1
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Köbler C, Schmelling NM, Wiegard A, Pawlowski A, Pattanayak GK, Spät P, Scheurer NM, Sebastian KN, Stirba FP, Berwanger LC, Kolkhof P, Maček B, Rust MJ, Axmann IM, Wilde A. Two KaiABC systems control circadian oscillations in one cyanobacterium. Nat Commun 2024; 15:7674. [PMID: 39227593 PMCID: PMC11372060 DOI: 10.1038/s41467-024-51914-5] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/26/2023] [Accepted: 08/20/2024] [Indexed: 09/05/2024] Open
Abstract
The circadian clock of cyanobacteria, which predicts daily environmental changes, typically includes a standard oscillator consisting of proteins KaiA, KaiB, and KaiC. However, several cyanobacteria have diverse Kai protein homologs of unclear function. In particular, Synechocystis sp. PCC 6803 harbours, in addition to a canonical kaiABC gene cluster (named kaiAB1C1), two further kaiB and kaiC homologs (kaiB2, kaiB3, kaiC2, kaiC3). Here, we identify a chimeric KaiA homolog, named KaiA3, encoded by a gene located upstream of kaiB3. At the N-terminus, KaiA3 is similar to response-regulator receiver domains, whereas its C-terminal domain resembles that of KaiA. Homology analysis shows that a KaiA3-KaiB3-KaiC3 system exists in several cyanobacteria and other bacteria. Using the Synechocystis sp. PCC 6803 homologs, we observe circadian oscillations in KaiC3 phosphorylation in vitro in the presence of KaiA3 and KaiB3. Mutations of kaiA3 affect KaiC3 phosphorylation, leading to growth defects under both mixotrophic and chemoheterotrophic conditions. KaiC1 and KaiC3 exhibit phase-locked free-running phosphorylation rhythms. Deletion of either system (∆kaiAB1C1 or ∆kaiA3B3C3) alters the period of the cellular backscattering rhythm. Furthermore, both oscillators are required to maintain high-amplitude, self-sustained backscatter oscillations with a period of approximately 24 h, indicating their interconnected nature.
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Affiliation(s)
- Christin Köbler
- Institute of Biology III, Faculty of Biology, University of Freiburg, 79104, Freiburg, Germany
| | - Nicolas M Schmelling
- Institute for Synthetic Microbiology, Biology Department, Heinrich Heine University Düsseldorf, 40225, Düsseldorf, Germany
| | - Anika Wiegard
- Institute for Synthetic Microbiology, Biology Department, Heinrich Heine University Düsseldorf, 40225, Düsseldorf, Germany
| | - Alice Pawlowski
- Institute for Synthetic Microbiology, Biology Department, Heinrich Heine University Düsseldorf, 40225, Düsseldorf, Germany
| | - Gopal K Pattanayak
- Department of Molecular Genetics and Cell Biology, The University of Chicago, Chicago, IL, 60637, USA
| | - Philipp Spät
- Department of Quantitative Proteomics, Interfaculty Institute for Cell Biology, Eberhard Karls University Tübingen, 72076, Tübingen, Germany
| | - Nina M Scheurer
- Institute of Biology III, Faculty of Biology, University of Freiburg, 79104, Freiburg, Germany
| | - Kim N Sebastian
- Institute of Biology III, Faculty of Biology, University of Freiburg, 79104, Freiburg, Germany
| | - Florian P Stirba
- Institute for Synthetic Microbiology, Biology Department, Heinrich Heine University Düsseldorf, 40225, Düsseldorf, Germany
| | - Lutz C Berwanger
- Institute for Synthetic Microbiology, Biology Department, Heinrich Heine University Düsseldorf, 40225, Düsseldorf, Germany
| | - Petra Kolkhof
- Institute for Synthetic Microbiology, Biology Department, Heinrich Heine University Düsseldorf, 40225, Düsseldorf, Germany
| | - Boris Maček
- Department of Quantitative Proteomics, Interfaculty Institute for Cell Biology, Eberhard Karls University Tübingen, 72076, Tübingen, Germany
| | - Michael J Rust
- Department of Molecular Genetics and Cell Biology, The University of Chicago, Chicago, IL, 60637, USA
| | - Ilka M Axmann
- Institute for Synthetic Microbiology, Biology Department, Heinrich Heine University Düsseldorf, 40225, Düsseldorf, Germany.
| | - Annegret Wilde
- Institute of Biology III, Faculty of Biology, University of Freiburg, 79104, Freiburg, Germany.
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2
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Zhou Q, Wang R, Su Y, Wang B, Zhang Y, Qin X. The molecular circadian rhythms regulating the cell cycle. J Cell Biochem 2024; 125:e30539. [PMID: 38372014 DOI: 10.1002/jcb.30539] [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: 10/18/2023] [Revised: 01/25/2024] [Accepted: 02/02/2024] [Indexed: 02/20/2024]
Abstract
The circadian clock controls the expression of a large proportion of protein-coding genes in mammals and can modulate a wide range of physiological processes. Recent studies have demonstrated that disruption or dysregulation of the circadian clock is involved in the development and progression of several diseases, including cancer. The cell cycle is considered to be the fundamental process related to cancer. Accumulating evidence suggests that the circadian clock can control the expression of a large number of genes related to the cell cycle. This article reviews the mechanism of cell cycle-related genes whose chromatin regulatory elements are rhythmically occupied by core circadian clock transcription factors, while their RNAs are rhythmically expressed. This article further reviews the identified oscillatory cell cycle-related genes in higher organisms such as baboons and humans. The potential functions of these identified genes in regulating cell cycle progression are also discussed. Understanding how the molecular clock controls the expression of cell cycle genes will be beneficial for combating and treating cancer.
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Affiliation(s)
- Qin Zhou
- Institute of Health Sciences and Technology, Institutes of Physical Science and Information Technology, Anhui University, Hefei, Anhui Province, China
| | - Ruohan Wang
- Institute of Health Sciences and Technology, Institutes of Physical Science and Information Technology, Anhui University, Hefei, Anhui Province, China
| | - Yunxia Su
- Institute of Health Sciences and Technology, Institutes of Physical Science and Information Technology, Anhui University, Hefei, Anhui Province, China
| | - Bowen Wang
- Institute of Health Sciences and Technology, Institutes of Physical Science and Information Technology, Anhui University, Hefei, Anhui Province, China
| | - Yunfei Zhang
- Modern Experiment Technology Center, Institutes of Physical Science and Information Technology, Anhui University, Hefei, Anhui Province, China
| | - Ximing Qin
- Institute of Health Sciences and Technology, Institutes of Physical Science and Information Technology, Anhui University, Hefei, Anhui Province, China
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3
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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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4
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Siebieszuk A, Sejbuk M, Witkowska AM. Studying the Human Microbiota: Advances in Understanding the Fundamentals, Origin, and Evolution of Biological Timekeeping. Int J Mol Sci 2023; 24:16169. [PMID: 38003359 PMCID: PMC10671191 DOI: 10.3390/ijms242216169] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/12/2023] [Revised: 11/07/2023] [Accepted: 11/08/2023] [Indexed: 11/26/2023] Open
Abstract
The recently observed circadian oscillations of the intestinal microbiota underscore the profound nature of the human-microbiome relationship and its importance for health. Together with the discovery of circadian clocks in non-photosynthetic gut bacteria and circadian rhythms in anucleated cells, these findings have indicated the possibility that virtually all microorganisms may possess functional biological clocks. However, they have also raised many essential questions concerning the fundamentals of biological timekeeping, its evolution, and its origin. This narrative review provides a comprehensive overview of the recent literature in molecular chronobiology, aiming to bring together the latest evidence on the structure and mechanisms driving microbial biological clocks while pointing to potential applications of this knowledge in medicine. Moreover, it discusses the latest hypotheses regarding the evolution of timing mechanisms and describes the functions of peroxiredoxins in cells and their contribution to the cellular clockwork. The diversity of biological clocks among various human-associated microorganisms and the role of transcriptional and post-translational timekeeping mechanisms are also addressed. Finally, recent evidence on metabolic oscillators and host-microbiome communication is presented.
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Affiliation(s)
- Adam Siebieszuk
- Department of Physiology, Faculty of Medicine, Medical University of Bialystok, Mickiewicza 2C, 15-222 Białystok, Poland;
| | - Monika Sejbuk
- Department of Food Biotechnology, Faculty of Health Sciences, Medical University of Bialystok, Szpitalna 37, 15-295 Białystok, Poland;
| | - Anna Maria Witkowska
- Department of Food Biotechnology, Faculty of Health Sciences, Medical University of Bialystok, Szpitalna 37, 15-295 Białystok, Poland;
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5
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de Barros Dantas LL, Eldridge BM, Dorling J, Dekeya R, Lynch DA, Dodd AN. Circadian regulation of metabolism across photosynthetic organisms. THE PLANT JOURNAL : FOR CELL AND MOLECULAR BIOLOGY 2023; 116:650-668. [PMID: 37531328 PMCID: PMC10953457 DOI: 10.1111/tpj.16405] [Citation(s) in RCA: 2] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 04/27/2023] [Revised: 07/15/2023] [Accepted: 07/18/2023] [Indexed: 08/04/2023]
Abstract
Circadian regulation produces a biological measure of time within cells. The daily cycle in the availability of light for photosynthesis causes dramatic changes in biochemical processes in photosynthetic organisms, with the circadian clock having crucial roles in adaptation to these fluctuating conditions. Correct alignment between the circadian clock and environmental day-night cycles maximizes plant productivity through its regulation of metabolism. Therefore, the processes that integrate circadian regulation with metabolism are key to understanding how the circadian clock contributes to plant productivity. This forms an important part of exploiting knowledge of circadian regulation to enhance sustainable crop production. Here, we examine the roles of circadian regulation in metabolic processes in source and sink organ structures of Arabidopsis. We also evaluate possible roles for circadian regulation in root exudation processes that deposit carbon into the soil, and the nature of the rhythmic interactions between plants and their associated microbial communities. Finally, we examine shared and differing aspects of the circadian regulation of metabolism between Arabidopsis and other model photosynthetic organisms, and between circadian control of metabolism in photosynthetic and non-photosynthetic organisms. This synthesis identifies a variety of future research topics, including a focus on metabolic processes that underlie biotic interactions within ecosystems.
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Affiliation(s)
| | - Bethany M. Eldridge
- Department of Cell and Developmental BiologyJohn Innes Centre, Norwich Research ParkNorwichUK
| | - Jack Dorling
- Department of Cell and Developmental BiologyJohn Innes Centre, Norwich Research ParkNorwichUK
| | - Richard Dekeya
- Department of Cell and Developmental BiologyJohn Innes Centre, Norwich Research ParkNorwichUK
| | - Deirdre A. Lynch
- Department of Cell and Developmental BiologyJohn Innes Centre, Norwich Research ParkNorwichUK
| | - Antony N. Dodd
- Department of Cell and Developmental BiologyJohn Innes Centre, Norwich Research ParkNorwichUK
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6
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Lakin-Thomas P. The Case for the Target of Rapamycin Pathway as a Candidate Circadian Oscillator. Int J Mol Sci 2023; 24:13307. [PMID: 37686112 PMCID: PMC10488232 DOI: 10.3390/ijms241713307] [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: 08/09/2023] [Revised: 08/23/2023] [Accepted: 08/25/2023] [Indexed: 09/10/2023] Open
Abstract
The molecular mechanisms that drive circadian (24 h) rhythmicity have been investigated for many decades, but we still do not have a complete picture of eukaryotic circadian systems. Although the transcription/translation feedback loop (TTFL) model has been the primary focus of research, there are many examples of circadian rhythms that persist when TTFLs are not functioning, and we lack any good candidates for the non-TTFL oscillators driving these rhythms. In this hypothesis-driven review, the author brings together several lines of evidence pointing towards the Target of Rapamycin (TOR) signalling pathway as a good candidate for a non-TTFL oscillator. TOR is a ubiquitous regulator of metabolism in eukaryotes and recent focus in circadian research on connections between metabolism and rhythms makes TOR an attractive candidate oscillator. In this paper, the evidence for a role for TOR in regulating rhythmicity is reviewed, and the advantages of TOR as a potential oscillator are discussed. Evidence for extensive feedback regulation of TOR provides potential mechanisms for a TOR-driven oscillator. Comparison with ultradian yeast metabolic cycles provides an example of a potential TOR-driven self-sustained oscillation. Unanswered questions and problems to be addressed by future research are discussed.
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7
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Zhang G, Li Y. Temperature compensation and entrainment in cyanobacteria circadian rhythm. Chronobiol Int 2023; 40:795-802. [PMID: 37154032 DOI: 10.1080/07420528.2023.2209643] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/09/2022] [Revised: 12/02/2022] [Accepted: 04/21/2023] [Indexed: 05/10/2023]
Abstract
Circadian rhythm is an endogenous rhythmic behavior of organisms used to adapt to the external environment. Although most biochemical reactions accelerate with increasing temperature, the period of circadian rhythms remains relatively stable across a range of temperature, a phenomenon known as temperature compensation. Meanwhile, circadian rhythms can be reset by environmental signals, such as daily periodic light or temperature, a phenomenon known as entrainment. Cyanobacteria are the simplest organisms to have circadian rhythms. The effect of light on cyanobacteria circadian rhythm has been widely studied with mathematical models. However, the effect of temperature on cyanobacteria circadian rhythm and the mechanisms of temperature compensation and entrainment are far from clear. In this paper, we apply a recent model to incorporate temperature dependence by Van't Hoff rule. With numerical simulation, we study the temperature compensation and entrainment in detail. The results show that the system can exhibit temperature compensation when the post-transcription process is insensitive to temperature. The temperature compensation is caused by the cancellation of the increase of amplitude and the acceleration of speed, resulting in the stable period, when the temperature rises. The system can also exhibit temperature entrainment in constant light in a very limited temperature range. When the periodic light is added simultaneously to simulate more realistic environment, the temperature range of entrainment is greatly improved. The results also suggest that long-day condition is conducive to entrainment. The findings of this paper provide a theoretical reference for biological research and help us understand the dynamical mechanisms of cyanobacteria circadian rhythm.
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Affiliation(s)
- Guangkun Zhang
- College of Information Technology, Shanghai Ocean University, Shanghai, China
| | - Ying Li
- College of Information Technology, Shanghai Ocean University, Shanghai, China
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8
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Seki M, Ito H. Evolution of self-sustained circadian rhythms is facilitated by seasonal change of daylight. Proc Biol Sci 2022; 289:20220577. [PMID: 36416042 PMCID: PMC9682437 DOI: 10.1098/rspb.2022.0577] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/24/2022] Open
Abstract
Self-sustained oscillation is a fundamental property of circadian rhythms and has been repeatedly tested since the early days of circadian research, resulting in the discovery of almost all organisms possessing self-sustained circadian oscillations. However, the evolutionary advantage of self-sustainability has been only speculatively discussed. In this theoretical study, we sought the environmental constraints and selection pressure that drive the acquisition or degeneration of self-sustainability through the process of evolution. We considered the dynamics of a gene regulatory network having a light input pathway under 12 h light and 12 h dark cycles or multiple day length conditions and then optimized the network structure using an evolutionary algorithm. By designing the fitness function in the evolutionary algorithm, we investigated the environmental conditions that led to the evolution of the self-sustained oscillators. Then, we found that self-sustained oscillation is rarer than damped oscillation and hourglass-type behaviour. Moreover, networks with self-sustainability have a markedly high fitness score when we assume that a network has to generate a constantly periodic expression profile regardless of day length. This study is, to our knowledge, the first to show that seasonality facilitated the evolution of the self-sustained circadian clock, which was consistent with empirical records.
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Affiliation(s)
- Motohide Seki
- Faculty of Design, Kyushu Univesity, Fukuoka 815-8540, Japan
- Institute for Asian and Oceanian Studies, Kyushu University, Fukuoka 819-0395, Japan
| | - Hiroshi Ito
- Faculty of Design, Kyushu Univesity, Fukuoka 815-8540, Japan
- Institute for Asian and Oceanian Studies, Kyushu University, Fukuoka 819-0395, Japan
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9
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Kim P, Thati N, Peshori S, Jang HI, Kim YI. Shift in Conformational Equilibrium Underlies the Oscillatory Phosphoryl Transfer Reaction in the Circadian Clock. Life (Basel) 2021; 11:life11101058. [PMID: 34685430 PMCID: PMC8538168 DOI: 10.3390/life11101058] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/14/2021] [Revised: 10/01/2021] [Accepted: 10/05/2021] [Indexed: 11/26/2022] Open
Abstract
Oscillatory phosphorylation/dephosphorylation can be commonly found in a biological system as a means of signal transduction though its pivotal presence in the workings of circadian clocks has drawn significant interest: for example in a significant portion of the physiology of Synechococcus elongatus PCC 7942. The biological oscillatory reaction in the cyanobacterial circadian clock can be visualized through its reconstitution in a test tube by mixing three proteins—KaiA, KaiB and KaiC—with adenosine triphosphate and magnesium ions. Surprisingly, the oscillatory phosphorylation/dephosphorylation of the hexameric KaiC takes place spontaneously and almost indefinitely in a test tube as long as ATP is present. This autonomous post-translational modification is tightly regulated by the conformational change of the C-terminal peptide of KaiC called the “A-loop” between the exposed and the buried states, a process induced by the time-course binding events of KaiA and KaiB to KaiC. There are three putative hydrogen-bond forming residues of the A-loop that are important for stabilizing its buried conformation. Substituting the residues with alanine enabled us to observe KaiB’s role in dephosphorylating hyperphosphorylated KaiC, independent of KaiA’s effect. We found a novel role of KaiB that its binding to KaiC induces the A-loop toward its buried conformation, which in turn activates the autodephosphorylation of KaiC. In addition to its traditional role of sequestering KaiA, KaiB’s binding contributes to the robustness of cyclic KaiC phosphorylation by inhibiting it during the dephosphorylation phase, effectively shifting the equilibrium toward the correct phase of the clock.
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Affiliation(s)
- Pyonghwa Kim
- Department of Chemistry and Environmental Science, New Jersey Institute of Technology, Newark, NJ 07102, USA;
| | - Neha Thati
- Department of Biological Sciences, New Jersey Institute of Technology, Newark, NJ 07102, USA; (N.T.); (S.P.)
| | - Shreya Peshori
- Department of Biological Sciences, New Jersey Institute of Technology, Newark, NJ 07102, USA; (N.T.); (S.P.)
| | - Hye-In Jang
- School of Cosmetic Science and Beauty Biotechnology, Semyung University, Jecheon 27136, Korea
- Correspondence: (H.-I.J.); (Y.-I.K.)
| | - Yong-Ick Kim
- Department of Chemistry and Environmental Science, New Jersey Institute of Technology, Newark, NJ 07102, USA;
- Institute for Brain and Neuroscience Research, New Jersey Institute of Technology, Newark, NJ 07102, USA
- Correspondence: (H.-I.J.); (Y.-I.K.)
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10
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From circadian clock mechanism to sleep disorders and jet lag: Insights from a computational approach. Biochem Pharmacol 2021; 191:114482. [DOI: 10.1016/j.bcp.2021.114482] [Citation(s) in RCA: 6] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/22/2020] [Revised: 02/15/2021] [Accepted: 02/16/2021] [Indexed: 12/13/2022]
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11
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Putker M, Wong DCS, Seinkmane E, Rzechorzek NM, Zeng A, Hoyle NP, Chesham JE, Edwards MD, Feeney KA, Fischer R, Peschel N, Chen K, Vanden Oever M, Edgar RS, Selby CP, Sancar A, O’Neill JS. CRYPTOCHROMES confer robustness, not rhythmicity, to circadian timekeeping. EMBO J 2021; 40:e106745. [PMID: 33491228 PMCID: PMC8013833 DOI: 10.15252/embj.2020106745] [Citation(s) in RCA: 14] [Impact Index Per Article: 4.7] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/09/2020] [Revised: 12/08/2020] [Accepted: 12/18/2020] [Indexed: 12/22/2022] Open
Abstract
Circadian rhythms are a pervasive property of mammalian cells, tissues and behaviour, ensuring physiological adaptation to solar time. Models of cellular timekeeping revolve around transcriptional feedback repression, whereby CLOCK and BMAL1 activate the expression of PERIOD (PER) and CRYPTOCHROME (CRY), which in turn repress CLOCK/BMAL1 activity. CRY proteins are therefore considered essential components of the cellular clock mechanism, supported by behavioural arrhythmicity of CRY-deficient (CKO) mice under constant conditions. Challenging this interpretation, we find locomotor rhythms in adult CKO mice under specific environmental conditions and circadian rhythms in cellular PER2 levels when CRY is absent. CRY-less oscillations are variable in their expression and have shorter periods than wild-type controls. Importantly, we find classic circadian hallmarks such as temperature compensation and period determination by CK1δ/ε activity to be maintained. In the absence of CRY-mediated feedback repression and rhythmic Per2 transcription, PER2 protein rhythms are sustained for several cycles, accompanied by circadian variation in protein stability. We suggest that, whereas circadian transcriptional feedback imparts robustness and functionality onto biological clocks, the core timekeeping mechanism is post-translational.
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Affiliation(s)
| | | | | | | | - Aiwei Zeng
- MRC Laboratory of Molecular BiologyCambridgeUK
| | | | | | - Mathew D Edwards
- MRC Laboratory of Molecular BiologyCambridgeUK
- Present address:
UCL Sainsbury Wellcome Centre for Neural Circuits and BehaviourLondonUK
| | | | | | | | - Ko‐Fan Chen
- Institute of NeurologyUniversity College LondonLondonUK
- Present address:
Department of Genetics and Genome BiologyUniversity of LeicesterLeicesterUK
| | | | | | - Christopher P Selby
- Department of Biochemistry and BiophysicsUniversity of North Carolina School of MedicineChapel HillNCUSA
| | - Aziz Sancar
- Department of Biochemistry and BiophysicsUniversity of North Carolina School of MedicineChapel HillNCUSA
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12
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Abstract
Circadian rhythms are constituted by a complex dynamical system with intertwined feedback loops, molecular switches, and self-sustained oscillations. Mathematical modeling supports understanding available heterogeneous kinetic data, highlights basic mechanisms, and can guide experimental research. Here, we introduce the basic steps from a biological question to simple models providing insight into gene-regulatory mechanisms. We illustrate the general approach by three examples: modeling decay processes, clock-controlled genes, and self-sustained oscillations.
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Affiliation(s)
- J Patrick Pett
- Institute for Theoretical Biology, Humboldt-Universität zu Berlin, Berlin, Germany
| | - Pål O Westermark
- Leibniz Institute for Farm Animal Biology, Institute of Genetics and Biometry, Dummerstorf, Germany
| | - Hanspeter Herzel
- Institute for Theoretical Biology, Charité-Universitätsmedizin Berlin, Berlin, Germany.
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13
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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 SciencesUniversity of ChicagoChicagoILUSA
| | - Danylo O Lavrentovich
- Department of ChemistryUniversity of ChicagoChicagoILUSA
- Present address:
Department of Organismic and Evolutionary BiologyHarvard UniversityCambridgeMAUSA
| | - Archana Chavan
- School of Natural SciencesUniversity of CaliforniaMercedCAUSA
| | - Eugene Leypunskiy
- Graduate Program in Biophysical SciencesUniversity of ChicagoChicagoILUSA
| | - Eileen Li
- Department of StatisticsUniversity of ChicagoChicagoILUSA
| | - Charles Matthews
- Department of StatisticsUniversity of ChicagoChicagoILUSA
- Present address:
School of MathematicsUniversity of EdinburghEdinburghUK
| | - Andy LiWang
- School of Natural SciencesUniversity of CaliforniaMercedCAUSA
- Quantitative and Systems BiologyUniversity of CaliforniaMercedCAUSA
- Center for Circadian BiologyUniversity of CaliforniaSan Diego, La JollaCAUSA
- Chemistry and Chemical BiologyUniversity of CaliforniaMercedCAUSA
- Health Sciences Research InstituteUniversity of CaliforniaMercedCAUSA
- Center for Cellular and Biomolecular MachinesUniversity of CaliforniaMercedCAUSA
| | - Michael J Rust
- Department of Molecular Genetics and Cell BiologyUniversity of ChicagoChicagoILUSA
- Institute for Biophysical DynamicsUniversity of ChicagoChicagoILUSA
- Institute for Genomics and Systems BiologyUniversity of ChicagoChicagoILUSA
| | - Aaron R Dinner
- Department of ChemistryUniversity of ChicagoChicagoILUSA
- Institute for Biophysical DynamicsUniversity of ChicagoChicagoILUSA
- James Franck InstituteUniversity of ChicagoChicagoILUSA
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14
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Kawamoto N, Ito H, Tokuda IT, Iwasaki H. Damped circadian oscillation in the absence of KaiA in Synechococcus. Nat Commun 2020; 11:2242. [PMID: 32382052 PMCID: PMC7205874 DOI: 10.1038/s41467-020-16087-x] [Citation(s) in RCA: 13] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/27/2019] [Accepted: 04/09/2020] [Indexed: 01/05/2023] Open
Abstract
Proteins KaiA, KaiB and KaiC constitute a biochemical circadian oscillator in the cyanobacterium Synechococcus elongatus. It has been reported kaiA inactivation completely abolishes circadian oscillations. However, we show here that kaiBC promoter activity exhibits a damped, low-amplitude oscillation with a period of approximately 24 h in kaiA-inactivated strains. The damped rhythm resonates with external cycles with a period of 24–26 h, indicating that its natural frequency is similar to that of the circadian clock. Double-mutation experiments reveal that kaiC, kaiB, and sasA (encoding a KaiC-binding histidine kinase) are all required for the damped oscillation. Further analysis suggests that the kaiA-less damped transcriptional rhythm requires KaiB-KaiC complex formation and the transcription-translation feedback loop, but not the KaiC phosphorylation cycle. Our results provide insights into mechanisms that could potentially underlie the diurnal/circadian behaviors observed in other bacterial species that possess kaiB and kaiC homologues but lack a kaiA homologue. Proteins KaiA, KaiB and KaiC constitute a biochemical circadian oscillator in Synechococcus cyanobacteria. Here, Kawamoto et al. show that kaiBC promoter activity exhibits a damped, low-amplitude circadian oscillation in the absence of KaiA, which could explain the circadian rhythms observed in other bacteria that lack a kaiA homologue.
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Affiliation(s)
- Naohiro Kawamoto
- Department of Electrical Engineering and Biological Science, Waseda University, Tokyo, 162-0056, Japan
| | - Hiroshi Ito
- Faculty of Design, Kyushu University, Fukuoka, 815-8540, Japan
| | - Isao T Tokuda
- Graduate School of Science and Engineering, Ritsumeikan University, Shiga, 525-8577, Japan
| | - Hideo Iwasaki
- Department of Electrical Engineering and Biological Science, Waseda University, Tokyo, 162-0056, Japan.
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15
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Golden SS. Principles of rhythmicity emerging from cyanobacteria. Eur J Neurosci 2019; 51:13-18. [PMID: 31087440 DOI: 10.1111/ejn.14434] [Citation(s) in RCA: 7] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/14/2019] [Accepted: 05/08/2019] [Indexed: 12/21/2022]
Affiliation(s)
- Susan S Golden
- Center for Circadian Biology and Division of Biological Sciences, University of California, San Diego, California
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16
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Adeola HA, Papagerakis S, Papagerakis P. Systems Biology Approaches and Precision Oral Health: A Circadian Clock Perspective. Front Physiol 2019; 10:399. [PMID: 31040792 PMCID: PMC6476986 DOI: 10.3389/fphys.2019.00399] [Citation(s) in RCA: 12] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/05/2018] [Accepted: 03/22/2019] [Indexed: 12/20/2022] Open
Abstract
A vast majority of the pathophysiological and metabolic processes in humans are temporally controlled by a master circadian clock located centrally in the hypothalamic suprachiasmatic nucleus of the brain, as well as by specialized peripheral oscillators located in other body tissues. This circadian clock system generates a rhythmical diurnal transcriptional-translational cycle in clock genes and protein expression and activities regulating numerous downstream target genes. Clock genes as key regulators of physiological function and dysfunction of the circadian clock have been linked to various diseases and multiple morbidities. Emerging omics technologies permits largescale multi-dimensional investigations of the molecular landscape of a given disease and the comprehensive characterization of its underlying cellular components (e.g., proteins, genes, lipids, metabolites), their mechanism of actions, functional networks and regulatory systems. Ultimately, they can be used to better understand disease and interpatient heterogeneity, individual profile, identify personalized targetable key molecules and pathways, discover novel biomarkers and genetic alterations, which collectively can allow for a better patient stratification into clinically relevant subgroups to improve disease prediction and prevention, early diagnostic, clinical outcomes, therapeutic benefits, patient's quality of life and survival. The use of “omics” technologies has allowed for recent breakthroughs in several scientific domains, including in the field of circadian clock biology. Although studies have explored the role of clock genes using circadiOmics (which integrates circadian omics, such as genomics, transcriptomics, proteomics and metabolomics) in human disease, no such studies have investigated the implications of circadian disruption in oral, head and neck pathologies using multi-omics approaches and linking the omics data to patient-specific circadian profiles. There is a burgeoning body of evidence that circadian clock controls the development and homeostasis of oral and maxillofacial structures, such as salivary glands, teeth and oral epithelium. Hence, in the current era of precision medicine and dentistry and patient-centered health care, it is becoming evident that a multi-omics approach is needed to improve our understanding of the role of circadian clock-controlled key players in the regulation of head and neck pathologies. This review discusses current knowledge on the role of the circadian clock and the contribution of omics-based approaches toward a novel precision health era for diagnosing and treating head and neck pathologies, with an emphasis on oral, head and neck cancer and Sjögren's syndrome.
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Affiliation(s)
- Henry A Adeola
- Hair and Skin Research Laboratory, Division of Dermatology, Department of Medicine, Faculty of Health Sciences and Groote Schuur Hospital, University of Cape Town, Cape Town, South Africa.,Department of Oral and Maxillofacial Pathology, Faculty of Dentistry, University of the Western Cape and Tygerberg Hospital, Cape Town, South Africa
| | - Silvana Papagerakis
- Laboratory of Oral, Head & Neck Cancer-Personalized Diagnostics and Therapeutics, Division of Head and Neck Surgery, Department of Surgery, University of Saskatchewan, Saskatoon, SK, Canada
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17
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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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18
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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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19
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Circadian clock component PERIOD2 regulates diurnal expression of Na +/H + exchanger regulatory factor-1 and its scaffolding function. Sci Rep 2018; 8:9072. [PMID: 29899468 PMCID: PMC5998136 DOI: 10.1038/s41598-018-27280-w] [Citation(s) in RCA: 7] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/25/2017] [Accepted: 06/01/2018] [Indexed: 11/30/2022] Open
Abstract
A number of diverse cell-surface proteins are anchored to the cytoskeleton via scaffold proteins. Na+/H+ exchanger regulatory factor-1 (NHERF1), encoded by the Slc9a3r1 gene, functions as a scaffold protein, which is implicated in the regulation of membrane expression of various cell-surface proteins. Here, we demonstrate that the circadian clock component PERIOD2 (PER2) modulates transcription of the mouse Slc9a3r1 gene, generating diurnal accumulation of NHERF1 in the mouse liver. Basal expression of Slc9a3r1 was dependent on transcriptional activation by p65/p50. PER2 bound to p65 protein and prevented p65/p50-mediated transactivation of Slc9a3r1. The time-dependent interaction between PER2 and p65 underlay diurnal oscillation in the hepatic expression of Slc9a3r1/NHERF1. The results of immunoprecipitation experiments and liquid chromatography-mass spectrometry analysis of mouse liver revealed that NHERF1 time-dependently interacted with fatty acid transport protein-5 (FATP5). Temporary accumulation of NHERF1 protein stabilized plasmalemmal localization of FATP5, thereby enhancing hepatic uptake of fatty acids at certain times of the day. Our results suggest an unacknowledged role for PER2 in regulating the diurnal expression of NHERF1 in mouse liver. This machinery also contributed to diurnal changes in the ability of hepatic cells to uptake fatty acids.
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20
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Kinoshita C, Aoyama K, Nakaki T. Neuroprotection afforded by circadian regulation of intracellular glutathione levels: A key role for miRNAs. Free Radic Biol Med 2018; 119:17-33. [PMID: 29198727 DOI: 10.1016/j.freeradbiomed.2017.11.023] [Citation(s) in RCA: 21] [Impact Index Per Article: 3.5] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 07/28/2017] [Revised: 11/21/2017] [Accepted: 11/27/2017] [Indexed: 01/17/2023]
Abstract
Circadian rhythms are approximately 24-h oscillations of physiological and behavioral processes that allow us to adapt to daily environmental cycles. Like many other biological functions, cellular redox status and antioxidative defense systems display circadian rhythmicity. In the central nervous system (CNS), glutathione (GSH) is a critical antioxidant because the CNS is extremely vulnerable to oxidative stress; oxidative stress, in turn, causes several fatal diseases, including neurodegenerative diseases. It has long been known that GSH level shows circadian rhythm, although the mechanism underlying GSH rhythm production has not been well-studied. Several lines of recent evidence indicate that the expression of antioxidant genes involved in GSH homeostasis as well as circadian clock genes are regulated by post-transcriptional regulator microRNA (miRNA), indicating that miRNA plays a key role in generating GSH rhythm. Interestingly, several reports have shown that alterations of miRNA expression as well as circadian rhythm have been known to link with various diseases related to oxidative stress. A growing body of evidence implicates a strong correlation between antioxidative defense, circadian rhythm and miRNA function, therefore, their dysfunctions could cause numerous diseases. It is hoped that continued elucidation of the antioxidative defense systems controlled by novel miRNA regulation under circadian control will advance the development of therapeutics for the diseases caused by oxidative stress.
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Affiliation(s)
- Chisato Kinoshita
- Department of Pharmacology, Teikyo University School of Medicine, 2-11-1 Kaga, Itabashi-ku, Tokyo 173-8605, Japan
| | - Koji Aoyama
- Department of Pharmacology, Teikyo University School of Medicine, 2-11-1 Kaga, Itabashi-ku, Tokyo 173-8605, Japan
| | - Toshio Nakaki
- Department of Pharmacology, Teikyo University School of Medicine, 2-11-1 Kaga, Itabashi-ku, Tokyo 173-8605, Japan.
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21
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Piechura JR, Amarnath K, O'Shea EK. Natural changes in light interact with circadian regulation at promoters to control gene expression in cyanobacteria. eLife 2017; 6:32032. [PMID: 29239721 PMCID: PMC5785211 DOI: 10.7554/elife.32032] [Citation(s) in RCA: 21] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/15/2017] [Accepted: 12/13/2017] [Indexed: 12/31/2022] Open
Abstract
The circadian clock interacts with other regulatory pathways to tune physiology to predictable daily changes and unexpected environmental fluctuations. However, the complexity of circadian clocks in higher organisms has prevented a clear understanding of how natural environmental conditions affect circadian clocks and their physiological outputs. Here, we dissect the interaction between circadian regulation and responses to fluctuating light in the cyanobacterium Synechococcus elongatus. We demonstrate that natural changes in light intensity substantially affect the expression of hundreds of circadian-clock-controlled genes, many of which are involved in key steps of metabolism. These changes in expression arise from circadian and light-responsive control of RNA polymerase recruitment to promoters by a network of transcription factors including RpaA and RpaB. Using phenomenological modeling constrained by our data, we reveal simple principles that underlie the small number of stereotyped responses of dusk circadian genes to changes in light. Living things face daily, predictable challenges due to the regular day and night cycle imposed by the Earth’s rotation. Many of them have evolved an internal ‘circadian’ clock to anticipate daily changes in the environment. However, nature can also change in unpredictable ways, and in order to survive, organisms must account for both the time of day stipulated by their clocks and changes in their present environment. For example, cyanobacteria depend on the sun for survival and must cope with light variations throughout the day and the absence of light at nighttime. Circadian clocks are made up of specific genes and their proteins. Most of what we know about how these clocks control the behavior of an organism comes from experiments performed under constant conditions. Previous research has shown that under such circumstances, the circadian clock of cyanobacteria periodically turns on a set of genes every 24 hours via a protein called RpaA. However, to understand how cyanobacteria use this clock, we must know how it works in a fluctuating environment. To test this, Piechura, Amarnath and O’Shea measured the activation of genes in cyanobacteria that had been exposed to changes in light mimicking those in nature. Compared to constant conditions, fluctuating light drastically changed the timing of activation of circadian genes. When light decreased – as it would in nature during sunset or if a cloud blocks the sun – the circadian genes were activated. Changes in light did not change the ‘ticking’ of the clock, but did affect the ability of RpaA to turn on circadian genes. Moreover, the activity of a second protein called RpaB increased when light decreased and the genes were activated. Thus, cyanobacteria switch on circadian genes as the sun is setting or during unexpected shade, likely through RpaA and RpaB, to help them survive without light. This study shows that circadian clocks activate genes differently in the real world compared to unnatural, constant conditions. This may prompt scientists to think carefully about how an organism’s natural environment can affect its inner workings. A next step will be to see how else light affects circadian gene levels. A deeper understanding of how cyanobacteria control their genes in a natural environment will be useful for scientists who engineer these organisms to produce biofuels from sunlight.
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Affiliation(s)
- Joseph Robert Piechura
- Department of Molecular and Cellular Biology, Harvard University, Cambridge, United States.,FAS Center for Systems Biology, Harvard University, Cambridge, United States.,Howard Hughes Medical Institute, Harvard University, Cambridge, United States
| | - Kapil Amarnath
- FAS Center for Systems Biology, Harvard University, Cambridge, United States.,Howard Hughes Medical Institute, Harvard University, Cambridge, United States
| | - Erin K O'Shea
- Department of Molecular and Cellular Biology, Harvard University, Cambridge, United States.,FAS Center for Systems Biology, Harvard University, Cambridge, United States.,Howard Hughes Medical Institute, Harvard University, Cambridge, United States.,Department of Chemistry and Chemical Biology, Harvard University, Cambridge, United States
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22
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Egli M. Architecture and mechanism of the central gear in an ancient molecular timer. J R Soc Interface 2017; 14:rsif.2016.1065. [PMID: 28330987 DOI: 10.1098/rsif.2016.1065] [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: 12/31/2016] [Accepted: 02/27/2017] [Indexed: 12/16/2022] Open
Abstract
Molecular clocks are the product of natural selection in organisms from bacteria to human and their appearance early in evolution such as in the prokaryotic cyanobacterium Synechococcus elongatus suggests that these timers served a crucial role in genetic fitness. Thus, a clock allows cyanobacteria relying on photosynthesis and nitrogen fixation to temporally space the two processes and avoid exposure of nitrogenase carrying out fixation to high levels of oxygen produced during photosynthesis. Fascinating properties of molecular clocks are the long time constant, their precision and temperature compensation. Although these are hallmarks of all circadian oscillators, the actual cogs and gears that control clocks vary widely between organisms, indicating that circadian timers evolved convergently multiple times, owing to the selective pressure of an environment with a daily light/dark cycle. In S. elongatus, the three proteins KaiA, KaiB and KaiC in the presence of ATP constitute a so-called post-translational oscillator (PTO). The KaiABC PTO can be reconstituted in an Eppendorf tube and keeps time in a temperature-compensated manner. The ease by which the KaiABC clock can be studied in vitro has made it the best-investigated molecular clock system. Over the last decade, structures of all three Kai proteins and some of their complexes have emerged and mechanistic aspects have been analysed in considerable detail. This review focuses on the central gear of the S. elongatus clock and only enzyme among the three proteins: KaiC. Our determination of the three-dimensional structure of KaiC early in the quest for a better understanding of the inner workings of the cyanobacterial timer revealed its unusual architecture and conformational differences and unique features of the two RecA-like domains constituting KaiC. The structure also pinpointed phosphorylation sites and differential interactions with ATP molecules at subunit interfaces, and helped guide experiments to ferret out mechanistic aspects of the ATPase, auto-phosphorylation and auto-dephosphorylation reactions catalysed by the homo-hexamer. Comparisons between the structure of KaiC and those of nanomachines such as F1-ATPase and CaMKII also exposed shared architectural features (KaiC/ATPase), mechanistic principles (KaiC/CaMKII) and phenomena, such as subunit exchange between hexameric particles critical for function (clock synchronization, KaiABC; memory-storage, CaMKII).
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Affiliation(s)
- Martin Egli
- Department of Biochemistry, Vanderbilt University, Nashville, TN 37232, USA
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23
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Gan S, O'Shea EK. An Unstable Singularity Underlies Stochastic Phasing of the Circadian Clock in Individual Cyanobacterial Cells. Mol Cell 2017; 67:659-672.e12. [PMID: 28803778 DOI: 10.1016/j.molcel.2017.07.015] [Citation(s) in RCA: 11] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/24/2017] [Revised: 03/18/2017] [Accepted: 07/12/2017] [Indexed: 11/19/2022]
Abstract
The endogenous circadian clock synchronizes with environmental time by appropriately resetting its phase in response to external cues. Of note, some resetting stimuli induce attenuated oscillations of clock output, which has been observed at the population-level in several organisms and in studies of individual humans. To investigate what is happening in individual cellular clocks, we studied the unicellular cyanobacterium S. elongatus. By measuring its phase-resetting responses to temperature changes, we found that population-level arrhythmicity occurs when certain perturbations cause stochastic phases of oscillations in individual cells. Combining modeling with experiments, we related stochastic phasing to the dynamical structure of the cyanobacterial clock as an oscillator and explored the physiological relevance of the oscillator structure for accurately timed rhythmicity in changing environmental conditions. Our findings and approach can be applied to other biological oscillators.
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Affiliation(s)
- Siting Gan
- Howard Hughes Medical Institute, Harvard University Faculty of Arts and Sciences Center for Systems Biology, Harvard University, Cambridge, MA 02138, USA; Harvard Systems Biology Ph.D. Program, Harvard University, Cambridge, MA 02138, USA
| | - Erin K O'Shea
- Howard Hughes Medical Institute, Harvard University Faculty of Arts and Sciences Center for Systems Biology, Harvard University, Cambridge, MA 02138, USA; Department of Molecular and Cellular Biology, Harvard University, Cambridge, MA 02138, USA; Department of Chemistry and Chemical Biology, Harvard University, Cambridge, MA 02138, USA.
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24
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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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25
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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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26
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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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27
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Westermark S, Steuer R. Toward Multiscale Models of Cyanobacterial Growth: A Modular Approach. Front Bioeng Biotechnol 2016; 4:95. [PMID: 28083530 PMCID: PMC5183639 DOI: 10.3389/fbioe.2016.00095] [Citation(s) in RCA: 17] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/18/2016] [Accepted: 12/09/2016] [Indexed: 11/29/2022] Open
Abstract
Oxygenic photosynthesis dominates global primary productivity ever since its evolution more than three billion years ago. While many aspects of phototrophic growth are well understood, it remains a considerable challenge to elucidate the manifold dependencies and interconnections between the diverse cellular processes that together facilitate the synthesis of new cells. Phototrophic growth involves the coordinated action of several layers of cellular functioning, ranging from the photosynthetic light reactions and the electron transport chain, to carbon-concentrating mechanisms and the assimilation of inorganic carbon. It requires the synthesis of new building blocks by cellular metabolism, protection against excessive light, as well as diurnal regulation by a circadian clock and the orchestration of gene expression and cell division. Computational modeling allows us to quantitatively describe these cellular functions and processes relevant for phototrophic growth. As yet, however, computational models are mostly confined to the inner workings of individual cellular processes, rather than describing the manifold interactions between them in the context of a living cell. Using cyanobacteria as model organisms, this contribution seeks to summarize existing computational models that are relevant to describe phototrophic growth and seeks to outline their interactions and dependencies. Our ultimate aim is to understand cellular functioning and growth as the outcome of a coordinated operation of diverse yet interconnected cellular processes.
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Affiliation(s)
- Stefanie Westermark
- Fachinstitut für Theoretische Biologie (ITB), Institut für Biologie, Humboldt-Universität zu Berlin , Berlin , Germany
| | - Ralf Steuer
- Fachinstitut für Theoretische Biologie (ITB), Institut für Biologie, Humboldt-Universität zu Berlin , Berlin , Germany
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Guerreiro AC, Penning R, Raaijmakers LM, Axman IM, Heck AJ, Altelaar AM. Monitoring light/dark association dynamics of multi-protein complexes in cyanobacteria using size exclusion chromatography-based proteomics. J Proteomics 2016; 142:33-44. [DOI: 10.1016/j.jprot.2016.04.030] [Citation(s) in RCA: 9] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/18/2015] [Revised: 03/11/2016] [Accepted: 04/19/2016] [Indexed: 01/18/2023]
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Discrete gene replication events drive coupling between the cell cycle and circadian clocks. Proc Natl Acad Sci U S A 2016; 113:4063-8. [PMID: 27035936 DOI: 10.1073/pnas.1507291113] [Citation(s) in RCA: 40] [Impact Index Per Article: 5.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/25/2022] Open
Abstract
Many organisms possess both a cell cycle to control DNA replication and a circadian clock to anticipate changes between day and night. In some cases, these two rhythmic systems are known to be coupled by specific, cross-regulatory interactions. Here, we use mathematical modeling to show that, additionally, the cell cycle generically influences circadian clocks in a nonspecific fashion: The regular, discrete jumps in gene-copy number arising from DNA replication during the cell cycle cause a periodic driving of the circadian clock, which can dramatically alter its behavior and impair its function. A clock built on negative transcriptional feedback either phase-locks to the cell cycle, so that the clock period tracks the cell division time, or exhibits erratic behavior. We argue that the cyanobacterium Synechococcus elongatus has evolved two features that protect its clock from such disturbances, both of which are needed to fully insulate it from the cell cycle and give it its observed robustness: a phosphorylation-based protein modification oscillator, together with its accompanying push-pull read-out circuit that responds primarily to the ratios of different phosphoform concentrations, makes the clock less susceptible to perturbations in protein synthesis; the presence of multiple, asynchronously replicating copies of the same chromosome diminishes the effect of replicating any single copy of a gene.
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Qin X, Mori T, Zhang Y, Johnson CH. PER2 Differentially Regulates Clock Phosphorylation versus Transcription by Reciprocal Switching of CK1ε Activity. J Biol Rhythms 2016; 30:206-16. [PMID: 25994100 DOI: 10.1177/0748730415582127] [Citation(s) in RCA: 15] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/14/2023]
Abstract
Casein kinase 1ε (CK1ε) performs key phosphorylation reactions in the circadian clock mechanism that determine period. We show that the central clock protein PERIOD2 (PER2) not only acts as a transcriptional repressor but also inhibits the autoinactivation of CK1ε, thereby promoting CK1ε activity. Moreover, PER2 reciprocally regulates CK1ε's ability to phosphorylate other substrates. On output pathway substrates (e.g., P53), PER2 inhibits the activity of CK1ε. However, in the case of central clock proteins (e.g., CRYPTOCHROME2), PER2 stimulates the CK1ε-mediated phosphorylation of CRY2. CK1ε activity is temperature compensated on the core clock substrate CRY2 but not on output substrates, for example, the physiological output protein substrate P53 and its nonphysiological correlate, bovine serum albumin (BSA). These results indicate heretofore unrecognized pivotal roles of PER2; it not only regulates the central transcription/translation feedback loop but also differentially controls kinase activity CK1ε in its phosphorylation of central clock (e.g., CRY2) versus output (e.g., P53) substrates.
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Affiliation(s)
- Ximing Qin
- Department of Biological Sciences, Vanderbilt University, Nashville, Tennessee
| | - Tetsuya Mori
- Department of Biological Sciences, Vanderbilt University, Nashville, Tennessee
| | - Yunfei Zhang
- Department of Biological Sciences, Vanderbilt University, Nashville, Tennessee
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Hatakeyama TS, Kaneko K. Reciprocity Between Robustness of Period and Plasticity of Phase in Biological Clocks. PHYSICAL REVIEW LETTERS 2015; 115:218101. [PMID: 26636874 DOI: 10.1103/physrevlett.115.218101] [Citation(s) in RCA: 18] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 05/26/2015] [Indexed: 06/05/2023]
Abstract
Circadian clocks exhibit the robustness of period and plasticity of phase against environmental changes such as temperature and nutrient conditions. Thus far, however, it is unclear how both are simultaneously achieved. By investigating distinct models of circadian clocks, we demonstrate reciprocity between robustness and plasticity: higher robustness in the period implies higher plasticity in the phase, where changes in period and in phase follow a linear relationship with a negative coefficient. The robustness of period is achieved by the adaptation on the limit cycle via a concentration change of a buffer molecule, whose temporal change leads to a phase shift following a shift of the limit-cycle orbit in phase space. Generality of reciprocity in clocks with the adaptation mechanism is confirmed with theoretical analysis of simple models, while biological significance is discussed.
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Affiliation(s)
- Tetsuhiro S Hatakeyama
- Department of Basic Science, The University of Tokyo, 3-8-1 Komaba, Meguro-ku, Tokyo 153-8902, Japan
| | - Kunihiko Kaneko
- Department of Basic Science, The University of Tokyo, 3-8-1 Komaba, Meguro-ku, Tokyo 153-8902, Japan
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32
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Abstract
For a biological oscillator to function as a circadian pacemaker that confers a fitness advantage, its timing functions must be stable in response to environmental and metabolic fluctuations. One such stability enhancer, temperature compensation, has long been a defining characteristic of these timekeepers. However, an accurate biological timekeeper must also resist changes in metabolism, and this review suggests that temperature compensation is actually a subset of a larger phenomenon, namely metabolic compensation, which maintains the frequency of circadian oscillators in response to a host of factors that impinge on metabolism and would otherwise destabilize these clocks. The circadian system of prokaryotic cyanobacteria is an illustrative model because it is composed of transcriptional and nontranscriptional oscillators that are coupled to promote resilience. Moreover, the cyanobacterial circadian program regulates gene activity and metabolic pathways, and it can be manipulated to improve the expression of bioproducts that have practical value.
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33
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Affiliation(s)
- Martin Egli
- Department
of Biochemistry, Vanderbilt University,
School of Medicine, Nashville, Tennessee 37232, United States
| | - Carl H. Johnson
- Department
of Biological Sciences, College of Arts and Science, Vanderbilt University, Nashville, Tennessee 37235, United States
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34
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Abstract
Structural approaches have provided insight into the mechanisms of circadian clock oscillators. This review focuses upon the myriad structural methods that have been applied to the molecular architecture of cyanobacterial circadian proteins, their interactions with each other, and the mechanism of the KaiABC posttranslational oscillator. X-ray crystallography and solution NMR were deployed to gain an understanding of the three-dimensional structures of the three proteins KaiA, KaiB, and KaiC that make up the inner timer in cyanobacteria. A hybrid structural biology approach including crystallography, electron microscopy, and solution scattering has shed light on the shapes of binary and ternary Kai protein complexes. Structural studies of the cyanobacterial oscillator demonstrate both the strengths and the limitations of the divide-and-conquer strategy. Thus, investigations of complexes involving domains and/or peptides have afforded valuable information into Kai protein interactions. However, high-resolution structural data are still needed at the level of complexes between the 360-kDa KaiC hexamer that forms the heart of the clock and its KaiA and KaiB partners.
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35
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Effect of the Min system on timing of cell division in Escherichia coli. PLoS One 2014; 9:e103863. [PMID: 25090009 PMCID: PMC4121188 DOI: 10.1371/journal.pone.0103863] [Citation(s) in RCA: 9] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/28/2014] [Accepted: 07/03/2014] [Indexed: 11/19/2022] Open
Abstract
In Escherichia coli the Min protein system plays an important role in positioning the division site. We show that this system also has an effect on timing of cell division. We do this in a quantitative way by measuring the cell division waiting time (defined as time difference between appearance of a division site and the division event) and the Z-ring existence time. Both quantities are found to be different in WT and cells without functional Min system. We develop a series of theoretical models whose predictions are compared with the experimental findings. Continuous improvement leads to a final model that is able to explain all relevant experimental observations. In particular, it shows that the chromosome segregation defect caused by the absence of Min proteins has an important influence on timing of cell division. Our results indicate that the Min system affects the septum formation rate. In the absence of the Min proteins this rate is reduced, leading to the observed strongly randomized cell division events and the longer division waiting times.
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36
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O'Neill JS, Feeney KA. Circadian redox and metabolic oscillations in mammalian systems. Antioxid Redox Signal 2014; 20:2966-81. [PMID: 24063592 PMCID: PMC4038991 DOI: 10.1089/ars.2013.5582] [Citation(s) in RCA: 31] [Impact Index Per Article: 3.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 09/10/2013] [Accepted: 09/25/2013] [Indexed: 01/06/2023]
Abstract
SIGNIFICANCE A substantial proportion of mammalian physiology is organized around the day/night cycle, being regulated by the co-ordinated action of numerous cell-autonomous circadian oscillators throughout the body. Disruption of internal timekeeping, by genetic or environmental perturbation, leads to metabolic dysregulation, whereas changes in metabolism affect timekeeping. RECENT ADVANCES While gene expression cycles are essential for the temporal coordination of normal physiology, it has become clear that rhythms in metabolism and redox balance are cell-intrinsic phenomena, which may regulate gene expression cycles reciprocally, but persist in their absence. For example, a circadian rhythm in peroxiredoxin oxidation was recently observed in isolated human erythrocytes, fibroblast cell lines in vitro, and mouse liver in vivo. CRITICAL ISSUES Mammalian timekeeping is a cellular phenomenon. While we understand many of the cellular systems that contribute to this biological oscillation's fidelity and robustness, a comprehensive mechanistic understanding remains elusive. Moreover, the formerly clear distinction between "core clock components" and rhythmic cellular outputs is blurred since several outputs, for example, redox balance, can feed back to regulate timekeeping. As with any cyclical system, establishing causality becomes problematic. FUTURE DIRECTIONS A detailed molecular understanding of the temporal crosstalk between cellular systems, and the coincidence detection mechanisms that allow a cell to discriminate clock-relevant from irrelevant stimuli, will be essential as we move toward an integrated model of how this daily biological oscillation works. Such knowledge will highlight new avenues by which the functional consequences of circadian timekeeping can be explored in the context of human health and disease.
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Affiliation(s)
- John S O'Neill
- MRC Laboratory of Molecular Biology , Cambridge, United Kingdom
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37
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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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38
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Pattanayek R, Xu Y, Lamichhane A, Johnson CH, Egli M. An arginine tetrad as mediator of input-dependent and input-independent ATPases in the clock protein KaiC. ACTA CRYSTALLOGRAPHICA. SECTION D, BIOLOGICAL CRYSTALLOGRAPHY 2014; 70:1375-90. [PMID: 24816106 PMCID: PMC4722857 DOI: 10.1107/s1399004714003228] [Citation(s) in RCA: 12] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 12/20/2013] [Accepted: 02/12/2014] [Indexed: 11/10/2022]
Abstract
A post-translational oscillator (PTO) composed of the proteins KaiA, KaiB and KaiC is at the heart of the cyanobacterial circadian clock. KaiC interacts with KaiA and KaiB over the daily cycle, and CII domains undergo rhythmic phosphorylation/dephosphorylation with a 24 h period. Both the N-terminal (CI) and C-terminal (CII) rings of KaiC exhibit ATPase activity. The CI ATPase proceeds in an input-independent fashion, but the CII ATPase is subject to metabolic input signals. The crystal structure of KaiC from Thermosynechococcus elongatus allows insight into the different anatomies of the CI and CII ATPases. Four consecutive arginines in CI (Arg linker) that connect the P-loop, CI subunits and CI and CII at the ring interface are primary candidates for the coordination of the CI and CII activities. The mutation of linker residues alters the period or triggers arhythmic behavior. Comparison between the CI and CII structures also reveals differences in loop regions that are key to KaiA and KaiB binding and activation of CII ATPase and kinase. Common packing features in KaiC crystals shed light on the KaiB-KaiC interaction.
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Affiliation(s)
- Rekha Pattanayek
- Department of Biochemistry, School of Medicine, Vanderbilt University, Nashville, TN 37232, USA
| | - Yao Xu
- Department of Biological Sciences, College of Arts and Science, Vanderbilt University, Nashville, TN 35235, USA
| | - Aashish Lamichhane
- Department of Biochemistry, School of Medicine, Vanderbilt University, Nashville, TN 37232, USA
| | - Carl H. Johnson
- Department of Biological Sciences, College of Arts and Science, Vanderbilt University, Nashville, TN 35235, USA
| | - Martin Egli
- Department of Biochemistry, School of Medicine, Vanderbilt University, Nashville, TN 37232, USA
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39
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Guerreiro ACL, Benevento M, Lehmann R, van Breukelen B, Post H, Giansanti P, Maarten Altelaar AF, Axmann IM, Heck AJR. Daily rhythms in the cyanobacterium synechococcus elongatus probed by high-resolution mass spectrometry-based proteomics reveals a small defined set of cyclic proteins. Mol Cell Proteomics 2014; 13:2042-55. [PMID: 24677030 DOI: 10.1074/mcp.m113.035840] [Citation(s) in RCA: 64] [Impact Index Per Article: 6.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/29/2022] Open
Abstract
Circadian rhythms are self-sustained and adjustable cycles, typically entrained with light/dark and/or temperature cycles. These rhythms are present in animals, plants, fungi, and several bacteria. The central mechanism behind these "pacemakers" and the connection to the circadian regulated pathways are still poorly understood. The circadian rhythm of the cyanobacterium Synechococcus elongatus PCC 7942 (S. elongatus) is highly robust and controlled by only three proteins, KaiA, KaiB, and KaiC. This central clock system has been extensively studied functionally and structurally and can be reconstituted in vitro. These characteristics, together with a relatively small genome (2.7 Mbp), make S. elongatus an ideal model system for the study of circadian rhythms. Different approaches have been used to reveal the influence of the central S. elongatus clock on rhythmic gene expression, rhythmic mRNA abundance, rhythmic DNA topology changes, and cell division. However, a global analysis of its proteome dynamics has not been reported yet. To uncover the variation in protein abundances during 48 h under light and dark cycles (12:12 h), we used quantitative proteomics, with TMT 6-plex isobaric labeling. We queried the S. elongatus proteome at 10 different time points spanning a single 24-h period, leading to 20 time points over the full 48-h period. Employing multidimensional separation and high-resolution mass spectrometry, we were able to find evidence for a total of 82% of the S. elongatus proteome. Of the 1537 proteins quantified over the time course of the experiment, only 77 underwent significant cyclic variations. Interestingly, our data provide evidence for in- and out-of-phase correlation between mRNA and protein levels for a set of specific genes and proteins. As a range of cyclic proteins are functionally not well annotated, this work provides a resource for further studies to explore the role of these proteins in the cyanobacterial circadian rhythm.
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Affiliation(s)
- Ana C L Guerreiro
- From the ‡Biomolecular Mass Spectrometry and Proteomics Group, Utrecht Institute for Pharmaceutical Sciences and Bijvoet Centre for Biomolecular Research, Utrecht University, Padualaan 8, 3584 CH Utrecht, The Netherlands; §Netherlands Proteomics Centre, Padualaan 8, 3584 CH Utrecht, The Netherlands
| | - Marco Benevento
- From the ‡Biomolecular Mass Spectrometry and Proteomics Group, Utrecht Institute for Pharmaceutical Sciences and Bijvoet Centre for Biomolecular Research, Utrecht University, Padualaan 8, 3584 CH Utrecht, The Netherlands; §Netherlands Proteomics Centre, Padualaan 8, 3584 CH Utrecht, The Netherlands
| | - Robert Lehmann
- ¶Institute for Theoretical Biology (ITB), Humboldt-Universitaet zu Berlin, Invalidenstrasse 43, D-10115 Berlin, Germany
| | - Bas van Breukelen
- From the ‡Biomolecular Mass Spectrometry and Proteomics Group, Utrecht Institute for Pharmaceutical Sciences and Bijvoet Centre for Biomolecular Research, Utrecht University, Padualaan 8, 3584 CH Utrecht, The Netherlands; §Netherlands Proteomics Centre, Padualaan 8, 3584 CH Utrecht, The Netherlands
| | - Harm Post
- From the ‡Biomolecular Mass Spectrometry and Proteomics Group, Utrecht Institute for Pharmaceutical Sciences and Bijvoet Centre for Biomolecular Research, Utrecht University, Padualaan 8, 3584 CH Utrecht, The Netherlands; §Netherlands Proteomics Centre, Padualaan 8, 3584 CH Utrecht, The Netherlands
| | - Piero Giansanti
- From the ‡Biomolecular Mass Spectrometry and Proteomics Group, Utrecht Institute for Pharmaceutical Sciences and Bijvoet Centre for Biomolecular Research, Utrecht University, Padualaan 8, 3584 CH Utrecht, The Netherlands; §Netherlands Proteomics Centre, Padualaan 8, 3584 CH Utrecht, The Netherlands
| | - A F Maarten Altelaar
- From the ‡Biomolecular Mass Spectrometry and Proteomics Group, Utrecht Institute for Pharmaceutical Sciences and Bijvoet Centre for Biomolecular Research, Utrecht University, Padualaan 8, 3584 CH Utrecht, The Netherlands; §Netherlands Proteomics Centre, Padualaan 8, 3584 CH Utrecht, The Netherlands;
| | - Ilka M Axmann
- ¶Institute for Theoretical Biology (ITB), Humboldt-Universitaet zu Berlin, Invalidenstrasse 43, D-10115 Berlin, Germany; **Institute for Synthetic Microbiology, Heinrich-Heine-Universitaet Duesseldorf, Universitaetsstrasse 1, D-40225 Duesseldorf, Germany
| | - Albert J R Heck
- From the ‡Biomolecular Mass Spectrometry and Proteomics Group, Utrecht Institute for Pharmaceutical Sciences and Bijvoet Centre for Biomolecular Research, Utrecht University, Padualaan 8, 3584 CH Utrecht, The Netherlands; §Netherlands Proteomics Centre, Padualaan 8, 3584 CH Utrecht, The Netherlands;
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40
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Circadian control of global gene expression by the cyanobacterial master regulator RpaA. Cell 2014; 155:1396-408. [PMID: 24315105 PMCID: PMC3935230 DOI: 10.1016/j.cell.2013.11.005] [Citation(s) in RCA: 108] [Impact Index Per Article: 10.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/10/2013] [Revised: 09/23/2013] [Accepted: 10/28/2013] [Indexed: 01/09/2023]
Abstract
The cyanobacterial circadian clock generates genome-wide transcriptional oscillations and regulates cell division, but the underlying mechanisms are not well understood. Here, we show that the response regulator RpaA serves as the master regulator of these clock outputs. Deletion of rpaA abrogates gene expression rhythms globally and arrests cells in a dawn-like expression state. Although rpaA deletion causes core oscillator failure by perturbing clock gene expression, rescuing oscillator function does not restore global expression rhythms. We show that phosphorylated RpaA regulates the expression of not only clock components, generating feedback on the core oscillator, but also a small set of circadian effectors that, in turn, orchestrate genome-wide transcriptional rhythms. Expression of constitutively active RpaA is sufficient to switch cells from a dawn-like to a dusk-like expression state as well as to block cell division. Hence, complex global circadian phenotypes can be generated by controlling the phosphorylation of a single transcription factor.
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41
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Diversity of KaiC-based timing systems in marine Cyanobacteria. Mar Genomics 2014; 14:3-16. [PMID: 24388874 DOI: 10.1016/j.margen.2013.12.006] [Citation(s) in RCA: 45] [Impact Index Per Article: 4.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/01/2013] [Revised: 11/19/2013] [Accepted: 12/18/2013] [Indexed: 12/21/2022]
Abstract
The coordination of biological activities into daily cycles provides an important advantage for the fitness of diverse organisms. Most eukaryotes possess an internal clock ticking with a periodicity of about one day to anticipate sunrise and sunset. The 24-hour period of the free-running rhythm is highly robust against many changes in the natural environment. Among prokaryotes, only Cyanobacteria are known to harbor such a circadian clock. Its core oscillator consists of just three proteins, KaiA, KaiB, and KaiC that produce 24-hour oscillations of KaiC phosphorylation, even in vitro. This unique three-protein oscillator is well documented for the freshwater cyanobacterium Synechococcus elongatus PCC 7942. Several physiological studies demonstrate a circadian clock also for other Cyanobacteria including marine species. Genes for the core clock components are present in nearly all marine cyanobacterial species, though there are large differences in the specific composition of these genes. In the first section of this review we summarize data on the model circadian clock from S. elongatus PCC 7942 and compare it to the reduced clock system of the marine cyanobacterium Prochlorococcus marinus MED4. In the second part we discuss the diversity of timing mechanisms in other marine Cyanobacteria with regard to the presence or absence of different components of the clock.
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Abstract
Circadian clocks are cellular timekeeping mechanisms that coordinate behavior and physiology around the 24-h day in most living organisms. Misalignment of an organism's clock with its environment is associated with long-term adverse fitness consequences, as exemplified by the link between circadian disruption and various age-related diseases in humans. Current eukaryotic models of the circadian oscillator rely on transcription/translation feedback loop mechanisms, supplemented with accessory cytosolic loops that connect them to cellular physiology. However, mounting evidence is questioning the absolute necessity of transcription-based oscillators for circadian rhythmicity, supported by the recent discovery of oxidation-reduction cycles of peroxiredoxin proteins, which persist even in the absence of transcription. A more fundamental mechanism based on metabolic cycles could thus underlie circadian transcriptional and cytosolic rhythms, thereby promoting circadian oscillations to integral properties of cellular metabolism.
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Affiliation(s)
- Akhilesh B. Reddy
- Department of Clinical Neurosciences, University of Cambridge Metabolic Research Laboratories, National Institutes of Health Biomedical Research Center, and Wellcome Trust–Medical Research Council Institute of Metabolic Science, University of Cambridge, Addenbrooke's Hospital, Cambridge CB2 0QQ, United Kingdom
| | - Guillaume Rey
- Department of Clinical Neurosciences, University of Cambridge Metabolic Research Laboratories, National Institutes of Health Biomedical Research Center, and Wellcome Trust–Medical Research Council Institute of Metabolic Science, University of Cambridge, Addenbrooke's Hospital, Cambridge CB2 0QQ, United Kingdom
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43
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Hypersensitive photic responses and intact genome-wide transcriptional control without the KaiC phosphorylation cycle in the Synechococcus circadian system. J Bacteriol 2013; 196:548-55. [PMID: 24244001 DOI: 10.1128/jb.00892-13] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
Abstract
Cyanobacteria are unique organisms with remarkably stable circadian oscillations. These are controlled by a network architecture that comprises two regulatory factors: posttranslational oscillation (PTO) and a transcription/translation feedback loop (TTFL). The clock proteins KaiA, KaiB, and KaiC are essential for the circadian rhythm of the unicellular species Synechococcus elongatus PCC 7942. Temperature-compensated autonomous cycling of KaiC phosphorylation has been proposed as the primary oscillator mechanism that maintains the circadian clock, even in the dark, and it controls genome-wide gene expression rhythms under continuous-light conditions (LL). However, the kaiC(EE) mutation (where "EE" represents the amino acid changes Ser431Glu and Thr432Glu), where phosphorylation cycling does not occur in vivo, has a damped but clear kaiBC expression rhythm with a long period. This suggests that there must be coupling between the robust PTO and the "slave" unstable TTFL. Here, we found that the kaiC(EE) mutant strain in LL was hypersensitive to the dark acclimation required for phase shifting. Twenty-three percent of the genes in the kaiC(EE) mutant strain exhibited genome-wide transcriptional rhythms with a period of 48 h in LL. The circadian phase distribution was also conserved significantly in most of the wild-type and kaiC(EE) mutant strain cycling genes, which suggests that the output mechanism was not damaged severely even in the absence of KaiC phosphorylation cycles. These results strongly suggest that the KaiC phosphorylation cycle is not essential for generating the genome-wide rhythm under light conditions, whereas it is important for appropriate circadian timing in the light and dark.
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44
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Circadian yin-yang regulation and its manipulation to globally reprogram gene expression. Curr Biol 2013; 23:2365-74. [PMID: 24210617 DOI: 10.1016/j.cub.2013.10.011] [Citation(s) in RCA: 17] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/02/2013] [Revised: 09/13/2013] [Accepted: 10/02/2013] [Indexed: 11/20/2022]
Abstract
BACKGROUND The cyanobacterial circadian program exerts genome-wide control of gene expression. KaiC undergoes rhythms of phosphorylation that are regulated by interactions with KaiA and KaiB. The phosphorylation status of KaiC is thought to mediate global transcription via output factors SasA, CikA, LabA, RpaA, and RpaB. Overexpression of kaiC has been reported to globally repress gene expression. RESULTS Here, we show that the positive circadian component KaiA upregulates "subjective dusk" genes and that its overexpression deactivates rhythmic gene expression without significantly affecting growth rates in constant light. We analyze the global patterns of expression that are regulated by KaiA versus KaiC and find in contrast to the previous report of KaiC repression that there is a "yin-yang" regulation of gene expression whereby kaiA overexpression activates "dusk genes" and represses "dawn genes," whereas kaiC overexpression complementarily activates dawn genes and represses dusk genes. Moreover, continuous induction of kaiA latched KaiABC-regulated gene expression to provide constitutively increased transcript levels of diverse endogenous and heterologous genes that are expressed in the predominant subjective dusk phase. In addition to analyzing KaiA regulation of endogenous gene expression, we apply these insights to the expression of heterologous proteins whose products are of potential value, namely human proinsulin, foreign luciferase, and exogenous hydrogenase. CONCLUSIONS Both KaiC and KaiA complementarily contribute to the regulation of circadian gene expression via yin-yang switching. Circadian patterns can be reprogrammed by overexpression of kaiA or kaiC to constitutively enhance gene expression, and this reprogramming can improve 24/7 production of heterologous proteins that are useful as pharmaceuticals or biofuels.
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45
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Attenuation of the posttranslational oscillator via transcription-translation feedback enhances circadian-phase shifts in Synechococcus. Proc Natl Acad Sci U S A 2013; 110:14486-91. [PMID: 23940358 DOI: 10.1073/pnas.1302243110] [Citation(s) in RCA: 16] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/31/2023] Open
Abstract
Circadian rhythms are endogenous biological timing processes that are ubiquitous in organisms ranging from cyanobacteria to humans. In the photoautotrophic unicellular cyanobacterium Synechococcus elongatus PCC 7942, under continuous light (LL) conditions, the transcription-translation feedback loop (TTFL) of KaiC generates a rhythmic change in the accumulation of KaiC relative to KaiA clock proteins (KaiC/KaiA ratio), which peak and trough at subjective dawn and dusk, respectively. However, the role of TTFL in the cyanobacterial circadian system remains unclear because it is not an essential requirement for the basic oscillation driven by the Kai-based posttranslational oscillator (PTO) and the transcriptional output mechanisms. Here, we show that TTFL is important for the circadian photic resetting property in Synechococcus. The robustness of PTO, which is exemplified by the amplitude of the KaiC phosphorylation cycle, changed depending on the KaiC/KaiA ratio, which was cyclic under LL. After cells were transferred from LL to the dark, the clock protein levels remained constant in the dark. When cells were transferred from LL to continuous dark at subjective dawn, the KaiC phosphorylation cycle was attenuated with a lower KaiC/KaiA ratio, a higher KaiC phosphorylation level, and a lower amplitude than that in cells transferred at subjective dusk. We also found that the greater the degree to which PTO was attenuated in continuous dark, the greater the phase shifts upon the subsequent light exposure. Based on these results, we propose that TTFL enhances resetting of the Kai-based PTO in Synechococcus.
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46
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Chaves M, Preto M. Hierarchy of models: from qualitative to quantitative analysis of circadian rhythms in cyanobacteria. CHAOS (WOODBURY, N.Y.) 2013; 23:025113. [PMID: 23822511 DOI: 10.1063/1.4810922] [Citation(s) in RCA: 9] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/02/2023]
Abstract
A hierarchy of models, ranging from high to lower levels of abstraction, is proposed to construct "minimal" but predictive and explanatory models of biological systems. Three hierarchical levels will be considered: Boolean networks, piecewise affine differential (PWA) equations, and a class of continuous, ordinary, differential equations' models derived from the PWA model. This hierarchy provides different levels of approximation of the biological system and, crucially, allows the use of theoretical tools to more exactly analyze and understand the mechanisms of the system. The Kai ABC oscillator, which is at the core of the cyanobacterial circadian rhythm, is analyzed as a case study, showing how several fundamental properties-order of oscillations, synchronization when mixing oscillating samples, structural robustness, and entrainment by external cues-can be obtained from basic mechanisms.
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Affiliation(s)
- M Chaves
- BIOCORE, INRIA Sophia Antipolis, 2004 Route des Lucioles, BP 93, 06902 Sophia Antipolis, France.
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Teng SW, Mukherji S, Moffitt JR, de Buyl S, O'Shea EK. Robust circadian oscillations in growing cyanobacteria require transcriptional feedback. Science 2013; 340:737-40. [PMID: 23661759 PMCID: PMC3696982 DOI: 10.1126/science.1230996] [Citation(s) in RCA: 88] [Impact Index Per Article: 8.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/22/2023]
Abstract
The remarkably stable circadian oscillations of single cyanobacteria enable a population of growing cells to maintain synchrony for weeks. The cyanobacterial pacemaker is a posttranslational regulation (PTR) circuit that generates circadian oscillations in the phosphorylation state of the clock protein KaiC. Layered on top of the PTR is transcriptional-translational feedback regulation (TTR), common to all circadian systems, consisting of a negative feedback loop in which KaiC regulates its own production. We found that the PTR circuit is sufficient to generate oscillations in growing cyanobacteria. However, in the absence of TTR, individual oscillators were less stable and synchrony was not maintained in a population of cells. Experimentally constrained mathematical modeling reproduced sustained oscillations in the PTR circuit alone and demonstrated the importance of TTR for oscillator synchrony.
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Affiliation(s)
- Shu-Wen Teng
- Howard Hughes Medical Institute, Faculty of Arts and Sciences Center for Systems Biology, Department of Molecular and Cellular Biology, Harvard University, Cambridge, MA 02138, USA
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Egli M, Johnson CH. A circadian clock nanomachine that runs without transcription or translation. Curr Opin Neurobiol 2013; 23:732-40. [PMID: 23571120 DOI: 10.1016/j.conb.2013.02.012] [Citation(s) in RCA: 28] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/11/2013] [Revised: 02/21/2013] [Accepted: 02/23/2013] [Indexed: 11/15/2022]
Abstract
The biochemical basis of circadian timekeeping is best characterized in cyanobacteria. The structures of its key molecular players, KaiA, KaiB, and KaiC are known and these proteins can reconstitute a remarkable circadian oscillation in a test tube. KaiC is rhythmically phosphorylated and its phospho-status is a marker of circadian phase that regulates ATPase activity and the oscillating assembly of a nanomachine. Analyses of the nanomachines have revealed how their timing circuit is ratcheted to be unidirectional and how they stay in synch to ensure a robust oscillator. These insights are likely to elucidate circadian timekeeping in higher organisms, including how transcription and translation could appear to be a core circadian timer when the true pacemaker is an embedded biochemical oscillator.
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Affiliation(s)
- Martin Egli
- Department of Biochemistry, Vanderbilt University, School of Medicine, Nashville, TN 37232, USA.
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Hertel S, Brettschneider C, Axmann IM. Revealing a two-loop transcriptional feedback mechanism in the cyanobacterial circadian clock. PLoS Comput Biol 2013; 9:e1002966. [PMID: 23516349 PMCID: PMC3597532 DOI: 10.1371/journal.pcbi.1002966] [Citation(s) in RCA: 14] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/17/2012] [Accepted: 01/15/2013] [Indexed: 01/29/2023] Open
Abstract
Molecular genetic studies in the circadian model organism Synechococcus have revealed that the KaiC protein, the central component of the circadian clock in cyanobacteria, is involved in activation and repression of its own gene transcription. During 24 hours, KaiC hexamers run through different phospho-states during daytime. So far, it has remained unclear which phospho-state of KaiC promotes kaiBC expression and which opposes transcriptional activation. We systematically analyzed various combinations of positive and negative transcriptional feedback regulation by introducing a combined TTFL/PTO model consisting of our previous post-translational oscillator that considers all four phospho-states of KaiC and a transcriptional/translational feedback loop. Only a particular two-loop feedback mechanism out of 32 we have extensively tested is able to reproduce existing experimental observations, including the effects of knockout or overexpression of kai genes. Here, threonine and double phosphorylated KaiC hexamers activate and unphosphorylated KaiC hexamers suppress kaiBC transcription. Our model simulations suggest that the peak expression ratio of the positive and the negative component of kaiBC expression is the main factor for how the different two-loop feedback models respond to removal or to overexpression of kai genes. We discuss parallels between our proposed TTFL/PTO model and two-loop feedback structures found in the mammalian clock. Many organisms possess a true circadian clock and coordinate their activities into daily cycles. Among the simplest organisms harboring such a 24 h-clock are cyanobacteria. Interactions among three proteins, KaiA, KaiB, KaiC, and cyclic KaiC phosphorylation govern the daily rhythm from gene expression to metabolism. Thus, the control of the kaiBC gene cluster expression is important for regulating the cyanobacterial clockwork. A picture has emerged in which different KaiC phospho-states activate and inhibit kaiBC expression. However, the mechanism remains to be solved. Here, we investigated the impact of each KaiC phospho-state on kaiBC expression by introducing a model that combines the circadian transcription/translation rhythm with the KaiABC-protein oscillator. We tested 32 combinations of positive and negative transcriptional regulation. It turns out that the kaiBC expression and KaiC phosphorylation dynamics in wild type and kai mutants can only be described by one mechanism: threonine and double phosphorylated KaiC hexamers activate kaiBC expression and the unphosphorylated state suppresses it. Further, we propose that the activator-to-repressor abundance ratio very likely determines the kaiBC expression dynamics in the simulated kai mutants. Our suggested clock model can be extended by further kinetic mechanisms to gain deeper insights into the various underlying processes of circadian gene regulation.
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Affiliation(s)
- Stefanie Hertel
- Institute for Theoretical Biology, Charité-Universitätsmedizin Berlin, Berlin, Germany
- * E-mail:
| | - Christian Brettschneider
- Mathematical Modelling of Cellular Processes, Max Delbrück Center for Molecular Medicine, Berlin, Germany
| | - Ilka M. Axmann
- Institute for Theoretical Biology, Charité-Universitätsmedizin Berlin, Berlin, Germany
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Egli M, Pattanayek R, Sheehan JH, Xu Y, Mori T, Smith JA, Johnson CH. Loop-loop interactions regulate KaiA-stimulated KaiC phosphorylation in the cyanobacterial KaiABC circadian clock. Biochemistry 2013; 52:1208-20. [PMID: 23351065 PMCID: PMC3587310 DOI: 10.1021/bi301691a] [Citation(s) in RCA: 26] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
Abstract
The Synechococcus elongatus KaiA, KaiB, and KaiC proteins in the presence of ATP generate a post-translational oscillator that runs in a temperature-compensated manner with a period of 24 h. KaiA dimer stimulates phosphorylation of KaiC hexamer at two sites per subunit, T432 and S431, and KaiB dimers antagonize KaiA action and induce KaiC subunit exchange. Neither the mechanism of KaiA-stimulated KaiC phosphorylation nor that of KaiB-mediated KaiC dephosphorylation is understood in detail at present. We demonstrate here that the A422V KaiC mutant sheds light on the former mechanism. It was previously reported that A422V is less sensitive to dark pulse-induced phase resetting and has a reduced amplitude of the KaiC phosphorylation rhythm in vivo. A422 maps to a loop (422-loop) that continues toward the phosphorylation sites. By pulling on the C-terminal peptide of KaiC (A-loop), KaiA removes restraints from the adjacent 422-loop whose increased flexibility indirectly promotes kinase activity. We found in the crystal structure that A422V KaiC lacks phosphorylation at S431 and exhibits a subtle, local conformational change relative to wild-type KaiC. Molecular dynamics simulations indicate higher mobility of the 422-loop in the absence of the A-loop and mobility differences in other areas associated with phosphorylation activity between wild-type and mutant KaiCs. The A-loop-422-loop relay that informs KaiC phosphorylation sites of KaiA dimer binding propagates to loops from neighboring KaiC subunits, thus providing support for a concerted allosteric mechanism of phosphorylation.
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Affiliation(s)
- Martin Egli
- Department of Biochemistry, Vanderbilt University, School of Medicine, Nashville, TN 37232, USA.
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