7WDC

Crystal Structure of Cyanobacterial Circadian Clock Protein KaiC

Summary for 7WDC

• Entry DOI: 10.2210/pdb7wdc/pdb
• Descriptor: Circadian clock protein kinase KaiC, ADENOSINE-5'-TRIPHOSPHATE, MAGNESIUM ION, ... (4 entities in total)
• Functional Keywords: clock protein, transferase
• Biological source: Synechococcus elongatus (strain PCC 7942 / FACHB-805)
• Total number of polymer chains: 2
• Total formula weight: 118349.57

Authors

Furuike, Y.,Akiyama, S. (deposition date: 2021-12-21, release date: 2022-07-20, Last modification date: 2023-11-29)

Primary citation

Mukaiyama, A.,Furuike, Y.,Yamashita, E.,Akiyama, S.
Highly sensitive tryptophan fluorescence probe for detecting rhythmic conformational changes of KaiC in the cyanobacterial circadian clock system.
Biochem.J., 479:1505-1515, 2022

PubMed Abstract: KaiC, a core protein of the cyanobacterial circadian clock, consists of an N-terminal CI domain and a C-terminal CII domain, and assembles into a double-ring hexamer upon binding with ATP. KaiC rhythmically phosphorylates and dephosphorylates its own two adjacent residues Ser431 and Thr432 at the CII domain with a period of ∼24 h through assembly and disassembly with the other clock proteins, KaiA and/or KaiB. In this study, to understand how KaiC alters its conformation as the source of circadian rhythm, we investigated structural changes of an inner-radius side of the CII ring using time-resolved Trp fluorescence spectroscopy. A KaiC mutant harboring a Trp fluorescence probe at a position of 419 exhibited a robust circadian rhythm with little temperature sensitivity in the presence of KaiA and KaiB. Our fluorescence observations show a remarkable environmental change at the inner-radius side of the CII ring during circadian oscillation. Crystallographic analysis revealed that a side chain of Trp at the position of 419 was oriented toward a region undergoing a helix-coil transition, which is considered to be a key event to allosterically regulate the CI ring that plays a crucial role in determining the cycle period. The present study provides a dynamical insight into how KaiC generates circadian oscillation.

PubMed: 35771042
DOI: 10.1042/BCJ20210544

Experimental method

X-RAY DIFFRACTION (2.84 Å)