Q79PF5 · KAIB_SYNE7
- ProteinCircadian clock oscillator protein KaiB
- GenekaiB
- StatusUniProtKB reviewed (Swiss-Prot)
- Amino acids102 (go to sequence)
- Protein existenceEvidence at protein level
- Annotation score5/5
Function
function
Key component of the KaiABC oscillator complex, which constitutes the main circadian regulator in cyanobacteria (PubMed:17717528, 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. KaiA binding to the KaiC CII domain yields KaiA(2-4):KaiC6 complexes which stimulate KaiC autophosphorylation. Phospho-Ser-431 KaiC accumulation triggers binding of KaiB to form the KaiB6:KaiC6 complex, leading to changes in the output regulators CikA and SasA. KaiB switches to a thioredoxin-like fold (KaiB(fs)) in complex with KaiC (PubMed:26113641, PubMed:28302851, PubMed:28302852).
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 (PubMed:17717528, PubMed:17916691, PubMed:28302852).
Complete dephosphorylation of KaiC leads to dissociation of KaiA2:KaiB1, completing 1 cycle of the Kai oscillator (PubMed:28302852).
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 yields KaiA(2-4):KaiC6 complexes which stimulate KaiC autophosphorylation. Phospho-Ser-431 KaiC accumulation triggers binding of KaiB to form the KaiB6:KaiC6 complex, leading to changes in the output regulators CikA and SasA. KaiB switches to a thioredoxin-like fold (KaiB(fs)) in complex with KaiC (PubMed:26113641, PubMed:28302851, PubMed:28302852).
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 (PubMed:17717528, PubMed:17916691, PubMed:28302852).
Complete dephosphorylation of KaiC leads to dissociation of KaiA2:KaiB1, completing 1 cycle of the Kai oscillator (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 (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).
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).
A metamorphic protein which reversibly switches between an inactive tetrameric fold and a rare, thioredoxin-like monomeric fold (KaiB(fs)). KaiB(fs) binds phospho-KaiC, KaiA and CikA. KaiA and CikA compete for binding to KaiB(fs), and KaiB(fs) and SasA compete for binding to KaiC, thus the clock oscillator and output signal pathway are tightly coupled.
Miscellaneous
'Kai' means 'cycle' in Japanese.
GO annotations
Aspect | Term | |
---|---|---|
Cellular Component | cytoplasm | |
Cellular Component | plasma membrane | |
Molecular Function | identical protein binding | |
Biological Process | circadian rhythm | |
Biological Process | entrainment of circadian clock | |
Biological Process | negative regulation of phosphorylation | |
Biological Process | regulation of circadian rhythm |
Keywords
- Biological process
Enzyme and pathway databases
Names & Taxonomy
Protein names
- Recommended nameCircadian clock oscillator protein KaiB
Gene names
Organism names
- Strain
- Taxonomic lineageBacteria > Cyanobacteriota > Cyanophyceae > Synechococcales > Synechococcaceae > Synechococcus
Accessions
- Primary accessionQ79PF5
- Secondary accessions
Proteomes
Subcellular Location
UniProt Annotation
GO Annotation
Cell membrane ; Peripheral membrane protein
Note: From circadian time (CT) 12-16 to CT 20 the major fraction is membrane-associated, is then translocated to the cytosol, where it probably interacts with KaiC and KaiA.
Keywords
- Cellular component
Phenotypes & Variants
Disruption phenotype
Not essential for growth on low light, loss of circadian cycle and rhythmicity (PubMed:9727980).
Cells elongate (PubMed:26113641, PubMed:28302851).
Cells elongate (PubMed:26113641, PubMed:28302851).
Features
Showing features for mutagenesis.
Type | ID | Position(s) | Description | |||
---|---|---|---|---|---|---|
Mutagenesis | 11 | In kaiB1; shortens the period of the circadian rhythm to 21 hours. | ||||
Sequence: L → F | ||||||
Mutagenesis | 22 | Decrease in cooperativity of KaiB(fs) recruitment. | ||||
Sequence: R → A | ||||||
Mutagenesis | 40 | Disrupts circadian rhythms in vivo, cells elongate. | ||||
Sequence: A → D | ||||||
Mutagenesis | 42 | Loss of KaiA binding. | ||||
Sequence: K → A | ||||||
Mutagenesis | 42 | Disrupts circadian rhythms in vivo. | ||||
Sequence: K → E | ||||||
Mutagenesis | 74 | In kaiB2; shortens the period of the circadian rhythm to 22 hours. | ||||
Sequence: R → W | ||||||
Mutagenesis | 88 | Stabilizes the KaiB(fs) form, disrupts KaiC phosphorylation rhythms, forms a complex with KaiA, wild-type regulation of SasA, disturbs regulation of CikA, dominant-negative over wild-type protein, restores normal cell-length to disruption strains (i.e. contributes to SasA and CikA regulation). | ||||
Sequence: G → A | ||||||
Mutagenesis | 88-90 | Stabilizes the KaiB(fs) form, disrupts KaiC phosphorylation rhythms, does not form a complex with KaiA, dominant-negative over wild-type protein, restores normal cell-length to disruption strains, disturbs regulation of SasA and CikA. Binds CikAPsR. | ||||
Sequence: GLD → ALR | ||||||
Mutagenesis | 95-101 | Circadian rhythm strongly weakened and destabilized. | ||||
Sequence: ELQDSDD → QELQNNSN | ||||||
Mutagenesis | 95-102 | Circadian rhythm strongly weakened and destabilized. | ||||
Sequence: Missing |
PTM/Processing
Features
Showing features for chain.
Type | ID | Position(s) | Description | |||
---|---|---|---|---|---|---|
Chain | PRO_0000217767 | 1-102 | Circadian clock oscillator protein KaiB | |||
Sequence: MSPRKTYILKLYVAGNTPNSVRALKTLKNILEVEFQGVYALKVIDVLKNPQLAEEDKILATPTLAKVLPLPVRRIIGDLSDREKVLIGLDLLYGELQDSDDF |
Proteomic 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 (PubMed:9727980).
Down-regulated by KaiC (PubMed:14709675, PubMed:9727980).
Down-regulated by KaiC (PubMed:14709675, PubMed:9727980).
Developmental stage
Accumulates in a circadian fashion, peaking at CT 15-18.
Interaction
Subunit
Undergoes a major conformational rearrangment; in the free state forms homotetramers with 2 dimers (PubMed:23796516).
When bound to the CI domain of KaiC switches to a monomeric thioredoxin-fold (KaiB(fs)) (PubMed:26113641, PubMed:28302851, PubMed:28302852).
Monomers, homodimers and homotetramers are detected in solution; at low concentrations only monomers are seen. In vitro forms KaiC6:KaiB1 and KaiC6:KaiB6 complexes (PubMed:24474762).
Only associates with 'Ser-431'-phosphorylated KaiC (and not with 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).
In low resolution cryo-EM forms a KaiC6:KaiB6 complex (PubMed:23796516).
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).
The KaiB:KaiC complex is more prevalent at 16 hours (in the dark) than at 4 hours (in the light) in the circadian cycle (PubMed:10786837).
The KaiA:KaiB complex is only found at 20-24 hours in the circadian cycle (subjective night) (PubMed:15347812).
Binds to the CI domain of KaiC; SasA and KaiB compete to bind to the CI domain (PubMed:26113641, PubMed:28302851, PubMed:28302852).
When bound to the CI domain of KaiC switches to a monomeric thioredoxin-fold (KaiB(fs)) (PubMed:26113641, PubMed:28302851, PubMed:28302852).
Monomers, homodimers and homotetramers are detected in solution; at low concentrations only monomers are seen. In vitro forms KaiC6:KaiB1 and KaiC6:KaiB6 complexes (PubMed:24474762).
Only associates with 'Ser-431'-phosphorylated KaiC (and not with 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).
In low resolution cryo-EM forms a KaiC6:KaiB6 complex (PubMed:23796516).
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).
The KaiB:KaiC complex is more prevalent at 16 hours (in the dark) than at 4 hours (in the light) in the circadian cycle (PubMed:10786837).
The KaiA:KaiB complex is only found at 20-24 hours in the circadian cycle (subjective night) (PubMed:15347812).
Binds to the CI domain of KaiC; SasA and KaiB compete to bind to the CI domain (PubMed:26113641, PubMed:28302851, PubMed:28302852).
Binary interactions
Type | Entry 1 | Entry 2 | Number of experiments | Intact | |
---|---|---|---|---|---|
BINARY | Q79PF5 | kaiA Q79PF6 | 11 | EBI-619150, EBI-592281 | |
BINARY | Q79PF5 | kaiB Q79PF5 | 5 | EBI-619150, EBI-619150 | |
BINARY | Q79PF5 | kaiC Q79PF4 | 12 | EBI-619150, EBI-592287 |
Protein-protein interaction databases
Structure
Family & Domains
Domain
The C-terminal region may confer species specificity; C-terminal hybrids do not all rescue deletions in S.elongatus PCC 7942 (PubMed:16227211).
Has 2 forms, fold switches to a thioredoxin-like fold (KaiB(fs)) when bound to KaiC (PubMed:26113641, PubMed:28302852).
The KaiB(fs) form binds faster to KaiC than wild-type, thus less fully phosphorylated KaiC forms; the KaiB(fs) form activates signaling through CikA and inhibits signaling through SasA (Probable) (PubMed:26113641).
A mutant locked in the KaiB(fs) form binds the CikA PsR domain (PubMed:26113641).
Has 2 forms, fold switches to a thioredoxin-like fold (KaiB(fs)) when bound to KaiC (PubMed:26113641, PubMed:28302852).
The KaiB(fs) form binds faster to KaiC than wild-type, thus less fully phosphorylated KaiC forms; the KaiB(fs) form activates signaling through CikA and inhibits signaling through SasA (Probable) (PubMed:26113641).
A mutant locked in the KaiB(fs) form binds the CikA PsR domain (PubMed:26113641).
Sequence similarities
Belongs to the KaiB family.
Phylogenomic databases
Family and domain databases
Sequence
- Sequence statusComplete
- Length102
- Mass (Da)11,436
- Last updated2004-07-05 v1
- Checksum4E7FD086742A398F
Keywords
- Technical term
Sequence databases
Nucleotide Sequence | Protein Sequence | Molecule Type | Status | |
---|---|---|---|---|
AB010691 EMBL· GenBank· DDBJ | BAA37102.1 EMBL· GenBank· DDBJ | Genomic DNA | ||
AY120853 EMBL· GenBank· DDBJ | AAM82685.1 EMBL· GenBank· DDBJ | Genomic DNA | ||
CP000100 EMBL· GenBank· DDBJ | ABB57247.1 EMBL· GenBank· DDBJ | Genomic DNA |