Voltage-gated potassium channel

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Voltage-gated potassium channels are transmembrane channels specific for potassium and sensitive to voltage changes in the cell's membrane potential. They play a crucial role during action potentials in returning the depolarized cell to a resting state.

Contents 1 Classification 2 Animal research 3 Structure 4 Selectivity 5 Open and closed conformations 6 See also 7 External links 8 References

[edit] Classification

According to MeSH, these channels can be grouped into the following three families:

• delayed rectifier potassium channels (including KvLQT1)
• ether-a-go-go potassium channels
• shaker superfamily of potassium channels

[edit] Animal research

The voltage-gated K⁺ channels that provide the outward currents of action potentials have similarities to bacterial K⁺ channels.

These channels have been studied by X-ray diffraction, allowing determination of structural features at atomic resolution.

The function of these channels is explored by electrophysiological studies.

Genetic approaches include screening for behavioral changes in animals with mutations in K⁺ channel genes. Such genetic methods allowed the genetic identification of the "Shaker" K⁺ channel gene in Drosophila before ion channel gene sequences were well known.

Study of the altered properties of voltage-gated K⁺ channel proteins produced by mutated genes has helped reveal the functional roles of K⁺ channel protein domains and even individual amino acids within their structures.

[edit] Structure

Voltage-gated K⁺ channels of vertebrates typically have four protein subunits arranged as a ring, each contributing to the wall of the trans-membrane K⁺ pore.

There are six major α-helical sequences in each subunit. Some of these are hydrophobic transmembrane sequences.

[edit] Selectivity

Voltage-gated K⁺ channels are selective for K⁺ over other cations such as Na⁺. There is a selectivity filter at the narrowest part of the transmembrane pore.

Channel mutation studies revealed the parts of the subunits that are essential for ion selectivity. They include the amino acid sequence (Thr-Val-Gly-Tyr-Gly) or (Thr-Val-Gly-Phe-Gly) typical to the selectivity filter of voltage-gated K⁺ channels. As K⁺ passes through the pore, interactions between potassium ions and water molecules are prevented and the K⁺ interacts with specific atomic components of the Thr-Val-Gly-X-Gly sequences from the four channel subunits[1].

[edit] Open and closed conformations

Attempts continue to relate the structure of the mammalian voltage-gated K⁺ channel to its ability to respond to the voltage that exists across the membrane.^[1] Specific domains of the channel subunits have been identified that are important for voltage-sensing and converting between the open conformation of the channel and closed conformations. There are at least two closed conformations; in one, the channel can open if the membrane potential becomes positive inside. Voltage-gated K⁺ channels inactivate after opening, entering a distinctive, second closed conformation. In the inactivated conformation, the channel cannot open, even if the transmembrane voltage is favorable. A domain at one end of the K⁺ channel protein mediates inactivation. This end of the protein can transiently plug the inner opening of the pore, preventing ion movement through the channel.

[edit] See also

• Ion channel

[edit] External links

• MeSH Voltage-Gated+Potassium+Channels
• Li B, Gallin W. "VKCDB: voltage-gated potassium channel database.". BMC Bioinformatics 5: 3. PMID 14715090. 
• "Voltage-gated potassium channel database (VKCDB)" at ualberta.ca
• UMich Orientation of Proteins in Membranes families/superfamily-8 - Spatial positions of voltage gated potassium channels in membranes

[edit] References

1. ^ Lee S, Lee A, Chen J, MacKinnon R (2005). "Structure of the KvAP voltage-dependent K+ channel and its dependence on the lipid membrane.". Proc Natl Acad Sci U S A 102 (43): 15441-6. PMID 16223877.  link