Homologous Superfamily

KaiA/RbsU helical domain superfamily (IPR017944)

Short name: KaiA/RbsU_helical_domain_sf

Overlapping entries


This superfamily represents a structural domain consisting of four helices in a bundle with a right-handed superhelix. Homologous structural domains can be found in:

  • The C-terminal domain of the circadian clock protein KaiA
  • The N-terminal domain of the phosphoserine phosphatase protein RsbU

The cyanobacterial clock proteins KaiA, KaiB and KaiC are proposed as regulators of the circadian rhythm in cyanobacteria. KaiA activates the expression of the kaiBC locus, while KaiC represses it. KaiA is composed of three functional domains: the N-terminal amplitude-amplifier domain, the central period-adjuster domain and the C-terminal clock-oscillator domain. The C-terminal domain is responsible for dimer formation, binding to KaiC, enhancing KaiC phosphorylation and generating the circadian oscillations [PMID: 15170179]. The KaiA protein from Anabaena sp. (strain PCC 7120) lacks the N-terminal CheY-like domain.

The phosphoserine phosphatase RsbU acts as a positive regulator of the general stress-response factor of Gram-positive organisms, sigma-B. RsbU dephosphorylates rsbV in response to environmental stress conveyed from the rsbXST module. The phosphatase activity of RsbU is stimulated during the stress response by associating with the RsbT kinase. This association leads to the induction of sigmaB activity. The N-terminal domain forms a helix-swapped dimer that is otherwise similar to the KaiA domain dimer. Deletions in the N-terminal domain are deleterious to the activity of RsbU. The C-terminal domain of RsbU is similar to the catalytic domains of PP2C-type phosphatases [PMID: 15263010].

GO terms

Biological Process

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.