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Open AccessArticle

Cooperative Binding of KaiB to the KaiC Hexamer Ensures Accurate Circadian Clock Oscillation in Cyanobacteria

1
Graduate School of Pharmaceutical Sciences, Nagoya City University, 3-1 Tanabe-dori, Mizuho-ku, Nagoya 467-8603, Japan
2
Institute for Molecular Science, National Institutes of Natural Sciences, 5-1 Higashiyama, Myodaiji-cho, Okazaki 444-8787, Japan
3
Department of Creative Research, Exploratory Research Center on Life and Living Systems (ExCELLS), National Institutes of Natural Sciences, 5-1 Higashiyama, Myodaiji-cho, Okazaki 444-8787, Japan
4
Graduate School of Life Sciences, Ritsumeikan University, 1-1-1 Noji-higashi, Kusatsu, Shiga 525-8577, Japan
5
Department of Biotechnology, Graduate School of Engineering, Osaka University, 2-1 Yamadaoka, Suita, Osaka 565-0871, Japan
*
Author to whom correspondence should be addressed.
Present address: Research Promotion and support headquarters, Fujita Health University Graduate School of Health Sciences, Toyoake, Aichi 470-1192, Japan.
These two authors contributed equally to this work.
Int. J. Mol. Sci. 2019, 20(18), 4550; https://doi.org/10.3390/ijms20184550
Received: 30 July 2019 / Revised: 8 September 2019 / Accepted: 11 September 2019 / Published: 13 September 2019
(This article belongs to the Collection Feature Papers in Molecular Biophysics)
The central oscillator generating cyanobacterial circadian rhythms comprises KaiA, KaiB, and KaiC proteins. Their interactions cause KaiC phosphorylation and dephosphorylation cycles over approximately 24 h. KaiB interacts with phosphorylated KaiC in competition with SasA, an output protein harboring a KaiB-homologous domain. Structural data have identified KaiB–KaiC interaction sites; however, KaiB mutations distal from the binding surfaces can impair KaiB–KaiC interaction and the circadian rhythm. Reportedly, KaiB and KaiC exclusively form a complex in a 6:6 stoichiometry, indicating that KaiB–KaiC hexamer binding shows strong positive cooperativity. Here, mutational analysis was used to investigate the functional significance of this cooperative interaction. Results demonstrate that electrostatic complementarity between KaiB protomers promotes their cooperative assembly, which is indispensable for accurate rhythm generation. SasA does not exhibit such electrostatic complementarity and noncooperatively binds to KaiC. Thus, the findings explain KaiB distal mutation effects, providing mechanistic insights into clock protein interplay. View Full-Text
Keywords: cooperative interaction; circadian rhythm; clock protein; native mass spectrometry; cooperativity cooperative interaction; circadian rhythm; clock protein; native mass spectrometry; cooperativity
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MDPI and ACS Style

Murakami, R.; Yunoki, Y.; Ishii, K.; Terauchi, K.; Uchiyama, S.; Yagi, H.; Kato, K. Cooperative Binding of KaiB to the KaiC Hexamer Ensures Accurate Circadian Clock Oscillation in Cyanobacteria. Int. J. Mol. Sci. 2019, 20, 4550.

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