Circadian clock protein KaiA, C-terminal (IPR020856)

Short name: Circadian_clock_protein_KaiA_C

Overlapping homologous superfamilies

Domain relationships



This entry represents the C-terminal domain of Circadian clock protein KaiA.

Cyanobacteria are the most primitive organisms known to exhibit circadian rhythms. KaiA, kaiB and kaiC constitute the circadian clock machinery in cyanobacteria, and kaiA activates kaiBC expression whereas kaiC represses it [PMID: 15170179]. Apparent homologues of kaiB and kaiC are found among noncyanobacterial eubacteria and the archaea. However kaiA appears confined within the cyanobacteria, which are the only prokaryotes with demonstrated circadian rhythms [PMID: 12438647].

There are at least two types of kaiA proteins: long and short [PMID: 12438647]. The long versions consist of ~300 aminoacyl residues. There is limited sequence conservation in the amino-terminal 200 residues of these proteins but a high degree of conservation in the carboxyl-terminal 100 residues. They thus appear to contain two independently folded domains, the amino and carboxyl regions, connected by a canonical linker. The short versions are essentially independent carboxyl-terminal domains.

The kaiA N-terminal domain consists of a central five-stranded (beta1 to beta5) parallel beta-sheet flanked by two groups of alpha-helices (alpha1, alpha4 and alpha2, alpha3) packed on either side of the beta-sheet and an additional alpha helix (alpha5) lying near the amino terminus of the central beta-strand [PMID: 12438647, PMID: 15007067]. The structure of the N-terminal domain of kaiA is that of a pseudo-receiver domain, similar to those found in bacterial response regulators. Although the fold is that of a canonical receiver domain, the primary sequence is dissimilar, and it lacks the conserved aspartate residue necessary for phosphorylation. KaiA activation most likely involves direct protein-protein interactions of the N-terminal domain that result in functional modulation of the C-terminal effector domain. The C-terminal kaiA domain is reponsible for dimer formation, binding to kaiC, enhancing kaiC phosphorylation and generating the circadian oscillations. It adopts a novel all alpha-helical homodimeric structure [PMID: 15170179, PMID: 15007067, PMID: 14749515, PMID: 15256595]. The kaiA C-terminal domain contains two parallel helix-hairpin- helix motifs that form a four helix bundle, which represents a new protein folding motif.

GO terms

Biological Process

GO:0007623 circadian rhythm
GO:0006468 protein phosphorylation

Molecular Function

No terms assigned in this category.

Cellular Component

No terms assigned in this category.

Contributing signatures

Signatures from InterPro member databases are used to construct an entry.
PROSITE profiles