PROSITE documentation PDOC51201 [for PROSITE entry PS51201]

RCK N-terminal and C-terminal domain profiles


Regulators of K+ conductance (RCK) domain is found in many ligand-gated K+ channels, most often attached to the intracellular carboxy terminus. The domain is prevalent among prokaryotic K+ channels, and also found in eukaryotic, high-conductance Ca2+-activated K+ channels (BK channels). [1,4,5]. Largely involved in redox-linked regulation of potassium channels, the N-terminal part of the RCK domain is predicted to be an active dehydrogenase at least in some cases [1]. Some have a conserved sequence motif (G-x-G-x-x-G-x(n)-[DE]) for NAD+ binding [2], but others do not, reflecting the diversity of ligands for RCK domains. The C-terminal part is less conserved, being absent in some channels, such as the kefC antiporter from Escherichia coli. It is predicted to bind unidentified ligands and to regulate sulfate, sodium and other transporters.

The X-ray structure of several RCK domains has been solved (see for example <PDB:1LNQ>) [3,4,5]. It reveals an α-β fold similar to dehydrogenase enzymes. The domain forms a homodimer, producing a cleft between two lobes. It has a composite structure, with an N-terminal (RCK-N), and a C-terminal (RCK-C) subdomains. The RCK-N subdomain forms a Rossmann fold with two α helices (α A and α B) on one side of a six stranded parallel β sheet (β A to β F) and three α helices (α C, α D and α E) on the other side. The RCK-C subdomain is an all-β-strand fold. It forms an extention of the dimer interface and further stabilizes the RCK homodimer [3,4,5]. Ca2+ is a ligand that opens the channel in a concentration-dependent manner. Two Ca2+ ions are located at the base of a cleft between two RCK domains, coordinated by the carboxylate groups of two glutamate residues, and by an aspartate residue [3,4,5].

RCK domains occur in at least five different contexts:

  • As a single domain on the C terminus of some K+ channels (for example, many prokaryotic K+ channels).
  • As two tandem RCK domains on the C terminus of some transporters that form gating rings (for example, eukaryotic BK channels). The gating ring has an arrangement of eight identical RCK domains, one from each of the four pore-forming subunits and four from the intracellular solution.
  • As two domains, one at the N terminus and another at the C terminus of transporter (for example, the prokaryotic trk system potassium uptake protein A).
  • As a soluble protein (not part of a K+ channel) consisting of two tandem RCK domains.
  • As a soluble protein consisting of a single RCK domain.

We developed two profiles for this domain, one that spans the RCK-N subdomain and the other which covers the RCK-C subdomain.


The RCK domain is also named as trkA or KTN.

Last update:

June 2006 / Profile revised.

Technical section

PROSITE methods (with tools and information) covered by this documentation:

RCK_N, PS51201; RCK N-terminal domain profile  (MATRIX)

RCK_C, PS51202; RCK C-terminal domain profile  (MATRIX)


1AuthorsAnantharaman V., Koonin E.V., Aravind L.
TitleRegulatory potential, phyletic distribution and evolution of ancient, intracellular small-molecule-binding domains.
SourceJ. Mol. Biol. 307:1271-1292(2001).
PubMed ID11292341

2AuthorsSchlosser A., Hamann A., Bossemeyer D., Schneider E., Bakker E.P.
TitleNAD+ binding to the Escherichia coli K(+)-uptake protein TrkA and sequence similarity between TrkA and domains of a family of dehydrogenases suggest a role for NAD+ in bacterial transport.
SourceMol. Microbiol. 9:533-543(1993).
PubMed ID8412700

3AuthorsDong J., Shi N., Berke I., Chen L., Jiang Y.
TitleStructures of the MthK RCK domain and the effect of Ca2+ on gating ring stability.
SourceJ. Biol. Chem. 280:41716-41724(2005).
PubMed ID16227203

4AuthorsJiang Y., Pico A., Cadene M., Chait B.T., MacKinnon R.
TitleStructure of the RCK domain from the E. coli K+ channel and demonstration of its presence in the human BK channel.
SourceNeuron 29:593-601(2001).
PubMed ID11301020

5AuthorsJiang Y., Lee A., Chen J., Cadene M., Chait B.T., MacKinnon R.
TitleCrystal structure and mechanism of a calcium-gated potassium channel.
SourceNature 417:515-522(2002).
PubMed ID12037559

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