Protein-Protein Interactions in the Cyanobacterial Circadian Clock: Structure of KaiA Dimer in Complex with C-Terminal KaiC Peptides at 2.8 Å Resolution

Biochemistry. 2015 Aug 4;54(30):4575-8. doi: 10.1021/acs.biochem.5b00694. Epub 2015 Jul 24.


In the cyanobacterial circadian clock, the KaiA, -B, and -C proteins with ATP constitute a post-translational oscillator. KaiA stimulates the KaiC autokinase, and KaiB antagonizes KaiA action. KaiA contacts the intrinsically disordered C-terminal regions of KaiC hexamer to promote phosphorylation across subunit interfaces. The crystal structure of KaiA dimer from Synechococcus elongatus with two KaiC C-terminal 20mer peptides bound reveals that the latter adopt an α-helical conformation and contact KaiA α-helical bundles via mostly hydrophobic interactions. This complex and the crystal structure of KaiC hexamer with truncated C-terminal tails can be fit into the electron microscopy (EM) density of the KaiA:KaiC complex. The hybrid model helps rationalize clock phenotypes of KaiA and KaiC mutants.

Publication types

  • Research Support, N.I.H., Extramural
  • Research Support, Non-U.S. Gov't

MeSH terms

  • Bacterial Proteins / chemistry*
  • Bacterial Proteins / genetics
  • Circadian Rhythm Signaling Peptides and Proteins / chemistry*
  • Circadian Rhythm Signaling Peptides and Proteins / genetics
  • Crystallography, X-Ray
  • Models, Molecular*
  • Mutation
  • Peptides / chemistry*
  • Peptides / genetics
  • Protein Multimerization*
  • Protein Structure, Quaternary
  • Protein Structure, Secondary
  • Synechococcus / chemistry*
  • Synechococcus / genetics


  • Bacterial Proteins
  • Circadian Rhythm Signaling Peptides and Proteins
  • KaiA protein, cyanobacteria
  • KaiC protein, cyanobacteria
  • Peptides

Associated data

  • PDB/5C5E