Circadian clock oscillator protein KaiA

UniProtKB accession:  Q79V62

Grouped By:  Matching UniProtKB accession

UniProtKB description:  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. KaiA binding to the KaiC CII domain during the subjective day yields KaiA(2-4):KaiC(6) complexes which stimulate KaiC autophosphorylation. Phospho-Ser-431 KaiC accumulation triggers binding of KaiB during the subjective night to form the KaiB(6):KaiC(6) complex, leading to changes in the output regulators CikA and SasA. KaiB(6):KaiC(6) formation exposes a site for KaiA binding on KaiB that sequesters KaiA from KaiC's CII domain, making the KaiC(6):KaiB(6):KaiA(12) complex resulting in KaiC autodephosphorylation. Complete dephosphorylation of KaiC leads to dissociation of KaiA(2):KaiB(1), completing 1 cycle of the Kai oscillator (By similarity). Formation of the KaiB:KaiC complex is promoted by KaiA, helping switch KaiC from its autophosphorylation to autodephosphatase function (PubMed:24112939).