PII Is Important in Regulation of Nitrogen Metabolism but Not Required for Heterocyst Formation in the Cyanobacterium Anabaena sp. PCC 7120

Zhang, Ying; Pu, Hai; Wang, Qingsong; Cheng, Shu; Zhao, Weixing; Yan, Zhang; Zhao, Jindong

doi:10.1074/jbc.m706500200

Cited by 31 publications

(47 citation statements)

References 53 publications

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“…strain PCC 7120, previous attempts to inactivate glnB were unsuccessful (26). However, that report was followed by two others in which the obtention of glnB null mutants was described (38,49). In the most recent of these, the authors showed that successful inactivation of glnB could only be achieved when the expression pattern of downstream genes of unknown function was altered (38).…”

Section: Discussionmentioning

confidence: 89%

Mutations atpipXSuppress Lethality of P_II-Deficient Mutants ofSynechococcus elongatusPCC 7942

et al. 2009

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The P II proteins are found in all three domains of life as key integrators of signals reflecting the balance of nitrogen and carbon. Genetic inactivation of P II proteins is typically associated with severe growth defects or death. However, the molecular basis of these defects depends on the specific functions of the proteins with which P II proteins interact to regulate nitrogen metabolism in different organisms. In Synechococcus elongatus PCC 7942, where P II forms complexes with the NtcA coactivator PipX, attempts to engineer P II -deficient strains failed in a wild-type background but were successful in pipX null mutants. Consistent with the idea that P II is essential to counteract the activity of PipX, four different spontaneous mutations in the pipX gene were found in cultures in which glnB had been genetically inactivated.Cyanobacteria are phototrophic organisms that perform oxygenic photosynthesis. Autotrophic growth requires the constant assimilation of ammonium via the coordinated action of glutamine synthetase (GS) and glutamate synthase, also known as the GS-GOGAT cycle, resulting in consumption of 2-oxoglutarate (34). Due to the lack of 2-oxoglutarate dehydrogenase in cyanobacteria, synthesis of 2-oxoglutarate represents the final step in the oxidative branch of the trichloroacetic acid cycle and directly links 2-oxoglutarate levels to nitrogen assimilation (35). Thus, 2-oxoglutarate accumulates during nitrogen starvation, making this metabolite an excellent indicator of the intracellular carbon-nitrogen balance (12,25).In cyanobacteria, multiple metabolic and developmental processes are induced by nitrogen starvation. NtcA, the global regulator for nitrogen control, activates genes involved in nitrogen assimilation, heterocyst differentiation, and acclimation to nitrogen starvation (20,30,41). 2-Oxoglutarate, the signal of nitrogen deficiency, stimulates binding of NtcA to target sites (45), transcription activation in vitro (44), and complex formation between the global nitrogen regulator NtcA and its coactivator factor PipX, a regulatory protein conserved in cyanobacteria (5, 9). The interaction between PipX and NtcA is known to be relevant for maximal activation of NtcA-dependent genes under nitrogen limitation (9, 10). PipX-deficient cultures of Synechococcus elongatus PCC 7942 showed reduced activity of nitrogen assimilation enzymes, retarded nitrogen induction, a slower rate of nitrate consumption, and when subjected to nitrogen starvation, retarded phycobilisome degradation and faster reduction of the chlorophyll content (10).The homotrimeric P II protein is one of the most conserved and widespread signal transduction proteins in nature and plays key roles in nitrogen assimilatory processes (28). P II proteins contain three binding sites (one per subunit) for 2-oxoglutarate and ATP, and their primary function is to regulate, by direct protein-protein interactions, the activity of proteins implicated in nitrogen metabolism (reviewed in reference 13). In cyanobacteria, several proteins are k...

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Section: Discussionmentioning

confidence: 89%

Mutations atpipXSuppress Lethality of P_II-Deficient Mutants ofSynechococcus elongatusPCC 7942

et al. 2009

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“…No PII phosphorylation could be detected in Nostoc punctiforme extracts but the N. punctiforme PII protein could be phosphorylated in vitro by S. elongatus cell extracts (Hanson et al 1998). Mass spectroscopic analysis of the PII protein from Anabaena extracts revealed Tyr51 to be subjected to nitration under diazotrophic conditions while no phosphorylation at Ser49 was detected (Zhang et al 2007). Absence of PII phosphorylation in the Nostocales is, however, in contrast to the presence of a PphA homologue.…”

Section: Modification Of Pii Proteinsmentioning

confidence: 99%

From cyanobacteria to plants: conservation of PII functions during plastid evolution

Chellamuthu

Alva

Forchhammer

2012

Planta

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This article reviews the current state-of-the-art concerning the functions of the signal processing protein PII in cyanobacteria and plants, with a special focus on evolutionary aspects. We start out with a general introduction to PII proteins, their distribution, and their evolution. We also discuss PII-like proteins and domains, in particular, the similarity between ATP-phosphoribosyltransferase (ATP-PRT) and its PII-like domain and the complex between N-acetyl-L-glutamate kinase (NAGK) and its PII activator protein from oxygenic phototrophs. The structural basis of the function of PII as an ATP/ADP/ 2-oxoglutarate signal processor is described for Synechococcus elongatus PII. In both cyanobacteria and plants, a major target of PII regulation is NAGK, which catalyzes the committed step of arginine biosynthesis. The common principles of NAGK regulation by PII are outlined. Based on the observation that PII proteins from cyanobacteria and plants can functionally replace each other, the hypothesis that PII-dependent NAGK control was under selective pressure during the evolution of plastids of Chloroplastida and Rhodophyta is tested by bioinformatics approaches. It is noteworthy that two lineages of heterokont algae, diatoms and brown algae, also possess NAGK, albeit lacking PII; their NAGK however appears to have descended from an alphaproteobacterium and not from a cyanobacterium as in plants. We end this article by coming to the conclusion that during the evolution of plastids, PII lost its function in coordinating gene expression through the PipX-NtcA network but preserved its role in nitrogen (arginine) storage metabolism, and subsequently took over the fine-tuned regulation of carbon (fatty acid) storage metabolism, which is important in certain developmental stages of plants.

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“…NtcA is the main 2-oxoglutarate sensor for the initiation of heterocyst differentiation (239). The otherwise important signal protein PII, which is involved in regulation of nitrogen metabolism in bacteria and plants, is apparently not required for heterocyst formation (240). Nitrogenase synthesis has a high demand for Fe.…”

Section: Occurrence Of Nitrogenases In Heterocystsmentioning

confidence: 99%

Nitrogen Fixation and Hydrogen Metabolism in Cyanobacteria

Bothe

Schmitz²,

Yates

et al. 2010

Microbiol Mol Biol Rev

365

222

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SUMMARY This review summarizes recent aspects of (di)nitrogen fixation and (di)hydrogen metabolism, with emphasis on cyanobacteria. These organisms possess several types of the enzyme complexes catalyzing N2 fixation and/or H2 formation or oxidation, namely, two Mo nitrogenases, a V nitrogenase, and two hydrogenases. The two cyanobacterial Ni hydrogenases are differentiated as either uptake or bidirectional hydrogenases. The different forms of both the nitrogenases and hydrogenases are encoded by different sets of genes, and their organization on the chromosome can vary from one cyanobacterium to another. Factors regulating the expression of these genes are emerging from recent studies. New ideas on the potential physiological and ecological roles of nitrogenases and hydrogenases are presented. There is a renewed interest in exploiting cyanobacteria in solar energy conversion programs to generate H2 as a source of combustible energy. To enhance the rates of H2 production, the emphasis perhaps needs not to be on more efficient hydrogenases and nitrogenases or on the transfer of foreign enzymes into cyanobacteria. A likely better strategy is to exploit the use of radiant solar energy by the photosynthetic electron transport system to enhance the rates of H2 formation and so improve the chances of utilizing cyanobacteria as a source for the generation of clean energy.

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PII Is Important in Regulation of Nitrogen Metabolism but Not Required for Heterocyst Formation in the Cyanobacterium Anabaena sp. PCC 7120

Cited by 31 publications

References 53 publications

Mutations atpipXSuppress Lethality of P_II-Deficient Mutants ofSynechococcus elongatusPCC 7942

Mutations atpipXSuppress Lethality of P_II-Deficient Mutants ofSynechococcus elongatusPCC 7942

From cyanobacteria to plants: conservation of PII functions during plastid evolution

Nitrogen Fixation and Hydrogen Metabolism in Cyanobacteria

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PII Is Important in Regulation of Nitrogen Metabolism but Not Required for Heterocyst Formation in the Cyanobacterium Anabaena sp. PCC 7120

Cited by 31 publications

References 53 publications

Mutations atpipXSuppress Lethality of PII-Deficient Mutants ofSynechococcus elongatusPCC 7942

Mutations atpipXSuppress Lethality of PII-Deficient Mutants ofSynechococcus elongatusPCC 7942

From cyanobacteria to plants: conservation of PII functions during plastid evolution

Nitrogen Fixation and Hydrogen Metabolism in Cyanobacteria

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Product

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Mutations atpipXSuppress Lethality of P_II-Deficient Mutants ofSynechococcus elongatusPCC 7942

Mutations atpipXSuppress Lethality of P_II-Deficient Mutants ofSynechococcus elongatusPCC 7942