Molecule of the Month: Circadian Clock Proteins
Circadian clock proteins measure time in our cells
Counting the Hours
Synchronize Your Watches
Exploring the Structure
KaiC Circadian Clock Protein (PDB entry 2gbl)
The KaiC clock protein (PDB entry 2gbl ) is composed of six identical subunits that form a barrel-shaped structure. The protein is shown from side here, with two subunits removed to show the tunnel that runs through the middle. The phosphates that tick off the hours of each day are added to a serine and a threonine on each subunit. They are buried deep inside the tunnel, near the binding site for ATP, shown here in green. KaiA stimulates KaiC to add these phosphate groups to itself, and KaiB blocks the action of KaiA, allowing KaiC to remove these phosphates from itself. The speed of these reactions are all calibrated so that the whole process takes 24 hours to complete. To explore this structure in more detail, click on the image for an interactive JSmol.
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- M. J. Rust, J. S. Markson, W. S. Lane, D. S. Fisher and E. K O'Shea. (2007) Ordered phosphorylation governs oscillation of a three-protein circadian clock. Science 318, 809-812.
- J. Arendt and D. J. Skene (2005) Melatonin as a chronobiotic. Sleep Medicine Reviews 9, 25-39.
- D. Bell-Pedersen, V. M. Cassone, D. J. earnest, S. S. Golden, P. E. Hardin, T. L. Thomas and M. J. Zoran (2005) Circadian rhythms from multiple oscillators: lessons from diverse organisms. Nature Reviews Genetics 6, 544-556.
- S. L. Harmer, S. Panda and S. A. Kay (2001) Molecular bases of circadian rhythms. Annual Review of Cell and Developmental Biology 17, 215-253.
January 2008, David Goodsellhttp://doi.org/10.2210/rcsb_pdb/mom_2008_1