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Sasai M. Role of the reaction-structure coupling in temperature compensation of the KaiABC circadian rhythm. PLoS Comput Biol 2022; 18:e1010494. [PMID: 36067222 PMCID: PMC9481178 DOI: 10.1371/journal.pcbi.1010494] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/19/2021] [Revised: 09/16/2022] [Accepted: 08/17/2022] [Indexed: 11/19/2022] Open
Abstract
When the mixture solution of cyanobacterial proteins, KaiA, KaiB, and KaiC, is incubated with ATP in vitro, the phosphorylation level of KaiC shows stable oscillations with the temperature-compensated circadian period. Elucidating this temperature compensation is essential for understanding the KaiABC circadian clock, but its mechanism has remained a mystery. We analyzed the KaiABC temperature compensation by developing a theoretical model describing the feedback relations among reactions and structural transitions in the KaiC molecule. The model showed that the reduced structural cooperativity should weaken the negative feedback coupling among reactions and structural transitions, which enlarges the oscillation amplitude and period, explaining the observed significant period extension upon single amino-acid residue substitution. We propose that an increase in thermal fluctuations similarly attenuates the reaction-structure feedback, explaining the temperature compensation in the KaiABC clock. The model explained the experimentally observed responses of the oscillation phase to the temperature shift or the ADP-concentration change and suggested that the ATPase reactions in the CI domain of KaiC affect the period depending on how the reaction rates are modulated. The KaiABC clock provides a unique opportunity to analyze how the reaction-structure coupling regulates the system-level synchronized oscillations of molecules.
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Affiliation(s)
- Masaki Sasai
- Department of Applied Physics, Nagoya University, Nagoya, Japan
- Department of Complex Systems Science, Nagoya University, Nagoya, Japan
- Fukui Institute for Fundamental Chemistry, Kyoto University, Kyoto, Japan
- * E-mail:
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Mechanism of autonomous synchronization of the circadian KaiABC rhythm. Sci Rep 2021; 11:4713. [PMID: 33633230 PMCID: PMC7907350 DOI: 10.1038/s41598-021-84008-z] [Citation(s) in RCA: 5] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/03/2020] [Accepted: 02/11/2021] [Indexed: 11/28/2022] Open
Abstract
The cyanobacterial circadian clock can be reconstituted by mixing three proteins, KaiA, KaiB, and KaiC, in vitro. In this protein mixture, oscillations of the phosphorylation level of KaiC molecules are synchronized to show the coherent oscillations of the ensemble of many molecules. However, the molecular mechanism of this synchronization has not yet been fully elucidated. In this paper, we explain a theoretical model that considers the multifold feedback relations among the structure and reactions of KaiC. The simulated KaiC hexamers show stochastic switch-like transitions at the level of single molecules, which are synchronized in the ensemble through the sequestration of KaiA into the KaiC–KaiB–KaiA complexes. The proposed mechanism quantitatively reproduces the synchronization that was observed by mixing two solutions oscillating in different phases. The model results suggest that biochemical assays with varying concentrations of KaiA or KaiB can be used to test this hypothesis.
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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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