7WDC image
Entry Detail
PDB ID:
7WDC
Keywords:
Title:
Crystal Structure of Cyanobacterial Circadian Clock Protein KaiC
Biological Source:
PDB Version:
Deposition Date:
2021-12-21
Release Date:
2022-07-20
Method Details:
Experimental Method:
Resolution:
2.84 Å
R-Value Free:
0.32
R-Value Work:
0.28
R-Value Observed:
0.28
Space Group:
P 63
Macromolecular Entities
Polymer Type:polypeptide(L)
Description:Circadian clock protein kinase KaiC
Mutations:F419W
Chain IDs:A, B
Chain Length:519
Number of Molecules:2
Biological Source:Synechococcus elongatus (strain PCC 7942 / FACHB-805)
Primary Citation
Highly sensitive tryptophan fluorescence probe for detecting rhythmic conformational changes of KaiC in the cyanobacterial circadian clock system.
Biochem.J. 479 1505 1515 (2022)
PMID: 35771042 DOI: 10.1042/BCJ20210544

Abstact

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.

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