Q79PF4 · KAIC_SYNE7
- ProteinCircadian clock oscillator protein KaiC
- GenekaiC
- StatusUniProtKB reviewed (Swiss-Prot)
- Amino acids519 (go to sequence)
- Protein existenceEvidence at protein level
- Annotation score5/5
Function
function
The KaiABC oscillator complex constitutes the main circadian regulator in cyanobacteria (PubMed:15831759, PubMed:17717528, PubMed:26113637, PubMed:28302852, PubMed:9727980).
Complex composition changes during the circadian cycle to control KaiC phosphorylation; KaiA stimulates KaiC autophosphorylation, while KaiB sequesters KaiA, leading to KaiC autodephosphorylation (PubMed:26113637, PubMed:28302852).
The Kai complex controls chromosome condensation, leading to a transcription accessible chromosome during the first half of the circadian cycle and a compact, less transcription-accessible chromosome during the latter half (PubMed:16707582).
Clock output pathways impact the RpaA transcriptional regulator (PubMed:20133618, PubMed:26113637, PubMed:28302852).
Circadian oscillations can be generated in vitro by incubating KaiA, KaiB and KaiC with 1 mM ATP. The cycle is self-sustainable for at least 3 cycles and resistant to temperature changes. Mutations in KaiC alone prolong or reduce the circadian rhythm (PubMed:15831759).
A very robust clock is reconstituted with KaiA, KaiB, KaiC, SasA, CikA and RpaA; output is measured by transcription from an appropriate reporter (PubMed:34618577).
Complex composition changes during the circadian cycle to control KaiC phosphorylation; KaiA stimulates KaiC autophosphorylation, while KaiB sequesters KaiA, leading to KaiC autodephosphorylation (PubMed:26113637, PubMed:28302852).
The Kai complex controls chromosome condensation, leading to a transcription accessible chromosome during the first half of the circadian cycle and a compact, less transcription-accessible chromosome during the latter half (PubMed:16707582).
Clock output pathways impact the RpaA transcriptional regulator (PubMed:20133618, PubMed:26113637, PubMed:28302852).
Circadian oscillations can be generated in vitro by incubating KaiA, KaiB and KaiC with 1 mM ATP. The cycle is self-sustainable for at least 3 cycles and resistant to temperature changes. Mutations in KaiC alone prolong or reduce the circadian rhythm (PubMed:15831759).
A very robust clock is reconstituted with KaiA, KaiB, KaiC, SasA, CikA and RpaA; output is measured by transcription from an appropriate reporter (PubMed:34618577).
The level of KaiC phosphorylation and KaiC ATPase activity represent the key features of the biochemical oscillator. KaiA homodimer binding to the KaiC CII domain stimulates KaiC's ATPase activity and forms KaiA(2-4):KaiC6 complexes, which stimulate KaiC autophosphorylation first on Thr-432 then Ser-431. Phospho-Ser-431-KaiC accumulation triggers binding of KaiB to CI to form the KaiB6:KaiC6 complex, leading to changes in the output regulators CikA and SasA. KaiB6:KaiC6 formation exposes a site for KaiA binding that sequesters KaiA from the CII domain, making the KaiC6:KaiB6:KaiA12 complex that results in KaiC autodephosphorylation. Complete dephosphorylation of KaiC leads to dissociation of KaiA2:KaiB1, completing 1 cycle of the Kai oscillator.
Has a weak, temperature-independent ATPase activity (about 15 molecules of ATP per day); the addition of KaiA and KaiB increases activity slightly and makes the activity oscillate with a circadian period in vitro for over 60 hours. ATPase activity defines the circadian period. The phosphorylation state of KaiC modulates its ATPase activity and effects KaiB binding.
There are several clock output pathways; SasA/RpaA, CikA/RpaA and LabA (PubMed:20133618).
KaiC enhances the autophosphorylation activity of SasA, which then transfers its phosphate group to RpaA to activate it. Phosphotransfer is maximal when KaiC phosphorylation is active during the circadian cycle (PubMed:16707582, PubMed:16882723, PubMed:23541768, PubMed:26113641, PubMed:34618577).
KaiB and KaiC together enhance the phosphatase activity of CikA on phospho-RpaA (PubMed:23541768, PubMed:34618577).
KaiC enhances the autophosphorylation activity of SasA, which then transfers its phosphate group to RpaA to activate it. Phosphotransfer is maximal when KaiC phosphorylation is active during the circadian cycle (PubMed:16707582, PubMed:16882723, PubMed:23541768, PubMed:26113641, PubMed:34618577).
KaiB and KaiC together enhance the phosphatase activity of CikA on phospho-RpaA (PubMed:23541768, PubMed:34618577).
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.
Miscellaneous
'Kai' means 'cycle' in Japanese.
Catalytic activity
- ATP + L-seryl-[protein] = ADP + H+ + O-phospho-L-seryl-[protein]This reaction proceeds in the forward and the backward directions.
- ATP + H2O = ADP + H+ + phosphateThis reaction proceeds in the forward and the backward directions.
Cofactor
Note: Binds 2 Mg2+ ions per subunit, one in each domain. Mg2+ is required for hexamerization and phosphatase activity.
Activity regulation
Interaction with KaiA stimulates autophosphorylation, KaiC interaction with KaiB sequesters KaiA, preventing it stimulating the KaiC kinase, leading to autodephosphorylation. A KaiA dimer is sufficient to enhance KaiC phosphorylation (PubMed:12391300, PubMed:12727878, PubMed:12727879, PubMed:15347812).
Interaction of KaiA with the A-loop stimulates autokinase activity (PubMed:18728181).
Interaction of KaiA with the A-loop stimulates autokinase activity (PubMed:18728181).
Temperature Dependence
ATPase activity is stable from 25 to 35 degrees Celsius.
Features
Showing features for binding site, active site.
Type | ID | Position(s) | Description | |||
---|---|---|---|---|---|---|
Binding site | 49 | ATP 1 (UniProtKB | ChEBI); ligand shared between homodimeric partners | ||||
Sequence: G | ||||||
Binding site | 50 | ATP 1 (UniProtKB | ChEBI); ligand shared between homodimeric partners | ||||
Sequence: T | ||||||
Binding site | 51 | ATP 1 (UniProtKB | ChEBI); ligand shared between homodimeric partners | ||||
Sequence: G | ||||||
Binding site | 52 | ATP 1 (UniProtKB | ChEBI); ligand shared between homodimeric partners | ||||
Sequence: K | ||||||
Binding site | 53 | ATP 1 (UniProtKB | ChEBI); ligand shared between homodimeric partners | ||||
Sequence: T | ||||||
Binding site | 53 | Mg2+ 1 (UniProtKB | ChEBI) | ||||
Sequence: T | ||||||
Binding site | 54 | ATP 1 (UniProtKB | ChEBI); ligand shared between homodimeric partners | ||||
Sequence: L | ||||||
Active site | 77 | Proton acceptor in CI (KaiC 1) | ||||
Sequence: E | ||||||
Binding site | 89 | ATP 1 (UniProtKB | ChEBI); ligand shared between homodimeric partners | ||||
Sequence: S | ||||||
Binding site | 224 | ATP 1 (UniProtKB | ChEBI); ligand shared between homodimeric partners | ||||
Sequence: K | ||||||
Binding site | 225 | ATP 1 (UniProtKB | ChEBI); ligand shared between homodimeric partners | ||||
Sequence: L | ||||||
Binding site | 226 | ATP 1 (UniProtKB | ChEBI); ligand shared between homodimeric partners | ||||
Sequence: R | ||||||
Binding site | 228 | ATP 1 (UniProtKB | ChEBI); ligand shared between homodimeric partners | ||||
Sequence: T | ||||||
Binding site | 230 | ATP 1 (UniProtKB | ChEBI); ligand shared between homodimeric partners | ||||
Sequence: H | ||||||
Binding site | 240 | ATP 1 (UniProtKB | ChEBI); ligand shared between homodimeric partners | ||||
Sequence: T | ||||||
Binding site | 241 | ATP 1 (UniProtKB | ChEBI); ligand shared between homodimeric partners | ||||
Sequence: D | ||||||
Binding site | 290 | ATP 2 (UniProtKB | ChEBI); ligand shared between homodimeric partners | ||||
Sequence: T | ||||||
Binding site | 291 | ATP 2 (UniProtKB | ChEBI); ligand shared between homodimeric partners | ||||
Sequence: G | ||||||
Binding site | 292 | ATP 2 (UniProtKB | ChEBI); ligand shared between homodimeric partners | ||||
Sequence: T | ||||||
Binding site | 293 | ATP 2 (UniProtKB | ChEBI); ligand shared between homodimeric partners | ||||
Sequence: G | ||||||
Binding site | 294 | ATP 2 (UniProtKB | ChEBI); ligand shared between homodimeric partners | ||||
Sequence: K | ||||||
Binding site | 295 | ATP 2 (UniProtKB | ChEBI); ligand shared between homodimeric partners | ||||
Sequence: T | ||||||
Binding site | 295 | Mg2+ 2 (UniProtKB | ChEBI) | ||||
Sequence: T | ||||||
Binding site | 296 | ATP 2 (UniProtKB | ChEBI); ligand shared between homodimeric partners | ||||
Sequence: L | ||||||
Active site | 318 | Proton acceptor in CII (KaiC 2) | ||||
Sequence: E | ||||||
Binding site | 318 | Mg2+ 2 (UniProtKB | ChEBI) | ||||
Sequence: E | ||||||
Binding site | 331 | ATP 2 (UniProtKB | ChEBI); ligand shared between homodimeric partners | ||||
Sequence: W | ||||||
Binding site | 451 | ATP 2 (UniProtKB | ChEBI); ligand shared between homodimeric partners | ||||
Sequence: R | ||||||
Binding site | 457 | ATP 2 (UniProtKB | ChEBI); ligand shared between homodimeric partners | ||||
Sequence: K | ||||||
Binding site | 458 | ATP 2 (UniProtKB | ChEBI); ligand shared between homodimeric partners | ||||
Sequence: M | ||||||
Binding site | 459 | ATP 2 (UniProtKB | ChEBI); ligand shared between homodimeric partners | ||||
Sequence: R | ||||||
Binding site | 461 | ATP 2 (UniProtKB | ChEBI); ligand shared between homodimeric partners | ||||
Sequence: S | ||||||
Binding site | 463 | ATP 2 (UniProtKB | ChEBI); ligand shared between homodimeric partners | ||||
Sequence: H | ||||||
Binding site | 465 | ATP 2 (UniProtKB | ChEBI); ligand shared between homodimeric partners | ||||
Sequence: K |
GO annotations
Aspect | Term | |
---|---|---|
Molecular Function | ATP binding | |
Molecular Function | ATP hydrolysis activity | |
Molecular Function | DNA binding | |
Molecular Function | identical protein binding | |
Molecular Function | magnesium ion binding | |
Molecular Function | protein serine kinase activity | |
Molecular Function | protein serine/threonine kinase activity | |
Molecular Function | protein serine/threonine/tyrosine kinase activity | |
Biological Process | circadian rhythm | |
Biological Process | entrainment of circadian clock | |
Biological Process | negative regulation of circadian rhythm | |
Biological Process | regulation of DNA-templated transcription | |
Biological Process | regulation of phosphorelay signal transduction system |
Keywords
- Molecular function
- Biological process
- Ligand
Enzyme and pathway databases
Names & Taxonomy
Protein names
- Recommended nameCircadian clock oscillator protein KaiC
- EC number
Gene names
Organism names
- Strain
- Taxonomic lineageBacteria > Cyanobacteriota > Cyanophyceae > Synechococcales > Synechococcaceae > Synechococcus
Accessions
- Primary accessionQ79PF4
- Secondary accessions
Proteomes
Phenotypes & Variants
Disruption phenotype
Not essential for growth on low light, loss of circadian cycle and rhythmicity (PubMed:9727980).
Loss of rhythmic chromosome compaction (PubMed:16707582).
No visible phenotype during growth in a light/dark regime for 5-7 days (at 150 umol photons/m2/s). Accumulates much larger amounts of primary metabolites (especially those in and connected to the oxidative pentose phosphate pathway) in 4 hours after dark-light transition. Glycogen accumulates 4-5 hours earlier than normal, overall levels are higher, no change in glycogen degradation kinetics (PubMed:25825710).
Loss of rhythmic chromosome compaction (PubMed:16707582).
No visible phenotype during growth in a light/dark regime for 5-7 days (at 150 umol photons/m2/s). Accumulates much larger amounts of primary metabolites (especially those in and connected to the oxidative pentose phosphate pathway) in 4 hours after dark-light transition. Glycogen accumulates 4-5 hours earlier than normal, overall levels are higher, no change in glycogen degradation kinetics (PubMed:25825710).
Features
Showing features for mutagenesis.
Type | ID | Position(s) | Description | |||
---|---|---|---|---|---|---|
Mutagenesis | 42 | Extends the period of the circadian rhythm to 28 hours in reconstituted KaiABC complex. Decreased endogenous ATPase. | ||||
Sequence: T → S | ||||||
Mutagenesis | 52 | Induces an arrhythmic phenotype, significantly reduced ATP-binding. | ||||
Sequence: K → A | ||||||
Mutagenesis | 71 | Lowers the amplitude and distords the waveform of the circadian rhythm. | ||||
Sequence: G → A | ||||||
Mutagenesis | 87 | In kaiC1; shortens the period of the circadian rhythm to 22 hours. | ||||
Sequence: A → V | ||||||
Mutagenesis | 92 | Increases photoperiod in presence of KaiA and KaiB. | ||||
Sequence: W → F | ||||||
Mutagenesis | 108 | No longer binds KaiB, no formation of KaiCBA, still phosphorylated. | ||||
Sequence: A → E | ||||||
Mutagenesis | 108 | Reduced binding of KaiB, reduced formation of KaiCBA, still phosphorylated. | ||||
Sequence: A → L | ||||||
Mutagenesis | 114 | Extends the period of the circadian rhythm to 27 hours. | ||||
Sequence: G → A | ||||||
Mutagenesis | 115 | Abolishes the circadian rhythm. | ||||
Sequence: Q → A | ||||||
Mutagenesis | 146 | CI hydrolysis rate halves, increases period of the circadian rhythm by nearly 50%. | ||||
Sequence: S → P | ||||||
Mutagenesis | 146 | Loss of stable oscillation in presence of KaiA and KaiB. | ||||
Sequence: S → W | ||||||
Mutagenesis | 153 | Higher CIATPase activity, clock speeds up. | ||||
Sequence: Q → A | ||||||
Mutagenesis | 157 | In kaiC2; extends the period of the circadian rhythm to 29 hours. Lower CIATPase activity, clock slows down. | ||||
Sequence: S → C | ||||||
Mutagenesis | 157 | Shortens the period of the circadian rhythm to 21 hours in reconstituted KaiABC complex. Increased endogenous ATPase. Higher CIATPase activity, clock speeds up. | ||||
Sequence: S → P | ||||||
Mutagenesis | 157 | Arrhythmic. | ||||
Sequence: S → W | ||||||
Mutagenesis | 215 | In kaiC3; shortens the period of the circadian rhythm to 16 hours and decreases the interaction with KaiA. | ||||
Sequence: R → C | ||||||
Mutagenesis | 229 | Increases photoperiod in presence of KaiA and KaiB. | ||||
Sequence: S → W | ||||||
Mutagenesis | 236 | In kaiC4; extends the period of the circadian rhythm to 28 hours. | ||||
Sequence: P → S | ||||||
Mutagenesis | 248 | In kaiC6; induces a low amplitude phenotype and decreases the interaction with KaiA. | ||||
Sequence: P → L | ||||||
Mutagenesis | 248 | In kaiC5; induces an arrhythmic phenotype. | ||||
Sequence: P → S | ||||||
Mutagenesis | 251 | Increased endogenous ATPase. | ||||
Sequence: A → V | ||||||
Mutagenesis | 253 | In kaiC7; extends the period of the circadian rhythm to 40 hours. | ||||
Sequence: R → H | ||||||
Mutagenesis | 273 | In kaiC8; extends the period of the circadian rhythm to 37 hours. | ||||
Sequence: M → I | ||||||
Mutagenesis | 294 | Induces a long period phenotype, no change in ATP-binding. | ||||
Sequence: K → A | ||||||
Mutagenesis | 318 | Abolishes clock rhythmicity, phosphosphorylates T-432 but not S-431. | ||||
Sequence: E → A | ||||||
Mutagenesis | 318-319 | No kinase activity. | ||||
Sequence: EE → AA | ||||||
Mutagenesis | 319 | Low phosphorylation. | ||||
Sequence: E → G | ||||||
Mutagenesis | 319 | Strongly phosphorylated, arhythmic in vivo. | ||||
Sequence: E → Q | ||||||
Mutagenesis | 321 | In kaiC9; shortens the period of the circadian rhythm to 21 hours. | ||||
Sequence: R → Q | ||||||
Mutagenesis | 331 | Arrhythmic. | ||||
Sequence: W → F | ||||||
Mutagenesis | 393 | Decreased endogenous ATPase. | ||||
Sequence: R → C | ||||||
Mutagenesis | 394 | Constitutive KaiC phosphorylation. | ||||
Sequence: Q → E | ||||||
Mutagenesis | 394 | Very slow phosphorylation in presence of KaiA, none in presence of KaiA-KaiB. | ||||
Sequence: Q → K | ||||||
Mutagenesis | 409 | In kaiC10; extends the period of the circadian rhythm to 27 hours. | ||||
Sequence: T → A | ||||||
Mutagenesis | 421 | In kaiC11; extends the period of the circadian rhythm to 44 hours and increases the interaction with KaiA. | ||||
Sequence: G → R | ||||||
Mutagenesis | 422 | In kaiC15; able to suppress the kaiA2 extended phenotype. | ||||
Sequence: A → T | ||||||
Mutagenesis | 426 | Decreased phosphorylation in vivo, does not restore rhythmicity, hexamerizes and down-regulates operon. | ||||
Sequence: T → A | ||||||
Mutagenesis | 426-431 | About wild-type phosphorylation in vivo, does not restore rhythmicity, hexamerizes and down-regulates operon. | ||||
Sequence: TDSHIS → ADSHIA | ||||||
Mutagenesis | 426-432 | No phosphorylation in vivo, does not restore rhythmicity, hexamerizes and down-regulates operon. | ||||
Sequence: TDSHIST → ADSHIAA | ||||||
Mutagenesis | 427 | Arhythmic. | ||||
Sequence: D → A | ||||||
Mutagenesis | 431 | Increased phosphorylation in vivo, does not restore rhythmicity, hexamerizes and down-regulates operon. A single phosphorylated form occurs in vitro, accumulates in presence of KaiA, arrhythmic in vivo. Not dephosphorylated, even by KaiA. | ||||
Sequence: S → A | ||||||
Mutagenesis | 431 | Arrhythmic. | ||||
Sequence: S → C | ||||||
Mutagenesis | 431 | Poorly phosphorylated by itself or KaiA, mimics phosphorylation of this residue. | ||||
Sequence: S → D | ||||||
Mutagenesis | 431 | Severely attenuated growth after 5-7 days in a light/dark regime, glycogen degradation in dark stops early leaving high levels of glycogen in cell, mimics phosphorylation of this residue. | ||||
Sequence: S → E | ||||||
Mutagenesis | 431-432 | No phosphorylation in vitro, hexamerizes, presence of KaiA does not enhance phosphorylation, arrhythmic in vivo, prevents formation of the KaiABC-SasA complex, transiently down-regulates operon. 1.8 fold increase in endogenous ATPase. Reduced ATP synthase. | ||||
Sequence: ST → AA | ||||||
Mutagenesis | 431-432 | 75% endogenous ATPase. | ||||
Sequence: ST → DE | ||||||
Mutagenesis | 432 | Loss of function. Significantly decreased phosphorylation in vivo, does not restore rhythmicity, hexamerizes, down-regulates operon. A single phosphorylated form occurs in vitro, accumulates in presence of KaiA, dephosphorylated in the presence of KaiA and KaiB, arrhythmic in vivo. | ||||
Sequence: T → A | ||||||
Mutagenesis | 432 | Not dephosphorylated, mimics phosphorylation of this residue. Arrhythmic in vitro. | ||||
Sequence: T → E | ||||||
Mutagenesis | 432 | Has in vitro phosphorylation, ATPase and KaiABC assembly-disassembly cycle with a period of 51 hours. | ||||
Sequence: T → V | ||||||
Mutagenesis | 442 | In kaiC12; extends the period of the circadian rhythm to 60 hours and increases the interaction with KaiA. | ||||
Sequence: Y → H | ||||||
Mutagenesis | 444 | Constitutively hyperphosphorylated, insensitive to KaiA or KaiB. | ||||
Sequence: E → D | ||||||
Mutagenesis | 460 | In kaiC13; induces an arrhythmic phenotype. | ||||
Sequence: G → E | ||||||
Mutagenesis | 462 | Loss of stable oscillation in presence of KaiA and KaiB. | ||||
Sequence: W → F | ||||||
Mutagenesis | 468 | Higher affinity for KaiB, extends the period of the circadian rhythm to 55 hours. | ||||
Sequence: R → C | ||||||
Mutagenesis | 470 | Shortens the period of the circadian rhythm to 17 hours in reconstituted KaiABC complex. Increased endogenous ATPase. | ||||
Sequence: F → Y | ||||||
Mutagenesis | 487 | Constitutively phosphorylated. | ||||
Sequence: E → A | ||||||
Mutagenesis | 487-519 | Constitutively phosphorylated, insensitive to KaiB, dominant negative to wild-type, abolishes circadian rhythmicity. | ||||
Sequence: Missing | ||||||
Mutagenesis | 495 | In kaiC14; induces an arrhythmic phenotype. A different group shows shortens the period of the circadian rhythm to 14 hours, chromosome condensation periodicity is also 14 hours. Constitutively 80% phosphorylated. | ||||
Sequence: T → A | ||||||
Mutagenesis | 496-519 | Constitutively 80% phosphorylated. | ||||
Sequence: Missing | ||||||
Mutagenesis | 497-519 | Low levels of phosphorylation, insensitive to KaiA, dominant negative to wild-type, abolishes circadian rhythmicity. | ||||
Sequence: Missing |
PTM/Processing
Features
Showing features for chain, modified residue.
Type | ID | Position(s) | Description | |||
---|---|---|---|---|---|---|
Chain | PRO_0000217782 | 1-519 | Circadian clock oscillator protein KaiC | |||
Sequence: MTSAEMTSPNNNSEHQAIAKMRTMIEGFDDISHGGLPIGRSTLVSGTSGTGKTLFSIQFLYNGIIEFDEPGVFVTFEETPQDIIKNARSFGWDLAKLVDEGKLFILDASPDPEGQEVVGGFDLSALIERINYAIQKYRARRVSIDSVTSVFQQYDASSVVRRELFRLVARLKQIGATTVMTTERIEEYGPIARYGVEEFVSDNVVILRNVLEGERRRRTLEILKLRGTSHMKGEYPFTITDHGINIFPLGAMRLTQRSSNVRVSSGVVRLDEMCGGGFFKDSIILATGATGTGKTLLVSRFVENACANKERAILFAYEESRAQLLRNAYSWGMDFEEMERQNLLKIVCAYPESAGLEDHLQIIKSEINDFKPARIAIDSLSALARGVSNNAFRQFVIGVTGYAKQEEITGLFTNTSDQFMGAHSITDSHISTITDTIILLQYVEIRGEMSRAINVFKMRGSWHDKAIREFMISDKGPDIKDSFRNFERIISGSPTRITVDEKSELSRIVRGVQEKGPES | ||||||
Modified residue | 431 | Phosphoserine; by autocatalysis | ||||
Sequence: S | ||||||
Modified residue | 432 | Phosphothreonine; by autocatalysis | ||||
Sequence: T |
Post-translational modification
Has a 4 step phosphorylation cycle; the autokinase acts first on Thr-432, then Ser-431. When Ser-431 is modified KaiC switches to an autophosphatase mode, acting first on phospho-Thr-432 then phospho-Ser-431 (PubMed:17717528, PubMed:17916691).
Phosphorylated and dephosphorylated on serine/threonine residues by autocatalysis. Unphosphorylated, mono- and di-phosphorylated forms exist. The phosphorylated form correlates with clock speed (PubMed:12391300, PubMed:15347812).
The presence of KaiA increases phosphorylation and stabilizes these forms (PubMed:12391300, PubMed:15347812).
Phosphorylated and dephosphorylated on serine/threonine residues by autocatalysis. Unphosphorylated, mono- and di-phosphorylated forms exist. The phosphorylated form correlates with clock speed (PubMed:12391300, PubMed:15347812).
The presence of KaiA increases phosphorylation and stabilizes these forms (PubMed:12391300, PubMed:15347812).
Phosphorylated on serine and threonine residues by autocatalysis. Has a 4 step phosphorylation cycle; the autokinase acts first on Thr-432, then Ser-431. When Ser-431 is modified KaiC switches to an autophosphatase mode, acting first on phospho-Thr-432 then phospho-Ser-431.
Keywords
- PTM
Proteomic databases
PTM databases
Expression
Induction
Transcribed in a circadian rhythm with maximal expression at 12 hours and minimal expression 12 hours later; expressed as a kaiB-kaiC opperon, this gene does not have its own promoter (PubMed:9727980).
Autorepresses expression (PubMed:14709675, PubMed:15347809, PubMed:9727980).
Negatively regulated by labA (PubMed:17210789).
Non-phosphorylatable kaiC mutants still down-regulate the kaiBC operon (PubMed:15347809).
Autorepresses expression (PubMed:14709675, PubMed:15347809, PubMed:9727980).
Negatively regulated by labA (PubMed:17210789).
Non-phosphorylatable kaiC mutants still down-regulate the kaiBC operon (PubMed:15347809).
Developmental stage
Accumulates in a circadian fashion, peaking at circadian time (CT) 15-18.
Interaction
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 KaiC6, KaiA(2-4):KaiC6, KaiB6:KaiC6 and KaiC6:KaiB6:KaiA12 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 KaiC6:KaiB1 and KaiC6:KaiB6 complexes (PubMed:23796516, PubMed:24474762).
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 KaiC6, KaiA(2-4):KaiC6, KaiB6:KaiC6 and KaiC6:KaiB6:KaiA12 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 KaiC6:KaiB1 and KaiC6:KaiB6 complexes (PubMed:23796516, PubMed:24474762).
Binary interactions
Type | Entry 1 | Entry 2 | Number of experiments | Intact | |
---|---|---|---|---|---|
BINARY | Q79PF4 | kaiA Q79PF6 | 22 | EBI-592287, EBI-592281 | |
BINARY | Q79PF4 | kaiB Q79PF5 | 12 | EBI-592287, EBI-619150 | |
BINARY | Q79PF4 | kaiC Q79PF4 | 12 | EBI-592287, EBI-592287 | |
BINARY | Q79PF4 | sasA Q06904 | 6 | EBI-592287, EBI-626872 |
Protein-protein interaction databases
Structure
Family & Domains
Features
Showing features for domain, region.
Type | ID | Position(s) | Description | |||
---|---|---|---|---|---|---|
Domain | 1-247 | KaiC 1 | ||||
Sequence: MTSAEMTSPNNNSEHQAIAKMRTMIEGFDDISHGGLPIGRSTLVSGTSGTGKTLFSIQFLYNGIIEFDEPGVFVTFEETPQDIIKNARSFGWDLAKLVDEGKLFILDASPDPEGQEVVGGFDLSALIERINYAIQKYRARRVSIDSVTSVFQQYDASSVVRRELFRLVARLKQIGATTVMTTERIEEYGPIARYGVEEFVSDNVVILRNVLEGERRRRTLEILKLRGTSHMKGEYPFTITDHGINIF | ||||||
Region | 115-122 | B-loop, required to bind KaiB and SasA | ||||
Sequence: QEVVGGFD | ||||||
Region | 248-260 | Linker | ||||
Sequence: PLGAMRLTQRSSN | ||||||
Domain | 261-519 | KaiC 2 | ||||
Sequence: VRVSSGVVRLDEMCGGGFFKDSIILATGATGTGKTLLVSRFVENACANKERAILFAYEESRAQLLRNAYSWGMDFEEMERQNLLKIVCAYPESAGLEDHLQIIKSEINDFKPARIAIDSLSALARGVSNNAFRQFVIGVTGYAKQEEITGLFTNTSDQFMGAHSITDSHISTITDTIILLQYVEIRGEMSRAINVFKMRGSWHDKAIREFMISDKGPDIKDSFRNFERIISGSPTRITVDEKSELSRIVRGVQEKGPES | ||||||
Region | 488-497 | A-loop, interacts with KaiA | ||||
Sequence: RIISGSPTRI |
Domain
In the homohexamer the 2 domains (called CI and CII, joined by a linker) self-associate to each form a 'donut' layer; the compactness and local conformation of the domains varies over the cell cycle and impacts function (PubMed:15304218, PubMed:15347809, PubMed:16628225, PubMed:29892030, PubMed:35427168).
CII has the autokinase and autophosphatase activities, both CI and CII have (weak) ATPase activity; CI has the clock pacemaker role (PubMed:17901204, PubMed:22304631, PubMed:26113637).
The CI ring undergoes structural changes driven by ATP hydrolysis that together with the KaiC phosphorylation state regulate KaiB binding (PubMed:29892030).
The C-terminus of CII (residues 488-519) is disordered, extending from the top of the structure near the central pore (PubMed:15304218, PubMed:15347809, PubMed:16628225).
The A-loop (residues 488-497) switches between a buried and exposed state, determining the levels of autokinase and autophosphatase activities. When the A-loop is exposed it interacts with KaiA, activating the autokinase activity (PubMed:18728181).
Binding to KaiA occurs via the extreme C-terminus which assumes a coiled-coil structure upon binding (PubMed:26200123).
KaiB interacts with the CI domain which has bound ADP (PubMed:28302852).
Communication between CI and CII occurs via the Glu-214-Arg-217-Gln-394 triad (PubMed:35427168).
CII has the autokinase and autophosphatase activities, both CI and CII have (weak) ATPase activity; CI has the clock pacemaker role (PubMed:17901204, PubMed:22304631, PubMed:26113637).
The CI ring undergoes structural changes driven by ATP hydrolysis that together with the KaiC phosphorylation state regulate KaiB binding (PubMed:29892030).
The C-terminus of CII (residues 488-519) is disordered, extending from the top of the structure near the central pore (PubMed:15304218, PubMed:15347809, PubMed:16628225).
The A-loop (residues 488-497) switches between a buried and exposed state, determining the levels of autokinase and autophosphatase activities. When the A-loop is exposed it interacts with KaiA, activating the autokinase activity (PubMed:18728181).
Binding to KaiA occurs via the extreme C-terminus which assumes a coiled-coil structure upon binding (PubMed:26200123).
KaiB interacts with the CI domain which has bound ADP (PubMed:28302852).
Communication between CI and CII occurs via the Glu-214-Arg-217-Gln-394 triad (PubMed:35427168).
In the homohexamer the 2 domains (called CI and CII) self-associate to each form a 'donut' layer; the compactness and local conformation of the domains varies over the cell cycle and impacts function. CII has the autokinase and autophosphatase activities, both CI and CII have (weak) ATPase activity; CI has the clock pacemaker role.
Sequence similarities
Belongs to the KaiC family.
Keywords
- Domain
Phylogenomic databases
Family and domain databases
Sequence
- Sequence statusComplete
- Length519
- Mass (Da)58,003
- Last updated2004-07-05 v1
- Checksum855DFE131EFFF3CF
Keywords
- Technical term
Sequence databases
Nucleotide Sequence | Protein Sequence | Molecule Type | Status | |
---|---|---|---|---|
AB010691 EMBL· GenBank· DDBJ | BAA37103.1 EMBL· GenBank· DDBJ | Genomic DNA | ||
AY120853 EMBL· GenBank· DDBJ | AAM82686.1 EMBL· GenBank· DDBJ | Genomic DNA | ||
CP000100 EMBL· GenBank· DDBJ | ABB57246.1 EMBL· GenBank· DDBJ | Genomic DNA |