1vgl
Crystal structure of tetrameric KaiB from T.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 PubMedKaiB is a component of the circadian clock molecular machinery in cyanobacteria, which are the simplest organisms that exhibit circadian rhythms. Here we report the x-ray crystal structure of KaiB from the thermophilic cyanobacterium Thermosynechococcus elongatus BP-1. The KaiB crystal diffracts at a resolution of 2.6 A and includes four subunits organized as a dimer of dimers, each composed of two non-equivalent subunits. The overall shape of the tetramer is an elongated hexagonal plate, with a single positively charged cleft flanked by two negatively charged ridges whose surfaces includes several terminal chains. Site-directed mutagenesis of Synechococcus KaiB confirmed that alanine substitution of residues Lys-11 or Lys-43 in the cleft, or deletion of C-terminal residues 95-108, which forms part of the ridges, strongly weakens in vivo circadian rhythms. Characteristics of KaiB deduced from the x-ray crystal structure were also confirmed by physicochemical measurements of KaiB in solution. These data suggest that the positively charged cleft and flanking negatively charged ridges in KaiB are essential for the biological function of KaiB in the circadian molecular machinery in cyanobacteria. Functionally important substructures of circadian clock protein KaiB in a unique tetramer complex.,Iwase R, Imada K, Hayashi F, Uzumaki T, Morishita M, Onai K, Furukawa Y, Namba K, Ishiura M J Biol Chem. 2005 Dec 30;280(52):43141-9. Epub 2005 Oct 13. PMID:16227211[7] From MEDLINE®/PubMed®, a database of the U.S. National Library of Medicine. See AlsoReferences
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