Recombinant Synechococcus elongatus Circadian clock oscillator protein KaiA (kaiA)

Function

KaiA binds oxidized quinones via its N-terminal PsR domain and is able to sense redox signals directly; quinone analog DBMIB (2,5-dibromo-3-methyl-6-isopropyl-p-benzoquinone) blocks KaiA stimulation of KaiC phosphorylation (PubMed:20231482). The homodimer binds up to 8 quinones in the crystal structure, 3 in the PsR domain and 1 via the C-terminal helical bundle. Binding of oxidized quinone to the KaiA C-terminal domain reduces the phosphorylation of KaiC slightly; quinones may interact in a complex manner with KaiA to mediate clock input (PubMed:23020633)

Subunit

Homodimer (PubMed:15007067, PubMed:23020633, PubMed:26200123). The KaiABC complex composition changes during the circadian cycle to control KaiC phosphorylation. Complexes KaiC(6), KaiA(2-4):KaiC(6), KaiB(6):KaiC(6) and KaiC(6):KaiB(6):KaiA(12) are among the most important forms, many form cooperatively (PubMed:28302852, PubMed:34618577). The KaiA:KaiB complex is only found at 20-24 hours in the circadian cycle (subjective night) (PubMed:15347812). Binds to the C-terminal A-loop of KaiC via a coiled-coil structure (PubMed:26200123). KaiA and CikA compete for binding to KaiB(fs) (PubMed:26113641, PubMed:28302851). CikA copurifies with this protein in the clock complex (PubMed:17088557). Interacts with LdpA (PubMed:15775978)

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• Holtman C.K. et al. Synechococcus elongatus PCC7942 cosmid 7G3. (JUN-)
• Copeland A. et al. Complete sequence of chromosome 1 of Synechococcus elongatus PCC 7942. (AUG-)
• Iwasaki H. et al. Physical interactions among circadian clock proteins KaiA, KaiB and KaiC in cyanobacteria. — EMBO J. (1999)
• Iwasaki H. et al. A kaiC-interacting sensory histidine kinase, SasA, necessary to sustain robust circadian oscillation in cyanobacteria. — Cell (2000)
• Taniguchi Y. et al. Two KaiA-binding domains of cyanobacterial circadian clock protein KaiC. — FEBS Lett. (2001)
• Nishimura H. et al. Mutations in KaiA, a clock protein, extend the period of circadian rhythm in the cyanobacterium Synechococcus elongatus PCC 7942. — Microbiology (2002)
• Iwasaki H. et al. KaiA-stimulated KaiC phosphorylation in circadian timing loops in cyanobacteria. — Proc. Natl. Acad. Sci. U.S.A. (2002)