Circadian Clock Protein KaiC
From Proteopedia
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== KaiC Homohexameric Complex == | == KaiC Homohexameric Complex == | ||
<StructureSection load='1TF7' size='350' side='right' caption='Structure of KaiC (PDB entry [[1TF7]])' scene=''> | <StructureSection load='1TF7' size='350' side='right' caption='Structure of KaiC (PDB entry [[1TF7]])' scene=''> | ||
| - | The structure of KaiC resembles a double donut formation with a central pore through the center. It is comprised of two subunits, CI and CII, and each subunit is made up of six | + | The structure of KaiC resembles a double donut formation with a central pore through the center. It is comprised of two subunits, CI and CII, and each subunit is made up of six nearly homologous monomers. The entire molecule is massive, comprising of 519 amino acid residues, and spanning 100 Angstroms in diameter. The waist of the molecule (the region between CI and CII) has a diameter of 62 Angstroms. The central pore that runs through the molecule is wider at the CI subunit end, 22 Angstroms, and narrows to a nearly closed conformation appears to be secured by six arginine residues. Their basic, polar nature and untidiness of this region indicate the possibility of conformational change, such as closing and opening. (1) |
</StructureSection> | </StructureSection> | ||
Revision as of 01:17, 3 December 2012
Contents |
Introduction
Biological Circadian Clocks are self-sustaining oscillators that function on a rhythmic cycle of or around 24 hours. The are found in almost all organisms, the simplest of which are cyanobacteria, which have been extensively studied in order to determine the mechanism of the fine-tunes biological process of circadian rhythmicity.
KaiC - KaiA - KaiB System
KaiC is the central clock protein, which has autokinase and autophosphorylase activity. Yet in the presence of ATP, KaiC cannot perform it's autophosphorylation function. It requires two other proteins, KaiA and KaiB, the genes of which are found in the same cluster on the chromosome (1). Although KaiC phosphorylates itself, the presence of KaiA and KaiB are essential to rhythmicity. KaiA stimulates KaiC autophosphorylation, while KaiB antagonizes the process possibly by enhancing KaiC dephosphorylation. Even in the presence of high ATP, KaiB still prompts KaiC to dephosphorylate.
KaiC Homohexameric Complex
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KaiC Autophosphorylation Sites
(difference between ATP binding and phosphorylation residues) (Key residues = T432, S431, T426) (show 3D image of these sites and highlight bonds/interactions)
KaiA <-> KaiC Interaction Site
(show 3D image of KaiC site for KaiA binding and highlight key residues in interaction -weak? strong? any ions in site? how does it stabilize autophosporylation?) KaiA binds to the interface of the two donut-shaped KaiC subunits, CI and CII. This area, known as the "waist" of the molecule
KaiB <-> KaiC Interaction Site
(show 3D image of KaiC site for KaiB binding and highlight key residues in interaction -weak? strong? ions in site? how does it stabilize dephosphorylation/destabilize phosphorylation/destabilize KaiA?)
Biological Importance
- Nearly all promoters in a cyanobacteria are under circadian control. [function is important to whole life cycle] (1)
Proteopedia Page Contributors and Editors (what is this?)
Ashley Beechan, Michal Harel, Alexander Berchansky, Jaime Prilusky
