Tracking and visualizing the circadian ticking of the cyanobacterial clock protein KaiC in solution.
The circadian clock in cyanobacteria persists even without the transcription/translation feedbacks proposed for eukaryotic systems. The period of the cyanobacterial clock is tuned to the circadian range by the ATPase activity of a clock protein known as KaiC. Here, we provide structural evidence on how KaiC ticks away 24 h while coupling the ATPase activity in its N-terminal ring to the phosphorylation state in its C-terminal ring. During the phosphorylation cycle, the C-terminal domains of KaiC are repositioned in a stepwise manner to affect global expansion and contraction motions of the C-terminal ring. Arg393 of KaiC has a critical function in expanding the C-terminal ring and its replacement with Cys affects the temperature compensation of the period--a fundamental property of circadian clocks. The conformational ticking of KaiC observed here in solution serves as a timing cue for assembly/disassembly of other clock proteins (KaiA and KaiB), and is interlocked with its auto-inhibitory ATPase underlying circadian periodicity of cyanobacteria.
Division of Biological Science, Graduate School of Science, Nagoya University, Nagoya, Japan.
Yoriko
Y
Murayama
Atsushi
A
Mukaiyama
Keiko
K
Imai
Yasuhiro
Y
Onoue
Akina
A
Tsunoda
Atsushi
A
Nohara
Tatsuro
T
Ishida
Yuichiro
Y
Maéda
Kazuki
K
Terauchi
Takao
T
Kondo
Shuji
S
Akiyama
D000251:Adenosine Triphosphatases / Q000378:metabolism; D001426:Bacterial Proteins / Q000737:chemistry* / Q000378:metabolism*; D057906:Circadian Clocks; D056925:Circadian Rhythm Signaling Peptides and Proteins / Q000737:chemistry* / Q000378:metabolism*; D000458:Cyanobacteria / Q000737:chemistry / Q000378:metabolism*; D008958:Models, Molecular; D011487:Protein Conformation; D055503:Protein Multimerization
D001426:Bacterial Proteins; D056925:Circadian Rhythm Signaling Peptides and Proteins; C114271:KaiC protein, cyanobacteria; D000251:Adenosine Triphosphatases