Circadian clock oscillator protein KaiA

UniProtKB accession:  Q79PF6

Grouped By:  Matching UniProtKB accession

UniProtKB description:  Key component of the KaiABC oscillator complex, which constitutes the main circadian regulator in cyanobacteria (PubMed:28302852, PubMed:9727980, PubMed:17717528). Complex composition changes during the circadian cycle to control KaiC phosphorylation (PubMed:28302852). KaiA stimulates KaiC autophosphorylation, while KaiB sequesters KaiA, leading to KaiC autodephosphorylation (PubMed:28302852, PubMed:17717528, PubMed:17916691). KaiA binding to the KaiC CII domain during the subjective day yields KaiA(2-4):KaiC(6) complexes which stimulate KaiC autophosphorylation (PubMed:28302852). A KaiA dimer is sufficient to enhance KaiC hexamer phosphorylation (PubMed:12391300, PubMed:15347812). 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 (PubMed:28302852).