title: ATP-induced hexameric ring structure of the cyanobacterial circadian clock protein KaiC.
abstract: 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 micro m. 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 A and with a relatively large cavity (73 A deep and 18-34 A 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.
  
  
  CONCLUSIONS
  ATP-induced KaiC hexamerization is necessary for the clock function of KaiC.
authors.affiliation: Center for Gene Research, Nagoya University, Furo, Chikusa, Nagoya, 464-8602, Japan.
authors.forename: Fumio
authors.initials: F
authors.lastname: Hayashi
authors.forename: Hirofumi
authors.initials: H
authors.lastname: Suzuki
authors.forename: Ryo
authors.initials: R
authors.lastname: Iwase
authors.forename: Tatsuya
authors.initials: T
authors.lastname: Uzumaki
authors.forename: Asako
authors.initials: A
authors.lastname: Miyake
authors.forename: Jian-Ren
authors.initials: JR
authors.lastname: Shen
authors.forename: Katsumi
authors.initials: K
authors.lastname: Imada
authors.forename: Yukio
authors.initials: Y
authors.lastname: Furukawa
authors.forename: Koji
authors.initials: K
authors.lastname: Yonekura
authors.forename: Keiichi
authors.initials: K
authors.lastname: Namba
authors.forename: Masahiro
authors.initials: M
authors.lastname: Ishiura
mesh_terms: D000255:Adenosine Triphosphate / Q000378:metabolism*; D000595:Amino Acid Sequence; D001426:Bacterial Proteins / Q000737:chemistry* / Q000378:metabolism / Q000648:ultrastructure; D002940:Circadian Rhythm / Q000235:genetics*; D056925:Circadian Rhythm Signaling Peptides and Proteins; D008854:Microscopy, Electron; D008969:Molecular Sequence Data; D011108:Polymers / Q000737:chemistry; D016415:Sequence Alignment
chemical_list: D001426:Bacterial Proteins; D056925:Circadian Rhythm Signaling Peptides and Proteins; C114271:KaiC protein, cyanobacteria; D011108:Polymers; D000255:Adenosine Triphosphate