title: Intersubunit communications within KaiC hexamers contribute the robust rhythmicity of the cyanobacterial circadian clock.
abstract: Circadian rhythms, endogenous oscillations with periods of ~24 h, are found in many organisms, and they enhance fitness in alternating day/night environments. In cyanobacteria, three clock proteins, KaiA, KaiB, and KaiC, control the timekeeping mechanism. KaiC, the central component of the system, is a hexameric ATPase that also has autokinase and autophosphatase activities. It has been assumed that KaiC's hexameric structure was critical for regulation of the circadian clock; however, the underlying molecular mechanism of such regulation has remained unclear. Recently, we elucidated the regulation of KaiC's activities by its phosphorylation state, in the context of its hexameric structure. We found that local interactions at subunit interfaces regulate KaiC's activities by coupling the nucleotide-binding states. We also discovered the mechanism of regulation by intersubunit communication in KaiC hexamers. Our observations suggest that intersubunit communication precisely synchronizes KaiC subunits to avoid dephasing, and contributes to the robustness of circadian rhythms in cyanobacteria [Kitayama, Y.et al.Nat. Commun. 4:2897 doi: 10.1038/ncomms3897 (2013)].
authors.affiliation: Division of Biological Science, Graduate School of Science, Nagoya University and CREST, Japan Science and Technology Agency (JST), Furo-cho, Chikusa-ku, Nagoya 464-8602, Japan.
authors.forename: Yohko
authors.initials: Y
authors.lastname: Kitayama
authors.affiliation: Division of Biological Science, Graduate School of Science, Nagoya University and CREST, Japan Science and Technology Agency (JST), Furo-cho, Chikusa-ku, Nagoya 464-8602, Japan. ; Present address: Institute of Transformative Bio-Molecules (WPI-ITbM), Nagoya University, Furo-cho, Chikusa-ku, Nagoya 464-8602, Japan.
authors.forename: Taeko
authors.initials: T
authors.lastname: Nishiwaki-Ohkawa
authors.affiliation: Division of Biological Science, Graduate School of Science, Nagoya University and CREST, Japan Science and Technology Agency (JST), Furo-cho, Chikusa-ku, Nagoya 464-8602, Japan.
authors.forename: Takao
authors.initials: T
authors.lastname: Kondo
keywords: ATPase; circadian rhythm; in vitro reconstitution; nucleotide-bound state; phosphatase