ATP-induced hexameric ring structure of the cyanobacterial circadian clock protein KaiC

Fumio Hayashi, Hirofumi Suzuki, Ryo Iwase, Tatsuya Uzumaki, Asako Miyake, Jian Ren Shen, Katsumi Imada, Yukio Furukawa, Koji Yonekura, Keiichi Namba, Masahiro Ishiura

Research output: Contribution to journalArticlepeer-review

111 Citations (Scopus)


Background: KaiA, KaiB and KaiC are cyanobacterial circadian clock proteins. KaiC contains two ATP/GTP-binding Walker's motif As, and mutations in these regions affect the clock oscillations. Results: ATP induced the hexamerization of KaiC. The Km value for the ATP for the hexamerization was 1.9 μM. Triphosphate nucleotides bound to the two Walker's motif As, and their binding functioned cooperatively for the hexamerization. An unhydrolysable substrate, 5′-adenylylimidodiphosphate (AMPPNP), also induced the hexamerization, indicating that nucleotide binding, but not its hydrolysis, is essential for the hexamerization. Mutations in each of the two Walker's motif As that affect the clock phenotype increased the Km value for ATP and inhibited the hexamerization. Thus, the KaiC hexamerization seems to be necessary for its clock function. The KaiC hexamer has the shape of a hexagonal pot with a diameter and height of approximately 100 Å and with a relatively large cavity (73 Å deep and 18-34 Å wide) inside. This pot-shaped structure suggests that KaiC functions in a similar manner to F1-ATPase, helicase or ATP-dependent protease/chaperon, all of which have dynamic activities inside the central cavity of their hexameric rings. Conclusion: ATP-induced KaiC hexamerization is necessary for the clock function of KaiC.

Original languageEnglish
Pages (from-to)287-296
Number of pages10
JournalGenes to Cells
Issue number3
Publication statusPublished - Mar 1 2003
Externally publishedYes

ASJC Scopus subject areas

  • Genetics
  • Cell Biology


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