1
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Chavan A, Heisler J, Chang YG, Golden SS, Partch CL, LiWang A. Protocols for in vitro reconstitution of the cyanobacterial circadian clock. Biopolymers 2024; 115:e23559. [PMID: 37421636 PMCID: PMC10772220 DOI: 10.1002/bip.23559] [Citation(s) in RCA: 1] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/03/2023] [Revised: 05/26/2023] [Accepted: 06/16/2023] [Indexed: 07/10/2023]
Abstract
Circadian clocks are intracellular systems that orchestrate metabolic processes in anticipation of sunrise and sunset by providing an internal representation of local time. Because the ~24-h metabolic rhythms they produce are important to health across diverse life forms there is growing interest in their mechanisms. However, mechanistic studies are challenging in vivo due to the complex, that is, poorly defined, milieu of live cells. Recently, we reconstituted the intact circadian clock of cyanobacteria in vitro. It oscillates autonomously and remains phase coherent for many days with a fluorescence-based readout that enables real-time observation of individual clock proteins and promoter DNA simultaneously under defined conditions without user intervention. We found that reproducibility of the reactions required strict adherence to the quality of each recombinant clock protein purified from Escherichia coli. Here, we provide protocols for preparing in vitro clock samples so that other labs can ask questions about how changing environments, like temperature, metabolites, and protein levels are reflected in the core oscillator and propagated to regulation of transcription, providing deeper mechanistic insights into clock biology.
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Affiliation(s)
- Archana Chavan
- Center for Circadian Biology, University of California – San Diego, La Jolla, CA 92093
- School of Natural Sciences, University of California – Merced, Merced, CA 95343
| | - Joel Heisler
- Center for Circadian Biology, University of California – San Diego, La Jolla, CA 92093
- School of Natural Sciences, University of California – Merced, Merced, CA 95343
| | - Yong-Gang Chang
- Center for Circadian Biology, University of California – San Diego, La Jolla, CA 92093
- School of Natural Sciences, University of California – Merced, Merced, CA 95343
| | - Susan S. Golden
- Center for Circadian Biology, University of California – San Diego, La Jolla, CA 92093
- Department of Molecular Biology, University of California – San Diego, La Jolla, CA 92093
| | - Carrie L. Partch
- Center for Circadian Biology, University of California – San Diego, La Jolla, CA 92093
- Department of Chemistry & Biochemistry, University of California – Santa Cruz, Santa Cruz, CA 95064
| | - Andy LiWang
- Center for Circadian Biology, University of California – San Diego, La Jolla, CA 92093
- School of Natural Sciences, University of California – Merced, Merced, CA 95343
- Department of Chemistry & Biochemistry, University of California – Merced, Merced, CA 95343
- Center for Cellular and Biomolecular Machines, University of California – Merced, Merced, CA 95343
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2
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Fang M, LiWang A, Golden SS, Partch CL. The inner workings of an ancient biological clock. Trends Biochem Sci 2024; 49:236-246. [PMID: 38185606 PMCID: PMC10939747 DOI: 10.1016/j.tibs.2023.12.007] [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: 09/09/2023] [Revised: 11/30/2023] [Accepted: 12/15/2023] [Indexed: 01/09/2024]
Abstract
Circadian clocks evolved in diverse organisms as an adaptation to the daily swings in ambient light and temperature that derive from Earth's rotation. These timing systems, based on intracellular molecular oscillations, synchronize organisms' behavior and physiology with the 24-h environmental rhythm. The cyanobacterial clock serves as a special model for understanding circadian rhythms because it can be fully reconstituted in vitro. This review summarizes recent advances that leverage new biochemical, biophysical, and mathematical approaches to shed light on the molecular mechanisms of cyanobacterial Kai proteins that support the clock, and their homologues in other bacteria. Many questions remain in circadian biology, and the tools developed for the Kai system will bring us closer to the answers.
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Affiliation(s)
- Mingxu Fang
- Department of Molecular Biology, University of California - San Diego, La Jolla, CA 92093, USA; Center for Circadian Biology, University of California - San Diego, La Jolla, CA 92093, USA
| | - Andy LiWang
- Center for Circadian Biology, University of California - San Diego, La Jolla, CA 92093, USA; Department of Chemistry and Biochemistry, University of California - Merced, Merced, CA 95343, USA; Center for Cellular and Biomolecular Machines, University of California - Merced, Merced, CA 95343, USA
| | - Susan S Golden
- Department of Molecular Biology, University of California - San Diego, La Jolla, CA 92093, USA; Center for Circadian Biology, University of California - San Diego, La Jolla, CA 92093, USA
| | - Carrie L Partch
- Center for Circadian Biology, University of California - San Diego, La Jolla, CA 92093, USA; Department of Chemistry & Biochemistry, University of California - Santa Cruz, Santa Cruz, CA 95064, USA.
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3
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Pitsawong W, Pádua RAP, Grant T, Hoemberger M, Otten R, Bradshaw N, Grigorieff N, Kern D. From primordial clocks to circadian oscillators. Nature 2023; 616:183-189. [PMID: 36949197 PMCID: PMC10076222 DOI: 10.1038/s41586-023-05836-9] [Citation(s) in RCA: 6] [Impact Index Per Article: 6.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/29/2022] [Accepted: 02/13/2023] [Indexed: 03/24/2023]
Abstract
Circadian rhythms play an essential part in many biological processes, and only three prokaryotic proteins are required to constitute a true post-translational circadian oscillator1. The evolutionary history of the three Kai proteins indicates that KaiC is the oldest member and a central component of the clock2. Subsequent additions of KaiB and KaiA regulate the phosphorylation state of KaiC for time synchronization. The canonical KaiABC system in cyanobacteria is well understood3-6, but little is known about more ancient systems that only possess KaiBC. However, there are reports that they might exhibit a basic, hourglass-like timekeeping mechanism7-9. Here we investigate the primordial circadian clock in Rhodobacter sphaeroides, which contains only KaiBC, to elucidate its inner workings despite missing KaiA. Using a combination of X-ray crystallography and cryogenic electron microscopy, we find a new dodecameric fold for KaiC, in which two hexamers are held together by a coiled-coil bundle of 12 helices. This interaction is formed by the carboxy-terminal extension of KaiC and serves as an ancient regulatory moiety that is later superseded by KaiA. A coiled-coil register shift between daytime and night-time conformations is connected to phosphorylation sites through a long-range allosteric network that spans over 140 Å. Our kinetic data identify the difference in the ATP-to-ADP ratio between day and night as the environmental cue that drives the clock. They also unravel mechanistic details that shed light on the evolution of self-sustained oscillators.
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Affiliation(s)
- Warintra Pitsawong
- Howard Hughes Medical Institute and Department of Biochemistry, Brandeis University, Waltham, MA, USA
- Biomolecular Discovery, Relay Therapeutics, Cambridge, MA, USA
| | - Ricardo A P Pádua
- Howard Hughes Medical Institute and Department of Biochemistry, Brandeis University, Waltham, MA, USA
| | - Timothy Grant
- Janelia Research Campus, Howard Hughes Medical Institute, Ashburn, VA, USA
- John and Jeanne Rowe Center for Research in Virology, Morgridge Institute for Research, Madison, Madison, WI, USA
- Department of Biochemistry, University of Wisconsin-Madison, Madison, WI, USA
| | - Marc Hoemberger
- Howard Hughes Medical Institute and Department of Biochemistry, Brandeis University, Waltham, MA, USA
- Treeline Biosciences, Watertown, MA, USA
| | - Renee Otten
- Howard Hughes Medical Institute and Department of Biochemistry, Brandeis University, Waltham, MA, USA
- Treeline Biosciences, Watertown, MA, USA
| | - Niels Bradshaw
- Department of Biochemistry, Brandeis University, Waltham, MA, USA
| | - Nikolaus Grigorieff
- Janelia Research Campus, Howard Hughes Medical Institute, Ashburn, VA, USA
- Howard Hughes Medical Institute, RNA Therapeutics Institute, University of Massachusetts Chan Medical School, Worcester, MA, USA
| | - Dorothee Kern
- Howard Hughes Medical Institute and Department of Biochemistry, Brandeis University, Waltham, MA, USA.
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4
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Berger M, Wolde PRT. Robust replication initiation from coupled homeostatic mechanisms. Nat Commun 2022; 13:6556. [PMID: 36344507 PMCID: PMC9640692 DOI: 10.1038/s41467-022-33886-6] [Citation(s) in RCA: 10] [Impact Index Per Article: 5.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/21/2021] [Accepted: 10/05/2022] [Indexed: 11/09/2022] Open
Abstract
The bacterium Escherichia coli initiates replication once per cell cycle at a precise volume per origin and adds an on average constant volume between successive initiation events, independent of the initiation size. Yet, a molecular model that can explain these observations has been lacking. Experiments indicate that E. coli controls replication initiation via titration and activation of the initiator protein DnaA. Here, we study by mathematical modelling how these two mechanisms interact to generate robust replication-initiation cycles. We first show that a mechanism solely based on titration generates stable replication cycles at low growth rates, but inevitably causes premature reinitiation events at higher growth rates. In this regime, the DnaA activation switch becomes essential for stable replication initiation. Conversely, while the activation switch alone yields robust rhythms at high growth rates, titration can strongly enhance the stability of the switch at low growth rates. Our analysis thus predicts that both mechanisms together drive robust replication cycles at all growth rates. In addition, it reveals how an origin-density sensor yields adder correlations.
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Affiliation(s)
- Mareike Berger
- grid.417889.b0000 0004 0646 2441Biochemical Networks Group, Department of Information in Matter, AMOLF, 1098 XG Amsterdam, The Netherlands
| | - Pieter Rein ten Wolde
- grid.417889.b0000 0004 0646 2441Biochemical Networks Group, Department of Information in Matter, AMOLF, 1098 XG Amsterdam, The Netherlands
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5
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Swan JA, Sandate CR, Chavan AG, Freeberg AM, Etwaru D, Ernst DC, Palacios JG, Golden SS, LiWang A, Lander GC, Partch CL. Coupling of distant ATPase domains in the circadian clock protein KaiC. Nat Struct Mol Biol 2022; 29:759-766. [PMID: 35864165 DOI: 10.1038/s41594-022-00803-w] [Citation(s) in RCA: 4] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/20/2021] [Accepted: 06/06/2022] [Indexed: 11/09/2022]
Abstract
The AAA+ family member KaiC is the central pacemaker for circadian rhythms in the cyanobacterium Synechococcus elongatus. Composed of two hexameric rings of adenosine triphosphatase (ATPase) domains with tightly coupled activities, KaiC undergoes a cycle of autophosphorylation and autodephosphorylation on its C-terminal (CII) domain that restricts binding of clock proteins on its N-terminal (CI) domain to the evening. Here, we use cryogenic-electron microscopy to investigate how daytime and nighttime states of CII regulate KaiB binding on CI. We find that the CII hexamer is destabilized during the day but takes on a rigidified C2-symmetric state at night, concomitant with ring-ring compression. Residues at the CI-CII interface are required for phospho-dependent KaiB association, coupling ATPase activity on CI to cooperative KaiB recruitment. Together, these studies clarify a key step in the regulation of cyanobacterial circadian rhythms by KaiC phosphorylation.
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Affiliation(s)
- Jeffrey A Swan
- Department of Chemistry and Biochemistry, University of California, Santa Cruz, CA, USA
| | - Colby R Sandate
- Department of Integrative Structural and Computational Biology, The Scripps Research Institute, La Jolla, CA, USA
| | - Archana G Chavan
- Department of Chemistry and Biochemistry, University of California, Merced, CA, USA
| | - Alfred M Freeberg
- Department of Chemistry and Biochemistry, University of California, Santa Cruz, CA, USA
| | - Diana Etwaru
- Department of Chemistry and Biochemistry, University of California, Santa Cruz, CA, USA
| | - Dustin C Ernst
- Center for Circadian Biology, University of California, San Diego, La Jolla, CA, USA
| | - Joseph G Palacios
- Department of Chemistry and Biochemistry, University of California, Santa Cruz, CA, USA
| | - Susan S Golden
- Center for Circadian Biology, University of California, San Diego, La Jolla, CA, USA.,Division of Biological Sciences, University of California, San Diego, La Jolla, CA, USA
| | - Andy LiWang
- Department of Chemistry and Biochemistry, University of California, Merced, CA, USA.,Center for Circadian Biology, University of California, San Diego, La Jolla, CA, USA.,Center for Cellular and Biomolecular Machines, University of California, Merced, CA, USA
| | - Gabriel C Lander
- Department of Integrative Structural and Computational Biology, The Scripps Research Institute, La Jolla, CA, USA.
| | - Carrie L Partch
- Department of Chemistry and Biochemistry, University of California, Santa Cruz, CA, USA. .,Division of Biological Sciences, University of California, San Diego, La Jolla, CA, USA.
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6
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Abstract
KaiC, a core clock protein in the cyanobacterial circadian clock system, hydrolyzes adenosine triphosphate (ATP) at two distinct sites in a slow but ordered manner to measure the circadian timescale. We used biochemical and structural biology techniques to characterize the properties and interplay of dual-adenosine triphosphatase (ATPase) active sites. Our results show that the N-terminal and C-terminal ATPases communicate with each other through an interface between the N-terminal and C-terminal domains in KaiC. The dual-ATPase sites are regulated rhythmically in a concerted or opposing manner dependent on the phase of the circadian clock system, controlling the affinities of KaiC for other clock proteins, KaiA and KaiB. KaiC is a dual adenosine triphosphatase (ATPase), with one active site in its N-terminal domain and another in its C-terminal domain, that drives the circadian clock system of cyanobacteria through sophisticated coordination of the two sites. To elucidate the coordination mechanism, we studied the contribution of the dual-ATPase activities in the ring-shaped KaiC hexamer and these structural bases for activation and inactivation. At the N-terminal active site, a lytic water molecule is sequestered between the N-terminal domains, and its reactivity to adenosine triphosphate (ATP) is controlled by the quaternary structure of the N-terminal ring. The C-terminal ATPase activity is regulated mostly by water-incorporating voids between the C-terminal domains, and the size of these voids is sensitive to phosphoryl modification of S431. The up-regulatory effect on the N-terminal ATPase activity inversely correlates with the affinity of KaiC for KaiB, a clock protein constitutes the circadian oscillator together with KaiC and KaiA, and the complete dissociation of KaiB from KaiC requires KaiA-assisted activation of the dual ATPase. Delicate interactions between the N-terminal and C-terminal rings make it possible for the components of the dual ATPase to work together, thereby driving the assembly and disassembly cycle of KaiA and KaiB.
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7
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Dimer dissociation is a key energetic event in the fold-switch pathway of KaiB. Biophys J 2022; 121:943-955. [PMID: 35151633 PMCID: PMC8943816 DOI: 10.1016/j.bpj.2022.02.012] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/21/2021] [Revised: 12/14/2021] [Accepted: 02/09/2022] [Indexed: 11/21/2022] Open
Abstract
Cyanobacteria possesses the simplest circadian clock, composed of three proteins that act as a phosphorylation oscillator: KaiA, KaiB, and KaiC. The timing of this oscillator is determined by the fold-switch of KaiB, a structural rearrangement of its C-terminal half that is accompanied by a change in the oligomerization state. During the day, KaiB forms a stable tetramer (gsKaiB), whereas it adopts a monomeric thioredoxin-like fold during the night (fsKaiB). Although the structures and functions of both native states are well studied, little is known about the sequence and structure determinants that control their structural interconversion. Here, we used confinement molecular dynamics (CCR-MD) and folding simulations using structure-based models to show that the dissociation of the gsKaiB dimer is a key energetic event for the fold-switch. Hydrogen-deuterium exchange mass spectrometry (HDXMS) recapitulates the local stability of protein regions reported by CCR-MD, with both approaches consistently indicating that the energy and backbone flexibility changes are solely associated with the region that fold-switches between gsKaiB and fsKaiB and that the localized regions that differentially stabilize gsKaiB also involve regions outside the dimer interface. Moreover, two mutants (R23C and R75C) previously reported to be relevant for altering the rhythmicity of the Kai clock were also studied by HDXMS. Particularly, R75C populates dimeric and monomeric states with a deuterium incorporation profile comparable to the one observed for fsKaiB, emphasizing the importance of the oligomerization state of KaiB for the fold-switch. These findings suggest that the information necessary to control the rhythmicity of the cyanobacterial biological clock is, to a great extent, encoded within the KaiB sequence.
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8
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Chow GK, Chavan AG, Heisler J, Chang YG, Zhang N, LiWang A, Britt RD. A Night-Time Edge Site Intermediate in the Cyanobacterial Circadian Clock Identified by EPR Spectroscopy. J Am Chem Soc 2022; 144:184-194. [PMID: 34979080 DOI: 10.1021/jacs.1c08103] [Citation(s) in RCA: 6] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Abstract
As the only circadian oscillator that can be reconstituted in vitro with its constituent proteins KaiA, KaiB, and KaiC using ATP as an energy source, the cyanobacterial circadian oscillator serves as a model system for detailed mechanistic studies of day-night transitions of circadian clocks in general. The day-to-night transition occurs when KaiB forms a night-time complex with KaiC to sequester KaiA, the latter of which interacts with KaiC during the day to promote KaiC autophosphorylation. However, how KaiB forms the complex with KaiC remains poorly understood, despite the available structures of KaiB bound to hexameric KaiC. It has been postulated that KaiB-KaiC binding is regulated by inter-KaiB cooperativity. Here, using spin labeling continuous-wave electron paramagnetic resonance spectroscopy, we identified and quantified two subpopulations of KaiC-bound KaiB, corresponding to the "bulk" and "edge" KaiBC sites in stoichiometric and substoichiometric KaiBiC6 complexes (i = 1-5). We provide kinetic evidence to support the intermediacy of the "edge" KaiBC sites as bridges and nucleation sites between free KaiB and the "bulk" KaiBC sites. Furthermore, we show that the relative abundance of "edge" and "bulk" sites is dependent on both KaiC phosphostate and KaiA, supporting the notion of phosphorylation-state controlled inter-KaiB cooperativity. Finally, we demonstrate that the interconversion between the two subpopulations of KaiC-bound KaiB is intimately linked to the KaiC phosphorylation cycle. These findings enrich our mechanistic understanding of the cyanobacterial clock and demonstrate the utility of EPR in elucidating circadian clock mechanisms.
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Affiliation(s)
- Gary K Chow
- Department of Chemistry, University of California, Davis, California 95616, United States
| | - Archana G Chavan
- School of Natural Sciences, University of California, Merced, California 95343, United States
| | - Joel Heisler
- Chemistry and Chemical Biology, University of California, Merced, California 95343, United States
| | - Yong-Gang Chang
- School of Natural Sciences, University of California, Merced, California 95343, United States
| | - Ning Zhang
- School of Natural Sciences, University of California, Merced, California 95343, United States
| | - Andy LiWang
- School of Natural Sciences, Chemistry and Biochemistry, Health Sciences Research Institute, and Center for Cellular and Biomolecular Machines, University of California, Merced, California 95343, United States.,Center for Circadian Biology, University of California, San Diego, La Jolla, California 92093, United States
| | - R David Britt
- Department of Chemistry, University of California, Davis, California 95616, United States
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9
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Chow GK, Chavan AG, Heisler JC, Chang YG, LiWang A, Britt RD. Monitoring Protein-Protein Interactions in the Cyanobacterial Circadian Clock in Real Time via Electron Paramagnetic Resonance Spectroscopy. Biochemistry 2020; 59:2387-2400. [PMID: 32453554 PMCID: PMC7346098 DOI: 10.1021/acs.biochem.0c00279] [Citation(s) in RCA: 9] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/11/2022]
Abstract
![]()
The cyanobacterial circadian clock
in Synechococcus elongatus consists of three proteins,
KaiA, KaiB, and KaiC. KaiA and KaiB
rhythmically interact with KaiC to generate stable oscillations of
KaiC phosphorylation with a period of 24 h. The observation of stable
circadian oscillations when the three clock proteins are reconstituted
and combined in vitro makes it an ideal system for understanding its
underlying molecular mechanisms and circadian clocks in general. These
oscillations were historically monitored in vitro by gel electrophoresis
of reaction mixtures based on the differing electrophoretic mobilities
between various phosphostates of KaiC. As the KaiC phospho-distribution
represents only one facet of the oscillations, orthogonal tools are
necessary to explore other interactions to generate a full description
of the system. However, previous biochemical assays are discontinuous
or qualitative. To circumvent these limitations, we developed a spin-labeled
KaiB mutant that can differentiate KaiC-bound KaiB from free KaiB
using continuous-wave electron paramagnetic resonance spectroscopy
that is minimally sensitive to KaiA. Similar to wild-type (WT-KaiB),
this labeled mutant, in combination with KaiA, sustains robust circadian
rhythms of KaiC phosphorylation. This labeled mutant is hence a functional
surrogate of WT-KaiB and thus participates in and reports on autonomous
macroscopic circadian rhythms generated by mixtures that include KaiA,
KaiC, and ATP. Quantitative kinetics could be extracted with improved
precision and time resolution. We describe design principles, data
analysis, and limitations of this quantitative binding assay and discuss
future research necessary to overcome these challenges.
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Affiliation(s)
- Gary K Chow
- Department of Chemistry, University of California, Davis, California 95616, United States
| | | | | | | | - Andy LiWang
- Center for Circadian Biology, University of California, San Diego, La Jolla, California 92093, United States
| | - R David Britt
- Department of Chemistry, University of California, Davis, California 95616, United States
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10
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Hong L, Lavrentovich DO, Chavan A, Leypunskiy E, Li E, Matthews C, LiWang A, Rust MJ, Dinner AR. Bayesian modeling reveals metabolite-dependent ultrasensitivity in the cyanobacterial circadian clock. Mol Syst Biol 2020; 16:e9355. [PMID: 32496641 PMCID: PMC7271899 DOI: 10.15252/msb.20199355] [Citation(s) in RCA: 8] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/12/2019] [Revised: 04/21/2020] [Accepted: 04/24/2020] [Indexed: 12/22/2022] Open
Abstract
Mathematical models can enable a predictive understanding of mechanism in cell biology by quantitatively describing complex networks of interactions, but such models are often poorly constrained by available data. Owing to its relative biochemical simplicity, the core circadian oscillator in Synechococcus elongatus has become a prototypical system for studying how collective dynamics emerge from molecular interactions. The oscillator consists of only three proteins, KaiA, KaiB, and KaiC, and near-24-h cycles of KaiC phosphorylation can be reconstituted in vitro. Here, we formulate a molecularly detailed but mechanistically naive model of the KaiA-KaiC subsystem and fit it directly to experimental data within a Bayesian parameter estimation framework. Analysis of the fits consistently reveals an ultrasensitive response for KaiC phosphorylation as a function of KaiA concentration, which we confirm experimentally. This ultrasensitivity primarily results from the differential affinity of KaiA for competing nucleotide-bound states of KaiC. We argue that the ultrasensitive stimulus-response relation likely plays an important role in metabolic compensation by suppressing premature phosphorylation at nighttime.
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Affiliation(s)
- Lu Hong
- Graduate Program in Biophysical Sciences, University of Chicago, Chicago, IL, USA
| | | | - Archana Chavan
- School of Natural Sciences, University of California, Merced, CA, USA
| | - Eugene Leypunskiy
- Graduate Program in Biophysical Sciences, University of Chicago, Chicago, IL, USA
| | - Eileen Li
- Department of Statistics, University of Chicago, Chicago, IL, USA
| | - Charles Matthews
- Department of Statistics, University of Chicago, Chicago, IL, USA
| | - Andy LiWang
- School of Natural Sciences, University of California, Merced, CA, USA
- Quantitative and Systems Biology, University of California, Merced, CA, USA
- Center for Circadian Biology, University of California, San Diego, La Jolla, CA, USA
- Chemistry and Chemical Biology, University of California, Merced, CA, USA
- Health Sciences Research Institute, University of California, Merced, CA, USA
- Center for Cellular and Biomolecular Machines, University of California, Merced, CA, USA
| | - Michael J Rust
- Department of Molecular Genetics and Cell Biology, University of Chicago, Chicago, IL, USA
- Institute for Biophysical Dynamics, University of Chicago, Chicago, IL, USA
- Institute for Genomics and Systems Biology, University of Chicago, Chicago, IL, USA
| | - Aaron R Dinner
- Department of Chemistry, University of Chicago, Chicago, IL, USA
- Institute for Biophysical Dynamics, University of Chicago, Chicago, IL, USA
- James Franck Institute, University of Chicago, Chicago, IL, USA
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11
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Partch CL. Orchestration of Circadian Timing by Macromolecular Protein Assemblies. J Mol Biol 2020; 432:3426-3448. [DOI: 10.1016/j.jmb.2019.12.046] [Citation(s) in RCA: 33] [Impact Index Per Article: 8.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/18/2019] [Revised: 12/13/2019] [Accepted: 12/18/2019] [Indexed: 12/13/2022]
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12
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Yunoki Y, Ishii K, Yagi-Utsumi M, Murakami R, Uchiyama S, Yagi H, Kato K. ATP hydrolysis by KaiC promotes its KaiA binding in the cyanobacterial circadian clock system. Life Sci Alliance 2019; 2:2/3/e201900368. [PMID: 31160381 PMCID: PMC6549140 DOI: 10.26508/lsa.201900368] [Citation(s) in RCA: 10] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/06/2019] [Revised: 05/16/2019] [Accepted: 05/17/2019] [Indexed: 12/01/2022] Open
Abstract
ATP hydrolysis in the KaiC hexamer triggers the exposure of its C-terminal segments into the solvent so as to capture KaiA, providing mechanistic insights into the circadian periodicity regulation. The cyanobacterial clock is controlled via the interplay among KaiA, KaiB, and KaiC, which generate a periodic oscillation of KaiC phosphorylation in the presence of ATP. KaiC forms a homohexamer harboring 12 ATP-binding sites and exerts ATPase activities associated with its autophosphorylation and dephosphorylation. The KaiC nucleotide state is a determining factor of the KaiB–KaiC interaction; however, its relationship with the KaiA–KaiC interaction has not yet been elucidated. With the attempt to address this, our native mass spectrometric analyses indicated that ATP hydrolysis in the KaiC hexamer promotes its interaction with KaiA. Furthermore, our nuclear magnetic resonance spectral data revealed that ATP hydrolysis is coupled with conformational changes in the flexible C-terminal segments of KaiC, which carry KaiA-binding sites. From these data, we conclude that ATP hydrolysis in KaiC is coupled with the exposure of its C-terminal KaiA-binding sites, resulting in its high affinity for KaiA. These findings provide mechanistic insights into the ATP-mediated circadian periodicity.
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Affiliation(s)
- Yasuhiro Yunoki
- Graduate School of Pharmaceutical Sciences, Nagoya City University, Nagoya, Japan.,Institute for Molecular Science, National Institutes of Natural Sciences, Okazaki, Japan
| | - Kentaro Ishii
- Graduate School of Pharmaceutical Sciences, Nagoya City University, Nagoya, Japan.,Exploratory Research Center on Life and Living Systems (ExCELLS), National Institutes of Natural Sciences, Okazaki, Japan.,Institute for Molecular Science, National Institutes of Natural Sciences, Okazaki, Japan
| | - Maho Yagi-Utsumi
- Graduate School of Pharmaceutical Sciences, Nagoya City University, Nagoya, Japan.,Exploratory Research Center on Life and Living Systems (ExCELLS), National Institutes of Natural Sciences, Okazaki, Japan.,Institute for Molecular Science, National Institutes of Natural Sciences, Okazaki, Japan
| | - Reiko Murakami
- Graduate School of Pharmaceutical Sciences, Nagoya City University, Nagoya, Japan
| | - Susumu Uchiyama
- Exploratory Research Center on Life and Living Systems (ExCELLS), National Institutes of Natural Sciences, Okazaki, Japan.,Department of Biotechnology, Graduate School of Engineering, Osaka University, Osaka, Japan
| | - Hirokazu Yagi
- Graduate School of Pharmaceutical Sciences, Nagoya City University, Nagoya, Japan
| | - Koichi Kato
- Graduate School of Pharmaceutical Sciences, Nagoya City University, Nagoya, Japan .,Exploratory Research Center on Life and Living Systems (ExCELLS), National Institutes of Natural Sciences, Okazaki, Japan.,Institute for Molecular Science, National Institutes of Natural Sciences, Okazaki, Japan
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13
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Abstract
Circadian oscillators are networks of biochemical feedback loops that generate 24-hour rhythms in organisms from bacteria to animals. These periodic rhythms result from a complex interplay among clock components that are specific to the organism, but share molecular mechanisms across kingdoms. A full understanding of these processes requires detailed knowledge, not only of the biochemical properties of clock proteins and their interactions, but also of the three-dimensional structure of clockwork components. Posttranslational modifications and protein–protein interactions have become a recent focus, in particular the complex interactions mediated by the phosphorylation of clock proteins and the formation of multimeric protein complexes that regulate clock genes at transcriptional and translational levels. This review covers the structural aspects of circadian oscillators, and serves as a primer for this exciting realm of structural biology.
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Affiliation(s)
- Reena Saini
- Center for Biocrystallographic Research, Institute of Bioorganic Chemistry, Polish Academy of Sciences, Poznan, Poland.,Max-Planck-Institut für Pflanzenzüchtungsforschung, Cologne, Germany
| | - Mariusz Jaskolski
- Center for Biocrystallographic Research, Institute of Bioorganic Chemistry, Polish Academy of Sciences, Poznan, Poland.,Department of Crystallography, Faculty of Chemistry, A. Mickiewicz University, Poznan, Poland
| | - Seth J Davis
- Max-Planck-Institut für Pflanzenzüchtungsforschung, Cologne, Germany. .,Department of Biology, University of York, York, UK.
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14
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Abstract
Life has adapted to Earth's day-night cycle with the evolution of endogenous biological clocks. Whereas these circadian rhythms typically involve extensive transcription-translation feedback in higher organisms, cyanobacteria have a circadian clock, which functions primarily as a protein-based post-translational oscillator. Known as the Kai system, it consists of three proteins KaiA, KaiB, and KaiC. In this chapter, we provide a detailed structural overview of the Kai components and how they interact to produce circadian rhythms of global gene expression in cyanobacterial cells. We discuss how the circadian oscillation is coupled to gene expression, intertwined with transcription-translation feedback mechanisms, and entrained by input from the environment. We discuss the use of mathematical models and summarize insights into the cyanobacterial circadian clock from theoretical studies. The molecular details of the Kai system are well documented for the model cyanobacterium Synechococcus elongatus, but many less understood varieties of the Kai system exist across the highly diverse phylum of Cyanobacteria. Several species contain multiple kai-gene copies, while others like marine Prochlorococcus strains have a reduced kaiBC-only system, lacking kaiA. We highlight recent findings on the genomic distribution of kai genes in Bacteria and Archaea and finally discuss hypotheses on the evolution of the Kai system.
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Affiliation(s)
- Joost Snijder
- Snijder Bioscience, Zevenwouden 143, 3524CN, Utrecht, The Netherlands
- Biomolecular Mass Spectrometry and Proteomics, Bijvoet Center for Biomolecular Research, Utrecht University, Padualaan 8, 3584 CH, Utrecht, The Netherlands
| | - Ilka Maria Axmann
- Synthetic Microbiology, Biology Department, Heinrich Heine University Düsseldorf, Universitätsstraße 1, 40225, Düsseldorf, Germany.
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15
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Hong L, Vani BP, Thiede EH, Rust MJ, Dinner AR. Molecular dynamics simulations of nucleotide release from the circadian clock protein KaiC reveal atomic-resolution functional insights. Proc Natl Acad Sci U S A 2018; 115:E11475-E11484. [PMID: 30442665 PMCID: PMC6298084 DOI: 10.1073/pnas.1812555115] [Citation(s) in RCA: 15] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/05/2023] Open
Abstract
The cyanobacterial clock proteins KaiA, KaiB, and KaiC form a powerful system to study the biophysical basis of circadian rhythms, because an in vitro mixture of the three proteins is sufficient to generate a robust ∼24-h rhythm in the phosphorylation of KaiC. The nucleotide-bound states of KaiC critically affect both KaiB binding to the N-terminal domain (CI) and the phosphotransfer reactions that (de)phosphorylate the KaiC C-terminal domain (CII). However, the nucleotide exchange pathways associated with transitions among these states are poorly understood. In this study, we integrate recent advances in molecular dynamics methods to elucidate the structure and energetics of the pathway for Mg·ADP release from the CII domain. We find that nucleotide release is coupled to large-scale conformational changes in the KaiC hexamer. Solvating the nucleotide requires widening the subunit interface leading to the active site, which is linked to extension of the A-loop, a structure implicated in KaiA binding. These results provide a molecular hypothesis for how KaiA acts as a nucleotide exchange factor. In turn, structural parallels between the CI and CII domains suggest a mechanism for allosteric coupling between the domains. We relate our results to structures observed for other hexameric ATPases, which perform diverse functions.
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Affiliation(s)
- Lu Hong
- Graduate Program in Biophysical Sciences, The University of Chicago, Chicago, IL 60637
| | - Bodhi P Vani
- Department of Chemistry, The University of Chicago, Chicago, IL 60637
| | - Erik H Thiede
- Department of Chemistry, The University of Chicago, Chicago, IL 60637
| | - Michael J Rust
- Department of Molecular Genetics and Cell Biology, The University of Chicago, Chicago, IL 60637;
- Institute for Biophysical Dynamics, The University of Chicago, Chicago, IL 60637
- Institute for Genomics and Systems Biology, The University of Chicago, Chicago, IL 60637
| | - Aaron R Dinner
- Department of Chemistry, The University of Chicago, Chicago, IL 60637;
- Institute for Biophysical Dynamics, The University of Chicago, Chicago, IL 60637
- James Franck Institute, The University of Chicago, Chicago, IL 60637
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16
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Wanat P, Kasprzyk R, Kopcial M, Sikorski PJ, Strzelecka D, Jemielity J, Kowalska J. ExciTides: NTP-derived probes for monitoring pyrophosphatase activity based on excimer-to-monomer transitions. Chem Commun (Camb) 2018; 54:9773-9776. [PMID: 30105342 DOI: 10.1039/c8cc04968h] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022]
Abstract
We describe a new type of nucleotide-derived fluorescent probe designed for monitoring pyrophosphatase activity based on excimer-to-monomer transitions, called ExciTide. The nucleotides were designed with two self-interacting dye moieties and synthesised using copper-catalysed azide-alkyne cycloaddition click chemistry. We applied these probes for enzyme activity monitoring and inhibitor evaluation. Some of the probes permeated into living cells, yielding interesting prospects for future applications.
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Affiliation(s)
- Przemyslaw Wanat
- Division of Biophysics, Institute of Experimental Physics, Faculty of Physics, University of Warsaw, Pasteura 5, 02-093 Warsaw, Poland.
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17
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Mori T, Sugiyama S, Byrne M, Johnson CH, Uchihashi T, Ando T. Revealing circadian mechanisms of integration and resilience by visualizing clock proteins working in real time. Nat Commun 2018; 9:3245. [PMID: 30108211 PMCID: PMC6092398 DOI: 10.1038/s41467-018-05438-4] [Citation(s) in RCA: 27] [Impact Index Per Article: 4.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/09/2018] [Accepted: 07/09/2018] [Indexed: 11/09/2022] Open
Abstract
The circadian clock proteins KaiA, KaiB, and KaiC reconstitute a remarkable circa-24 h oscillation of KaiC phosphorylation that persists for many days in vitro. Here we use high-speed atomic force microscopy (HS-AFM) to visualize in real time and quantify the dynamic interactions of KaiA with KaiC on sub-second timescales. KaiA transiently interacts with KaiC, thereby stimulating KaiC autokinase activity. As KaiC becomes progressively more phosphorylated, KaiA's affinity for KaiC weakens, revealing a feedback of KaiC phosphostatus back onto the KaiA-binding events. These non-equilibrium interactions integrate high-frequency binding and unbinding events, thereby refining the period of the longer term oscillations. Moreover, this differential affinity phenomenon broadens the range of Kai protein stoichiometries that allow rhythmicity, explaining how the oscillation is resilient in an in vivo milieu that includes noise. Therefore, robustness of rhythmicity on a 24-h scale is explainable by molecular events occurring on a scale of sub-seconds.
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Affiliation(s)
- Tetsuya Mori
- Department of Biological Sciences, Vanderbilt University, Nashville, TN, 37235, USA
| | - Shogo Sugiyama
- Department of Physics, College of Science and Engineering, Kanazawa University, Kanazawa, 920-1192, Japan
| | - Mark Byrne
- Department of Chemistry, Physics, and Engineering, Spring Hill College, 4000 Dauphin St., Mobile, AL, 36608, USA
| | - Carl Hirschie Johnson
- Department of Biological Sciences, Vanderbilt University, Nashville, TN, 37235, USA. .,Department of Molecular Physiology and Biophysics, Vanderbilt University School of Medicine, Nashville, TN, 37232, USA.
| | - Takayuki Uchihashi
- Department of Physics and Structural Biology Research Center, Nagoya University, Chikusa-ku, Nagoya, 464-8602, Japan.
| | - Toshio Ando
- Nano Life Science Institute (WPI-NanoLSI), Kanazawa University, Kanazawa, 920-1192, Japan.
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18
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Swan JA, Golden SS, LiWang A, Partch CL. Structure, function, and mechanism of the core circadian clock in cyanobacteria. J Biol Chem 2018; 293:5026-5034. [PMID: 29440392 DOI: 10.1074/jbc.tm117.001433] [Citation(s) in RCA: 51] [Impact Index Per Article: 8.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/12/2017] [Revised: 02/09/2018] [Indexed: 01/09/2023] Open
Abstract
Circadian rhythms enable cells and organisms to coordinate their physiology with the cyclic environmental changes that come as a result of Earth's light/dark cycles. Cyanobacteria make use of a post-translational oscillator to maintain circadian rhythms, and this elegant system has become an important model for circadian timekeeping mechanisms. Composed of three proteins, the KaiABC system undergoes an oscillatory biochemical cycle that provides timing cues to achieve a 24-h molecular clock. Together with the input/output proteins SasA, CikA, and RpaA, these six gene products account for the timekeeping, entrainment, and output signaling functions in cyanobacterial circadian rhythms. This Minireview summarizes the current structural, functional and mechanistic insights into the cyanobacterial circadian clock.
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Affiliation(s)
- Jeffrey A Swan
- From the Department of Chemistry and Biochemistry, University of California Santa Cruz, Santa Cruz, California 95064
| | - Susan S Golden
- the Department of Molecular Biology and.,Center for Circadian Biology and Division of Biological Sciences, University of California San Diego, La Jolla, California 92093, and
| | - Andy LiWang
- Center for Circadian Biology and Division of Biological Sciences, University of California San Diego, La Jolla, California 92093, and.,the Department of Chemistry and Chemical Biology, University of California Merced, Merced, California 95343
| | - Carrie L Partch
- From the Department of Chemistry and Biochemistry, University of California Santa Cruz, Santa Cruz, California 95064, .,Center for Circadian Biology and Division of Biological Sciences, University of California San Diego, La Jolla, California 92093, and
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19
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Oyama K, Azai C, Matsuyama J, Terauchi K. Phosphorylation at Thr432 induces structural destabilization of the CII ring in the circadian oscillator KaiC. FEBS Lett 2017; 592:36-45. [PMID: 29265368 DOI: 10.1002/1873-3468.12945] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/19/2017] [Revised: 11/28/2017] [Accepted: 12/09/2017] [Indexed: 01/08/2023]
Abstract
KaiC is the central oscillator protein in the cyanobacterial circadian clock. KaiC oscillates autonomously between phosphorylated and dephosphorylated states on a 24-h cycle in vitro by mixing with KaiA and KaiB in the presence of ATP. KaiC forms a C6 -symmetrical hexamer, which is a double ring structure of homologous N-terminal and C-terminal domains termed CI and CII, respectively. Here, through the characterization of an isolated CII domain protein, CIIKaiC , we show that phosphorylation of KaiC Thr432 destabilizes the hexameric state of the CII ring to a monomeric state. The results suggest that the stable hexameric CI ring acts as a molecular bundle to hold the CII ring, which undergoes dynamic structural changes upon phosphorylation.
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Affiliation(s)
- Katsuaki Oyama
- Graduate School of Life Sciences, Ritsumeikan University, Kusatsu, Japan
| | - Chihiro Azai
- College of Life Sciences, Ritsumeikan University, Kusatsu, Japan
| | - Jun Matsuyama
- Graduate School of Life Sciences, Ritsumeikan University, Kusatsu, Japan
| | - Kazuki Terauchi
- Graduate School of Life Sciences, Ritsumeikan University, Kusatsu, Japan.,College of Life Sciences, Ritsumeikan University, Kusatsu, Japan
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20
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Schmelling NM, Lehmann R, Chaudhury P, Beck C, Albers SV, Axmann IM, Wiegard A. Minimal tool set for a prokaryotic circadian clock. BMC Evol Biol 2017; 17:169. [PMID: 28732467 PMCID: PMC5520375 DOI: 10.1186/s12862-017-0999-7] [Citation(s) in RCA: 37] [Impact Index Per Article: 5.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/13/2017] [Accepted: 06/15/2017] [Indexed: 11/10/2022] Open
Abstract
BACKGROUND Circadian clocks are found in organisms of almost all domains including photosynthetic Cyanobacteria, whereby large diversity exists within the protein components involved. In the model cyanobacterium Synechococcus elongatus PCC 7942 circadian rhythms are driven by a unique KaiABC protein clock, which is embedded in a network of input and output factors. Homologous proteins to the KaiABC clock have been observed in Bacteria and Archaea, where evidence for circadian behavior in these domains is accumulating. However, interaction and function of non-cyanobacterial Kai-proteins as well as homologous input and output components remain mainly unclear. RESULTS Using a universal BLAST analyses, we identified putative KaiC-based timing systems in organisms outside as well as variations within Cyanobacteria. A systematic analyses of publicly available microarray data elucidated interesting variations in circadian gene expression between different cyanobacterial strains, which might be correlated to the diversity of genome encoded clock components. Based on statistical analyses of co-occurrences of the clock components homologous to Synechococcus elongatus PCC 7942, we propose putative networks of reduced and fully functional clock systems. Further, we studied KaiC sequence conservation to determine functionally important regions of diverged KaiC homologs. Biochemical characterization of exemplary cyanobacterial KaiC proteins as well as homologs from two thermophilic Archaea demonstrated that kinase activity is always present. However, a KaiA-mediated phosphorylation is only detectable in KaiC1 orthologs. CONCLUSION Our analysis of 11,264 genomes clearly demonstrates that components of the Synechococcus elongatus PCC 7942 circadian clock are present in Bacteria and Archaea. However, all components are less abundant in other organisms than Cyanobacteria and KaiA, Pex, LdpA, and CdpA are only present in the latter. Thus, only reduced KaiBC-based or even simpler, solely KaiC-based timing systems might exist outside of the cyanobacterial phylum, which might be capable of driving diurnal oscillations.
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Affiliation(s)
- Nicolas M. Schmelling
- Institute for Synthetic Microbiology, Cluster of Excellence on Plant Sciences (CEPLAS), Heinrich Heine University Duesseldorf, Universitaetsstrasse 1, Duesseldorf, 40225 Germany
| | - Robert Lehmann
- Institute for Theoretical Biology, Humboldt University Berlin, Invalidenstrasse 43, Berlin, 10115 Germany
| | - Paushali Chaudhury
- Molecular Biology of Archaea, Albert-Ludwigs-University Freiburg, Institute of Biology II, Schaenzlestrasse 1, Freiburg, 79104 Germany
| | - Christian Beck
- Institute for Theoretical Biology, Humboldt University Berlin, Invalidenstrasse 43, Berlin, 10115 Germany
| | - Sonja-Verena Albers
- Molecular Biology of Archaea, Albert-Ludwigs-University Freiburg, Institute of Biology II, Schaenzlestrasse 1, Freiburg, 79104 Germany
| | - Ilka M. Axmann
- Institute for Synthetic Microbiology, Cluster of Excellence on Plant Sciences (CEPLAS), Heinrich Heine University Duesseldorf, Universitaetsstrasse 1, Duesseldorf, 40225 Germany
| | - Anika Wiegard
- Institute for Synthetic Microbiology, Cluster of Excellence on Plant Sciences (CEPLAS), Heinrich Heine University Duesseldorf, Universitaetsstrasse 1, Duesseldorf, 40225 Germany
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21
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Paijmans J, Lubensky DK, Ten Wolde PR. Period Robustness and Entrainability of the Kai System to Changing Nucleotide Concentrations. Biophys J 2017; 113:157-173. [PMID: 28700914 PMCID: PMC5510911 DOI: 10.1016/j.bpj.2017.05.048] [Citation(s) in RCA: 11] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/10/2017] [Revised: 05/01/2017] [Accepted: 05/30/2017] [Indexed: 10/19/2022] Open
Abstract
Circadian clocks must be able to entrain to time-varying signals to keep their oscillations in phase with the day-night rhythm. On the other hand, they must also exhibit input compensation: their period must remain approximately one day in different constant environments. The posttranslational oscillator of the Kai system can be entrained by transient or oscillatory changes in the ATP fraction, yet is insensitive to constant changes in this fraction. We study in three different models of this system how these two seemingly conflicting criteria are met. We find that one of these (our recently published Paijmans model) exhibits the best tradeoff between input compensation and entrainability: on the footing of equal phase-response curves, it exhibits the strongest input compensation. Performing stochastic simulations at the level of individual hexamers allows us to identify a new, to our knowledge, mechanism, which is employed by the Paijmans model to achieve input compensation: at lower ATP fraction, the individual hexamers make a shorter cycle in the phosphorylation state space, which compensates for the slower pace at which they traverse the cycle.
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Affiliation(s)
- Joris Paijmans
- AMOLF, Amsterdam, the Netherlands, University of Michigan, Ann Arbor, Michigan
| | - David K Lubensky
- Department of Physics, University of Michigan, Ann Arbor, Michigan
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22
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Paijmans J, Lubensky DK, ten Wolde PR. A thermodynamically consistent model of the post-translational Kai circadian clock. PLoS Comput Biol 2017; 13:e1005415. [PMID: 28296888 PMCID: PMC5371392 DOI: 10.1371/journal.pcbi.1005415] [Citation(s) in RCA: 24] [Impact Index Per Article: 3.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/16/2016] [Revised: 03/29/2017] [Accepted: 02/15/2017] [Indexed: 11/18/2022] Open
Abstract
The principal pacemaker of the circadian clock of the cyanobacterium S. elongatus is a protein phosphorylation cycle consisting of three proteins, KaiA, KaiB and KaiC. KaiC forms a homohexamer, with each monomer consisting of two domains, CI and CII. Both domains can bind and hydrolyze ATP, but only the CII domain can be phosphorylated, at two residues, in a well-defined sequence. While this system has been studied extensively, how the clock is driven thermodynamically has remained elusive. Inspired by recent experimental observations and building on ideas from previous mathematical models, we present a new, thermodynamically consistent, statistical-mechanical model of the clock. At its heart are two main ideas: i) ATP hydrolysis in the CI domain provides the thermodynamic driving force for the clock, switching KaiC between an active conformational state in which its phosphorylation level tends to rise and an inactive one in which it tends to fall; ii) phosphorylation of the CII domain provides the timer for the hydrolysis in the CI domain. The model also naturally explains how KaiA, by acting as a nucleotide exchange factor, can stimulate phosphorylation of KaiC, and how the differential affinity of KaiA for the different KaiC phosphoforms generates the characteristic temporal order of KaiC phosphorylation. As the phosphorylation level in the CII domain rises, the release of ADP from CI slows down, making the inactive conformational state of KaiC more stable. In the inactive state, KaiC binds KaiB, which not only stabilizes this state further, but also leads to the sequestration of KaiA, and hence to KaiC dephosphorylation. Using a dedicated kinetic Monte Carlo algorithm, which makes it possible to efficiently simulate this system consisting of more than a billion reactions, we show that the model can describe a wealth of experimental data. Circadian clocks are biological timekeeping devices with a rhythm of 24 hours in living cells pertaining to all kingdoms of life. They help organisms to coordinate their behavior with the day-night cycle. The circadian clock of the cyanobacterium Synechococcus elongatus is one of the simplest and best characterized clocks in biology. The central clock component is the protein KaiC, which is phosphorylated and dephosphorylated in a cyclical manner with a 24 hr period. While we know from elementary thermodynamics that oscillations require a net turnover of fuel molecules, in this case ATP, how ATP hydrolysis drives the clock has remained elusive. Based on recent experimental observations and building on ideas from existing models, we construct the most detailed mathematical model of this system to date. KaiC consists of two domains, CI and CII, which each can bind ATP, yet only CII can be phosphorylated. Moreover, KaiC can exist in two conformational states, an active one in which the phosphorylation level tends to rise, and an inactive one in which it tends to fall. Our model predicts that ATP hydrolysis in the CI domain is the principal energetic driver of the clock, driving the switching between the two conformational states, while phosphorylation in the CII domain provides the timer for the conformational switch. The coupling between ATP hydrolysis in the CI domain and phosphorylation in the CII domain leads to novel testable predictions.
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Affiliation(s)
| | - David K. Lubensky
- Department of Physics, University of Michigan, Ann Arbor, Michigan, United States of America
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23
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Abstract
Chronobiological studies of prokaryotic organisms have generally lagged far behind the study of endogenous circadian clocks in eukaryotes, in which such systems are essentially ubiquitous. However, despite only being studied during the past 25 years, cyanobacteria have become important model organisms for the study of circadian rhythms and, presently, their timekeeping mechanism is the best understood of any system in terms of biochemistry, structural biology, biophysics and adaptive importance. Nevertheless, intrinsic daily rhythmicity among bacteria other than cyanobacteria is essentially unknown; some tantalizing information suggests widespread daily timekeeping among Eubacteria and Archaea through mechanisms that share common elements with the cyanobacterial clock but are distinct. Moreover, the recent surge of information about microbiome-host interactions has largely neglected the temporal dimension and yet daily cycles control important aspects of their relationship.
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Schmelling NM, Lehmann R, Chaudhury P, Beck C, Albers SV, Axmann IM, Wiegard A. Minimal Tool Set for a Prokaryotic Circadian Clock.. [DOI: 10.1101/075291] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 07/19/2023]
Abstract
AbstractBackgroundCircadian clocks are found in organisms of almost all domains including photosynthetic Cyanobacteria, whereby large diversity exists within the protein components involved. In the model cyanobacteriumSynechococcus elongatusPCC 7942 circadian rhythms are driven by a unique KaiABC protein clock, which is embedded in a network of input and output factors. Homologous proteins to the KaiABC clock have been observed in Bacteria and Archaea, where evidence for circadian behavior in these domains is accumulating. However, interaction and function of non-cyanobacterial Kai-proteins as well as homologous input and output components remain mainly unclear.ResultsUsing a universal BLAST analyses, we identified putative KaiC-based timing systems in organisms outside as well as variations within Cyanobacteria. A systematic analyses of publicly available microarray data elucidated interesting variations in circadian gene expression between different cyanobacterial strains, which might be correlated to the diversity of genome encoded clock components. Based on statistical analyses of co-occurrences of the clock components homologous toSynechococcus elongatusPCC 7942, we propose putative networks of reduced and fully functional clock systems. Further, we studied KaiC sequence conservation to determine functionally important regions of diverged KaiC homologs. Biochemical characterization of exemplary cyanobacterial KaiC proteins as well as homologs from two thermophilic Archaea demonstrated that kinase activity is always present. However, a KaiA-mediated phosphorylation is only detectable in KaiC1 orthologs.ConclusionOur analysis of 11,264 genomes clearly demonstrates that components of theSynechococcus elongatusPCC 7942 circadian clock are present in Bacteria and Archaea. However, all components are less abundant in other organisms than Cyanobacteria and KaiA, Pex, LdpA, and CdpA are only present in the latter. Thus, only reduced KaiBC-based or even simpler, solely KaiC-based timing systems might exist outside of the cyanobacterial phylum, which might be capable of driving diurnal oscillations.
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25
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Conversion between two conformational states of KaiC is induced by ATP hydrolysis as a trigger for cyanobacterial circadian oscillation. Sci Rep 2016; 6:32443. [PMID: 27580682 PMCID: PMC5007536 DOI: 10.1038/srep32443] [Citation(s) in RCA: 30] [Impact Index Per Article: 3.8] [Reference Citation Analysis] [Abstract] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/24/2016] [Accepted: 08/03/2016] [Indexed: 11/12/2022] Open
Abstract
The cyanobacterial circadian oscillator can be reconstituted in vitro by mixing three clock proteins, KaiA, KaiB and KaiC, with ATP. KaiC is the only protein with circadian rhythmic activities. In the present study, we tracked the complex formation of the three Kai proteins over time using blue native (BN) polyacrylamide gel electrophoresis (PAGE), in which proteins are charged with the anionic dye Coomassie brilliant blue (CBB). KaiC was separated as three bands: the KaiABC complex, KaiC hexamer and KaiC monomer. However, no KaiC monomer was observed using gel filtration chromatography and CBB-free native PAGE. These data indicate two conformational states of KaiC hexamer and show that the ground-state KaiC (gs-KaiC) is stable and competent-state KaiC (cs-KaiC) is labile and degraded into monomers by the binding of CBB. Repeated conversions from gs-KaiC to cs-KaiC were observed over 24 h using an in vitro reconstitution system. Phosphorylation of KaiC promoted the conversion from gs-KaiC to cs-KaiC. KaiA sustained the gs-KaiC state, and KaiB bound only cs-KaiC. An E77Q/E78Q-KaiC variant that lacked N-terminal ATPase activity remained in the gs-KaiC state. Taken together, ATP hydrolysis induces the formation of cs-KaiC and promotes the binding of KaiB, which is a trigger for circadian oscillations.
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26
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Egli M. Intricate protein-protein interactions in the cyanobacterial circadian clock. J Biol Chem 2014; 289:21267-75. [PMID: 24936066 DOI: 10.1074/jbc.r114.579607] [Citation(s) in RCA: 21] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
The cyanobacterial circadian clock consists of a post-translational oscillator (PTO) and a PTO-dependent transcription-translation feedback loop (TTFL). The PTO can be reconstituted in vitro with the KaiA, KaiB, and KaiC proteins, enabling detailed biochemical and biophysical investigations. Both the CI and the CII halves of the KaiC hexamer harbor ATPases, but only the C-terminal CII ring exhibits kinase and phospho-transferase activities. KaiA stimulates the kinase and KaiB associates with KaiC during the dephosphorylation phase and sequesters KaiA. Recent research has led to conflicting models of the KaiB-KaiC interaction, precluding a clear understanding of KaiB function and KaiABC clock mechanism.
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Affiliation(s)
- Martin Egli
- From the Department of Biochemistry and Center for Structural Biology, Vanderbilt University, School of Medicine, Nashville, Tennessee 37232-0146
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