title: Circadian rhythms. A protein fold switch joins the circadian oscillator to clock output in cyanobacteria.
abstract: 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.
authors.affiliation: School of Natural Sciences, University of California, Merced, CA 95343, USA.
authors.forename: Yong-Gang
authors.initials: YG
authors.lastname: Chang
authors.affiliation: Center for Circadian Biology, University of California, San Diego, La Jolla, CA 92093, USA.
authors.forename: Susan E
authors.initials: SE
authors.lastname: Cohen
authors.affiliation: Department of Molecular Genetics and Cell Biology, University of Chicago, Chicago, IL 60637, USA.
authors.forename: Connie
authors.initials: C
authors.lastname: Phong
authors.affiliation: Department of Chemistry, University of California, Davis, CA 95616, USA.
authors.forename: William K
authors.initials: WK
authors.lastname: Myers
authors.affiliation: Center for Circadian Biology, University of California, San Diego, La Jolla, CA 92093, USA.
authors.forename: Yong-Ick
authors.initials: YI
authors.lastname: Kim
authors.affiliation: School of Natural Sciences, University of California, Merced, CA 95343, USA. Quantitative and Systems Biology, University of California, Merced, CA 95343, USA.
authors.forename: Roger
authors.initials: R
authors.lastname: Tseng
authors.affiliation: Department of Molecular Genetics and Cell Biology, University of Chicago, Chicago, IL 60637, USA.
authors.forename: Jenny
authors.initials: J
authors.lastname: Lin
authors.affiliation: School of Natural Sciences, University of California, Merced, CA 95343, USA.
authors.forename: Li
authors.initials: L
authors.lastname: Zhang
authors.affiliation: Center for Circadian Biology, University of California, San Diego, La Jolla, CA 92093, USA.
authors.forename: Joseph S
authors.initials: JS
authors.lastname: Boyd
authors.affiliation: Division of Biological Sciences, University of California, San Diego, La Jolla, CA 92093, USA.
authors.forename: Yvonne
authors.initials: Y
authors.lastname: Lee
authors.affiliation: Division of Biological Sciences, University of California, San Diego, La Jolla, CA 92093, USA.
authors.forename: Shannon
authors.initials: S
authors.lastname: Kang
authors.affiliation: Department of Medicine, University of California, San Diego, La Jolla, CA 92093, USA.
authors.forename: David
authors.initials: D
authors.lastname: Lee
authors.affiliation: Department of Medicine, University of California, San Diego, La Jolla, CA 92093, USA.
authors.forename: Sheng
authors.initials: S
authors.lastname: Li
authors.affiliation: Department of Chemistry, University of California, Davis, CA 95616, USA.
authors.forename: R David
authors.initials: RD
authors.lastname: Britt
authors.affiliation: Department of Molecular Genetics and Cell Biology, University of Chicago, Chicago, IL 60637, USA.
authors.forename: Michael J
authors.initials: MJ
authors.lastname: Rust
authors.affiliation: Center for Circadian Biology, University of California, San Diego, La Jolla, CA 92093, USA. Division of Biological Sciences, University of California, San Diego, La Jolla, CA 92093, USA.
authors.forename: Susan S
authors.initials: SS
authors.lastname: Golden
authors.affiliation: School of Natural Sciences, University of California, Merced, CA 95343, USA. Center for Circadian Biology, University of California, San Diego, La Jolla, CA 92093, USA. Quantitative and Systems Biology, University of California, Merced, CA 95343, USA. Chemistry and Chemical Biology, University of California, Merced, CA 95343, USA. Health Sciences Research Institute, University of California, Merced, CA 95343, USA. aliwang@ucmerced.edu.
authors.forename: Andy
authors.initials: A
authors.lastname: LiWang
mesh_terms: D001426:Bacterial Proteins / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism*; D002940:Circadian Rhythm; D056925:Circadian Rhythm Signaling Peptides and Proteins / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism*; D010766:Phosphorylation; D017510:Protein Folding; D017433:Protein Structure, Secondary; D046940:Synechococcus / Q000378:metabolism / Q000502:physiology*
chemical_list: D001426:Bacterial Proteins; D056925:Circadian Rhythm Signaling Peptides and Proteins; C114269:KaiA protein, cyanobacteria; C114270:KaiB protein, cyanobacteria; C114271:KaiC protein, cyanobacteria