Calcium-activated potassium channel subunit alpha-1
Template:PBB Calcium-activated potassium channel subunit alpha-1 also known as potassium large conductance calcium-activated channel, subfamily M, alpha member 1 (KCa1.1), or BK for short, is a voltage gated ion channel encoded by the KCNMA1 gene and characterized by their large conductance of potassium ions (K+) through cell membranes.[1]
| Calcium-activated BK potassium channel alpha subunit | |||||||||
|---|---|---|---|---|---|---|---|---|---|
| Identifiers | |||||||||
| Symbol | BK_channel_a | ||||||||
| Pfam | PF03493 | ||||||||
| InterPro | IPR003929 | ||||||||
| |||||||||
Function
BK channels are activated (opened) by changes in membrane electrical potential and/or by increases in concentration of intracellular calcium ion (Ca2+).[2][3] Opening of BK channels allows K+ to passively flow through the channel, down the electrochemical gradient. Under typical physiological conditions, this results in an efflux of K+ from the cell, which leads to cell membrane hyperpolarization (a decrease in the electrical potential across the cell membrane) and a decrease in cell excitability (a decrease in the probability that the cell will transmit an action potential).
BK channels are essential for the regulation of several key physiological processes including smooth muscle tone and neuronal excitability.[1] They control the contraction of smooth muscle and are involved with the electrical tuning of hair cells in the cochlea. BK channels also contribute to the behavioral effects of ethanol in the worm C. elegans under high concentrations (> 100 mM, or approximately 0.50% BAC).[4] It remains to be determined if BK channels contribute to intoxication in humans.
Structure
BK channels have a tetrameric structure. Each monomer of the channel-forming alpha subunit is the product of the KCNMA1 gene. Modulatory beta subunits (encoded by KCNMB1, KCNMB2, KCNMB3, or KCNMB4) can associate with the tetrametic channel. Alternatively spliced transcript variants encoding different isoforms have been identified.[1]
Each BK channel alpha subunit consists of (from N- to C-terminal):
- A unique transmembrane domain (S0)[5] that precedes the 6 transmembrane domains (S1-S6) conserved in all voltage-dependent K+ channels.
- A voltage sensing domain (S1-S4).
- A K+ channel pore domain (S5, selectivity filter, and S6).
- A cytoplasmic C-terminal domain (CTD) consisting of a pair of RCK domains that assemble into an octameric gating ring on the intracellular side of the tetrameric channel.[3][6][7][8][9][10][11] The CTD contains four primary binding sites for Ca2+, called "calcium bowls", encoded within the second RCK domain of each monomer.[11][3][6][10]
Available X-ray structures:
- 3U6N - Open Structure of the BK channel Gating Ring[11]
- 3MT5 - Crystal Structure of the Human BK Gating Apparatus[3]
- 3NAF - Structure of the Intracellular Gating Ring from the Human High-conductance Ca2+ gated K+ Channel (BK Channel)[6]
See also
References
- ^ a b c "Entrez Gene: KCNMA1 potassium large conductance calcium-activated channel, subfamily M, alpha member 1". Cite error: The named reference "entrez" was defined multiple times with different content (see the help page).
- ^ Miller C (2000). "An overview of the potassium channel family". Genome Biol. 1 (4): reviews0004.1–reviews0004.5. doi:10.1126/science.1190414. PMC 138870. PMID 11178249.
- ^ a b c d Yuan P, Leonetti MD, Pico AR, Hsiung Y, MacKinnon R (2010). "Structure of the human BK channel Ca2+-activation apparatus at 3.0 A resolution". Science. 329 (5988): 182–6. doi:10.1126/science.1190414. PMC 3022345. PMID 20508092.
{{cite journal}}: Unknown parameter|month=ignored (help)CS1 maint: multiple names: authors list (link) Cite error: The named reference "pmid20508092" was defined multiple times with different content (see the help page). - ^ Davies AG, Pierce-Shimomura JT, Kim H, VanHoven MK, Thiele TR, Bonci A, Bargmann CI, McIntire SL (2003). "A central role of the BK potassium channel in behavioral responses to ethanol in C. elegans". Cell. 115 (6): 655–66. doi:10.1016/S0092-8674(03)00979-6. PMID 14675531.
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|pmid=11301020instead. - ^ Pico A. 2003. RCK domain model of calcium activation in BK channels. PhD thesis. The Rockfeller University, New York.
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Further reading
This article incorporates text from the United States National Library of Medicine, which is in the public domain.
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