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Structural features discriminating hybrid histidine kinase Rec domains from response regulator homologs. Nat Commun 2023; 14:1002. [PMID: 36864019 PMCID: PMC9981736 DOI: 10.1038/s41467-023-36597-8] [Citation(s) in RCA: 6] [Impact Index Per Article: 6.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/06/2022] [Accepted: 02/07/2023] [Indexed: 03/04/2023] Open
Abstract
In two-component systems, the information gathered by histidine kinases (HKs) are relayed to cognate response regulators (RRs). Thereby, the phosphoryl group of the auto-phosphorylated HK is transferred to the receiver (Rec) domain of the RR to allosterically activate its effector domain. In contrast, multi-step phosphorelays comprise at least one additional Rec (Recinter) domain that is typically part of the HK and acts as an intermediary for phosphoryl-shuttling. While RR Rec domains have been studied extensively, little is known about discriminating features of Recinter domains. Here we study the Recinter domain of the hybrid HK CckA by X-ray crystallography and NMR spectroscopy. Strikingly, all active site residues of the canonical Rec-fold are pre-arranged for phosphoryl-binding and BeF3- binding does not alter secondary or quaternary structure, indicating the absence of allosteric changes, the hallmark of RRs. Based on sequence-covariation and modeling, we analyze the intra-molecular DHp/Rec association in hybrid HKs.
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A Single-Domain Response Regulator Functions as an Integrating Hub To Coordinate General Stress Response and Development in Alphaproteobacteria. mBio 2018; 9:mBio.00809-18. [PMID: 29789370 PMCID: PMC5964349 DOI: 10.1128/mbio.00809-18] [Citation(s) in RCA: 20] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/18/2022] Open
Abstract
The alphaproteobacterial general stress response is governed by a conserved partner-switching mechanism that is triggered by phosphorylation of the response regulator PhyR. In the model organism Caulobacter crescentus, PhyR was proposed to be phosphorylated by the histidine kinase PhyK, but biochemical evidence in support of such a role of PhyK is missing. Here, we identify a single-domain response regulator, MrrA, that is essential for general stress response activation in C. crescentus We demonstrate that PhyK does not function as a kinase but accepts phosphoryl groups from MrrA and passes them on to PhyR, adopting the role of a histidine phosphotransferase. MrrA is phosphorylated by at least six histidine kinases that likely serve as stress sensors. MrrA also transfers phosphate to LovK, a histidine kinase involved in C. crescentus holdfast production and attachment, which also negatively regulates the general stress response. We show that LovK together with the response regulator LovR acts as a phosphate sink to redirect phosphate flux away from the PhyKR branch. In agreement with the biochemical data, an mrrA mutant is unable to activate the general stress response and shows a hyperattachment phenotype, which is linked to decreased expression of the major holdfast inhibitory protein HfiA. We propose that MrrA serves as a central phosphorylation hub that coordinates the general stress response with C. crescentus development and other adaptive behaviors. The characteristic bow-tie architecture of this phosphorylation network with MrrA as the central knot may expedite the evolvability and species-specific niche adaptation of this group of bacteria.IMPORTANCE Two-component systems (TCSs) consisting of a histidine kinase and a cognate response regulator are predominant signal transduction systems in bacteria. To avoid cross talk, TCSs are generally thought to be highly insulated from each other. However, this notion is based largely on studies of the HisKA subfamily of histidine kinases, while little information is available for the HWE and HisKA2 subfamilies. The latter have been implicated in the alphaproteobacterial general stress response. Here, we show that in the model organism Caulobacter crescentus an atypical FATGUY-type single-domain response regulator, MrrA, is highly promiscuous in accepting and transferring phosphoryl groups from and to multiple up- and downstream kinases, challenging the current view of strictly insulated TCSs. Instead, we propose that FATGUY response regulators have evolved in alphaproteobacteria as central phosphorylation hubs to broadly sample information and distribute phosphoryl groups between the general stress response pathway and other TCSs, thereby coordinating multiple cellular behaviors.
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Gottschlich L, Bortfeld-Miller M, Gäbelein C, Dintner S, Vorholt JA. Phosphorelay through the bifunctional phosphotransferase PhyT controls the general stress response in an alphaproteobacterium. PLoS Genet 2018; 14:e1007294. [PMID: 29652885 PMCID: PMC5898713 DOI: 10.1371/journal.pgen.1007294] [Citation(s) in RCA: 15] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/08/2017] [Accepted: 03/06/2018] [Indexed: 11/19/2022] Open
Abstract
Two-component systems constitute phosphotransfer signaling pathways and enable adaptation to environmental changes, an essential feature for bacterial survival. The general stress response (GSR) in the plant-protecting alphaproteobacterium Sphingomonas melonis Fr1 involves a two-component system consisting of multiple stress-sensing histidine kinases (Paks) and the response regulator PhyR; PhyR in turn regulates the alternative sigma factor EcfG, which controls expression of the GSR regulon. While Paks had been shown to phosphorylate PhyR in vitro, it remained unclear if and under which conditions direct phosphorylation happens in the cell, as Paks also phosphorylate the single domain response regulator SdrG, an essential yet enigmatic component of the GSR signaling pathway. Here, we analyze the role of SdrG and investigate an alternative function of the membrane-bound PhyP (here re-designated PhyT), previously assumed to act as a PhyR phosphatase. In vitro assays show that PhyT transfers a phosphoryl group from SdrG to PhyR via phosphoryl transfer on a conserved His residue. This finding, as well as complementary GSR reporter assays, indicate the participation of SdrG and PhyT in a Pak-SdrG-PhyT-PhyR phosphorelay. Furthermore, we demonstrate complex formation between PhyT and PhyR. This finding is substantiated by PhyT-dependent membrane association of PhyR in unstressed cells, while the response regulator is released from the membrane upon stress induction. Our data support a model in which PhyT sequesters PhyR, thereby favoring Pak-dependent phosphorylation of SdrG. In addition, PhyT assumes the role of the SdrG-phosphotransferase to activate PhyR. Our results place SdrG into the GSR signaling cascade and uncover a dual role of PhyT in the GSR.
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Affiliation(s)
| | | | | | | | - Julia A. Vorholt
- Institute of Microbiology, ETH Zurich, Zurich, Switzerland
- * E-mail:
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4
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Luebke JL, Eaton DS, Sachleben JR, Crosson S. Allosteric control of a bacterial stress response system by an anti-σ factor. Mol Microbiol 2018; 107:164-179. [PMID: 29052909 PMCID: PMC5760481 DOI: 10.1111/mmi.13868] [Citation(s) in RCA: 8] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Accepted: 10/17/2017] [Indexed: 11/28/2022]
Abstract
Bacterial signal transduction systems commonly use receiver (REC) domains, which regulate adaptive responses to the environment as a function of their phosphorylation state. REC domains control cell physiology through diverse mechanisms, many of which remain understudied. We have defined structural features that underlie activation of the multi-domain REC protein, PhyR, which functions as an anti-anti-σ factor and regulates transcription of genes required for stress adaptation and host-microbe interactions in Alphaproteobacteria. Though REC phosphorylation is necessary for PhyR function in vivo, we did not detect expected changes in inter-domain interactions upon phosphorylation by solution X-ray scattering. We sought to understand this result by defining additional molecular requirements for PhyR activation. We uncovered specific interactions between unphosphorylated PhyR and an intrinsically disordered region (IDR) of the anti-σ factor, NepR, by solution NMR spectroscopy. Our data support a model whereby nascent NepR(IDR)-PhyR interactions and REC phosphorylation coordinately impart the free energy to shift PhyR to an open, active conformation that binds and inhibits NepR. This mechanism ensures PhyR is activated only when NepR and an activating phosphoryl signal are present. Our study provides new structural understanding of the molecular regulatory logic underlying a conserved environmental response system.
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Affiliation(s)
- Justin L. Luebke
- Department of Biochemistry and Molecular Biology, The University of Chicago, Chicago, Illinois, USA
| | - Daniel S. Eaton
- Department of Biochemistry and Molecular Biology, The University of Chicago, Chicago, Illinois, USA
| | - Joseph R. Sachleben
- Biomolecular NMR Core Facility, Biological Sciences Division, The University of Chicago, Chicago, Illinois, USA
| | - Sean Crosson
- Department of Biochemistry and Molecular Biology, The University of Chicago, Chicago, Illinois, USA
- Department of Microbiology, The University of Chicago, Chicago, Illinois, USA
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5
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Otrusinová O, Demo G, Padrta P, Jaseňáková Z, Pekárová B, Gelová Z, Szmitkowska A, Kadeřávek P, Jansen S, Zachrdla M, Klumpler T, Marek J, Hritz J, Janda L, Iwaï H, Wimmerová M, Hejátko J, Žídek L. Conformational dynamics are a key factor in signaling mediated by the receiver domain of a sensor histidine kinase from Arabidopsis thaliana. J Biol Chem 2017; 292:17525-17540. [PMID: 28860196 DOI: 10.1074/jbc.m117.790212] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/07/2017] [Revised: 08/28/2017] [Indexed: 11/06/2022] Open
Abstract
Multistep phosphorelay (MSP) cascades mediate responses to a wide spectrum of stimuli, including plant hormonal signaling, but several aspects of MSP await elucidation. Here, we provide first insight into the key step of MSP-mediated phosphotransfer in a eukaryotic system, the phosphorylation of the receiver domain of the histidine kinase CYTOKININ-INDEPENDENT 1 (CKI1RD) from Arabidopsis thaliana We observed that the crystal structures of free, Mg2+-bound, and beryllofluoridated CKI1RD (a stable analogue of the labile phosphorylated form) were identical and similar to the active state of receiver domains of bacterial response regulators. However, the three CKI1RD variants exhibited different conformational dynamics in solution. NMR studies revealed that Mg2+ binding and beryllofluoridation alter the conformational equilibrium of the β3-α3 loop close to the phosphorylation site. Mutations that perturbed the conformational behavior of the β3-α3 loop while keeping the active-site aspartate intact resulted in suppression of CKI1 function. Mechanistically, homology modeling indicated that the β3-α3 loop directly interacts with the ATP-binding site of the CKI1 histidine kinase domain. The functional relevance of the conformational dynamics observed in the β3-α3 loop of CKI1RD was supported by a comparison with another A. thaliana histidine kinase, ETR1. In contrast to the highly dynamic β3-α3 loop of CKI1RD, the corresponding loop of the ETR1 receiver domain (ETR1RD) exhibited little conformational exchange and adopted a different orientation in crystals. Biochemical data indicated that ETR1RD is involved in phosphorylation-independent signaling, implying a direct link between conformational behavior and the ability of eukaryotic receiver domains to participate in MSP.
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Affiliation(s)
- Olga Otrusinová
- From the Central European Institute of Technology and.,Faculty of Science, National Centre for Biomolecular Research, Masaryk University, Kamenice 5, CZ-625 00 Brno, Czech Republic and
| | - Gabriel Demo
- From the Central European Institute of Technology and
| | - Petr Padrta
- From the Central European Institute of Technology and.,Faculty of Science, National Centre for Biomolecular Research, Masaryk University, Kamenice 5, CZ-625 00 Brno, Czech Republic and
| | - Zuzana Jaseňáková
- From the Central European Institute of Technology and.,Faculty of Science, National Centre for Biomolecular Research, Masaryk University, Kamenice 5, CZ-625 00 Brno, Czech Republic and
| | - Blanka Pekárová
- From the Central European Institute of Technology and.,Faculty of Science, National Centre for Biomolecular Research, Masaryk University, Kamenice 5, CZ-625 00 Brno, Czech Republic and
| | - Zuzana Gelová
- From the Central European Institute of Technology and.,Faculty of Science, National Centre for Biomolecular Research, Masaryk University, Kamenice 5, CZ-625 00 Brno, Czech Republic and
| | - Agnieszka Szmitkowska
- From the Central European Institute of Technology and.,Faculty of Science, National Centre for Biomolecular Research, Masaryk University, Kamenice 5, CZ-625 00 Brno, Czech Republic and
| | - Pavel Kadeřávek
- From the Central European Institute of Technology and.,Faculty of Science, National Centre for Biomolecular Research, Masaryk University, Kamenice 5, CZ-625 00 Brno, Czech Republic and
| | - Séverine Jansen
- From the Central European Institute of Technology and.,Faculty of Science, National Centre for Biomolecular Research, Masaryk University, Kamenice 5, CZ-625 00 Brno, Czech Republic and
| | - Milan Zachrdla
- From the Central European Institute of Technology and.,Faculty of Science, National Centre for Biomolecular Research, Masaryk University, Kamenice 5, CZ-625 00 Brno, Czech Republic and
| | | | - Jaromír Marek
- From the Central European Institute of Technology and
| | - Jozef Hritz
- From the Central European Institute of Technology and
| | - Lubomír Janda
- From the Central European Institute of Technology and.,Faculty of Science, National Centre for Biomolecular Research, Masaryk University, Kamenice 5, CZ-625 00 Brno, Czech Republic and
| | - Hideo Iwaï
- the Institute of Biotechnology, University of Helsinki, Viikinkaari 1 (P. O. Box 65), 00014 Helsinki, Finland
| | - Michaela Wimmerová
- From the Central European Institute of Technology and.,Faculty of Science, National Centre for Biomolecular Research, Masaryk University, Kamenice 5, CZ-625 00 Brno, Czech Republic and
| | - Jan Hejátko
- From the Central European Institute of Technology and.,Faculty of Science, National Centre for Biomolecular Research, Masaryk University, Kamenice 5, CZ-625 00 Brno, Czech Republic and
| | - Lukáš Žídek
- From the Central European Institute of Technology and .,Faculty of Science, National Centre for Biomolecular Research, Masaryk University, Kamenice 5, CZ-625 00 Brno, Czech Republic and
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Jin Y, Richards NG, Waltho JP, Blackburn GM. Metal Fluorides as Analogues for Studies on Phosphoryl Transfer Enzymes. Angew Chem Int Ed Engl 2017; 56:4110-4128. [PMID: 27862756 DOI: 10.1002/anie.201606474] [Citation(s) in RCA: 35] [Impact Index Per Article: 5.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/04/2016] [Indexed: 12/27/2022]
Abstract
The 1994 structure of a transition-state analogue with AlF4- and GDP complexed to G1α, a small G protein, heralded a new field of research into the structure and mechanism of enzymes that manipulate the transfer of phosphoryl (PO3- ) groups. The number of enzyme structures in the PDB containing metal fluorides (MFx ) as ligands that imitate either a phosphoryl or a phosphate group was 357 at the end of 2016. They fall into three distinct geometrical classes: 1) Tetrahedral complexes based on BeF3- that mimic ground-state phosphates; 2) octahedral complexes, primarily based on AlF4- , which mimic "in-line" anionic transition states for phosphoryl transfer; and 3) trigonal bipyramidal complexes, represented by MgF3- and putative AlF30 moieties, which mimic the geometry of the transition state. The interpretation of these structures provides a deeper mechanistic understanding into the behavior and manipulation of phosphate monoesters in molecular biology. This Review provides a comprehensive overview of these structures, their uses, and their computational development.
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Affiliation(s)
- Yi Jin
- Department of Chemistry, University of York, York, YO10 5DD, UK
| | | | | | - G Michael Blackburn
- Department of Molecular Biology and Biotechnology, University of Sheffield, Sheffield, S10 2TN, UK
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7
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Jin Y, Richards NG, Waltho JP, Blackburn GM. Metallfluoride als Analoga für Studien an Phosphoryltransferenzymen. Angew Chem Int Ed Engl 2017. [DOI: 10.1002/ange.201606474] [Citation(s) in RCA: 7] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/23/2022]
Affiliation(s)
- Yi Jin
- Department of Chemistry; University of York; York YO10 5DD Großbritannien
| | - Nigel G. Richards
- School of Chemistry; Cardiff University; Cardiff CF10 3AT Großbritannien
| | | | - G. Michael Blackburn
- Department of Molecular Biology and Biotechnology; University of Sheffield; Sheffield S10 2TN Großbritannien
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8
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Metal Fluorides: Tools for Structural and Computational Analysis of Phosphoryl Transfer Enzymes. Top Curr Chem (Cham) 2017; 375:36. [PMID: 28299727 PMCID: PMC5480424 DOI: 10.1007/s41061-017-0130-y] [Citation(s) in RCA: 20] [Impact Index Per Article: 2.9] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/02/2016] [Accepted: 03/01/2017] [Indexed: 10/31/2022]
Abstract
The phosphoryl group, PO3-, is the dynamic structural unit in the biological chemistry of phosphorus. Its transfer from a donor to an acceptor atom, with oxygen much more prevalent than nitrogen, carbon, or sulfur, is at the core of a great majority of enzyme-catalyzed reactions involving phosphate esters, anhydrides, amidates, and phosphorothioates. The serendipitous discovery that the phosphoryl group could be labeled by "nuclear mutation," by substitution of PO3- by MgF3- or AlF4-, has underpinned the application of metal fluoride (MF x ) complexes to mimic transition states for enzymatic phosphoryl transfer reactions, with sufficient stability for experimental analysis. Protein crystallography in the solid state and 19F NMR in solution have enabled direct observation of ternary and quaternary protein complexes embracing MF x transition state models with precision. These studies have underpinned a radically new mechanistic approach to enzyme catalysis for a huge range of phosphoryl transfer processes, as varied as kinases, phosphatases, phosphomutases, and phosphohydrolases. The results, without exception, have endorsed trigonal bipyramidal geometry (tbp) for concerted, "in-line" stereochemistry of phosphoryl transfer. QM computations have established the validity of tbp MF x complexes as reliable models for true transition states, delivering similar bond lengths, coordination to essential metal ions, and virtually identical hydrogen bond networks. The emergence of protein control of reactant orbital overlap between bond-forming species within enzyme transition states is a new challenging theme for wider exploration.
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9
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Foster CA, West AH. Use of restrained molecular dynamics to predict the conformations of phosphorylated receiver domains in two-component signaling systems. Proteins 2016; 85:155-176. [PMID: 27802580 PMCID: PMC5242315 DOI: 10.1002/prot.25207] [Citation(s) in RCA: 12] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/02/2016] [Revised: 10/22/2016] [Accepted: 10/25/2016] [Indexed: 01/22/2023]
Abstract
Two‐component signaling (TCS) is the primary means by which bacteria, as well as certain plants and fungi, respond to external stimuli. Signal transduction involves stimulus‐dependent autophosphorylation of a sensor histidine kinase and phosphoryl transfer to the receiver domain of a downstream response regulator. Phosphorylation acts as an allosteric switch, inducing structural and functional changes in the pathway's components. Due to their transient nature, phosphorylated receiver domains are challenging to characterize structurally. In this work, we provide a methodology for simulating receiver domain phosphorylation to predict conformations that are nearly identical to experimental structures. Using restrained molecular dynamics, phosphorylated conformations of receiver domains can be reliably sampled on nanosecond timescales. These simulations also provide data on conformational dynamics that can be used to identify regions of functional significance related to phosphorylation. We first validated this approach on several well‐characterized receiver domains and then used it to compare the upstream and downstream components of the fungal Sln1 phosphorelay. Our results demonstrate that this technique provides structural insight, obtained in the absence of crystallographic or NMR information, regarding phosphorylation‐induced conformational changes in receiver domains that regulate the output of their associated signaling pathway. To our knowledge, this is the first time such a protocol has been described that can be broadly applied to TCS proteins for predictive purposes. Proteins 2016; 85:155–176. © 2016 Wiley Periodicals, Inc.
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Affiliation(s)
- Clay A Foster
- Department of Chemistry and Biochemistry, University of Oklahoma, Norman, Oklahoma
| | - Ann H West
- Department of Chemistry and Biochemistry, University of Oklahoma, Norman, Oklahoma
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10
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Campagne S, Dintner S, Gottschlich L, Thibault M, Bortfeld-Miller M, Kaczmarczyk A, Francez-Charlot A, Allain FHT, Vorholt JA. Role of the PFXFATG[G/Y] Motif in the Activation of SdrG, a Response Regulator Involved in the Alphaproteobacterial General Stress Response. Structure 2016; 24:1237-1247. [PMID: 27396826 DOI: 10.1016/j.str.2016.05.015] [Citation(s) in RCA: 13] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/14/2016] [Revised: 05/23/2016] [Accepted: 05/23/2016] [Indexed: 11/19/2022]
Abstract
Two-component systems are major signal transduction pathways, which consist of histidine kinases and response regulators that communicate through phosphorylation. Here, we highlight a distinct class of single-domain response regulators containing the PFXFATG[G/Y] motif that are activated by a mechanism distinct from the Y-T coupling described for prototypical receiver domains. We first solved the structures of inactive and active SdrG, a representative of the FAT GUY family, and then biochemically and genetically characterized variants in which residues in this motif were mutated. Our results support a model of activation mainly driven by a conserved lysine and reveal that the rotation of the threonine induces the reorganization of several aromatic residues in and around the PFXFATG[G/Y] motif to generate intermediates resembling those occurring during classical Y-T coupling. Overall, this helps define a new subfamily of response regulators that emerge as important players in physiological adaptation.
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Affiliation(s)
- Sébastien Campagne
- Institute of Microbiology, ETH Zurich, Vladimir-Prelog-Weg 1-5/10, 8093 Zürich, Switzerland; Institute of Molecular Biology and Biophysics, ETH Zurich, Hönggerbergring 64, 8093 Zürich, Switzerland.
| | - Sebastian Dintner
- Institute of Microbiology, ETH Zurich, Vladimir-Prelog-Weg 1-5/10, 8093 Zürich, Switzerland
| | - Lisa Gottschlich
- Institute of Microbiology, ETH Zurich, Vladimir-Prelog-Weg 1-5/10, 8093 Zürich, Switzerland
| | - Maxence Thibault
- Institute of Molecular Biology and Biophysics, ETH Zurich, Hönggerbergring 64, 8093 Zürich, Switzerland
| | - Miriam Bortfeld-Miller
- Institute of Microbiology, ETH Zurich, Vladimir-Prelog-Weg 1-5/10, 8093 Zürich, Switzerland
| | - Andreas Kaczmarczyk
- Institute of Microbiology, ETH Zurich, Vladimir-Prelog-Weg 1-5/10, 8093 Zürich, Switzerland
| | - Anne Francez-Charlot
- Institute of Microbiology, ETH Zurich, Vladimir-Prelog-Weg 1-5/10, 8093 Zürich, Switzerland
| | - Frédéric H-T Allain
- Institute of Molecular Biology and Biophysics, ETH Zurich, Hönggerbergring 64, 8093 Zürich, Switzerland
| | - Julia A Vorholt
- Institute of Microbiology, ETH Zurich, Vladimir-Prelog-Weg 1-5/10, 8093 Zürich, Switzerland
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Ocasio VJ, Corrêa F, Gardner KH. Ligand-induced folding of a two-component signaling receiver domain. Biochemistry 2015; 54:1353-63. [PMID: 25629646 DOI: 10.1021/bi501143b] [Citation(s) in RCA: 14] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/08/2023]
Abstract
To survive and adapt to environmental changes, bacteria commonly use two-component signaling systems. Minimally, these pathways use histidine kinases (HKs) to detect environmental signals, harnessing these to control phosphorylation levels of receiver (REC) domains of downstream response regulators that convert this signal into physiological responses. Studies of several prototypical REC domains suggest that phosphorylation shifts these proteins between inactive and active structures that are globally similar and well-folded. However, it is unclear how globally these findings hold within REC domains in general, particularly when they are considered within full-length proteins. Here, we present EL_LovR, a full-length REC-only protein that is phosphorylated in response to blue light in the marine α-proteobacterium, Erythrobacter litoralis HTCC2594. Notably, EL_LovR is similar to comparable REC-only proteins used in bacterial general stress responses, where genetic evidence suggests that their potent phosphatase activity is important to shut off such systems. Size exclusion chromatography, light scattering, and solution NMR experiments show that EL_LovR is monomeric and unfolded in solution under conditions routinely used for other REC structure determinations. Addition of Mg(2+) and phosphorylation induce progressively greater degrees of tertiary structure stabilization, with the solution structure of the fully activated EL_LovR adopting the canonical receiver domain fold. Parallel functional assays show that EL_LovR has a fast dephosphorylation rate, consistent with its proposed function as a phosphate sink that depletes the HK phosphoryl group, promoting the phosphatase activity of this enzyme. Our findings demonstrate that EL_LovR undergoes substantial ligand-dependent conformational changes that have not been reported for other RRs, expanding the scope of conformational changes and regulation used by REC domains, critical components of bacterial signaling systems.
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Affiliation(s)
- Victor J Ocasio
- Departments of Biophysics and Biochemistry, UT Southwestern Medical Center , Dallas, Texas 75390-8816, United States
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