1wwj
From Proteopedia
crystal structure of KaiB from Synechocystis sp.
Structural highlights
Function[KAIB_SYNY3] Component of the KaiABC clock protein complex, which constitutes the main circadian regulator in cyanobacteria. The KaiABC complex may act as a promoter-non-specific transcription regulator that represses transcription, possibly by acting on the state of chromosome compaction. In the complex, it decreases the phosphorylation status of KaiC. It has no effect on KaiC by itself, but instead needs the presence of both KaiA and KaiC, suggesting that it acts by antagonizing the interaction between KaiA and KaiC (By similarity). Evolutionary Conservation Check, as determined by ConSurfDB. You may read the explanation of the method and the full data available from ConSurf. Publication Abstract from PubMedCyanobacteria are among the simplest organisms that show daily rhythmicity. Their circadian rhythms consist of the localization, interaction, and accumulation of various proteins, including KaiA, KaiB, KaiC, and SasA. We have determined the 1.9-angstroms resolution crystallographic structure of the cyanobacterial KaiB clock protein from Synechocystis sp. PCC6803. This homotetrameric structure reveals a novel KaiB interface for protein-protein interaction; the protruding hydrophobic helix-turn-helix motif of one subunit fits into a groove between two beta-strands of the adjacent subunit. A cyanobacterial mutant, in which the Asp-Lys salt bridge mediating this tetramer-forming interaction is disrupted by mutation of Asp to Gly, exhibits severely impaired rhythmicity (a short free-running period; approximately 19 h). The KaiB tetramer forms an open square, with positively charged residues around the perimeter. KaiB is localized on the phospholipid-rich membrane and translocates to the cytosol to interact with the other Kai components, KaiA and KaiC. KaiB antagonizes the action of KaiA on KaiC, and shares a sequence-homologous domain with the SasA kinase. Based on our structure, we discuss functional roles for KaiB in the circadian clock. Tetrameric architecture of the circadian clock protein KaiB. A novel interface for intermolecular interactions and its impact on the circadian rhythm.,Hitomi K, Oyama T, Han S, Arvai AS, Getzoff ED J Biol Chem. 2005 May 13;280(19):19127-35. Epub 2005 Feb 16. PMID:15716274[1] From MEDLINE®/PubMed®, a database of the U.S. National Library of Medicine. See AlsoReferences
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