The biological clock of cyanobacteria is composed of three proteins, KaiA, KaiB, and KaiC. The KaiB-KaiC binding brings the slowness into the system, which is essential for the long period of the circadian rhythm. However, there is no consensus as to the origin of the slowness due to the pre-binding conformational transition of either KaiB or KaiC. In this study, we propose a simple KaiB-KaiC binding scheme in a hexameric form with an attractive interaction between adjacent bound KaiB monomers, which is independent of KaiB's conformational change. We then show that the present scheme can explain several important experimental results on the binding, including that used as evidence for the slow conformational transition of KaiB. The present result thus indicates that the slowness arises from KaiC rather than KaiB.
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Site directed spin labeling to elucidating the mechanism of the cyanobacterial circadian clock.
Methods Enzymol
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Department of Chemistry, University of California, Davis, CA, United States. Electronic address:
Electron Paramagnetic Resonance (EPR) is a spectroscopic technique that provides structural and dynamic information on unpaired spins and their surrounding environments. Introduction of exogenous spin labels via site directed spin labeling (SDSL) enables characterization of systems of interests lacking intrinsic unpaired spins. This chapter describes the use of SDSL in quantifying KaiB-KaiC binding in the cyanobacterial circadian clock (Kai Clock), exploiting the changes in mobility of the local environment around the spin label on KaiB-KaiC interactions.
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Department of Theoretical and Computational Molecular Science, Institute for Molecular Science, Okazaki, Aichi, Japan.
Circadian clocks tick a rhythm with a nearly 24-hour period in a variety of organisms. In the clock proteins of cyanobacteria, KaiA, KaiB, and KaiC, known as a minimum circadian clock, the slow KaiB-KaiC complex formation is essential in determining the clock period. This complex formation, occurring when the C1 domain of KaiC hexamer binds ADP molecules produced by the ATPase activity of C1, is considered to be promoted by accumulating ADP molecules in C1 through inhibiting the ADP/ATP exchange (ADP release) rather than activating the ATP hydrolysis (ADP production).
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Sci Rep
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Department of Theoretical and Computational Molecular Science, Institute for Molecular Science, 38 Nishigo-Naka, Myodaiji, Okazaki, Aichi, 444-8585, Japan.
The biological clock of cyanobacteria is composed of three proteins, KaiA, KaiB, and KaiC. The KaiB-KaiC binding brings the slowness into the system, which is essential for the long period of the circadian rhythm. However, there is no consensus as to the origin of the slowness due to the pre-binding conformational transition of either KaiB or KaiC.
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Nat Commun
May 2020
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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.
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