4kso | pdb_00004kso
Crystal Structure of Circadian clock protein KaiB from S.Elongatus
Structural highlights
FunctionKAIB_SYNE7 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 need the presence of both KaiA and KaiC, suggesting that it acts by antagonizing the interaction between KaiA and KaiC.[1] [2] [3] [4] Publication Abstract from PubMedThe circadian control of cellular processes in cyanobacteria is regulated by a posttranslational oscillator formed by three Kai proteins. During the oscillator cycle KaiA serves to promote autophosphorylation of KaiC while KaiB counteracts this effect. Here we present a crystallographic structure of the wild-type Synechococcus elongatus KaiB and a cryoEM structure of a KaiBC complex. The crystal structure shows the expected dimer core structure and significant conformational variations of the KaiB C-terminal region, which is functionally important in maintaining rhythmicity. The KaiBC sample was formed with a C-terminally truncated form of KaiC, KaiC-Delta489, which is persistently phosphorylated. The KaiB-KaiC-Delta489 structure reveals that the KaiC hexamer can bind six monomers of KaiB, which form a continuous ring of density in the KaiBC complex. We performed cryoEM guided molecular dynamics flexible fitting simulations with crystal structures of KaiB and KaiC to probe the KaiBC protein-protein interface. This analysis indicated a favorable binding mode for the KaiB monomer on the CII end of KaiC, involving two adjacent KaiC subunits and spanning an ATP binding cleft. A KaiC mutation, R468C, which has been shown to affect the affinity of KaiB for KaiC and lengthen the period in a bioluminescence rhythm assay, is found within the middle of the predicted KaiBC interface. The proposed KaiB binding mode blocks access to the ATP binding cleft in the CII ring of KaiC, which provides insight into how KaiB might influence the phosphorylation status of KaiC. CryoEM and Molecular Dynamics of the Circadian KaiB-KaiC Complex Indicates KaiB Monomers Interact with KaiC and Block ATP Binding Clefts.,Villarreal SA, Pattanayek R, Williams DR, Mori T, Qin X, Johnson CH, Egli M, Stewart PL J Mol Biol. 2013 Jun 21. pii: S0022-2836(13)00397-5. doi:, 10.1016/j.jmb.2013.06.018. PMID:23796516[5] From MEDLINE®/PubMed®, a database of the U.S. National Library of Medicine. See AlsoReferences
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