5jyt
From Proteopedia
NMR structure of foldswitch-stablized KaiB from Thermosynechococcus elongatus
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] Publication Abstract from PubMedCircadian clocks are ubiquitous timing systems that induce rhythms of biological activities in synchrony with night and day. In cyanobacteria, timing is generated by a posttranslational clock consisting of KaiA, KaiB, and KaiC proteins and a set of output signaling proteins, SasA and CikA, which transduce this rhythm to control gene expression. Here, we describe crystal and nuclear magnetic resonance structures of KaiB-KaiC,KaiA-KaiB-KaiC, and CikA-KaiB complexes. They reveal how the metamorphic properties of KaiB, a protein that adopts two distinct folds, and the post-adenosine triphosphate hydrolysis state of KaiC create a hub around which nighttime signaling events revolve, including inactivation of KaiA and reciprocal regulation of the mutually antagonistic signaling proteins, SasA and CikA. Structural basis of the day-night transition in a bacterial circadian clock.,Tseng R, Goularte NF, Chavan A, Luu J, Cohen SE, Chang YG, Heisler J, Li S, Michael AK, Tripathi S, Golden SS, LiWang A, Partch CL Science. 2017 Mar 17;355(6330):1174-1180. doi: 10.1126/science.aag2516. Epub 2017, Mar 16. PMID:28302851[7] From MEDLINE®/PubMed®, a database of the U.S. National Library of Medicine. See AlsoReferences
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