Structural highlights
Function
KAIA_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
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Publication Abstract from PubMed
KaiA is a two-domain circadian clock protein in cyanobacteria, acting as the positive element in a feedback loop that sustains the oscillation. The structure of the N-terminal domain of KaiA is that of a pseudo-receiver, similar to those of bacterial response regulators, which likely interacts with components of the clock-resetting pathway. The C-terminal domain of KaiA is highly conserved among cyanobacteria and enhances the autokinase activity of KaiC. Here we present the NMR structure of the C-terminal domain of KaiA from the thermophilic cyanobacterium Thermosynechococcus elongatus BP-1. This domain adopts a novel all alpha-helical homodimeric structure. Several mutations known to affect the period of the circadian oscillator are shown to be located at an exposed groove near the dimer interface. This NMR structure and a 21-A-resolution electron microscopy structure of the hexameric KaiC particle allow us to postulate a mode of KaiA-KaiC interaction, in which KaiA binds a linker region connecting two globular KaiC domains.
NMR structure of the KaiC-interacting C-terminal domain of KaiA, a circadian clock protein: implications for KaiA-KaiC interaction.,Vakonakis I, Sun J, Wu T, Holzenburg A, Golden SS, LiWang AC Proc Natl Acad Sci U S A. 2004 Feb 10;101(6):1479-84. Epub 2004 Jan 28. PMID:14749515[2]
From MEDLINE®/PubMed®, a database of the U.S. National Library of Medicine.
See Also
References
- ↑ Tseng R, Chang YG, Bravo I, Latham R, Chaudhary A, Kuo NW, Liwang A. Cooperative KaiA-KaiB-KaiC interactions affect KaiB/SasA competition in the circadian clock of cyanobacteria. J Mol Biol. 2014 Jan 23;426(2):389-402. PMID:24112939 doi:10.1016/j.jmb.2013.09.040
- ↑ Vakonakis I, Sun J, Wu T, Holzenburg A, Golden SS, LiWang AC. NMR structure of the KaiC-interacting C-terminal domain of KaiA, a circadian clock protein: implications for KaiA-KaiC interaction. Proc Natl Acad Sci U S A. 2004 Feb 10;101(6):1479-84. Epub 2004 Jan 28. PMID:14749515 doi:10.1073/pnas.0305516101
