2qke
Wild Type Crystal Structure of Full Length Circadian Clock Protein KaiB from Thermosynechococcus elongatus BP-1
Structural highlights
FunctionKAIB_THEVB Key component of the KaiABC oscillator complex, which constitutes the main circadian regulator in cyanobacteria (PubMed:24112939, PubMed:16227211, PubMed:28302851). Its composition changes during the circadian cycle to control KaiC phosphorylation. KaiA stimulates KaiC autophosphorylation, while KaiB sequesters KaiA, leading to KaiC autodephosphorylation. KaiA binding to KaiC yields KaiA(2-4):KaiC(6) complexes which stimulate KaiC autophosphorylation. Phospho-Ser-431 KaiC accumulation triggers binding of KaiB to form the KaiB(6):KaiC(6) complex, leading to changes in the output regulators CikA and SasA (PubMed:28302851). KaiB switches to a thioredoxin-like fold (KaiB(fs)) in complex with KaiC (PubMed:26113641, PubMed:28302851). KaiB(6):KaiC(6) formation exposes a site for KaiA binding that sequesters KaiA from the CII domain, making the KaiC(6):KaiB(6):KaiA(12) complex that results in KaiC autodephosphorylation. Complete dephosphorylation of KaiC leads to dissociation of KaiA(2):KaiB(1), completing 1 cycle of the Kai oscillator (PubMed:28302851).[1] [2] [3] [4] A metamorphic protein which reversibly switches between an inactive tetrameric fold and a rare, thioredoxin-like monomeric fold (KaiB(fs)). KaiB(fs) binds phospho-KaiC, KaiA and CikA. KaiA and CikA compete for binding to KaiB(fs), and KaiB(fs) and SasA compete for binding to KaiC, thus the clock oscillator and output signal pathway are tightly coupled.[HAMAP-Rule:MF_01835][5] [6] 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 PubMedThe circadian clock of the cyanobacterium Synechococcus elongatus can be reconstituted in vitro by the KaiA, KaiB and KaiC proteins in the presence of ATP. The principal clock component, KaiC, undergoes regular cycles between hyper- and hypo-phosphorylated states with a period of ca. 24 h that is temperature compensated. KaiA enhances KaiC phosphorylation and this enhancement is antagonized by KaiB. Throughout the cycle Kai proteins interact in a dynamic manner to form complexes of different composition. We present a three-dimensional model of the S. elongatus KaiB-KaiC complex based on X-ray crystallography, negative-stain and cryo-electron microscopy, native gel electrophoresis and modelling techniques. We provide experimental evidence that KaiB dimers interact with KaiC from the same side as KaiA and for a conformational rearrangement of the C-terminal regions of KaiC subunits. The enlarged central channel and thus KaiC subunit separation in the C-terminal ring of the hexamer is consistent with KaiC subunit exchange during the dephosphorylation phase. The proposed binding mode of KaiB explains the observation of simultaneous binding of KaiA and KaiB to KaiC, and provides insight into the mechanism of KaiB's antagonism of KaiA. Structural model of the circadian clock KaiB-KaiC complex and mechanism for modulation of KaiC phosphorylation.,Pattanayek R, Williams DR, Pattanayek S, Mori T, Johnson CH, Stewart PL, Egli M EMBO J. 2008 Jun 18;27(12):1767-78. Epub 2008 May 22. PMID:18497745[7] From MEDLINE®/PubMed®, a database of the U.S. National Library of Medicine. See AlsoReferences
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