title: Quinone sensing by the circadian input kinase of the cyanobacterial circadian clock.
abstract: Circadian rhythms are endogenous cellular programs that time metabolic and behavioral events to occur at optimal times in the daily cycle. Light and dark cycles synchronize the endogenous clock with the external environment through a process called entrainment. Previously, we identified the bacteriophytochrome-like circadian input kinase CikA as a key factor for entraining the clock in the cyanobacterium Synechococcus elongatus PCC 7942. Here, we present evidence that CikA senses not light but rather the redox state of the plastoquinone pool, which, in photosynthetic organisms, varies as a function of the light environment. Furthermore, CikA associates with the Kai proteins of the circadian oscillator, and it influences the phosphorylation state of KaiC during resetting of circadian phase by a dark pulse. The abundance of CikA varies inversely with light intensity, and its stability decreases in the presence of the quinone analog 2,5-dibromo-3-methyl-6-isopropyl-p-benzoquinone (DBMIB). The pseudo-receiver domain of CikA is crucial for sensitivity to DBMIB, and it binds the quinone directly, a demonstration of a previously unrecognized ligand-binding role for the receiver fold. Our results suggest that resetting the clock in S. elongatus is metabolism-dependent and that it is accomplished through the interaction of the circadian oscillator with CikA.
authors.affiliation: Center for Research on Biological Clocks, Department of Biology, Texas A&M University, College Station, TX 77843, USA.
authors.forename: Natalia B
authors.initials: NB
authors.lastname: Ivleva
authors.forename: Tiyu
authors.initials: T
authors.lastname: Gao
authors.forename: Andy C
authors.initials: AC
authors.lastname: LiWang
authors.forename: Susan S
authors.initials: SS
authors.lastname: Golden
mesh_terms: D001426:Bacterial Proteins / Q000737:chemistry / Q000378:metabolism*; D002462:Cell Membrane / Q000187:drug effects / Q000378:metabolism; D002940:Circadian Rhythm / Q000187:drug effects*; D056925:Circadian Rhythm Signaling Peptides and Proteins; D000458:Cyanobacteria / Q000187:drug effects* / Q000235:genetics / Q000378:metabolism*; D003991:Dibromothymoquinone / Q000737:chemistry / Q000378:metabolism / Q000494:pharmacology*; D015964:Gene Expression Regulation, Bacterial; D008027:Light; D009682:Magnetic Resonance Spectroscopy; D008970:Molecular Weight; D010084:Oxidation-Reduction; D010766:Phosphorylation; D011485:Protein Binding; D011494:Protein Kinases / Q000737:chemistry / Q000378:metabolism*; D012680:Sensitivity and Specificity
chemical_list: D001426:Bacterial Proteins; D056925:Circadian Rhythm Signaling Peptides and Proteins; C114271:KaiC protein, cyanobacteria; D003991:Dibromothymoquinone; D011494:Protein Kinases; C411989:CikA protein, bacteria