2GBL: Crystal Structure Of Full Length Circadian Clock Protein Kaic With Phosphorylation Sites

The cyanobacterial circadian clock can be reconstituted in vitro by mixing recombinant KaiA, KaiB and KaiC proteins with ATP, producing KaiC phosphorylation and dephosphorylation cycles that have a regular rhythm with a ca. 24-h period and are temperature-compensated. KaiA and KaiB are modulators of KaiC phosphorylation, whereby KaiB antagonizes KaiA's action. Here, we present a complete crystallographic model of the Synechococcus elongatus KaiC hexamer that includes previously unresolved portions of the C-terminal regions, and a negative-stain electron microscopy study of S. elongatus and Thermosynechococcus elongatus BP-1 KaiA-KaiC complexes. Site-directed mutagenesis in combination with EM reveals that KaiA binds exclusively to the CII half of the KaiC hexamer. The EM-based model of the KaiA-KaiC complex reveals protein-protein interactions at two sites: the known interaction of the flexible C-terminal KaiC peptide with KaiA, and a second postulated interaction between the apical region of KaiA and the ATP binding cleft on KaiC. This model brings KaiA mutation sites that alter clock period or abolish rhythmicity into contact with KaiC and suggests how KaiA might regulate KaiC phosphorylation.
PDB ID: 2GBLDownload
MMDB ID: 43820
PDB Deposition Date: 2006/3/10
Updated in MMDB: 2012/11
Experimental Method:
x-ray diffraction
Resolution: 2.8  Å
Source Organism:
Similar Structures:
Biological Unit for 2GBL: hexameric; determined by author and by software (PISA)
Molecular Components in 2GBL
Label Count Molecule
Proteins (6 molecules)
Circadian Clock Protein Kinase Kaic
Molecule annotation
Circadian Clock Protein Kinase Kaic
Molecule annotation
Chemicals (18 molecules)
* Click molecule labels to explore molecular sequence information.

Citing MMDB