Recombinant Synechococcus elongatus Circadian clock protein kinase kaiC (kaiC)

Function

KaiC is important for metabolic partitioning during the dark to light shift, modulating the balance between the Calvin cycle and oxidative pentose phosphate pathway under natural growth conditions

Subunit

Homohexamer resembling 2 stacked donuts with a central pore nearly blocked on one side; hexamerization is dependent on ATP-binding. Binds 12 ATP; 6 between each subunit in both layers (PubMed:15304218, PubMed:15347809, PubMed:22304631, PubMed:24474762, PubMed:35427168). KaiB only binds to phospho-Ser-431 KaiC (not doubly phosphorylated KaiC) (PubMed:17717528, PubMed:29892030). Complex formation between KaiB and KaiC is regulated by the phosphorylation state of KaiC and by an ATP hydrolysis-driven conformation change in the CI ring of KaiC; complex formation is slow. Slow complex formation is crucial for the timing of the circadian period (PubMed:29892030). KaiB switches to a thioredoxin-like form called KaiB(fs) when bound to KaiC (PubMed:26113641). 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). Interacts directly with KaiB and SasA (PubMed:10786837). The CI domain binds to KaiB and SasA; as they have a similar fold they compete for the same site on CI (PubMed:29892030, PubMed:34618577). CikA interacts with this protein in the clock complex (PubMed:17088557). Binds to the C-terminus of KaiA via a coiled-coil structure (PubMed:26200123). Forms KaiC(6):KaiB(1) and KaiC(6):KaiB(6) complexes (PubMed:23796516, PubMed:24474762)

• Ishiura M. et al. Expression of a gene cluster kaiABC as a circadian feedback process in cyanobacteria. — Science (1998)
• 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-)
• Nishiwaki T. et al. Role of KaiC phosphorylation in the circadian clock system of Synechococcus elongatus PCC 7942. — Proc. Natl. Acad. Sci. U.S.A. (2004)
• Iwasaki H. et al. Physical interactions among circadian clock proteins KaiA, KaiB and KaiC in cyanobacteria. — EMBO J. (1999)
• Nishiwaki T. et al. Nucleotide binding and autophosphorylation of the clock protein KaiC as a circadian timing process of cyanobacteria. — Proc. Natl. Acad. Sci. U.S.A. (2000)
• 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)