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Nair G, Jain V. An intramolecular cross-talk in D29 mycobacteriophage endolysin governs the lytic cycle and phage-host population dynamics. SCIENCE ADVANCES 2024; 10:eadh9812. [PMID: 38335296 PMCID: PMC10857449 DOI: 10.1126/sciadv.adh9812] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Received: 03/27/2023] [Accepted: 01/10/2024] [Indexed: 02/12/2024]
Abstract
D29 mycobacteriophage encodes LysA endolysin, which mediates mycobacterial host cell lysis by targeting its peptidoglycan layer, thus projecting itself as a potential therapeutic. However, the regulatory mechanism of LysA during the phage lytic cycle remains ill defined. Here, we show that during D29 lytic cycle, structural and functional regulation of LysA not only orchestrates host cell lysis but also is critical for maintaining phage-host population dynamics by governing various phases of lytic cycle. We report that LysA exists in two conformations, of which only one is active, and the protein undergoes a host peptidoglycan-dependent conformational switch to become active for carrying out endogenous host cell lysis. D29 maintains a pool of inactive LysA, allowing complete assembly of phage progeny, thus helping avoid premature host lysis. In addition, we show that the switch reverses after lysis, thus preventing exogenous targeting of bystanders, which otherwise negatively affects phage propagation in the environment.
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Affiliation(s)
- Gokul Nair
- Microbiology and Molecular Biology Laboratory, Department of Biological Sciences, Indian Institute of Science Education and Research (IISER), Bhopal 462066, Madhya Pradesh, India
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2
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Sinha S, RS N, Devarakonda Y, Rathi A, Reddy Regatti P, Batra S, Syal K. Tale of Twin Bifunctional Second Messenger (p)ppGpp Synthetases and Their Function in Mycobacteria. ACS OMEGA 2023; 8:32258-32270. [PMID: 37720788 PMCID: PMC10500699 DOI: 10.1021/acsomega.3c03557] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Received: 05/21/2023] [Accepted: 08/16/2023] [Indexed: 09/19/2023]
Abstract
M. tuberculosis, an etiological agent of tuberculosis, requires a long treatment regimen due to its ability to respond to stress and persist inside the host. The second messenger (p)ppGpp-mediated stress response plays a critical role in such long-term survival, persistence, and antibiotic tolerance which may also lead to the emergence of multiple drug resistance. In mycobacteria, (pp)pGpp molecules are synthesized predominantly by two bifunctional enzymes-long RSH-Rel and short SAS-RelZ. The long RSH-Rel is a major (p)ppGpp synthetase and hydrolase. How it switches its activity from synthesis to hydrolysis remains unclear. RelMtb mutant has been reported to be defective in biofilm formation, cell wall function, and persister cell formation. The survival of such mutants has also been observed to be compromised in infection models. In M. smegmatis, short SAS-RelZ has RNase HII activity in addition to (pp)Gpp synthesis activity. The RNase HII function of RelZ has been implicated in resolving replication-transcription conflicts by degrading R-loops. However, the mechanism and regulatory aspects of such a regulation remain elusive. In this article, we have discussed (p)ppGpp metabolism and its role in managing the stress response network of mycobacteria, which is responsible for long-term survival inside the host, making it an important therapeutic target.
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Affiliation(s)
- Shubham
Kumar Sinha
- Genetics and Molecular Microbiology
Laboratory, Department of Biological Sciences, Institute of Eminence, Birla Institute of Technology and Sciences-Pilani, Hyderabad campus, Hyderabad, Telangana, India, 500078
| | - Neethu RS
- Genetics and Molecular Microbiology
Laboratory, Department of Biological Sciences, Institute of Eminence, Birla Institute of Technology and Sciences-Pilani, Hyderabad campus, Hyderabad, Telangana, India, 500078
| | - Yogeshwar Devarakonda
- Genetics and Molecular Microbiology
Laboratory, Department of Biological Sciences, Institute of Eminence, Birla Institute of Technology and Sciences-Pilani, Hyderabad campus, Hyderabad, Telangana, India, 500078
| | - Ajita Rathi
- Genetics and Molecular Microbiology
Laboratory, Department of Biological Sciences, Institute of Eminence, Birla Institute of Technology and Sciences-Pilani, Hyderabad campus, Hyderabad, Telangana, India, 500078
| | - Pavan Reddy Regatti
- Genetics and Molecular Microbiology
Laboratory, Department of Biological Sciences, Institute of Eminence, Birla Institute of Technology and Sciences-Pilani, Hyderabad campus, Hyderabad, Telangana, India, 500078
| | - Sakshi Batra
- Genetics and Molecular Microbiology
Laboratory, Department of Biological Sciences, Institute of Eminence, Birla Institute of Technology and Sciences-Pilani, Hyderabad campus, Hyderabad, Telangana, India, 500078
| | - Kirtimaan Syal
- Genetics and Molecular Microbiology
Laboratory, Department of Biological Sciences, Institute of Eminence, Birla Institute of Technology and Sciences-Pilani, Hyderabad campus, Hyderabad, Telangana, India, 500078
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3
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Petchiappan A, Naik SY, Chatterji D. Tracking the homeostasis of second messenger cyclic-di-GMP in bacteria. Biophys Rev 2020; 12:719-730. [PMID: 32060735 PMCID: PMC7311556 DOI: 10.1007/s12551-020-00636-1] [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: 01/07/2020] [Accepted: 02/05/2020] [Indexed: 01/09/2023] Open
Abstract
Cyclic-di-GMP (c-di-GMP) is an important second messenger in bacteria which regulates the bacterial transition from motile to sessile phase and also plays a major role in processes such as cell division, exopolysaccharide synthesis, and biofilm formation. Due to its crucial role in dictating the bacterial phenotype, the synthesis and hydrolysis of c-di-GMP is tightly regulated via multiple mechanisms. Perturbing the c-di-GMP homeostasis affects bacterial growth and survival, so it is necessary to understand the underlying mechanisms related to c-di-GMP metabolism. Most techniques used for estimating the c-di-GMP concentration lack single-cell resolution and do not provide information about any heterogeneous distribution of c-di-GMP inside cells. In this review, we briefly discuss how the activity of c-di-GMP metabolising enzymes, particularly bifunctional proteins, is modulated to maintain c-di-GMP homeostasis. We further highlight how fluorescence-based methods aid in understanding the spatiotemporal regulation of c-di-GMP signalling. Finally, we discuss the blind spots in our understanding of second messenger signalling and outline how they can be addressed in the future.
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Affiliation(s)
| | - Sujay Y Naik
- Molecular Biophysics Unit, Indian Institute of Science, Bangalore, India
| | - Dipankar Chatterji
- Molecular Biophysics Unit, Indian Institute of Science, Bangalore, India
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4
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RelZ-Mediated Stress Response in Mycobacterium smegmatis: pGpp Synthesis and Its Regulation. J Bacteriol 2020; 202:JB.00444-19. [PMID: 31659009 DOI: 10.1128/jb.00444-19] [Citation(s) in RCA: 18] [Impact Index Per Article: 4.5] [Reference Citation Analysis] [Abstract] [Key Words] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/05/2019] [Accepted: 10/21/2019] [Indexed: 11/20/2022] Open
Abstract
Stringent response is a conserved stress response mechanism in which bacteria employ the second messengers guanosine tetraphosphate and guanosine pentaphosphate [collectively termed (p)ppGpp] to reprogram their cellular processes under stress. In mycobacteria, these alarmones govern a multitude of cellular phenotypes, such as cell division, biofilm formation, antibiotic tolerance, and long-term survival. Mycobacterium smegmatis possesses the bifunctional RelMsm as a (p)ppGpp synthetase and hydrolase. In addition, it contains a short alarmone synthetase MS_RHII-RSD (renamed RelZ), which contains an RNase H domain in tandem with the (p)ppGpp synthetase domain. The physiological functions of RelMsm have been well documented, but there is no clear picture about the cellular functions of RelZ in M. smegmatis RelZ has been implicated in R-loop induced stress response due to its unique domain architecture. In this study, we elucidate the differential substrate utilization pattern of RelZ compared to that of RelMsm We unveil the ability of RelZ to use GMP as a substrate to synthesize pGpp, thereby expanding the repertoire of second messengers known in mycobacteria. We have demonstrated that the pGpp synthesis activity of RelZ is negatively regulated by RNA and pppGpp. Furthermore, we investigated its role in biofilm formation and antibiotic tolerance. Our findings highlight the complex role played by the RelZ in cellular physiology of M. smegmatis and sheds light upon its functions distinct from those of RelMsm IMPORTANCE Bacteria utilize nucleotide messengers to survive the hostile environmental conditions and the onslaught of attacks within the host. The second messengers guanosine tetraphosphate and pentaphosphate [(p)ppGpp] have a profound impact on the long-term survival, biofilm formation, antibiotic tolerance, virulence, and pathogenesis of bacteria. Therefore, understanding the stress response mechanism regulated by (p)ppGpp is essential for discovering inhibitors of stress response and potential drug targets. Mycobacterium smegmatis contains two (p)ppGpp synthetases: RelMsm and RelZ. Our study unravels the novel regulatory mechanisms of RelZ activity and its role in mediating antibiotic tolerance. We further reveal its ability to synthesize novel second messenger pGpp, which may have regulatory roles in mycobacteria.
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Vitamin C: A Natural Inhibitor of Cell Wall Functions and Stress Response in Mycobacteria. ADVANCES IN EXPERIMENTAL MEDICINE AND BIOLOGY 2019. [PMID: 30637707 DOI: 10.1007/978-981-13-3065-0_22] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 09/19/2023]
Abstract
Tuberculosis, caused by Mycobacterium tuberculosis, has re-emerged as a threat to human race. Conventional antibiotic treatments are failing due to different stress response strategies adopted by bacterial pathogens. Since time immemorial, Vitamin C is known to protect against pathogens by boosting immunity in humans. Recently, Vitamin C has been shown to directly kill M. tuberculosis including multiple drug-resistant strains by generation of oxidative radicals through Fenton's reaction. Concurrently, it inhibits (p)ppGpp-mediated stringent response thus effectively shutting down long-term survival and persistence in mycobacteria. Here, we have discussed historical perspective and recent evidences on Vitamin C-mediated inhibition of several key pathways of M. tuberculosis such as (p)ppGpp synthesis and mycobacterial cell wall function. Several cell wall components including mycolic acids are critical for mycobacterial virulence. We observed downregulation of various mycolic acids in M. smegmatis upon treatment with Vitamin C, and data have been presented here. Vitamin C has been shown to inhibit the biofilm growth as well as disrupt the formed biofilm in mycobacteria. Additionally, Vitamin C role in cell-mediated and humoral immunity has been elucidated. Vitamin C is toxic at high concentration; therefore we have proposed the idea of derivatizing Vitamin C in order to lower the minimal inhibition concentration (MIC) necessary to target M. tuberculosis.
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6
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Bharati BK, Mukherjee R, Chatterji D. Substrate-induced domain movement in a bifunctional protein, DcpA, regulates cyclic di-GMP turnover: Functional implications of a highly conserved motif. J Biol Chem 2018; 293:14065-14079. [PMID: 29980599 DOI: 10.1074/jbc.ra118.003917] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Key Words] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/11/2018] [Revised: 06/26/2018] [Indexed: 11/06/2022] Open
Abstract
In eubacteria, cyclic di-GMP (c-di-GMP) signaling is involved in virulence, persistence, motility and generally orchestrates multicellular behavior in bacterial biofilms. Intracellular c-di-GMP levels are maintained by the opposing activities of diguanylate cyclases (DGCs) and cognate phosphodiesterases (PDEs). The c-di-GMP homeostasis in Mycobacterium smegmatis is supported by DcpA, a conserved, bifunctional protein with both DGC and PDE activities. DcpA is a multidomain protein whose GAF-GGDEF-EAL domains are arranged in tandem and are required for these two activities. To gain insight into how interactions among these three domains affect DcpA activity, here we studied its domain dynamics using real-time FRET. We demonstrate that substrate binding in DcpA results in domain movement that prompts a switch from an "open" to a "closed" conformation and alters its catalytic activity. We found that a single point mutation in the conserved EAL motif (E384A) results in complete loss of the PDE activity of the EAL domain and in a significant decrease in the DGC activity of the GGDEF domain. Structural analyses revealed multiple hydrophobic and aromatic residues around Cys579 that are necessary for proper DcpA folding and maintenance of the active conformation. On the basis of these observations and taking into account additional bioinformatics analysis of EAL domain-containing proteins, we identified a critical putatively conserved motif, GCXXXQGF, that plays an important role in c-di-GMP turnover. We conclude that a substrate-induced conformational switch involving movement of a loop containing a conserved motif in the bifunctional diguanylate cyclase-phosphodiesterase DcpA controls c-di-GMP turnover in M. smegmatis.
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Affiliation(s)
- Binod K Bharati
- From the Molecular Biophysics Unit, Indian Institute of Science, Bangalore 560012, India and
| | - Raju Mukherjee
- Department of Biology, Indian Institute of Science Education and Research, Tirupati 517507, India
| | - Dipankar Chatterji
- From the Molecular Biophysics Unit, Indian Institute of Science, Bangalore 560012, India and
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7
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Prusa J, Zhu DX, Stallings CL. The stringent response and Mycobacterium tuberculosis pathogenesis. Pathog Dis 2018; 76:5035815. [PMID: 29947752 PMCID: PMC7191866 DOI: 10.1093/femspd/fty054] [Citation(s) in RCA: 29] [Impact Index Per Article: 4.8] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/26/2018] [Accepted: 06/08/2018] [Indexed: 12/23/2022] Open
Abstract
During infection, the host restrains Mycobacterium tuberculosis (Mtb) from proliferating by imposing an arsenal of stresses. Despite this onslaught of attacks, Mtb is able to persist for the lifetime of the host, indicating that this pathogen has substantial molecular mechanisms to resist host-inflicted damage. The stringent response is a conserved global stress response in bacteria that involves the production of the hyperphosphorylated guanine nucleotides ppGpp and pppGpp (collectively called (p)ppGpp). (p)ppGpp then regulates a number of cellular processes to adjust the physiology of the bacteria to promote survival in different environments. Survival in the presence of host-generated stresses is an essential quality of successful pathogens, and the stringent response is critical for the intracellular survival of a number of pathogenic bacteria. In addition, the stringent response has been linked to virulence gene expression, persistence, latency and drug tolerance. In Mtb, (p)ppGpp synthesis is required for survival in low nutrient conditions, long term culture and during chronic infection in animal models, all indicative of a strict requirement for (p)ppGpp during exposure to stresses associated with infection. In this review we discuss (p)ppGpp metabolism and how this functions as a critical regulator of Mtb virulence.
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Affiliation(s)
- Jerome Prusa
- Department of Molecular Microbiology, Washington University School of Medicine, St Louis, MO 63110, USA
| | - Dennis X Zhu
- Department of Molecular Microbiology, Washington University School of Medicine, St Louis, MO 63110, USA
| | - Christina L Stallings
- Department of Molecular Microbiology, Washington University School of Medicine, St Louis, MO 63110, USA
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8
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Singh MI, Jain V. Identification and Characterization of an Inside-Out Folding Intermediate of T4 Phage Sliding Clamp. Biophys J 2017; 113:1738-1749. [PMID: 29045868 DOI: 10.1016/j.bpj.2017.08.043] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/19/2017] [Revised: 08/15/2017] [Accepted: 08/28/2017] [Indexed: 10/18/2022] Open
Abstract
Protein folding process involves formation of transiently occurring intermediates that are difficult to isolate and characterize. It is both necessary and interesting to characterize the structural conformations adopted by these intermediates, also called molten globules (MG), to understand protein folding. Here, we investigated the equilibrium (un)folding intermediate state of T4 phage gene product 45 (gp45, also known as DNA polymerase processivity factor or sliding clamp) obtained during chemical denaturation. We show that gp45 undergoes substantial conformational rearrangement during unfolding and forms an expanded dry-MG. By monitoring the fluorescence of tryptophans that were strategically introduced at various sites, we demonstrate that the urea-treated molecule has its surface residues flip inside the core, and closely placed residues move farther. We were also able to isolate and purify the MG form of gp45 in native condition (i.e., nondenaturing buffer, at physiological pH and temperature); characteristics of this purified molecule substantially match with urea-treated wild-type gp45. To the best of our knowledge, this is one of the few reports that demonstrate the isolation and purification of a protein folding intermediate in native condition. We believe that our work not only allows us to dissect the process of protein folding, but will also help in the designing of folding inhibitors against sliding clamps to treat a wide variety of diseases from bacterial infection to cancer, due to the vast presence of clamps in all the domains of life.
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Affiliation(s)
- Manika Indrajit Singh
- Microbiology and Molecular Biology Laboratory, Department of Biological Sciences, Indian Institute of Science Education and Research (IISER), Bhopal, Madhya Pradesh, India
| | - Vikas Jain
- Microbiology and Molecular Biology Laboratory, Department of Biological Sciences, Indian Institute of Science Education and Research (IISER), Bhopal, Madhya Pradesh, India.
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9
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Structural plasticity of T4 transcription co-activator gp33 revealed by a protease-resistant unfolded state. Biochem Biophys Res Commun 2017; 492:61-66. [PMID: 28807826 DOI: 10.1016/j.bbrc.2017.08.038] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/30/2017] [Accepted: 08/10/2017] [Indexed: 11/24/2022]
Abstract
Gene 33 protein (gp33) is a transcriptional coactivator for late genes of the T4 bacteriophage. gp33 possesses a 5-helix bundle core, with unstructured N- and C-terminal regions that account for >50% of the protein sequence. It plays a unique role of interacting with host RNA polymerase, couples transcription with DNA replication, and plays the dual function as repressor and co-activator in phage transcription. Here, we identify protein structural plasticity as the molecular basis of the dual nature in gp33. We find that gp33 has the peculiar property of remaining protease insensitive in its urea-unfolded state. Using NMR studies with spectroscopic measurements, we propose that intra-protein interactions are replaced by protein-urea interactions in gp33. This process not only unfolds gp33 but also renders it protease-resistant. Our studies shed new light on the unique structural malleability of gp33 that might be important in its transition from a repressor to a late transcription co-activator.
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10
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Singal B, Balakrishna AM, Nartey W, Manimekalai MSS, Jeyakanthan J, Grüber G. Crystallographic and solution structure of the N-terminal domain of the Rel protein fromMycobacterium tuberculosis. FEBS Lett 2017; 591:2323-2337. [DOI: 10.1002/1873-3468.12739] [Citation(s) in RCA: 20] [Impact Index Per Article: 2.9] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/29/2017] [Revised: 06/23/2017] [Accepted: 06/27/2017] [Indexed: 11/06/2022]
Affiliation(s)
- Bharti Singal
- School of Biological Sciences; Nanyang Technological University; Singapore Singapore
| | | | - Wilson Nartey
- School of Biological Sciences; Nanyang Technological University; Singapore Singapore
| | | | | | - Gerhard Grüber
- School of Biological Sciences; Nanyang Technological University; Singapore Singapore
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11
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Synthetic (p)ppGpp Analogue Is an Inhibitor of Stringent Response in Mycobacteria. Antimicrob Agents Chemother 2017; 61:AAC.00443-17. [PMID: 28396544 DOI: 10.1128/aac.00443-17] [Citation(s) in RCA: 41] [Impact Index Per Article: 5.9] [Reference Citation Analysis] [Abstract] [Key Words] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/01/2017] [Accepted: 03/31/2017] [Indexed: 12/19/2022] Open
Abstract
Bacteria elicit an adaptive response against hostile conditions such as starvation and other kinds of stresses. Their ability to survive such conditions depends, in part, on stringent response pathways. (p)ppGpp, considered to be the master regulator of the stringent response, is a novel target for inhibiting the survival of bacteria. In mycobacteria, the (p)ppGpp synthetase activity of bifunctional Rel is critical for stress response and persistence inside a host. Our aim was to design an inhibitor of (p)ppGpp synthesis, monitor its efficiency using enzyme kinetics, and assess its phenotypic effects in mycobacteria. As such, new sets of inhibitors targeting (p)ppGpp synthesis were synthesized and characterized by mass spectrometry and nuclear magnetic resonance spectroscopy. We observed significant inhibition of (p)ppGpp synthesis by RelMsm in the presence of designed inhibitors in a dose-dependent manner, which we further confirmed by monitoring the enzyme kinetics. The Rel enzyme inhibitor binding kinetics were investigated by isothermal titration calorimetry. Subsequently, the effects of the compounds on long-term persistence, biofilm formation, and biofilm disruption were assayed in Mycobacterium smegmatis, where inhibition in each case was observed. In vivo, (p)ppGpp levels were found to be downregulated in M. smegmatis treated with the synthetic inhibitors. The compounds reported here also inhibited biofilm formation by the pathogen Mycobacterium tuberculosis The compounds were tested for toxicity by using an MTT assay with H460 cells and a hemolysis assay with human red blood cells, for which they were found to be nontoxic. The permeability of compounds across the cell membrane of human lung epithelial cells was also confirmed by mass spectrometry.
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12
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Arenz S, Abdelshahid M, Sohmen D, Payoe R, Starosta AL, Berninghausen O, Hauryliuk V, Beckmann R, Wilson DN. The stringent factor RelA adopts an open conformation on the ribosome to stimulate ppGpp synthesis. Nucleic Acids Res 2016; 44:6471-81. [PMID: 27226493 PMCID: PMC5291266 DOI: 10.1093/nar/gkw470] [Citation(s) in RCA: 95] [Impact Index Per Article: 11.9] [Reference Citation Analysis] [Abstract] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/06/2016] [Accepted: 05/12/2016] [Indexed: 11/13/2022] Open
Abstract
Under stress conditions, such as nutrient starvation, deacylated tRNAs bound within the ribosomal A-site are recognized by the stringent factor RelA, which converts ATP and GTP/GDP to (p)ppGpp. The signaling molecules (p)ppGpp globally rewire the cellular transcriptional program and general metabolism, leading to stress adaptation. Despite the additional importance of the stringent response for regulation of bacterial virulence, antibiotic resistance and persistence, structural insight into how the ribosome and deacylated-tRNA stimulate RelA-mediated (p)ppGpp has been lacking. Here, we present a cryo-EM structure of RelA in complex with the Escherichia coli 70S ribosome with an average resolution of 3.7 Å and local resolution of 4 to >10 Å for RelA. The structure reveals that RelA adopts a unique ‘open’ conformation, where the C-terminal domain (CTD) is intertwined around an A/T-like tRNA within the intersubunit cavity of the ribosome and the N-terminal domain (NTD) extends into the solvent. We propose that the open conformation of RelA on the ribosome relieves the autoinhibitory effect of the CTD on the NTD, thus leading to stimulation of (p)ppGpp synthesis by RelA.
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Affiliation(s)
- Stefan Arenz
- Gene Center and Department for Biochemistry, University of Munich, Munich 81377, Germany
| | - Maha Abdelshahid
- Gene Center and Department for Biochemistry, University of Munich, Munich 81377, Germany
| | - Daniel Sohmen
- Gene Center and Department for Biochemistry, University of Munich, Munich 81377, Germany
| | - Roshani Payoe
- University of Tartu, Institute of Technology, Nooruse 1, 50411 Tartu, Estonia
| | - Agata L Starosta
- Gene Center and Department for Biochemistry, University of Munich, Munich 81377, Germany
| | - Otto Berninghausen
- Gene Center and Department for Biochemistry, University of Munich, Munich 81377, Germany
| | - Vasili Hauryliuk
- University of Tartu, Institute of Technology, Nooruse 1, 50411 Tartu, Estonia Laboratory for Molecular Infection Medicine Sweden (MIMS), Umeå University, Building 6K and 6L, University Hospital Area, SE-901 87 Umeå, Sweden
| | - Roland Beckmann
- Gene Center and Department for Biochemistry, University of Munich, Munich 81377, Germany Center for integrated Protein Science Munich (CiPSM), University of Munich, Munich 81377, Germany
| | - Daniel N Wilson
- Gene Center and Department for Biochemistry, University of Munich, Munich 81377, Germany Center for integrated Protein Science Munich (CiPSM), University of Munich, Munich 81377, Germany
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13
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Syal K, Chatterji D. Differential binding of ppGpp and pppGpp to E. coli RNA polymerase: photo-labeling and mass spectral studies. Genes Cells 2015; 20:1006-16. [PMID: 26606426 DOI: 10.1111/gtc.12304] [Citation(s) in RCA: 15] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/19/2015] [Accepted: 09/06/2015] [Indexed: 11/28/2022]
Abstract
(p)ppGpp, a secondary messenger, is induced under stress and shows pleiotropic response. It binds to RNA polymerase and regulates transcription in Escherichia coli. More than 25 years have passed since the first discovery was made on the direct interaction of ppGpp with E. coli RNA polymerase. Several lines of evidence suggest different modes of ppGpp binding to the enzyme. Earlier cross-linking experiments suggested that the β-subunit of RNA polymerase is the preferred site for ppGpp, whereas recent crystallographic studies pinpoint the interface of β'/ω-subunits as the site of action. With an aim to validate the binding domain and to follow whether tetra- and pentaphosphate guanosines have different location on RNA polymerase, this work was initiated. RNA polymerase was photo-labeled with 8-azido-ppGpp/8-azido-pppGpp, and the product was digested with trypsin and subjected to mass spectrometry analysis. We observed three new peptides in the trypsin digest of the RNA polymerase labeled with 8-azido-ppGpp, of which two peptides correspond to the same pocket on β'-subunit as predicted by X-ray structural analysis, whereas the third peptide was mapped on the β-subunit. In the case of 8-azido-pppGpp-labeled RNA polymerase, we have found only one cross-linked peptide from the β'-subunit. However, we were unable to identify any binding site of pppGpp on the β-subunit. Interestingly, we observed that pppGpp at high concentration competes out ppGpp bound to RNA polymerase more efficiently, whereas ppGpp cannot titrate out pppGpp. The competition between tetraphosphate guanosine and pentaphosphate guanosine for E. coli RNA polymerase was followed by gel-based assay as well as by a new method known as DRaCALA assay.
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Affiliation(s)
- Kirtimaan Syal
- Molecular Biophysics Unit, Indian Institute of Science, Bangalore, 560012, India
| | - Dipankar Chatterji
- Molecular Biophysics Unit, Indian Institute of Science, Bangalore, 560012, India
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14
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Syal K, Joshi H, Chatterji D, Jain V. Novel pppGpp binding site at the C-terminal region of the Rel enzyme from Mycobacterium smegmatis. FEBS J 2015; 282:3773-85. [PMID: 26179484 DOI: 10.1111/febs.13373] [Citation(s) in RCA: 23] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [Abstract] [Key Words] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/04/2015] [Revised: 06/26/2015] [Accepted: 07/09/2015] [Indexed: 11/28/2022]
Abstract
Mycobacterium tuberculosis elicits the stringent response under unfavorable growth conditions, such as those encountered by the pathogen inside the host. The hallmark of this response is production of guanosine tetra- and pentaphosphates, collectively termed (p)ppGpp, which have pleiotropic effects on the bacterial physiology. As the stringent response is connected to survival under stress, it is now being targeted for developing inhibitors against bacterial persistence. The Rel enzyme in mycobacteria has two catalytic domains at its N-terminus that are involved in the synthesis and hydrolysis of (p)ppGpp, respectively. However, the function of the C-terminal region of the protein remained unknown. Here, we have identified a binding site for pppGpp in the C-terminal region of Rel. The binding affinity of pppGpp was quantified by isothermal titration calorimetry. The binding site was determined by crosslinking using the nucleotide analog azido-pppGpp, and examining the crosslink product by mass spectrometry. Additionally, mutations in the Rel protein were created to confirm the site of pppGpp binding by isothermal titration calorimetry. These mutants showed increased pppGpp synthesis and reduced hydrolytic activity. We believe that binding of pppGpp to Rel provides a feedback mechanism that allows the protein to detect and adjust the (p)ppGpp level in the cell. Our work suggests that such sites should also be considered while designing inhibitors to target the stringent response.
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Affiliation(s)
- Kirtimaan Syal
- Molecular Biophysics Unit, Indian Institute of Science, Bangalore, India
| | - Himanshu Joshi
- Microbiology and Molecular Biology Laboratory, Department of Biological Sciences, Indian Institute of Science Education and Research, Bhopal, India
| | - Dipankar Chatterji
- Molecular Biophysics Unit, Indian Institute of Science, Bangalore, India
| | - Vikas Jain
- Microbiology and Molecular Biology Laboratory, Department of Biological Sciences, Indian Institute of Science Education and Research, Bhopal, India
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15
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Ekal L, Ganesh B, Joshi H, Lama D, Jain V. Evidence of a conserved intrinsically disordered region in the C-terminus of the stringent response protein Rel from mycobacteria. FEBS Lett 2014; 588:1839-49. [PMID: 24717772 DOI: 10.1016/j.febslet.2014.03.048] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/09/2014] [Revised: 03/22/2014] [Accepted: 03/24/2014] [Indexed: 11/16/2022]
Abstract
The RelA/SpoT enzyme produces (p)ppGpp that helps the bacterium survive during stress. The domains present in it are interspersed with connecting linkers whose functions have been poorly elucidated. We rationally analyzed the sequence and structural property of the regulatory C-terminal region in the Rel family of proteins and report the presence of an intrinsically disordered region between two successive domains in this region that are separated by a defined amino acid sequence length. We show that the length and secondary structure of this linker are conserved in Rel proteins, further signifying its importance in rendering flexibility for domain movement and domain-domain interaction.
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Affiliation(s)
- Lakhan Ekal
- Microbiology and Molecular Biology Laboratory, Department of Biological Sciences, Indian Institute of Science Education and Research (IISER), Bhopal 462023, India
| | - Bylapudi Ganesh
- Microbiology and Molecular Biology Laboratory, Department of Biological Sciences, Indian Institute of Science Education and Research (IISER), Bhopal 462023, India
| | - Himanshu Joshi
- Microbiology and Molecular Biology Laboratory, Department of Biological Sciences, Indian Institute of Science Education and Research (IISER), Bhopal 462023, India
| | - Dilraj Lama
- Biomolecular Modeling and Design Division, Bioinformatics Institute, A(*)STAR, Singapore 138671, Singapore.
| | - Vikas Jain
- Microbiology and Molecular Biology Laboratory, Department of Biological Sciences, Indian Institute of Science Education and Research (IISER), Bhopal 462023, India.
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16
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Tare P, Mallick B, Nagaraja V. Co-evolution of specific amino acid in sigma 1.2 region and nucleotide base in the discriminator to act as sensors of small molecule effectors of transcription initiation in mycobacteria. Mol Microbiol 2013; 90:569-83. [PMID: 23998628 DOI: 10.1111/mmi.12384] [Citation(s) in RCA: 13] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [Journal Information] [Subscribe] [Scholar Register] [Accepted: 08/26/2013] [Indexed: 11/30/2022]
Abstract
The transcription from rrn and a number of other promoters is regulated by initiating ribonucleotides (iNTPs) and guanosine tetra/penta phosphate [(p)ppGpp], either by strengthening or by weakening of the RNA polymerase (RNAP)-promoter interactions during initiation. Studies in Escherichia coli revealed the importance of a sequence termed discriminator, located between -10 and the transcription start site of the responsive promoters in this mode of regulation. Instability of the open complex at these promoters is attributed to the lack of stabilizing interactions between the suboptimal discriminator and the 1.2 region of sigma 70 (Sig70) in RNAP holoenzyme. We demonstrate a different pattern of interaction between the promoters and sigma A (SigA) of Mycobacterium tuberculosis to execute similar regulation. Instead of cytosine and methionine, thymine at three nucleotides downstream to -10 element and leucine 232 in SigA are found to be essential for iNTPs and pppGpp mediated response at the rrn and gyr promoters of the organism. The specificity of the interaction is substantiated by mutational replacements, either in the discriminator or in SigA, which abolish the nucleotide mediated regulation in vitro or in vivo. Specific yet distinct bases and the amino acids appear to have 'co-evolved' to retain the discriminator-sigma 1.2 region regulatory switch operated by iNTPs/pppGpp during the transcription initiation in different bacteria.
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Affiliation(s)
- Priyanka Tare
- Department of Microbiology and Cell Biology, Indian Institute of Science, Bangalore, 560012, India
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17
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Kuboniwa M, Tribble GD, Hendrickson EL, Amano A, Lamont RJ, Hackett M. Insights into the virulence of oral biofilms: discoveries from proteomics. Expert Rev Proteomics 2013; 9:311-23. [PMID: 22809209 DOI: 10.1586/epr.12.16] [Citation(s) in RCA: 37] [Impact Index Per Article: 3.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/25/2022]
Abstract
This review covers developments in the study of polymicrobial communities, biofilms and selected areas of host response relevant to dental plaque and related areas of oral biology. The emphasis is on recent studies in which proteomic methods, particularly those using mass spectrometry as a readout, have played a major role in the investigation. The last 5-10 years have seen a transition of such methods from the periphery of oral biology to the mainstream, as in other areas of biomedical science. For reasons of focus and space, the authors do not discuss biomarker studies relevant to improved diagnostics for oral health, as this literature is rather substantial in its own right and deserves a separate treatment. Here, global gene regulation studies of plaque-component organisms, biofilm formation, multispecies interactions and host-microbe interactions are discussed. Several aspects of proteomics methodology that are relevant to the studies of multispecies systems are commented upon.
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Affiliation(s)
- Masae Kuboniwa
- Department of Preventive Dentistry, Osaka University Graduate School of Dentistry, 1-8 Yamadaoka, Suita, Osaka 565-0871, Japan.
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18
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MS_RHII-RSD, a dual-function RNase HII-(p)ppGpp synthetase from Mycobacterium smegmatis. J Bacteriol 2012; 194:4003-14. [PMID: 22636779 DOI: 10.1128/jb.00258-12] [Citation(s) in RCA: 40] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/12/2022] Open
Abstract
In the noninfectious soil saprophyte Mycobacterium smegmatis, intracellular levels of the stress alarmones guanosine tetraphosphate and guanosine pentaphosphate, together termed (p)ppGpp, are regulated by the enzyme Rel(Msm). This enzyme consists of a single, bifunctional polypeptide chain that is capable of both synthesizing and hydrolyzing (p)ppGpp. The rel(Msm) knockout strain of M. smegmatis (Δrel(Msm)) is expected to show a (p)ppGpp null [(p)ppGpp(0)] phenotype. Contrary to this expectation, the strain is capable of synthesizing (p)ppGpp in vivo. In this study, we identify and functionally characterize the open reading frame (ORF), MSMEG_5849, that encodes a second functional (p)ppGpp synthetase in M. smegmatis. In addition to (p)ppGpp synthesis, the 567-amino-acid-long protein encoded by this gene is capable of hydrolyzing RNA·DNA hybrids and bears similarity to the conventional RNase HII enzymes. We have classified this protein as actRel(Msm) in accordance with the recent nomenclature proposed and have named it MS_RHII-RSD, indicating the two enzymatic activities present [RHII, RNase HII domain, originally identified as domain of unknown function 429 (DUF429), and RSD, RelA_SpoT nucleotidyl transferase domain, the SYNTH domain responsible for (p)ppGpp synthesis activity]. MS_RHII-RSD is expressed and is constitutively active in vivo and behaves like a monofunctional (p)ppGpp synthetase in vitro. The occurrence of the RNase HII and (p)ppGpp synthetase domains together on the same polypeptide chain is suggestive of an in vivo role for this novel protein as a link connecting the essential life processes of DNA replication, repair, and transcription to the highly conserved stress survival pathway, the stringent response.
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19
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Atkinson GC, Tenson T, Hauryliuk V. The RelA/SpoT homolog (RSH) superfamily: distribution and functional evolution of ppGpp synthetases and hydrolases across the tree of life. PLoS One 2011; 6:e23479. [PMID: 21858139 PMCID: PMC3153485 DOI: 10.1371/journal.pone.0023479] [Citation(s) in RCA: 316] [Impact Index Per Article: 24.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/01/2011] [Accepted: 07/18/2011] [Indexed: 12/01/2022] Open
Abstract
RelA/SpoT Homologue (RSH) proteins, named for their sequence similarity to the RelA and SpoT enzymes of Escherichia coli, comprise a superfamily of enzymes that synthesize and/or hydrolyze the alarmone ppGpp, activator of the “stringent” response and regulator of cellular metabolism. The classical “long” RSHs Rel, RelA and SpoT with the ppGpp hydrolase, synthetase, TGS and ACT domain architecture have been found across diverse bacteria and plant chloroplasts, while dedicated single domain ppGpp-synthesizing and -hydrolyzing RSHs have also been discovered in disparate bacteria and animals respectively. However, there is considerable confusion in terms of nomenclature and no comprehensive phylogenetic and sequence analyses have previously been carried out to classify RSHs on a genomic scale. We have performed high-throughput sensitive sequence searching of over 1000 genomes from across the tree of life, in combination with phylogenetic analyses to consolidate previous ad hoc identification of diverse RSHs in different organisms and provide a much-needed unifying terminology for the field. We classify RSHs into 30 subgroups comprising three groups: long RSHs, small alarmone synthetases (SASs), and small alarmone hydrolases (SAHs). Members of nineteen previously unidentified RSH subgroups can now be studied experimentally, including previously unknown RSHs in archaea, expanding the “stringent response” to this domain of life. We have analyzed possible combinations of RSH proteins and their domains in bacterial genomes and compared RSH content with available RSH knock-out data for various organisms to determine the rules of combining RSHs. Through comparative sequence analysis of long and small RSHs, we find exposed sites limited in conservation to the long RSHs that we propose are involved in transmitting regulatory signals. Such signals may be transmitted via NTD to CTD intra-molecular interactions, or inter-molecular interactions either among individual RSH molecules or among long RSHs and other binding partners such as the ribosome.
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20
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Krol E, Becker A. ppGpp in Sinorhizobium meliloti: biosynthesis in response to sudden nutritional downshifts and modulation of the transcriptome. Mol Microbiol 2011; 81:1233-54. [PMID: 21696469 DOI: 10.1111/j.1365-2958.2011.07752.x] [Citation(s) in RCA: 45] [Impact Index Per Article: 3.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Abstract
Sinorhizobium meliloti Rm2011 responds to sudden shifts to nitrogen or carbon starvation conditions by an accumulation of the stringent response alarmone ppGpp and remodelling of the transcriptome. The gene product of relA, Rel(Sm) , responsible for synthesis of ppGpp, shows functional similarities to E. coli SpoT. Using promoter-egfp gene fusions, we showed that in Rm2011 relA is expressed at a low rate, as a readthrough from the rpoZ promoter and from its own weak promoter. The low level of relA expression is physiologically relevant, since overexpression of Rel(Sm) inhibits ppGpp accumulation. The N-terminal portion of Rel(Sm) is required for ppGpp degradation in nutrient-sufficient cells and might be involved in regulation of the ppGpp synthase and hydrolase activities of the protein. Expression profiling of S. meliloti subjected to sudden nitrogen or carbon downshifts revealed that repression of 'house-keeping' genes is largely dependent on relA whereas activation of gene targets of the stress sigma factor RpoE2 occurred independently of relA. The regulatory genes nifA, ntrB, aniA and sinR, as well as genes related to modulation of protein biosynthesis and nucleotide catabolism, were induced in a relA-dependent manner. dksA was required for the majority of the relA-dependent regulations.
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Affiliation(s)
- Elizaveta Krol
- Faculty of Biology and Center for Systems Biology, University of Freiburg, Schänzlestr. 1, 79104 Freiburg, Germany
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21
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Abstract
Guanosine 5'-(tri)diphosphate, 3'-diphosphate [(p) ppGpp] is a small nucleic acid that helps bacteria survive in limited environments. Gene chip shows that (p) ppGpp is a global transcription-regulator of genes related to important bacterial metabolic processes. Therefore, more attention should be focused on the molecular mechanisms of (p) ppGpp, as it is the foundation to understanding how bacteria adapt to extreme circumstances through the stringent response.
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Affiliation(s)
- Jun Wu
- Institute of Modern Biopharmaceuticals, School of Life Sciences, Education Ministry Key Laboratory on Luminescence and Real-Time Analysis, Southwest University, Chongqing, China
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22
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Sajish M, Kalayil S, Verma SK, Nandicoori VK, Prakash B. The significance of EXDD and RXKD motif conservation in Rel proteins. J Biol Chem 2009; 284:9115-23. [PMID: 19201753 PMCID: PMC2666561 DOI: 10.1074/jbc.m807187200] [Citation(s) in RCA: 37] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
Abstract
Monofunctional and bifunctional classes of Rel proteins catalyze
pyrophosphoryl transfer from ATP to 3′-OH of GTP/GDP to synthesize
(p)ppGpp, which is essential for normal microbial physiology and survival.
Bifunctional proteins additionally catalyze the hydrolysis of (p)ppGpp. We
have earlier demonstrated that although both catalyze identical the (p)ppGpp
synthesis reaction, they exhibit a differential response to Mg2+
due to a unique charge reversal in the synthesis domain; an RXKD
motif in the synthesis domain of bifunctional protein is substituted by an
EXDD motif in that of the monofunctional proteins. Here, we show that
these motifs also determine substrate specificities (GTP/GDP), cooperativity,
and regulation of catalytic activities at the N-terminal region through the
C-terminal region. Most importantly, a mutant bifunctional Rel carrying an
EXDD instigates a novel catalytic reaction, resulting in the
synthesis of pGpp by an independent hydrolysis of the
5′Pα-O-Pβ bond of GTP/GDP or (p)ppGpp.
Further experiments with RelA from Escherichia coli wherein
EXDD is naturally present also revealed the presence of pGpp, albeit
at low levels. This work brings out the biological significance of
RXKD/EXDD motif conservation in Rel proteins and reveals an
additional catalytic activity for the monofunctional proteins, prompting an
extensive investigation for the possible existence and role of pGpp in the
biological system.
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Affiliation(s)
- Mathew Sajish
- Department of Biological Sciences and Bioengineering, Indian Institute of Technology, Kanpur 208016, India
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23
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Rich RL, Myszka DG. Survey of the year 2007 commercial optical biosensor literature. J Mol Recognit 2008; 21:355-400. [DOI: 10.1002/jmr.928] [Citation(s) in RCA: 144] [Impact Index Per Article: 9.0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/11/2022]
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24
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Uncovering mechanisms of bistability in biological systems. Curr Opin Biotechnol 2008; 19:381-8. [PMID: 18634875 DOI: 10.1016/j.copbio.2008.06.009] [Citation(s) in RCA: 53] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/19/2008] [Accepted: 06/15/2008] [Indexed: 12/14/2022]
Abstract
As the systems biology era progresses, theoreticians and experimentalists continue uncovering the molecular mechanisms that underlie the regulation of complex cellular phenomena, including those governing proliferation, differentiation, and death. The discovery of bistability in cellular responses and their signaling pathways has become a recurring theme, and prompted strong interest in understanding both the design and function of these networks. Modeling these systems has been crucial in assisting experimentalists to better understand how this and other types of behavior can emerge from a subset of regulators, and also to analyze and identify systems-level characteristics that would otherwise be difficult to intuit. In this review, recent advances in both theoretical and experimental work investigating the mechanistic as well as biological basis for bistability will be presented. These will include the role of positive feedback loops, the potential function of dual phosphorylation cycles, and substrate competition as a means of generating ultrasensitivity.
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25
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Sajish M, Tiwari D, Rananaware D, Nandicoori VK, Prakash B. A charge reversal differentiates (p)ppGpp synthesis by monofunctional and bifunctional Rel proteins. J Biol Chem 2007; 282:34977-83. [PMID: 17911108 DOI: 10.1074/jbc.m704828200] [Citation(s) in RCA: 39] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
A major regulatory mechanism evolved by microorganisms to combat stress is the regulation mediated by (p)ppGpp (the stringent response molecule), synthesized and hydrolyzed by Rel proteins. These are divided into bifunctional and monofunctional proteins based on the presence or absence of the hydrolysis activity. Although these proteins require Mg(2+) for (p)ppGpp synthesis, high Mg(2+) was shown to inhibit this reaction in bifunctional Rel proteins from Mycobacterium tuberculosis and Streptococcus equisimilis. This is not a characteristic feature in enzymes that use a dual metal ion mechanism, such as DNA polymerases that are known to carry out a similar pyrophosphate transfer reaction. Comparison of polymerase Polbeta and Rel(Seq) structures that share a common fold led to the proposal that the latter would follow a single metal ion mechanism. Surprisingly, in contrast to bifunctional Rel, we did not find inhibition of guanosine 5'-triphosphate, 3'-diphosphate (pppGpp) synthesis at higher Mg(2+) in the monofunctional RelA from Escherichia coli. We show that a charge reversal in a conserved motif in the synthesis domains explains this contrast; an RXKD motif in the bifunctional proteins is reversed to an EXDD motif. The differential response of these proteins to Mg(2+) could also be noticed in fluorescent nucleotide binding and circular dichroism experiments. In mutants where the motifs were reversed, the differential effect could also be reversed. We infer that although a catalytic Mg(2+) is common to both bifunctional and monofunctional proteins, the latter would utilize an additional metal binding site formed by EXDD. This work, for the first time, brings out differences in (p)ppGpp synthesis by the two classes of Rel proteins.
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Affiliation(s)
- Mathew Sajish
- Department of Biological Sciences and Bioengineering, Indian Institute of Technology, Kanpur, 208016 India
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26
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Chowdhury RP, Chatterji D. Estimation of Förster's distance between two ends of Dps protein from mycobacteria: distance heterogeneity as a function of oligomerization and DNA binding. Biophys Chem 2007; 128:19-29. [PMID: 17368913 DOI: 10.1016/j.bpc.2007.02.005] [Citation(s) in RCA: 14] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/19/2007] [Revised: 02/23/2007] [Accepted: 02/27/2007] [Indexed: 10/23/2022]
Abstract
Dps protein (DNA binding Protein from Starved Cells) from Mycobacterium smegmatis (Ms-Dps) is known to undergo an in vitro irreversible oligomeric transition from trimer to dodecamer. This transition helps the protein to provide for bimodal protection to the bacterial DNA from the free radical and Fenton mediated damages in the stationary state. The protein exists as a stable trimer, when purified from E. coli cells transformed with an over-expression plasmid. Both trimer as well as dodecamer are known to exhibit ferroxidation activity, thus removing toxic hydroxyl radicals in vivo, whereas iron accumulation and non-sequence specific DNA binding activity are found in dodecamer only. This seems to be aided by the positively charged long C-terminal tail of the protein. We used frequency domain phase-modulation fluorescence spectroscopy and Förster Resonance Energy Transfer (FRET) to monitor this oligomeric switch from a trimer to a dodecamer and to elucidate the structure of DNA-Dps dodecamer complex. As Ms-Dps is devoid of any Cysteine residues, a Serine is mutated to Cysteine (S169C) at a position adjacent to the putative DNA binding domain. This Cysteine is subsequently labeled with fluorescent probe and another probe is placed at the N-terminus, as crystal structure of the protein reveals several side-chain interactions between these two termini, and both are exposed towards the surface of the protein. Here, we report the Förster's distance distribution in the trimer and the dodecamer in the presence and absence of DNA. Through discrete lifetime analysis of the probes tagged at the respective regions in the macromolecule, coupled with Maximum Entropy Method (MEM) analysis, we show that the dodecamer, upon DNA binding shows conformational heterogeneity in overall structure, perhaps mediated by a non-specific DNA-protein interaction. On the other hand, the nature of DNA-Dps interaction is not known and several models exist in literature. We show here with the help of fluorescence anisotropy measurements of labeled DNA having different length and unlabeled native dodecameric protein that tandem occupation of DNA binding sites by a series of Dps molecules perhaps guide the tight packing of Dps over DNA backbone.
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