RT Journal Article
SR Electronic
T1 From primordial clocks to circadian oscillators
JF bioRxiv
FD Cold Spring Harbor Laboratory
SP 2022.11.28.518275
DO 10.1101/2022.11.28.518275
A1 Warintra Pitsawong
A1 Ricardo A. P. Pádua
A1 Timothy Grant
A1 Marc Hoemberger
A1 Renee Otten
A1 Niels Bradshaw
A1 Nikolaus Grigorieff
A1 Dorothee Kern
YR 2022
UL http://biorxiv.org/content/early/2022/11/29/2022.11.28.518275.1.abstract
AB Circadian rhythms play an essential role in many biological processes and surprisingly only three prokaryotic proteins are required to constitute a true post-translational circadian oscillator. The evolutionary history of the three Kai proteins indicates that KaiC is the oldest member and central component of the clock, with subsequent additions of KaiB and KaiA to regulate its phosphorylation state for time synchronization. The canonical KaiABC system in cyanobacteria is well understood, but little is known about more ancient systems that possess just KaiBC, except for reports that they might exhibit a basic, hourglass-like timekeeping mechanism. Here, we investigate the primordial circadian clock in Rhodobacter sphaeroides (RS) that contains only KaiBC to elucidate its inner workings despite the missing KaiA. Using a combination X-ray crystallography and cryo-EM we find a novel dodecameric fold for KaiCRS where two hexamers are held together by a coiled-coil bundle of 12 helices. This interaction is formed by the C-terminal extension of KaiCRS and serves as an ancient regulatory moiety later superseded by KaiA. A coiled-coil register shift between daytime- and nighttime-conformations is connected to the phosphorylation sites through a long-range allosteric network that spans over 160 Å. Our kinetic data identify the difference in ATP-to-ADP ratio between day and night as the environmental cue that drives the clock and further unravels mechanistic details that shed light on the evolution of self-sustained oscillators.Competing Interest StatementD.K. is co-founder of Relay Therapeutics and MOMA Therapeutics. The remaining authors declare no competing interests.