Crystal structure of a Ba(2+)-bound gating ring reveals elementary steps in RCK domain activation

Structure. 2012 Dec 5;20(12):2038-47. doi: 10.1016/j.str.2012.09.014. Epub 2012 Oct 18.


RCK domains control activity of a variety of K(+) channels and transporters through binding of cytoplasmic ligands. To gain insight toward mechanisms of RCK domain activation, we solved the structure of the RCK domain from the Ca(2+)-gated K(+) channel, MthK, bound with Ba(2+), at 3.1 Å resolution. The Ba(2+)-bound RCK domain was assembled as an octameric gating ring, as observed in structures of the full-length MthK channel, and shows Ba(2+) bound at several positions. One of the Ba(2+) sites, termed C1, overlaps with a known Ca(2+)-activation site, determined by residues D184 and E210. Functionally, Ba(2+) can activate reconstituted MthK channels as observed in electrophysiological recordings, whereas Mg(2+) (up to 100 mM) was ineffective. Ba(2+) activation was abolished by the mutation D184N, suggesting that Ba(2+) activates primarily through the C1 site. Our results suggest a working hypothesis for a sequence of ligand-dependent conformational changes that may underlie RCK domain activation and channel gating.

Publication types

  • Research Support, N.I.H., Extramural

MeSH terms

  • Amino Acid Motifs
  • Archaeal Proteins / chemistry*
  • Barium / chemistry*
  • Binding Sites
  • Calcium / chemistry
  • Coordination Complexes / chemistry
  • Crystallography, X-Ray
  • Hydrogen-Ion Concentration
  • Ion Channel Gating
  • Lipid Bilayers / chemistry
  • Membrane Potentials
  • Methanobacteriaceae*
  • Models, Molecular
  • Phosphatidylethanolamines / chemistry
  • Phosphatidylglycerols / chemistry
  • Potassium Channels, Calcium-Activated / chemistry*
  • Protein Structure, Quaternary
  • Protein Structure, Tertiary


  • Archaeal Proteins
  • Coordination Complexes
  • Lipid Bilayers
  • Phosphatidylethanolamines
  • Phosphatidylglycerols
  • Potassium Channels, Calcium-Activated
  • 1-palmitoyl-2-oleoylphosphatidylethanolamine
  • Barium
  • 1-palmitoyl-2-oleoylglycero-3-phosphoglycerol
  • Calcium

Associated data

  • PDB/4EI2