Crystal structure of the redox-active cofactor dibromothymoquinone bound to circadian clock protein KaiA and structural basis for dibromothymoquinone's ability to prevent stimulation of KaiC phosphorylation by KaiA.

Pattanayek R, Sidiqi SK, Egli M
Biochemistry. 2012 51 (41): 8050-2

PMID: 23020633 · PMCID: PMC3561481 · DOI:10.1021/bi301222t

KaiA protein that stimulates KaiC phosphorylation in the cyanobacterial circadian clock was recently shown to be destabilized by dibromothymoquinone (DBMIB), thus revealing KaiA as a sensor of the plastoquinone (PQ) redox state and suggesting an indirect control of the clock by light through PQ redox changes. Here we show using X-ray crystallography that several DBMIBs are bound to KaiA dimer. Some binding modes are consistent with oligomerization of N-terminal KaiA pseudoreceiver domains and/or reduced interdomain flexibility. DBMIB bound to the C-terminal KaiA (C-KaiA) domain and limited stimulation of KaiC kinase activity by C-KaiA in the presence of DBMIB demonstrate that the cofactor may weakly inhibit KaiA-KaiC binding.

MeSH Terms (11)

Amino Acid Sequence Bacterial Proteins Circadian Rhythm Signaling Peptides and Proteins Crystallography, X-Ray Dibromothymoquinone Dimerization Electrophoresis, Polyacrylamide Gel Molecular Sequence Data Oxidation-Reduction Phosphorylation Protein Conformation

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