Crystal Structure Analysis of Kai A from PCC7120

Experimental Data Snapshot

  • Resolution: 2.00 Å
  • R-Value Free: 0.269 
  • R-Value Work: 0.241 

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Anabaena circadian clock proteins KaiA and KaiB reveal a potential common binding site to their partner KaiC

Garces, R.G.Wu, N.Gillon, W.Pai, E.F.

(2004) EMBO J 23: 1688-1698

  • DOI: https://doi.org/10.1038/sj.emboj.7600190
  • Primary Citation of Related Structures:  
    1R5P, 1R5Q

  • PubMed Abstract: 

    The cyanobacterial clock proteins KaiA and KaiB are proposed as regulators of the circadian rhythm in cyanobacteria. Mutations in both proteins have been reported to alter or abolish circadian rhythmicity. Here, we present molecular models of both KaiA and KaiB from the cyanobacteria Anabaena sp PCC7120 deduced by crystal structure analysis, and we discuss how clock-changing or abolishing mutations may cause their resulting circadian phenotype. The overall fold of the KaiA monomer is that of a four-helix bundle. KaiB, on the other hand, adopts an alpha-beta meander motif. Both proteins purify and crystallize as dimers. While the folds of the two proteins are clearly different, their size and some surface features of the physiologically relevant dimers are very similar. Notably, the functionally relevant residues Arg 69 of KaiA and Arg 23 of KaiB align well in space. The apparent structural similarities suggest that KaiA and KaiB may compete for a potential common binding site on KaiC.

  • Organizational Affiliation

    Department of Medical Biophysics, University of Toronto, Toronto, ON, Canada.

Find similar proteins by:  (by identity cutoff)  |  3D Structure
Entity ID: 1
MoleculeChains Sequence LengthOrganismDetailsImage
circadian oscillation regulator102Nostoc sp. PCC 7120 = FACHB-418Mutation(s): 0 
Gene Names: Kai A
Find proteins for Q8YT42 (Nostoc sp. (strain PCC 7120 / SAG 25.82 / UTEX 2576))
Explore Q8YT42 
Go to UniProtKB:  Q8YT42
Entity Groups  
Sequence Clusters30% Identity50% Identity70% Identity90% Identity95% Identity100% Identity
UniProt GroupQ8YT42
Sequence Annotations
  • Reference Sequence
Experimental Data & Validation

Experimental Data

  • Resolution: 2.00 Å
  • R-Value Free: 0.269 
  • R-Value Work: 0.241 
  • Space Group: P 65 2 2
Unit Cell:
Length ( Å )Angle ( ˚ )
a = 57.299α = 90
b = 57.299β = 90
c = 137.515γ = 120
Software Package:
Software NamePurpose
DENZOdata reduction
SCALEPACKdata scaling

Structure Validation

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Entry History 

Deposition Data

Revision History  (Full details and data files)

  • Version 1.0: 2004-05-04
    Type: Initial release
  • Version 1.1: 2008-04-29
    Changes: Version format compliance
  • Version 1.2: 2011-07-13
    Changes: Derived calculations, Source and taxonomy, Version format compliance