Mechanism of robust circadian oscillation of KaiC phosphorylation in vitro.
By incubating the mixture of three cyanobacterial proteins, KaiA, KaiB, and KaiC, with ATP in vitro, T. Kondo and his colleagues in recent work reconstituted the robust circadian rhythm of the phosphorylation level of KaiC. This finding indicates that protein-protein interactions and the associated hydrolysis of ATP suffice to generate the circadian rhythm. Several theoretical models have been proposed to explain the rhythm generated in this "protein-only" system, but the clear criterion to discern different possible mechanisms was not known. In this article, we discuss a model based on two basic assumptions: the assumption of the allosteric transition of a KaiC hexamer and the assumption of the monomer exchange between KaiC hexamers. The model shows a stable rhythmic oscillation of the phosphorylation level of KaiC, which is robust against changes in concentration of Kai proteins. We show that this robustness gives a clue to distinguish different possible mechanisms. We also discuss the robustness of oscillation against the change in the system size. Behaviors of the system with the cellular or subcellular size should shed light on the role of the protein-protein interactions in in vivo circadian oscillation.
Eguchi
Kohei
K
Department of Computational Science and Engineering, Nagoya University, Nagoya 464-8603, Japan.
Yoda
Mitsumasa
M
Terada
Tomoki P
TP
Sasai
Masaki
M
D001426:Bacterial Proteins / Q000502:physiology*; D001683:Biological Clocks / Q000502:physiology*; D002940:Circadian Rhythm / Q000502:physiology*; D056925:Circadian Rhythm Signaling Peptides and Proteins; D003198:Computer Simulation; D000458:Cyanobacteria / Q000502:physiology*; D008954:Models, Biological; D010766:Phosphorylation
D001426:Bacterial Proteins; D056925:Circadian Rhythm Signaling Peptides and Proteins; C114271:KaiC protein, cyanobacteria