Circadian rhythms. A protein fold switch joins the circadian oscillator to clock output in cyanobacteria

• Published in: Science (American Association for the Advancement of Science) Vol. 349; no. 6245; pp. 324 - 328
• Main Authors: Chang, Yong-Gang, Cohen, Susan E, Phong, Connie, Myers, William K, Kim, Yong-Ick, Tseng, Roger, Lin, Jenny, Zhang, Li, Boyd, Joseph S, Lee, Yvonne, Kang, Shannon, Lee, David, Li, Sheng, Britt, R David, Rust, Michael J, Golden, Susan S, LiWang, Andy
• Format: Journal Article
• Language: English
• Published: United States 17.07.2015
• Subjects: Bacterial Proteins - chemistry; Bacterial Proteins - genetics; Bacterial Proteins - metabolism; Circadian Rhythm; Circadian Rhythm Signaling Peptides and Proteins - chemistry; Circadian Rhythm Signaling Peptides and Proteins - genetics; Circadian Rhythm Signaling Peptides and Proteins - metabolism; Phosphorylation; Protein Folding; Protein Structure, Secondary; Synechococcus - metabolism; Synechococcus - physiology
• ISSN: 1095-9203
• DOI: 10.1126/science.1260031

Organisms are adapted to the relentless cycles of day and night, because they evolved timekeeping systems called circadian clocks, which regulate biological activities with ~24-hour rhythms. The clock of cyanobacteria is driven by a three-protein oscillator composed of KaiA, KaiB, and KaiC, which together generate a circadian rhythm of KaiC phosphorylation. We show that KaiB flips between two distinct three-dimensional folds, and its rare transition to an active state provides a time delay that is required to match the timing of the oscillator to that of Earth's rotation. Once KaiB switches folds, it binds phosphorylated KaiC and captures KaiA, which initiates a phase transition of the circadian cycle, and it regulates components of the clock-output pathway, which provides the link that joins the timekeeping and signaling functions of the oscillator.