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Jerez C, Llop A, Salinas P, Bibak S, Forchhammer K, Contreras A. Analysing the Cyanobacterial PipX Interaction Network Using NanoBiT Complementation in Synechococcus elongatus PCC7942. Int J Mol Sci 2024; 25:4702. [PMID: 38731921 PMCID: PMC11083307 DOI: 10.3390/ijms25094702] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/22/2024] [Revised: 04/17/2024] [Accepted: 04/23/2024] [Indexed: 05/13/2024] Open
Abstract
The conserved cyanobacterial protein PipX is part of a complex interaction network with regulators involved in essential processes that include metabolic homeostasis and ribosome assembly. Because PipX interactions depend on the relative levels of their different partners and of the effector molecules binding to them, in vivo studies are required to understand the physiological significance and contribution of environmental factors to the regulation of PipX complexes. Here, we have used the NanoBiT complementation system to analyse the regulation of complex formation in Synechococcus elongatus PCC 7942 between PipX and each of its two best-characterized partners, PII and NtcA. Our results confirm previous in vitro analyses on the regulation of PipX-PII and PipX-NtcA complexes by 2-oxoglutarate and on the regulation of PipX-PII by the ATP/ADP ratio, showing the disruption of PipX-NtcA complexes due to increased levels of ADP-bound PII in Synechococcus elongatus. The demonstration of a positive role of PII on PipX-NtcA complexes during their initial response to nitrogen starvation or the impact of a PipX point mutation on the activity of PipX-PII and PipX-NtcA reporters are further indications of the sensitivity of the system. This study reveals additional regulatory complexities in the PipX interaction network, opening a path for future research on cyanobacteria.
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Affiliation(s)
- Carmen Jerez
- Departamento de Fisiología, Genética y Microbiología, Universidad de Alicante, 03690 San Vicente del Raspeig, Spain; (C.J.); (A.L.); (P.S.); (S.B.)
- Interfaculty Institute of Microbiology and Infection Biology, University Tübingen, 72076 Tübingen, Germany;
| | - Antonio Llop
- Departamento de Fisiología, Genética y Microbiología, Universidad de Alicante, 03690 San Vicente del Raspeig, Spain; (C.J.); (A.L.); (P.S.); (S.B.)
| | - Paloma Salinas
- Departamento de Fisiología, Genética y Microbiología, Universidad de Alicante, 03690 San Vicente del Raspeig, Spain; (C.J.); (A.L.); (P.S.); (S.B.)
| | - Sirine Bibak
- Departamento de Fisiología, Genética y Microbiología, Universidad de Alicante, 03690 San Vicente del Raspeig, Spain; (C.J.); (A.L.); (P.S.); (S.B.)
| | - Karl Forchhammer
- Interfaculty Institute of Microbiology and Infection Biology, University Tübingen, 72076 Tübingen, Germany;
| | - Asunción Contreras
- Departamento de Fisiología, Genética y Microbiología, Universidad de Alicante, 03690 San Vicente del Raspeig, Spain; (C.J.); (A.L.); (P.S.); (S.B.)
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2
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Llop A, Tremiño L, Cantos R, Contreras A. The Signal Transduction Protein PII Controls the Levels of the Cyanobacterial Protein PipX. Microorganisms 2023; 11:2379. [PMID: 37894037 PMCID: PMC10609283 DOI: 10.3390/microorganisms11102379] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/05/2023] [Revised: 09/18/2023] [Accepted: 09/21/2023] [Indexed: 10/29/2023] Open
Abstract
Cyanobacteria, microorganisms performing oxygenic photosynthesis, must adapt their metabolic processes to environmental challenges such as day and night changes. PipX, a unique regulatory protein from cyanobacteria, provides a mechanistic link between the signalling protein PII, a widely conserved (in bacteria and plants) transducer of carbon/nitrogen/energy richness, and the transcriptional regulator NtcA, which controls a large regulon involved in nitrogen assimilation. PipX is also involved in translational regulation through interaction with the ribosome-assembly GTPase EngA. However, increases in the PipX/PII ratio are toxic, presumably due to the abnormally increased binding of PipX to other partner(s). Here, we present mutational and structural analyses of reported PipX-PII and PipX-NtcA complexes, leading to the identification of single amino acid changes that decrease or abolish PipX toxicity. Notably, 4 out of 11 mutations decreasing toxicity did not decrease PipX levels, suggesting that the targeted residues (F12, D23, L36, and R54) provide toxicity determinants. In addition, one of those four mutations (D23A) argued against the over-activation of NtcA as the cause of PipX toxicity. Most mutations at residues contacting PII decreased PipX levels, indicating that PipX stability would depend on its ability to bind to PII, a conclusion supported by the light-induced decrease of PipX levels in Synechococcus elongatus PCC7942 (hereafter S. elongatus).
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Affiliation(s)
| | | | | | - Asunción Contreras
- Departamento de Fisiología, Genética y Microbiología, Universidad de Alicante, 03690 San Vicente del Raspeig, Spain; (A.L.); (L.T.); (R.C.)
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3
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Llop A, Bibak S, Cantos R, Salinas P, Contreras A. The ribosome assembly GTPase EngA is involved in redox signaling in cyanobacteria. Front Microbiol 2023; 14:1242616. [PMID: 37637111 PMCID: PMC10448771 DOI: 10.3389/fmicb.2023.1242616] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/19/2023] [Accepted: 07/21/2023] [Indexed: 08/29/2023] Open
Abstract
Photosynthetic organisms must cope with environmental challenges, like those imposed by the succession of days and nights or by sudden changes in light intensities, that trigger global changes in gene expression and metabolism. The photosynthesis machinery is particularly susceptible to environmental changes and adaptation to them often involves redox-sensing proteins that are the targets of reactive oxygen species generated by photosynthesis activity. Here we show that EngA, an essential GTPase and ribosome-assembly protein involved in ribosome biogenesis in bacteria and chloroplasts, also plays a role in acclimatization to environmentally relevant stress in Synechococcus elongatus PCC7942 and that PipX, a promiscuous regulatory protein that binds to EngA, appears to fine-tune EngA activity. During growth in cold or high light conditions, the EngA levels rise, with a concomitant increase of the EngA/PipX ratio. However, a sudden increase in light intensity turns EngA into a growth inhibitor, a response involving residue Cys122 of EngA, which is part of the GD1-G4 motif NKCES of EngA proteins, with the cysteine conserved just in the cyanobacteria-chloroplast lineage. This work expands the repertoire of ribosome-related factors transmitting redox signals in photosynthetic organisms and provides additional insights into the complexity of the regulatory interactions mediated by EngA and PipX.
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Affiliation(s)
| | | | | | | | - Asunción Contreras
- Departamento de Fisiología, Genética y Microbiología, Facultad de Ciencias, Universidad de Alicante, Alicante, Spain
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4
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Llop A, Labella JI, Borisova M, Forchhammer K, Selim KA, Contreras A. Pleiotropic effects of PipX, PipY, or RelQ overexpression on growth, cell size, photosynthesis, and polyphosphate accumulation in the cyanobacterium Synechococcus elongatus PCC7942. Front Microbiol 2023; 14:1141775. [PMID: 37007489 PMCID: PMC10060972 DOI: 10.3389/fmicb.2023.1141775] [Citation(s) in RCA: 3] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/10/2023] [Accepted: 02/23/2023] [Indexed: 03/18/2023] Open
Abstract
The cyanobacterial protein PipY belongs to the Pyridoxal-phosphate (PLP)-binding proteins (PLPBP/COG0325) family of pyridoxal-phosphate-binding proteins, which are represented in all three domains of life. These proteins share a high degree of sequence conservation, appear to have purely regulatory functions, and are involved in the homeostasis of vitamin B6 vitamers and amino/keto acids. Intriguingly, the genomic context of the pipY gene in cyanobacteria connects PipY with PipX, a protein involved in signaling the intracellular energy status and carbon-to-nitrogen balance. PipX regulates its cellular targets via protein–protein interactions. These targets include the PII signaling protein, the ribosome assembly GTPase EngA, and the transcriptional regulators NtcA and PlmA. PipX is thus involved in the transmission of multiple signals that are relevant for metabolic homeostasis and stress responses in cyanobacteria, but the exact function of PipY is still elusive. Preliminary data indicated that PipY might also be involved in signaling pathways related to the stringent stress response, a pathway that can be induced in the unicellular cyanobacterium Synechococcus elongatus PCC7942 by overexpression of the (p)ppGpp synthase, RelQ. To get insights into the cellular functions of PipY, we performed a comparative study of PipX, PipY, or RelQ overexpression in S. elongatus PCC7942. Overexpression of PipY or RelQ caused similar phenotypic responses, such as growth arrest, loss of photosynthetic activity and viability, increased cell size, and accumulation of large polyphosphate granules. In contrast, PipX overexpression decreased cell length, indicating that PipX and PipY play antagonistic roles on cell elongation or cell division. Since ppGpp levels were not induced by overexpression of PipY or PipX, it is apparent that the production of polyphosphate in cyanobacteria does not require induction of the stringent response.
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Affiliation(s)
- Antonio Llop
- Departamento de Fisiología, Genética y Microbiología, Facultad de Ciencias, Universidad de Alicante, Alicante, Spain
- Interfaculty Institute for Microbiology and Infection Medicine, Organismic Interactions Department, Cluster of Excellence 'Controlling Microbes to Fight Infections', University of Tübingen, Tübingen, Germany
| | - Jose I. Labella
- Departamento de Fisiología, Genética y Microbiología, Facultad de Ciencias, Universidad de Alicante, Alicante, Spain
| | - Marina Borisova
- Interfaculty Institute for Microbiology and Infection Medicine, Organismic Interactions Department, Cluster of Excellence 'Controlling Microbes to Fight Infections', University of Tübingen, Tübingen, Germany
| | - Karl Forchhammer
- Interfaculty Institute for Microbiology and Infection Medicine, Organismic Interactions Department, Cluster of Excellence 'Controlling Microbes to Fight Infections', University of Tübingen, Tübingen, Germany
| | - Khaled A. Selim
- Interfaculty Institute for Microbiology and Infection Medicine, Organismic Interactions Department, Cluster of Excellence 'Controlling Microbes to Fight Infections', University of Tübingen, Tübingen, Germany
| | - Asunción Contreras
- Departamento de Fisiología, Genética y Microbiología, Facultad de Ciencias, Universidad de Alicante, Alicante, Spain
- *Correspondence: Asunción Contreras,
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The Conserved Family of the Pyridoxal Phosphate-Binding Protein (PLPBP) and Its Cyanobacterial Paradigm PipY. Life (Basel) 2022; 12:life12101622. [PMID: 36295057 PMCID: PMC9605639 DOI: 10.3390/life12101622] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/20/2022] [Revised: 10/05/2022] [Accepted: 10/15/2022] [Indexed: 11/16/2022] Open
Abstract
The PLPBP family of pyridoxal phosphate-binding proteins has a high degree of sequence conservation and is represented in all three domains of life. PLPBP members, of which a few representatives have been studied in different contexts, are single-domain proteins with no known enzymatic activity that exhibit the fold type III of PLP-holoenzymes, consisting in an α/β barrel (TIM-barrel), where the PLP cofactor is solvent-exposed. Despite the constant presence of cofactor PLP (a key catalytic element in PLP enzymes), PLPBP family members appear to have purely regulatory functions affecting the homeostasis of vitamin B6 vitamers and amino/keto acids. Perturbation of these metabolites and pleiotropic phenotypes have been reported in bacteria and zebrafish after PLPBP gene inactivation as well as in patients with vitamin B6-dependent epilepsy that results from loss-of-function mutations at the PLPBP. Here, we review information gathered from diverse studies and biological systems, emphasizing the structural and functional conservation of the PLPBP members and discussing the informative nature of model systems and experimental approaches. In this context, the relatively high level of structural and functional characterization of PipY from Synechococcus elongatus PCC 7942 provides a unique opportunity to investigate the PLPBP roles in the context of a signaling pathway conserved in cyanobacteria.
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Jerez C, Salinas P, Llop A, Cantos R, Espinosa J, Labella JI, Contreras A. Regulatory Connections Between the Cyanobacterial Factor PipX and the Ribosome Assembly GTPase EngA. Front Microbiol 2021; 12:781760. [PMID: 34956147 PMCID: PMC8696166 DOI: 10.3389/fmicb.2021.781760] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/23/2021] [Accepted: 11/05/2021] [Indexed: 11/13/2022] Open
Abstract
Cyanobacteria, phototrophic organisms performing oxygenic photosynthesis, must adapt their metabolic processes to important environmental challenges, like those imposed by the succession of days and nights. Not surprisingly, certain regulatory proteins are found exclusively in this phylum. One of these unique proteins, PipX, provides a mechanistic link between signals of carbon/nitrogen and of energy, transduced by the signaling protein PII, and the control of gene expression by the global nitrogen regulator NtcA. PII, required for cell survival unless PipX is inactivated or downregulated, functions by protein-protein interactions with transcriptional regulators, transporters, and enzymes. PipX also functions by protein-protein interactions, and previous studies suggested the existence of additional interacting partners or included it into a relatively robust six-node synteny network with proteins apparently unrelated to the nitrogen regulation system. To investigate additional functions of PipX while providing a proof of concept for the recently developed cyanobacterial linkage network, here we analyzed the physical and regulatory interactions between PipX and an intriguing component of the PipX synteny network, the essential ribosome assembly GTPase EngA. The results provide additional insights into the functions of cyanobacterial EngA and of PipX, showing that PipX interacts with the GD1 domain of EngA in a guanosine diphosphate-dependent manner and interferes with EngA functions in Synechococcus elongatus at a low temperature, an environmentally relevant context. Therefore, this work expands the PipX interaction network and establishes a possible connection between nitrogen regulation and the translation machinery. We discuss a regulatory model integrating previous information on PII-PipX with the results presented in this work.
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Affiliation(s)
- Carmen Jerez
- Departamento de Fisiología, Genética y Microbiología, Facultad de Ciencias, Universidad de Alicante, Alicante, Spain
| | - Paloma Salinas
- Departamento de Fisiología, Genética y Microbiología, Facultad de Ciencias, Universidad de Alicante, Alicante, Spain
| | - Antonio Llop
- Departamento de Fisiología, Genética y Microbiología, Facultad de Ciencias, Universidad de Alicante, Alicante, Spain
| | - Raquel Cantos
- Departamento de Fisiología, Genética y Microbiología, Facultad de Ciencias, Universidad de Alicante, Alicante, Spain
| | - Javier Espinosa
- Departamento de Fisiología, Genética y Microbiología, Facultad de Ciencias, Universidad de Alicante, Alicante, Spain
| | - Jose I Labella
- Departamento de Fisiología, Genética y Microbiología, Facultad de Ciencias, Universidad de Alicante, Alicante, Spain
| | - Asunción Contreras
- Departamento de Fisiología, Genética y Microbiología, Facultad de Ciencias, Universidad de Alicante, Alicante, Spain
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Sakamoto T, Takatani N, Sonoike K, Jimbo H, Nishiyama Y, Omata T. Dissection of the Mechanisms of Growth Inhibition Resulting from Loss of the PII Protein in the Cyanobacterium Synechococcus elongatus PCC 7942. PLANT & CELL PHYSIOLOGY 2021; 62:721-731. [PMID: 33650637 PMCID: PMC8474142 DOI: 10.1093/pcp/pcab030] [Citation(s) in RCA: 3] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 12/28/2020] [Accepted: 02/18/2021] [Indexed: 05/08/2023]
Abstract
In cyanobacteria, the PII protein (the glnB gene product) regulates a number of proteins involved in nitrogen assimilation including PipX, the coactivator of the global nitrogen regulator protein NtcA. In Synechococcus elongatus PCC 7942, construction of a PII-less mutant retaining the wild-type pipX gene is difficult because of the toxicity of uncontrolled action of PipX and the other defect(s) resulting from the loss of PIIper se, but the nature of the PipX toxicity and the PipX-independent defect(s) remains unclear. Characterization of a PipX-less glnB mutant (PD4) in this study showed that the loss of PII increases the sensitivity of PSII to ammonium. Ammonium was shown to stimulate the formation of reactive oxygen species in the mutant cells. The ammonium-sensitive growth phenotype of PD4 was rescued by the addition of an antioxidant α-tocopherol, confirming that photo-oxidative damage was the major cause of the growth defect. A targeted PII mutant retaining wild-type pipX was successfully constructed from the wild-type S. elongatus strain (SPc) in the presence of α-tocopherol. The resulting mutant (PD1X) showed an unusual chlorophyll fluorescence profile, indicating extremely slow reduction and re-oxidation of QA, which was not observed in mutants defective in both glnB and pipX. These results showed that the aberrant action of uncontrolled PipX resulted in an impairment of the electron transport reactions in both the reducing and oxidizing sides of QA.
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Affiliation(s)
- Takayuki Sakamoto
- Graduate School of Bioagricultural Sciences, Nagoya University, Nagoya, 464-8601 Japan
| | - Nobuyuki Takatani
- Graduate School of Bioagricultural Sciences, Nagoya University, Nagoya, 464-8601 Japan
| | - Kintake Sonoike
- Faculty of Education and Integrated Arts and Sciences, Waseda University, Tokyo, 162-8480 Japan
| | - Haruhiko Jimbo
- Graduate School of Science and Engineering, Saitama University, Saitama, 338-8570 Japan
- Graduate School of Arts and Sciences, University of Tokyo,Tokyo 153-8902Japan
| | - Yoshitaka Nishiyama
- Graduate School of Science and Engineering, Saitama University, Saitama, 338-8570 Japan
| | - Tatsuo Omata
- * Corresponding author: E-mail, ; Fax, +81-52-789-4107
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Labella JI, Cantos R, Salinas P, Espinosa J, Contreras A. Distinctive Features of PipX, a Unique Signaling Protein of Cyanobacteria. Life (Basel) 2020; 10:life10060079. [PMID: 32481703 PMCID: PMC7344720 DOI: 10.3390/life10060079] [Citation(s) in RCA: 8] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/10/2020] [Revised: 05/23/2020] [Accepted: 05/26/2020] [Indexed: 12/20/2022] Open
Abstract
PipX is a unique cyanobacterial protein identified by its ability to bind to PII and NtcA, two key regulators involved in the integration of signals of the nitrogen/carbon and energy status, with a tremendous impact on nitrogen assimilation and gene expression in cyanobacteria. PipX provides a mechanistic link between PII, the most widely distributed signaling protein, and NtcA, a global transcriptional regulator of cyanobacteria. PII, required for cell survival unless PipX is inactivated or down-regulated, functions by protein–protein interactions with transcriptional regulators, transporters, and enzymes. In addition, PipX appears to be involved in a wider signaling network, supported by the following observations: (i) PII–PipX complexes interact with PlmA, an as yet poorly characterized transcriptional regulator also restricted to cyanobacteria; (ii) the pipX gene is functionally connected with pipY, a gene encoding a universally conserved pyridoxal phosphate binding protein (PLPBP) involved in vitamin B6 and amino acid homeostasis, whose loss-of-function mutations cause B6-dependent epilepsy in humans, and (iii) pipX is part of a relatively robust, six-node synteny network that includes pipY and four additional genes that might also be functionally connected with pipX. In this overview, we propose that the study of the protein–protein interaction and synteny networks involving PipX would contribute to understanding the peculiarities and idiosyncrasy of signaling pathways that are conserved in cyanobacteria.
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Labella JI, Llop A, Contreras A. The default cyanobacterial linked genome: an interactive platform based on cyanobacterial linkage networks to assist functional genomics. FEBS Lett 2020; 594:1661-1674. [PMID: 32233038 DOI: 10.1002/1873-3468.13775] [Citation(s) in RCA: 7] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/22/2019] [Revised: 02/14/2020] [Accepted: 03/12/2020] [Indexed: 01/01/2023]
Abstract
A database of cyanobacterial linked genomes that can be accessed through an interactive platform (https://dfgm.ua.es/genetica/investigacion/cyanobacterial_genetics/Resources.html) was generated on the bases of conservation of gene neighborhood across 124 cyanobacterial species. It allows flexible generation of gene networks at different threshold values. The default cyanobacterial linked genome, whose global properties are analyzed here, connects most of the cyanobacterial core genes. The potential of the web tool is discussed in relation to other bioinformatics approaches based on guilty-by-association principles, with selected examples of networks illustrating its usefulness for genes found exclusively in cyanobacteria or in cyanobacteria and chloroplasts. We believe that this tool will provide useful predictions that are readily testable in Synechococcus elongatus PCC7942 and other model organisms performing oxygenic photosynthesis.
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Affiliation(s)
- Jose I Labella
- Departamento de Fisiología, Genética y Microbiología, Universidad de Alicante, Spain
| | - Antonio Llop
- Departamento de Fisiología, Genética y Microbiología, Universidad de Alicante, Spain
| | - Asuncion Contreras
- Departamento de Fisiología, Genética y Microbiología, Universidad de Alicante, Spain
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Cantos R, Labella JI, Espinosa J, Contreras A. The nitrogen regulator PipX acts in cis to prevent operon polarity. ENVIRONMENTAL MICROBIOLOGY REPORTS 2019; 11:495-507. [PMID: 30126050 DOI: 10.1111/1758-2229.12688] [Citation(s) in RCA: 9] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 05/25/2018] [Revised: 07/10/2018] [Accepted: 08/10/2018] [Indexed: 06/08/2023]
Abstract
Cyanobacteria, phototrophic organisms performing oxygenic photosynthesis, must adapt their metabolic processes to important environmental challenges, like those imposed by the succession of days and nights. Not surprisingly, certain regulatory proteins are found exclusively in this phylum. One of these unique factors, PipX, provides a mechanistic link between signals of carbon/nitrogen and of energy, transduced by the signalling protein PII, and the control of gene expression by the global nitrogen regulator NtcA. Here we report a new regulatory function of PipX: enhancement in cis of pipY expression, a gene encoding a universally conserved protein involved in amino/keto acid and Pyridoxal phosphate homeostasis. In Synechococcus elongatus and many other cyanobacteria these genes are expressed as a bicistronic pipXY operon. Despite being cis-acting, polarity suppression by PipX is nevertheless reminiscent of the function of NusG paralogues typified by RfaH, which are non-essential operon-specific bacterial factors acting in trans to upregulate horizontally-acquired genes. Furthermore, PipX and members of the NusG superfamily share a TLD/KOW structural domain, suggesting regulatory interactions of PipX with the translation machinery. Our results also suggest that the cis-acting function of PipX is a sophisticated regulatory strategy for maintaining appropriate PipX-PipY stoichiometry.
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Affiliation(s)
- Raquel Cantos
- Departamento de Fisiología, Genética y Microbiología, Universidad de Alicante, Alicante, Spain
| | - Jose I Labella
- Departamento de Fisiología, Genética y Microbiología, Universidad de Alicante, Alicante, Spain
| | - Javier Espinosa
- Departamento de Fisiología, Genética y Microbiología, Universidad de Alicante, Alicante, Spain
| | - Asunción Contreras
- Departamento de Fisiología, Genética y Microbiología, Universidad de Alicante, Alicante, Spain
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Forcada-Nadal A, Llácer JL, Contreras A, Marco-Marín C, Rubio V. The P II-NAGK-PipX-NtcA Regulatory Axis of Cyanobacteria: A Tale of Changing Partners, Allosteric Effectors and Non-covalent Interactions. Front Mol Biosci 2018; 5:91. [PMID: 30483512 PMCID: PMC6243067 DOI: 10.3389/fmolb.2018.00091] [Citation(s) in RCA: 35] [Impact Index Per Article: 5.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/26/2018] [Accepted: 10/18/2018] [Indexed: 11/13/2022] Open
Abstract
PII, a homotrimeric very ancient and highly widespread (bacteria, archaea, plants) key sensor-transducer protein, conveys signals of abundance or poorness of carbon, energy and usable nitrogen, converting these signals into changes in the activities of channels, enzymes, or of gene expression. PII sensing is mediated by the PII allosteric effectors ATP, ADP (and, in some organisms, AMP), 2-oxoglutarate (2OG; it reflects carbon abundance and nitrogen scarcity) and, in many plants, L-glutamine. Cyanobacteria have been crucial for clarification of the structural bases of PII function and regulation. They are the subject of this review because the information gathered on them provides an overall structure-based view of a PII regulatory network. Studies on these organisms yielded a first structure of a PII complex with an enzyme, (N-acetyl-Lglutamate kinase, NAGK), deciphering how PII can cause enzyme activation, and how it promotes nitrogen stockpiling as arginine in cyanobacteria and plants. They have also revealed the first clear-cut mechanism by which PII can control gene expression. A small adaptor protein, PipX, is sequestered by PII when nitrogen is abundant and is released when is scarce, swapping partner by binding to the 2OG-activated transcriptional regulator NtcA, co-activating it. The structures of PII-NAGK, PII-PipX, PipX alone, of NtcA in inactive and 2OG-activated forms and as NtcA-2OG-PipX complex, explain structurally PII regulatory functions and reveal the changing shapes and interactions of the T-loops of PII depending on the partner and on the allosteric effectors bound to PII. Cyanobacterial studies have also revealed that in the PII-PipX complex PipX binds an additional transcriptional factor, PlmA, thus possibly expanding PipX roles beyond NtcA-dependency. Further exploration of these roles has revealed a functional interaction of PipX with PipY, a pyridoxal-phosphate (PLP) protein involved in PLP homeostasis whose mutations in the human ortholog cause epilepsy. Knowledge of cellular levels of the different components of this PII-PipX regulatory network and of KD values for some of the complexes provides the basic background for gross modeling of the system at high and low nitrogen abundance. The cyanobacterial network can guide searches for analogous components in other organisms, particularly of PipX functional analogs.
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Affiliation(s)
- Alicia Forcada-Nadal
- Instituto de Biomedicina de Valencia del Consejo Superior de Investigaciones Científicas, Valencia, Spain.,Departamento de Fisiología, Genética y Microbiología, Universidad de Alicante, Alicante, Spain
| | - José Luis Llácer
- Instituto de Biomedicina de Valencia del Consejo Superior de Investigaciones Científicas, Valencia, Spain.,Group 739, Centro de Investigación Biomédica en Red de Enfermedades Raras - Instituto de Salud Carlos III, Valencia, Spain
| | - Asunción Contreras
- Departamento de Fisiología, Genética y Microbiología, Universidad de Alicante, Alicante, Spain
| | - Clara Marco-Marín
- Instituto de Biomedicina de Valencia del Consejo Superior de Investigaciones Científicas, Valencia, Spain.,Group 739, Centro de Investigación Biomédica en Red de Enfermedades Raras - Instituto de Salud Carlos III, Valencia, Spain
| | - Vicente Rubio
- Instituto de Biomedicina de Valencia del Consejo Superior de Investigaciones Científicas, Valencia, Spain.,Group 739, Centro de Investigación Biomédica en Red de Enfermedades Raras - Instituto de Salud Carlos III, Valencia, Spain
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Espinosa J, Labella JI, Cantos R, Contreras A. Energy drives the dynamic localization of cyanobacterial nitrogen regulators during diurnal cycles. Environ Microbiol 2018; 20:1240-1252. [PMID: 29441670 DOI: 10.1111/1462-2920.14071] [Citation(s) in RCA: 10] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/23/2017] [Revised: 02/07/2018] [Accepted: 02/08/2018] [Indexed: 12/31/2022]
Abstract
Cyanobacteria, phototrophic organisms performing oxygenic photosynthesis, must adapt their metabolic processes to the challenges imposed by the succession of days and nights. Two conserved cyanobacterial proteins, PII and PipX, function as hubs of the nitrogen interaction network, forming complexes with a variety of diverse targets. While PII proteins are found in all three domains of life as integrators of signals of the nitrogen and carbon balance, PipX proteins are unique to cyanobacteria, where they provide a mechanistic link between PII signalling and the control of gene expression by the global nitrogen regulator NtcA. Here we demonstrate that PII and PipX display distinct localization patterns during diurnal cycles, co-localizing into the same foci at the periphery and poles of the cells during dark periods, a circadian-independent process requiring a low ATP/ADP ratio. Genetic, cellular biology and biochemical approaches used here provide new insights into the nitrogen regulatory network, calling attention to the roles of PII as energy sensors and its interactions with PipX in the context of essential signalling pathways. This study expands the contribution of the nitrogen regulators PII and PipX to integrate and transduce key environmental signals that allow cyanobacteria to thrive in our planet.
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Affiliation(s)
- Javier Espinosa
- Departamento de Fisiología, Genética y Microbiología, Universidad de Alicante, Alicante, Spain
| | - José I Labella
- Departamento de Fisiología, Genética y Microbiología, Universidad de Alicante, Alicante, Spain
| | - Raquel Cantos
- Departamento de Fisiología, Genética y Microbiología, Universidad de Alicante, Alicante, Spain
| | - Asunción Contreras
- Departamento de Fisiología, Genética y Microbiología, Universidad de Alicante, Alicante, Spain
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Esteves-Ferreira AA, Inaba M, Fort A, Araújo WL, Sulpice R. Nitrogen metabolism in cyanobacteria: metabolic and molecular control, growth consequences and biotechnological applications. Crit Rev Microbiol 2018. [DOI: 10.1080/1040841x.2018.1446902] [Citation(s) in RCA: 33] [Impact Index Per Article: 5.5] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/17/2022]
Affiliation(s)
- Alberto A. Esteves-Ferreira
- National University of Ireland – Galway, Plant Systems Biology Lab, School of Natural Sciences, Plant and AgriBiosciences Research Centre, Galway, Ireland
- CAPES Foundation, Ministry of Education of Brazil, Brasilia, Brazil
| | - Masami Inaba
- National University of Ireland – Galway, Plant Systems Biology Lab, School of Natural Sciences, Plant and AgriBiosciences Research Centre, Galway, Ireland
| | - Antoine Fort
- National University of Ireland – Galway, Plant Systems Biology Lab, School of Natural Sciences, Plant and AgriBiosciences Research Centre, Galway, Ireland
| | - Wagner L. Araújo
- Max-Planck Partner Group at the Departamento de Biologia Vegetal, Universidade Federal de Viçosa, Viçosa, Brazil
| | - Ronan Sulpice
- National University of Ireland – Galway, Plant Systems Biology Lab, School of Natural Sciences, Plant and AgriBiosciences Research Centre, Galway, Ireland
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Labella JI, Obrebska A, Espinosa J, Salinas P, Forcada-Nadal A, Tremiño L, Rubio V, Contreras A. Expanding the Cyanobacterial Nitrogen Regulatory Network: The GntR-Like Regulator PlmA Interacts with the PII-PipX Complex. Front Microbiol 2016; 7:1677. [PMID: 27840625 PMCID: PMC5083789 DOI: 10.3389/fmicb.2016.01677] [Citation(s) in RCA: 18] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/08/2016] [Accepted: 10/06/2016] [Indexed: 11/17/2022] Open
Abstract
Cyanobacteria, phototrophic organisms that perform oxygenic photosynthesis, perceive nitrogen status by sensing 2-oxoglutarate levels. PII, a widespread signaling protein, senses and transduces nitrogen and energy status to target proteins, regulating metabolism and gene expression. In cyanobacteria, under conditions of low 2-oxoglutarate, PII forms complexes with the enzyme N-acetyl glutamate kinase, increasing arginine biosynthesis, and with PII-interacting protein X (PipX), making PipX unavailable for binding and co-activation of the nitrogen regulator NtcA. Both the PII-PipX complex structure and in vivo functional data suggested that this complex, as such, could have regulatory functions in addition to PipX sequestration. To investigate this possibility we performed yeast three-hybrid screening of genomic libraries from Synechococcus elongatus PCC7942, searching for proteins interacting simultaneously with PII and PipX. The only prey clone found in the search expressed PlmA, a member of the GntR family of transcriptional regulators proven here by gel filtration to be homodimeric. Interactions analyses further confirmed the simultaneous requirement of PII and PipX, and showed that the PlmA contacts involve PipX elements exposed in the PII-PipX complex, specifically the C-terminal helices and one residue of the tudor-like body. In contrast, PII appears not to interact directly with PlmA, possibly being needed indirectly, to induce an extended conformation of the C-terminal helices of PipX and for modulating the surface polarity at the PII-PipX boundary, two elements that appear crucial for PlmA binding. Attempts to inactive plmA confirmed that this gene is essential in S. elongatus. Western blot assays revealed that S. elongatus PlmA, irrespective of the nitrogen regime, is a relatively abundant transcriptional regulator, suggesting the existence of a large PlmA regulon. In silico studies showed that PlmA is universally and exclusively found in cyanobacteria. Based on interaction data, on the relative amounts of the proteins involved in PII-PipX-PlmA complexes, determined in western assays, and on the restrictions imposed by the symmetries of trimeric PII and dimeric PlmA molecules, a structural and regulatory model for PlmA function is discussed in the context of the cyanobacterial nitrogen interaction network.
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Affiliation(s)
- Jose I Labella
- Departamento de Fisiología, Genética y Microbiología, Universidad de Alicante Alicante, Spain
| | - Anna Obrebska
- Departamento de Fisiología, Genética y Microbiología, Universidad de Alicante Alicante, Spain
| | - Javier Espinosa
- Departamento de Fisiología, Genética y Microbiología, Universidad de Alicante Alicante, Spain
| | - Paloma Salinas
- Departamento de Fisiología, Genética y Microbiología, Universidad de Alicante Alicante, Spain
| | | | - Lorena Tremiño
- Instituto de Biomedicina de Valencia of the CSIC Valencia, Spain
| | - Vicente Rubio
- Instituto de Biomedicina de Valencia of the CSICValencia, Spain; Group 739, CIBER de Enfermedades Raras (CIBERER-ISCIII)Valencia, Spain
| | - Asunción Contreras
- Departamento de Fisiología, Genética y Microbiología, Universidad de Alicante Alicante, Spain
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Hauf W, Schmid K, Gerhardt ECM, Huergo LF, Forchhammer K. Interaction of the Nitrogen Regulatory Protein GlnB (P II) with Biotin Carboxyl Carrier Protein (BCCP) Controls Acetyl-CoA Levels in the Cyanobacterium Synechocystis sp. PCC 6803. Front Microbiol 2016; 7:1700. [PMID: 27833596 PMCID: PMC5080355 DOI: 10.3389/fmicb.2016.01700] [Citation(s) in RCA: 37] [Impact Index Per Article: 4.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/20/2016] [Accepted: 10/12/2016] [Indexed: 11/13/2022] Open
Abstract
The family of PII signal transduction proteins (members GlnB, GlnK, NifI) plays key roles in various cellular processes related to nitrogen metabolism at different functional levels. Recent studies implied that PII proteins may also be involved in the regulation of fatty acid metabolism, since GlnB proteins from Proteobacteria and from Arabidopsis thaliana were shown to interact with biotin carboxyl carrier protein (BCCP) of acetyl-CoA carboxylase (ACC). In case of Escherichia coli ACCase, this interaction reduces the kcat of acetyl-CoA carboxylation, which should have a marked impact on the acetyl-CoA metabolism. In this study we show that the PII protein of a unicellular cyanobacterium inhibits the biosynthetic activity of E. coli ACC and also interacts with cyanobacterial BCCP in an ATP and 2-oxoglutarate dependent manner. In a PII mutant strain of Synechocystis strain PCC 6803, the lacking control leads to reduced acetyl-CoA levels, slightly increased levels of fatty acids and formation of lipid bodies as well as an altered fatty acid composition.
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Affiliation(s)
- Waldemar Hauf
- Interfaculty Institute of Microbiology and Infection Medicine Tübingen, Eberhard-Karls-Universität Tübingen Tübingen, Germany
| | - Katharina Schmid
- Interfaculty Institute of Microbiology and Infection Medicine Tübingen, Eberhard-Karls-Universität Tübingen Tübingen, Germany
| | - Edileusa C M Gerhardt
- Departamento de Bioquímica e Biologia Molecular, Universidade Federal do Paraná Curitiba, Brazil
| | - Luciano F Huergo
- Departamento de Bioquímica e Biologia Molecular, Universidade Federal do ParanáCuritiba, Brazil; Setor Litoral, Universidade Federal do ParanáMatinhos, Brazil
| | - Karl Forchhammer
- Interfaculty Institute of Microbiology and Infection Medicine Tübingen, Eberhard-Karls-Universität Tübingen Tübingen, Germany
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16
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Abstract
To modulate the expression of genes involved in nitrogen assimilation, the cyanobacterial PII-interacting protein X (PipX) interacts with the global transcriptional regulator NtcA and the signal transduction protein PII, a protein found in all three domains of life as an integrator of signals of the nitrogen and carbon balance. PipX can form alternate complexes with NtcA and PII, and these interactions are stimulated and inhibited, respectively, by 2-oxoglutarate, providing a mechanistic link between PII signaling and NtcA-regulated gene expression. Here, we demonstrate that PipX is involved in a much wider interaction network. The effect of pipX alleles on transcript levels was studied by RNA sequencing of S. elongatus strains grown in the presence of either nitrate or ammonium, followed by multivariate analyses of relevant mutant/control comparisons. As a result of this process, 222 genes were classified into six coherent groups of differentially regulated genes, two of which, containing either NtcA-activated or NtcA-repressed genes, provided further insights into the function of NtcA-PipX complexes. The remaining four groups suggest the involvement of PipX in at least three NtcA-independent regulatory pathways. Our results pave the way to uncover new regulatory interactions and mechanisms in the control of gene expression in cyanobacteria.
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Schwarz D, Orf I, Kopka J, Hagemann M. Effects of Inorganic Carbon Limitation on the Metabolome of the Synechocystis sp. PCC 6803 Mutant Defective in glnB Encoding the Central Regulator PII of Cyanobacterial C/N Acclimation. Metabolites 2014; 4:232-47. [PMID: 24957024 PMCID: PMC4101504 DOI: 10.3390/metabo4020232] [Citation(s) in RCA: 25] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/27/2014] [Revised: 04/14/2014] [Accepted: 04/16/2014] [Indexed: 11/27/2022] Open
Abstract
Cyanobacteria are the only prokaryotes performing oxygenic photosynthesis. Non-diazotrophic strains such as the model Synechocystis sp. PCC 6803 depend on a balanced uptake and assimilation of inorganic carbon and nitrogen sources. The internal C/N ratio is sensed via the PII protein (GlnB). We analyzed metabolic changes of the ΔglnB mutant of Synechocystis sp. PCC 6803 under different CO2 availability. The identified metabolites provided a snapshot of the central C/N metabolism. Cells of the ΔglnB mutant shifted to carbon-limiting conditions, i.e. a decreased C/N ratio, showed changes in intermediates of the sugar storage and particularly of the tricarboxylic acid cycle, arginine, and glutamate metabolism. The changes of the metabolome support the notion that the PII protein is primarily regulating the N-metabolism whereas the changes in C-metabolism are probably secondary effects of the PII deletion.
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Affiliation(s)
- Doreen Schwarz
- Universität Rostock, Institut Biowissenschaften, Pflanzenphysiologie, Albert-Einstein-Str. 3, D-18059 Rostock, Germany.
| | - Isabel Orf
- Max-Planck-Institut für Molekulare Pflanzenphysiologie, Am Mühlenberg 1, 14476 Golm, Germany.
| | - Joachim Kopka
- Max-Planck-Institut für Molekulare Pflanzenphysiologie, Am Mühlenberg 1, 14476 Golm, Germany.
| | - Martin Hagemann
- Universität Rostock, Institut Biowissenschaften, Pflanzenphysiologie, Albert-Einstein-Str. 3, D-18059 Rostock, Germany.
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Chang Y, Takatani N, Aichi M, Maeda SI, Omata T. Evaluation of the Effects of PII Deficiency and the Toxicity of PipX on Growth Characteristics of the PII-Less Mutant of the Cyanobacterium Synechococcus elongatus. ACTA ACUST UNITED AC 2013; 54:1504-14. [DOI: 10.1093/pcp/pct092] [Citation(s) in RCA: 11] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/12/2022]
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Laichoubi KB, Espinosa J, Castells MA, Contreras A. Mutational analysis of the cyanobacterial nitrogen regulator PipX. PLoS One 2012; 7:e35845. [PMID: 22558239 PMCID: PMC3340408 DOI: 10.1371/journal.pone.0035845] [Citation(s) in RCA: 15] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/01/2011] [Accepted: 03/23/2012] [Indexed: 11/23/2022] Open
Abstract
PipX provides a functional link between the cyanobacterial global transcriptional regulator NtcA and the signal transduction protein PII, a protein found in all three domains of life as integrators of signals of the nitrogen and carbon balance. PipX, which is toxic in the absence of PII, can form alternative complexes with NtcA and PII and these interactions are respectively stimulated and inhibited by 2-oxoglutarate, providing a mechanism by which PII can modulate expression at the NtcA regulon. Structural information on PipX-NtcA complexes suggests that PipX coactivates NtcA controlled genes by stabilizing the active conformation of NtcA bound to 2-oxoglutarate and by possibly helping recruit RNA polymerase. To get insights into PipX functions, we perform here a mutational analysis of pipX informed by the structures of PipX-PII and PipX-NtcA complexes and evaluate the impact of point mutations on toxicity and gene expression. Two amino acid substitutions (Y32A and E4A) were of particular interest, since they increased PipX toxicity and activated NtcA dependent genes in vivo at lower 2-oxoglutarate levels than wild type PipX. While both mutations impaired complex formation with PII, only Y32A had a negative impact on PipX-NtcA interactions.
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20
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Laichoubi KB, Beez S, Espinosa J, Forchhammer K, Contreras A. The nitrogen interaction network in Synechococcus WH5701, a cyanobacterium with two PipX and two PII-like proteins. Microbiology (Reading) 2011; 157:1220-1228. [DOI: 10.1099/mic.0.047266-0] [Citation(s) in RCA: 13] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022] Open
Abstract
Nitrogen regulation involves the formation of different types of protein complexes between signal transducers and their transcriptional or metabolic targets. In oxygenic phototrophs, the signal integrator PII activates the enzyme N-acetyl-l-glutamate kinase (NAGK) by complex formation. PII also interacts with PipX, a protein with a tudor-like domain that mediates contacts with PII and with the transcriptional regulator NtcA, to which it binds to increase its activity. Here, we use a combination of in silico, yeast two-hybrid and in vitro approaches to investigate the nitrogen regulation network of Synechococcus WH5701, a marine cyanobacterium with two PII (GlnB_A and GlnB_B) and two PipX (PipX_I and PipX_II) proteins. Our results indicate that GlnB_A is functionally equivalent to the canonical PII protein from Synechococcus elongatus. GlnB_A interacted with PipX and NAGK proteins and stimulated NAGK activity, counteracting arginine inhibition. GlnB_B had only a slight stimulatory effect on NAGK activity, but its potential to bind effectors and form heterotrimers in Synechococcus WH5701 indicates additional regulatory functions. PipX_II, and less evidently PipX_I, specifically interacted with GlnB_A and NtcA, supporting a role for both Synechococcus WH5701 PipX proteins in partner swapping with GlnB_A and NtcA.
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Affiliation(s)
| | - Sabine Beez
- Lehrstuhl für Mikrobiologie, Organismische Interaktionen, University Tuebingen, Auf der Morgenstelle 28, D-72076 Tübingen, Germany
| | - Javier Espinosa
- División de Genética, Universidad de Alicante, Apartado 99, E-03080 Alicante, Spain
| | - Karl Forchhammer
- Lehrstuhl für Mikrobiologie, Organismische Interaktionen, University Tuebingen, Auf der Morgenstelle 28, D-72076 Tübingen, Germany
| | - Asunción Contreras
- División de Genética, Universidad de Alicante, Apartado 99, E-03080 Alicante, Spain
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Ohashi Y, Shi W, Takatani N, Aichi M, Maeda SI, Watanabe S, Yoshikawa H, Omata T. Regulation of nitrate assimilation in cyanobacteria. JOURNAL OF EXPERIMENTAL BOTANY 2011; 62:1411-1424. [PMID: 21282331 DOI: 10.1093/jxb/erq427] [Citation(s) in RCA: 90] [Impact Index Per Article: 6.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/30/2023]
Abstract
Nitrate assimilation by cyanobacteria is inhibited by the presence of ammonium in the growth medium. Both nitrate uptake and transcription of the nitrate assimilatory genes are regulated. The major intracellular signal for the regulation is, however, not ammonium or glutamine, but 2-oxoglutarate (2-OG), whose concentration changes according to the change in cellular C/N balance. When nitrogen is limiting growth, accumulation of 2-OG activates the transcription factor NtcA to induce transcription of the nitrate assimilation genes. Ammonium inhibits transcription by quickly depleting the 2-OG pool through its metabolism via the glutamine synthetase/glutamate synthase cycle. The P(II) protein inhibits the ABC-type nitrate transporter, and also nitrate reductase in some strains, by an unknown mechanism(s) when the cellular 2-OG level is low. Upon nitrogen limitation, 2-OG binds to P(II) to prevent the protein from inhibiting nitrate assimilation. A pathway-specific transcriptional regulator NtcB activates the nitrate assimilation genes in response to nitrite, either added to the medium or generated intracellularly by nitrate reduction. It plays an important role in selective activation of the nitrate assimilation pathway during growth under a limited supply of nitrate. P(II) was recently shown to regulate the activity of NtcA negatively by binding to PipX, a small coactivator protein of NtcA. On the basis of accumulating genome information from a variety of cyanobacteria and the molecular genetic data obtained from the representative strains, common features and group- or species-specific characteristics of the response of cyanobacteria to nitrogen is summarized and discussed in terms of ecophysiological significance.
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Affiliation(s)
- Yoshitake Ohashi
- Graduate School of Bioagricultural Sciences, Nagoya University, Furo, Chikusa, Nagoya 464-8601, Japan
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Structural basis for the regulation of NtcA-dependent transcription by proteins PipX and PII. Proc Natl Acad Sci U S A 2010; 107:15397-402. [PMID: 20716687 DOI: 10.1073/pnas.1007015107] [Citation(s) in RCA: 102] [Impact Index Per Article: 7.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022] Open
Abstract
PII, an ancient and widespread signaling protein, transduces nitrogen/carbon/energy abundance signals through interactions with target proteins. We clarify structurally how PII regulates gene expression mediated by the transcription factor NtcA, the global nitrogen regulator of cyanobacteria, shedding light on NtcA structure and function and on how NtcA is activated by 2-oxoglutarate (2OG) and coactivated by the nonenzymatic PII target, protein PipX. We determine for the cyanobacteria Synechococcus elongatus the crystal structures of the PII-PipX and PipX-NtcA complexes and of NtcA in active and inactive conformations (respective resolutions, 3.2, 2.25, 2.3, and 3.05 A). The structures and the conclusions derived from them are consistent with the results of present and prior site-directed mutagenesis and functional studies. A tudor-like domain (TLD) makes up most of the PipX structure and mediates virtually all the contacts of PipX with PII and NtcA. In the PII-PipX complex, one PII trimer sequesters the TLDs of three PipX molecules between its body and its extended T loops, preventing PipX activation of NtcA. Changes in T loop conformation triggered by 2OG explain PII-PipX dissociation when 2OG is bound. The structure of active dimeric NtcA closely resembles that of the active cAMP receptor protein (CRP). This strongly suggests that with these proteins DNA binding, transcription activation, and allosteric regulation occur by common mechanisms, although the effectors are different. The PipX-NtcA complex consists of one active NtcA dimer and two PipX monomers. PipX coactivates NtcA by stabilizing its active conformation and by possibly helping recruit RNA polymerase but not by providing extra DNA contacts.
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Espinosa J, Castells MA, Laichoubi KB, Forchhammer K, Contreras A. Effects of spontaneous mutations in PipX functions and regulatory complexes on the cyanobacterium Synechococcus elongatus strain PCC 7942. Microbiology (Reading) 2010; 156:1517-1526. [DOI: 10.1099/mic.0.037309-0] [Citation(s) in RCA: 19] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022] Open
Abstract
In Synechococcus elongatus sp. PCC 7942, PipX forms complexes with PII, a protein found in all three domains of life as an integrator of signals of the nitrogen and carbon balance, and with the cyanobacterial nitrogen regulator NtcA. We recently showed that previous inactivation of pipX facilitates subsequent inactivation of the glnB gene. Here, we show that the three spontaneous pipX point mutations pipX-92delT, pipX160C>T and pipX194T>A, initially found in different glnB strains, are indeed suppressor mutations. When these mutations were reconstructed in the wild-type background, the glnB gene could be efficiently inactivated. Furthermore, the point mutations have different effects on PipX levels, coactivation of NtcA-dependent genes and protein–protein interactions. Further support for an in vivo role of PipX–PII complexes is provided by interaction analysis with the in vivo-generated PII
T-loop+7 protein, a PII derivative unable to interact with its regulatory target N-acetyl-l-glutamate kinase, but which retains the ability to bind to PipX. The implications of these results are discussed.
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Affiliation(s)
- Javier Espinosa
- División de Genética, Universidad de Alicante, Apartado 99, E-03080 Alicante, Spain
| | | | | | - Karl Forchhammer
- Lehrstuhl für Mikrobiologie, Organismische Interaktionen, University Tübingen, Auf der Morgenstelle 28 D-72076 Tübingen, Germany
| | - Asunción Contreras
- División de Genética, Universidad de Alicante, Apartado 99, E-03080 Alicante, Spain
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24
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Forchhammer K. The Network of PII Signalling Protein Interactions in Unicellular Cyanobacteria. RECENT ADVANCES IN PHOTOTROPHIC PROKARYOTES 2010; 675:71-90. [DOI: 10.1007/978-1-4419-1528-3_5] [Citation(s) in RCA: 16] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 02/08/2023]
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