title: Structure and function of multiple Ca2+-binding sites in a K+ channel regulator of K+ conductance (RCK) domain.
abstract: Regulator of K(+) conductance (RCK) domains control the activity of a variety of K(+) transporters and channels, including the human large conductance Ca(2+)-activated K(+) channel that is important for blood pressure regulation and control of neuronal firing, and MthK, a prokaryotic Ca(2+)-gated K(+) channel that has yielded structural insight toward mechanisms of RCK domain-controlled channel gating. In MthK, a gating ring of eight RCK domains regulates channel activation by Ca(2+). Here, using electrophysiology and X-ray crystallography, we show that each RCK domain contributes to three different regulatory Ca(2+)-binding sites, two of which are located at the interfaces between adjacent RCK domains. The additional Ca(2+)-binding sites, resulting in a stoichiometry of 24 Ca(2+) ions per channel, is consistent with the steep relation between [Ca(2+)] and MthK channel activity. Comparison of Ca(2+)-bound and unliganded RCK domains suggests a physical mechanism for Ca(2+)-dependent conformational changes that underlie gating in this class of channels.
authors: Department of Biochemistry, Temple University School of Medicine, 3400 North Broad Street, Philadelphia, PA 19140, USA.
authors: Victor P T
authors: VP
authors: Pau
authors: Frank J
authors: FJ
authors: Smith
authors: Alexander B
authors: AB
authors: Taylor
authors: Liubov V
authors: LV
authors: Parfenova
authors: Elsie
authors: E
authors: Samakai
authors: Matthew M
authors: MM
authors: Callaghan
authors: Karin
authors: K
authors: Abarca-Heidemann
authors: P John
authors: PJ
authors: Hart
authors: Brad S
authors: BS
authors: Rothberg
mesh_terms: D001665:Binding Sites / Q000235:genetics*; D002118:Calcium / Q000378:metabolism*; D018360:Crystallography, X-Ray; D004594:Electrophysiology; D015640:Ion Channel Gating / Q000235:genetics*; D008051:Lipid Bilayers / Q000378:metabolism; D008958:Models, Molecular; D024681:Potassium Channels, Calcium-Activated / Q000235:genetics* / Q000378:metabolism*; D017434:Protein Structure, Tertiary
chemical_list: D008051:Lipid Bilayers; D024681:Potassium Channels, Calcium-Activated; D002118:Calcium