Calcium-activated potassium channel

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Calcium-activated potassium channels are potassium channels gated by calcium. In humans they are divided into BK channels, IK channels, and SK channels based on their conductance (big, intermediate, and small conductance).

This family of ion channels is, for the most part, activated by intracellular Ca2+ and contains 8 members in the human genome. However, some of these channels (the KCa4 and KCa5 channels) are responsive instead to intracellular Na+ and Cl. Furthermore, the KCa1 family is both Ca2+- and voltage-activated, further complicating the description of this family. The KCa channel α subunits have six transmembrane segments similar to the KVs, except KCa1, in which the N-terminus makes a seventh pass across the membrane to end up outside the cell. The α subunits make homo- and hetero-tetrameric complexes. The calcium binding domain may be contained in the α subunit sequence, as in KCa1, or may be through an additional calcium binding protein such as calmodulin.

Homology classification[edit]

Human KCa Channels[edit]

Below is a list of the 8 known human calcium-activated potassium channel grouped according to sequence homology of transmembrane hydrophobic cores:[1]

BK channel[edit]

SK channel[edit]

IK channel[edit]

Other subfamilies[edit]

Prokaryotic KCa Channels[edit]

A number of prokaryotic KCa channels have been described, both structurally and functionally. All are either gated by calcium or other ligands and are homologus to the human KCa channels, in particular the KCa1.1 gating ring. These structures have served as templates for ligand gating.

Protein Species Ligand Function Reference
Kch Escherichia coli Unknown Channel [2]
MthK Methanothermobacter thermautotrophicus Calcium, Cadmium, Barium, pH Channel [3][4][5][6][7]
TrkA/TrkH Vibrio parahaemolyticus ATP, ADP Channel [8][9]
KtrAB Bacillus subtilis ATP, ADP Transporter [10]
GsuK Geobacter sulfurreducens Calcium, ADP, NAD Channel [11]
TM1088 Thermotoga maritima Unknown Unknown [12]

See also[edit]


  1. ^ Wei AD, Gutman GA, Aldrich R, Chandy KG, Grissmer S, Wulff H; Gutman; Aldrich; Chandy; Grissmer; Wulff (2005). "International Union of Pharmacology. LII. Nomenclature and molecular relationships of calcium-activated potassium channels". Pharmacol Rev 57 (4): 463–72. doi:10.1124/pr.57.4.9. PMID 16382103. 
  2. ^ Jiang, Y; Pico, A; Cadene, M; Chait, B. T.; MacKinnon, R (2001). "Structure of the RCK domain from the E. Coli K+ channel and demonstration of its presence in the human BK channel". Neuron 29 (3): 593–601. PMID 11301020. 
  3. ^ Jiang, Y; Lee, A; Chen, J; Cadene, M; Chait, B. T.; MacKinnon, R (2002). "Crystal structure and mechanism of a calcium-gated potassium channel". Nature 417 (6888): 515–22. Bibcode:2002Natur.417..515J. doi:10.1038/417515a. PMID 12037559. 
  4. ^ Smith, F. J.; Pau, V. P.; Cingolani, G; Rothberg, B. S. (2013). "Structural basis of allosteric interactions among Ca2+-binding sites in a K+ channel RCK domain". Nature Communications 4: 2621. Bibcode:2013NatCo...4E2621S. doi:10.1038/ncomms3621. PMID 24126388. 
  5. ^ Ye, S; Li, Y; Chen, L; Jiang, Y (2006). "Crystal structures of a ligand-free MthK gating ring: Insights into the ligand gating mechanism of K+ channels". Cell 126 (6): 1161–73. doi:10.1016/j.cell.2006.08.029. PMID 16990139. 
  6. ^ Dvir, H; Valera, E; Choe, S (August 2010). "Structure of the MthK RCK in complex with cadmium.". Journal of structural biology 171 (2): 231–7. PMID 20371380. 
  7. ^ Smith, FJ; Pau, VP; Cingolani, G; Rothberg, BS (5 December 2012). "Crystal structure of a Ba(2+)-bound gating ring reveals elementary steps in RCK domain activation.". Structure (London, England : 1993) 20 (12): 2038–47. PMID 23085076. 
  8. ^ Cao, Y; Jin, X; Huang, H; Derebe, M. G.; Levin, E. J.; Kabaleeswaran, V; Pan, Y; Punta, M; Love, J; Weng, J; Quick, M; Ye, S; Kloss, B; Bruni, R; Martinez-Hackert, E; Hendrickson, W. A.; Rost, B; Javitch, J. A.; Rajashankar, K. R.; Jiang, Y; Zhou, M (2011). "Crystal structure of a potassium ion transporter, TrkH". Nature 471 (7338): 336–40. Bibcode:2011Natur.471..336C. doi:10.1038/nature09731. PMC 3077569. PMID 21317882. 
  9. ^ Cao, Y; Pan, Y; Huang, H; Jin, X; Levin, E. J.; Kloss, B; Zhou, M (2013). "Gating of the TrkH ion channel by its associated RCK protein TrkA". Nature 496 (7445): 317–22. Bibcode:2013Natur.496..317C. doi:10.1038/nature12056. PMC 3726529. PMID 23598339. 
  10. ^ Vieira-Pires, R. S.; Szollosi, A; Morais-Cabral, J. H. (2013). "The structure of the KtrAB potassium transporter". Nature 496 (7445): 323–8. Bibcode:2013Natur.496..323V. doi:10.1038/nature12055. PMID 23598340. 
  11. ^ Kong, C; Zeng, W; Ye, S; Chen, L; Sauer, D. B.; Lam, Y; Derebe, M. G.; Jiang, Y (2012). "Distinct gating mechanisms revealed by the structures of a multi-ligand gated K(+) channel". ELife 1: e00184. doi:10.7554/eLife.00184. PMC 3510474. PMID 23240087. 
  12. ^ Deller, M. C.; Johnson, H. A.; Miller, M. D.; Spraggon, G; Elsliger, M. A.; Wilson, I. A.; Lesley, S. A. (2015). "Crystal Structure of a Two-Subunit TrkA Octameric Gating Ring Assembly". PLoS ONE 10 (3): e0122512. doi:10.1371/journal.pone.0122512. PMC 4380455. PMID 25826626. 

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