6x61

From Proteopedia

Crystal structure of the N-terminal thioredoxin domain of SasA in complex with the N-terminal CI domain of KaiC from Thermosynchococcus elongatus

Structural highlights

6x61 is a 12 chain structure with sequence from Thermosynechococcus vestitus BP-1. Full crystallographic information is available from OCA. For a guided tour on the structure components use FirstGlance.
Method:	X-ray diffraction, Resolution 3.2Å
Ligands:
Resources:	FirstGlance, OCA, PDBe, RCSB, PDBsum, ProSAT

Function

KAIC_THEVB Core component of the KaiABC clock protein complex, which constitutes the main circadian regulator in cyanobacteria. Binds to DNA. The KaiABC complex may act as a promoter-nonspecific transcription regulator that represses transcription, possibly by acting on the state of chromosome compaction (By similarity).

Publication Abstract from PubMed

Circadian clocks control gene expression to provide an internal representation of local time. We report reconstitution of a complete cyanobacterial circadian clock in vitro, including the central oscillator, signal transduction pathways, downstream transcription factor, and promoter DNA. The entire system oscillates autonomously and remains phase coherent for many days with a fluorescence-based readout that enables real-time observation of each component simultaneously without user intervention. We identified the molecular basis for loss of cycling in an arrhythmic mutant and explored fundamental mechanisms of timekeeping in the cyanobacterial clock. We find that SasA, a circadian sensor histidine kinase associated with clock output, engages directly with KaiB on the KaiC hexamer to regulate period and amplitude of the central oscillator. SasA uses structural mimicry to cooperatively recruit the rare, fold-switched conformation of KaiB to the KaiC hexamer to form the nighttime repressive complex and enhance rhythmicity of the oscillator, particularly under limiting concentrations of KaiB. Thus, the expanded in vitro clock reveals previously unknown mechanisms by which the circadian system of cyanobacteria maintains the pace and rhythmicity under variable protein concentrations.

Reconstitution of an intact clock reveals mechanisms of circadian timekeeping.,Chavan AG, Swan JA, Heisler J, Sancar C, Ernst DC, Fang M, Palacios JG, Spangler RK, Bagshaw CR, Tripathi S, Crosby P, Golden SS, Partch CL, LiWang A Science. 2021 Oct 8;374(6564):eabd4453. doi: 10.1126/science.abd4453. Epub 2021 , Oct 8. PMID:34618577^[1]

From MEDLINE®/PubMed®, a database of the U.S. National Library of Medicine.

References

↑ Chavan AG, Swan JA, Heisler J, Sancar C, Ernst DC, Fang M, Palacios JG, Spangler RK, Bagshaw CR, Tripathi S, Crosby P, Golden SS, Partch CL, LiWang A. Reconstitution of an intact clock reveals mechanisms of circadian timekeeping. Science. 2021 Oct 8;374(6564):eabd4453. PMID:34618577 doi:10.1126/science.abd4453