction of GlnJ with cellular targets is regulated in vitro by the concentrations of manganese and 2-OG and the ADP : ATP ratio. Furthermore, we show here for the first time, to our knowledge, that in the interactions of GlnJ with the three different partners, the energy signal (ADP : ATP ratio) in fact overrides the carbon/nitrogen signal (2-OG). In addition, by generating specific amino acid substitutions in GlnJ we show that the interactions with different cellular targets are differentially affected, and the possible implications of these results are discussed. Our results are important to further the understanding of the regulatory role of PII proteins in R. rubrum, a photosynthetic bacterium in which the nitrogen fixation process and its intricate control mechanisms make the regulation of nitrogen metabolism even more complex than in other studied bacteria.
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| 5. |
- Teixeira, Pedro Filipe, 1983-
(författare)
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PII proteins as global regulators of bacterial nitrogen metabolism
- 2009
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Nitrogen is an essential element to sustain life, being a component of most biological macromolecules. In spite of the abundance of gaseous N2, the availability of nitrogen compounds that can be readily used by most microorganisms is scarce and its production energetically demanding. Due to the central importance of nitrogen metabolism, most microorganisms evolved elaborate mechanisms to ensure efficient regulation, balancing substrate availability, product formation and energy expenditure. In most bacteria, many archaea and some plants, the different aspects of nitrogen metabolism are coordinated by members of the PII family of signal transduction proteins, acting as fundamental molecular messengers controlling several cellular processes. In proteobacteria, including the nitrogen fixing organism Rhodospirillum rubrum, these proteins are involved in regulation at different levels: they regulate gene expression, modulating the activity of several transcription factors; they control the flux through the ammonium transport protein (AmtB); they influence the activity of key metabolic enzymes, e.g. glutamine synthetase (GS) and nitrogenase. The signal sensing and integration by these proteins is achieved in two different yet interdependent strategies: allosteric regulation (by the binding of metabolites like ATP, ADP, 2-oxoglutarate) and reversible post-translational modification. Signal integration likely results in different conformations of the proteins, influencing the direct protein-protein interaction with the cellular targets. In the present work, using R. rubrum as a model organism, we have studied some aspects of the biochemistry of PII proteins in terms of regulatory interactions with the ammonium transport protein AmtB1 and the adenylyltransferase GlnE (involved in GS regulation). Additionally, we have investigated the post-translational modification of PII proteins, showing for the first time in vivo in addition in vitro selectivity in the modification of different PII proteins. Our results contributed to elucidate several new aspects in the regulation by PII proteins and also strengthened the idea that these proteins act as global regulators in the context of bacterial nitrogen metabolism.
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