Orchestration of Proteins in cyanobacterial Circadian Clock System 1

Abstract

ABSTRACTCircadian rhythm by Cyanobacteria is one of the simplest biological clocks: the clock consists of only three proteins, KaiA, KaiB, and KaiC. Their oligomers, KaiA dimer (A2), KaiB tetramer (B4), and KaiC hexamer (C6) oscillate an association–disassociation cycle with 24-hr period. In a widely accepted model, the oscillation process is as follows. From the viewpoint of a base unit (C6), C6 homo-oligomer → A2C6 complex → B6C6 complex → AnB6C6 complex (n≤12) →C6 homo-oligomer. In this study, Small-Angle X-ray Scattering, Contrast Matching-Small-Angle Neutron Scattering, Analytical Ultracentrifuge, and phosphorylation-analysis PAGE measurements were performed to reveal the kinetics not only of KaiC hexamer but also of all components in a working Kai clock. The complementary analysis disclosed that the oscillation is not the single process as the widely accepted model but composed with synchronized multiple association-dissociation reactions between components. Namely, there are various reactions between components, which proceed simultaneously, in a working Kai-clock.