Fold-Switching Sets the Stage for Cooperativity and Competition in the Cyanobacterial Circadian Clock

Abstract

Circadian rhythms are an ancient evolutionary adaptation found across the domains of life that synchronize behavior and physiology to the daily solar cycle for optimal fitness. In cyanobacteria, timekeeping is generated by three Kai proteins (KaiA, B and C) that form distinct protein complexes throughout the day, comprising a molecular clock that measures time in ∼24-hour increments. We recently showed that KaiB undergoes a rare transition from a tetrameric ground state to a monomeric, fold-switched signaling state that binds to KaiC and plays a central organizing role in the evening phase of the clock.