Quantifying the rhythm of KaiB-C interaction for in vitro cyanobacterial circadian clock

Research output: Contribution to journalArticle

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Abstract

An oscillator consisting of KaiA, KaiB, and KaiC proteins comprises the core of cyanobacterial circadian clock. While one key reaction in this process-KaiC phosphorylation-has been extensively investigated and modeled, other key processes, such as the interactions among Kai proteins, are not understood well. Specifically, different experimental techniques have yielded inconsistent views about Kai A, B, and C interactions. Here, we first propose a mathematical model of cyanobacterial circadian clock that explains the recently observed dynamics of the four phospho-states of KaiC as well as the interactions among the three Kai proteins. Simulations of the model show that the interaction between KaiB and KaiC oscillates with the same period as the phosphorylation of KaiC, but displays a phase delay of ~8 hr relative to the total phosphorylated KaiC. Secondly, this prediction on KaiB-C interaction are evaluated using a novel FRET (Fluorescence Resonance Energy Transfer)-based assay by tagging fluorescent proteins Cerulean and Venus to KaiC and KaiB, respectively, and reconstituting fluorescent protein-labeled in vitro clock. The data show that the KaiB:KaiC interaction indeed oscillates with ~24 hr periodicity and ~8 hr phase delay relative to KaiC phosphorylation, consistent with model prediction. Moreover, it is noteworthy that our model indicates that the interlinked positive and negative feedback loops are the underlying mechanism for oscillation, with the serine phosphorylated-state (the "S-state") of KaiC being a hub for the feedback loops. Because the kinetics of the KaiB-C interaction faithfully follows that of the S-state, the FRET measurement may provide an important real-time probe in quantitative study of the cyanobacterial circadian clock.

Original languageEnglish (US)
Article numbere42581
JournalPLoS One
Volume7
Issue number8
DOIs
StatePublished - Aug 10 2012

Fingerprint

Circadian Clocks
circadian rhythm
Clocks
phosphorylation
Phosphorylation
energy transfer
Fluorescence Resonance Energy Transfer
fluorescence
Proteins
Feedback
prediction
proteins
periodicity
serine
Venus
oscillation
simulation models
mathematical models
kinetics
Periodicity

ASJC Scopus subject areas

  • Agricultural and Biological Sciences(all)
  • Biochemistry, Genetics and Molecular Biology(all)
  • Medicine(all)

Cite this

Quantifying the rhythm of KaiB-C interaction for in vitro cyanobacterial circadian clock. / Ma, Lan; Ranganathan, Rama.

In: PLoS One, Vol. 7, No. 8, e42581, 10.08.2012.

Research output: Contribution to journalArticle

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