HAMAP rule MF_01835
General rule information
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| Accession | MF_01835 |
| Dates | 13-SEP-2004 (Created) 1-JUN-2023 (Last updated, Version 15) |
| Name | KaiB |
| Scope | Bacteria; Cyanobacteriota |
| Templates | Q79PF5 (KAIB_SYNE7); Q8YT41 (KAIB_NOSS1); P74645 (KAIB1_SYNY3): [Recover all] |
| Triggered by |
Propagated annotation
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Identifier, protein and gene names
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| Identifier |
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| Protein name |
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| Gene name |
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Comments
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case not <OC:Prochlorococcus>
| Function | 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. Phospho-Ser-431 KaiC accumulation triggers binding of KaiB to form the KaiB(6):KaiC(6) complex, leading to changes in output regulators CikA and SasA. KaiB switches to a thioredoxin-like fold (KaiB(fs)) when bound to KaiC. KaiB(6):KaiC(6) formation exposes a site for KaiA binding that sequesters KaiA from KaiC, making the KaiC(6):KaiB(6):KaiA(12) complex that results in KaiC autodephosphorylation. |
| 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. | |
| Subunit | 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. Undergoes a major conformational rearrangment; in the free state forms homotetramers as a dimer of dimers. When bound to the CI domain of KaiC switches to a monomeric thioredoxin-fold (KaiB(fs)). KaiB(fs) binds CikA, leading it to dephosphorylate phospho-RpaA. |
| Domain | Has 2 forms, fold switches to a thioredoxin-like fold (KaiB(fs)) when bound to KaiC. |
end case
case <OC:Prochlorococcus>
| Function | Component of the KaiBC clock protein complex, which constitutes the main circadian regulator in cyanobacteria; it may modify the ATPase activity of KaiC. |
| May be a metamorphic protein which natively switches between an inactive tetrameric fold and a rare, thioredoxin-like monomeric fold (KaiB(fs)). KaiB(fs) binds phospho-KaiC, and perhaps clock output effectors. | |
| Subunit | May undergo a major conformational rearrangment; in the free state forms homooligomers. When bound to KaiC switches to a monomeric thioredoxin-fold (KaiB(fs)). The active oscillator complex is probably KaiC(6):KaiB(6). |
| Domain | Has 2 forms, fold switches to a thioredoxin-like fold (KaiB(fs)) when bound to KaiC. |
| Miscellaneous | The kiaA gene has been eliminated from Prochlorococcus during genome streamlining. It has been suggested that the central oscillator in Prochlorococcus does not have to be as robust as in other cyanobacteria because the former live in specific niches of the Earth's oceans; they divide exactly once a day and at the same time. Thus gene loss and changes in kaiB function compared to other cyanobacteria, can occur. |
end case
| Similarity | Belongs to the KaiB family. |
Keywords
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Gene Ontology
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GO:0007623; Biological process: circadian rhythm.
Cross-references
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Additional information
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| Size range | 102-119 amino acids |
| Related rules | None |
| Fusion | None |
| Comments | Prochlorococcus do not contain KaiA (which stimulates KaiC autophosphorylation activity), suggesting that regulation of circadian cycle is different in these bacteria. |