title: Cyanobacterial circadian pacemaker: Kai protein complex dynamics in the KaiC phosphorylation cycle in vitro.
abstract: KaiA, KaiB, and KaiC are essential proteins of the circadian clock in the cyanobacterium Synechococcus elongatus PCC 7942. The phosphorylation cycle of KaiC that occurs in vitro after mixing the three proteins and ATP is thought to be the master oscillation governing the circadian system. We analyzed the temporal profile of complexes formed between the three Kai proteins. In the phosphorylation phase, KaiA actively and repeatedly associated with KaiC to promote KaiC phosphorylation. High levels of phosphorylation of KaiC induced the association of the KaiC hexamer with KaiB and inactivate KaiA to begin the dephosphorylation phase, which is closely linked to shuffling of the monomeric KaiC subunits among the hexamer. By reducing KaiC phosphorylation, KaiB dissociated from KaiC, reactivating KaiA. We also confirmed that a similar model can be applied in cyanobacterial cells. The molecular model proposed here provides mechanisms for circadian timing systems.
authors.affiliation: Division of Biological Science, Graduate School of Science, Nagoya University and CREST & SORST, Japan Science and Technology Corporation, Furo-cho 1, Chikusa, Nagoya 464-8602, Japan.
authors.forename: Hakuto
authors.initials: H
authors.lastname: Kageyama
authors.forename: Taeko
authors.initials: T
authors.lastname: Nishiwaki
authors.forename: Masato
authors.initials: M
authors.lastname: Nakajima
authors.forename: Hideo
authors.initials: H
authors.lastname: Iwasaki
authors.forename: Tokitaka
authors.initials: T
authors.lastname: Oyama
authors.forename: Takao
authors.initials: T
authors.lastname: Kondo
mesh_terms: D001426:Bacterial Proteins / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D002940:Circadian Rhythm / Q000502:physiology*; D056925:Circadian Rhythm Signaling Peptides and Proteins; D000458:Cyanobacteria / Q000502:physiology*; D007700:Kinetics; D008954:Models, Biological; D008958:Models, Molecular; D046912:Multiprotein Complexes / Q000737:chemistry / Q000235:genetics / Q000378:metabolism; D010766:Phosphorylation; D011485:Protein Binding; D011994:Recombinant Proteins / Q000737:chemistry / Q000235:genetics / Q000378:metabolism; D015398:Signal Transduction; D020349:Surface Plasmon Resonance
chemical_list: D001426:Bacterial Proteins; D056925:Circadian Rhythm Signaling Peptides and Proteins; C114269:KaiA protein, cyanobacteria; C114270:KaiB protein, cyanobacteria; C114271:KaiC protein, cyanobacteria; D046912:Multiprotein Complexes; D011994:Recombinant Proteins