1v2z
From Proteopedia
Crystal structure of the C-terminal domain of Thermosynechococcus elongatus BP-1 KaiA
Structural highlights
FunctionKAIA_THEVB Key component of the KaiABC oscillator complex, which constitutes the main circadian regulator in cyanobacteria. Complex 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 the KaiC CII domain during the subjective day yields KaiA(2-4):KaiC(6) complexes which stimulate KaiC autophosphorylation. Phospho-Ser-431 KaiC accumulation triggers binding of KaiB during the subjective night to form the KaiB(6):KaiC(6) complex, leading to changes in the output regulators CikA and SasA. KaiB(6):KaiC(6) formation exposes a site for KaiA binding on KaiB that sequesters KaiA from KaiC's CII domain, making the KaiC(6):KaiB(6):KaiA(12) complex resulting in KaiC autodephosphorylation. Complete dephosphorylation of KaiC leads to dissociation of KaiA(2):KaiB(1), completing 1 cycle of the Kai oscillator (By similarity). Formation of the KaiB:KaiC complex is promoted by KaiA, helping switch KaiC from its autophosphorylation to autodephosphatase function (PubMed:24112939).[UniProtKB:Q79PF6][1] Binds oxidized quinones via the N-terminal PsR domain, allowing it to sense redox changes and possibly mediate clock input.[UniProtKB:Q79PF6] 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 PubMedKaiA, KaiB and KaiC constitute the circadian clock machinery in cyanobacteria, and KaiA activates kaiBC expression whereas KaiC represses it. Here we show that KaiA is composed of three functional domains, the N-terminal amplitude-amplifier domain, the central period-adjuster domain and the C-terminal clock-oscillator domain. The C-terminal domain is responsible for dimer formation, binding to KaiC, enhancing KaiC phosphorylation and generating the circadian oscillations. The X-ray crystal structure at a resolution of 1.8 A of the C-terminal clock-oscillator domain of KaiA from the thermophilic cyanobacterium Thermosynechococcus elongatus BP-1 shows that residue His270, located at the center of a KaiA dimer concavity, is essential to KaiA function. KaiA binding to KaiC probably occurs via the concave surface. On the basis of the structure, we predict the structural roles of the residues that affect circadian oscillations. Crystal structure of the C-terminal clock-oscillator domain of the cyanobacterial KaiA protein.,Uzumaki T, Fujita M, Nakatsu T, Hayashi F, Shibata H, Itoh N, Kato H, Ishiura M Nat Struct Mol Biol. 2004 Jul;11(7):623-31. Epub 2004 May 30. PMID:15170179[2] From MEDLINE®/PubMed®, a database of the U.S. National Library of Medicine. See AlsoReferences
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