View source for Light-gated ion channel



==Overview==
<b>Light-gated ion channels</b> are a group of [[transmembrane]] proteins that form [[ion channels]]; pores which open or close in response to light. Most light-gated ion channels have been synthesized in the laboratory for study, though one naturally occurring example, [[Channelrhodopsin]], is currently known.<ref>[http://pubs.acs.org/cgi-bin/abstract.cgi/bichaw/2006/45/i51/abs/bi0618058.html|"Engineering Light-Gated Ion Channels"] — <i>Biochemistry</i>, <b>45</b> (51), 15129 -15141, 2006</ref> There are, however, many known [[photoreceptor protein|photoreceptor proteins]], which act in a similar manner to light-gated ion channels but are generally [[G protein]] coupled receptors and not actually gated ion channels.

== Synthetic Purpose ==
Other types of gated ion channels, [[Ligand-gated ion channel|ligand-gated]] and [[Voltage-gated ion channel|voltage-gated]], have been synthesized with a light-gated component in an attempt to better understand their nature and properties. By the addition of a light-gated section, the kinetics and mechanisms of operation can be studied in depth. For example, the addition of a light-gated component allows for the introduction of many highly similar ligands to be introduced to the binding site of a ligand-gated ion channel to assist in the determination of the mechanism.<br>
In [[1980]], the first ion channel to be adapted for study with a light-gated mechanism was the [[nicotinic acetylcholine receptor]].<ref>[http://www.jgp.org/cgi/content/abstract/75/2/207|"A covalently bound photoisomerizable agonist. Comparison with reversibly bound agonists at electrophorus electroplaques"] — The Journal of General Physiology, Vol 75, 207-232</ref> This receptor was well-known at the time, and so was aptly suited to adaptation, and allowed for a study of the kinetics as not allowed before.

== Mechanism ==
Light-gated ion channels function in a similar manner to other gated ion channels. When exposed to a certain stimulus, a [[Tertiary_structure|conformational]] change occurs in the transmembrane proteins, which constitute the pore. This conformational change then opens or closes the ion channel, allowing for the flow of ions according to their electrochemical gradient. In the specific case of light-gated ion channels, the transmembrane proteins are usually coupled with a molecule that acts as a [[photoswitch]]. [[Retinal]] is a good example of a molecular photoswitch and is found in the naturally-occurring Channelrhodopsins. The photoswitch absorbs a specific [[photon]] and changes its conformation, which in-turn, changes the conformation of the transmembrane proteins opening or closing the pore through which ions flow.

== Examples ==
Examples of light-gated ion channels occur in both natural and synthetic environments. These include:
=== Naturally Occurring ===
*[[Channelrhodopsin|Channelrhodopsins]] were the first discovered family of light-gated ion channels.<br>
**[[Channelrhodopsin-1]] <br>
**[[Channelrhodopsin-2]] <br>
=== Synthetically Adapted ===
*[[nicotinic acetylcholine receptor]] was the first ion channel to be synthetically adapted with a light-gated mechanism.<br>
*Many other, fully-synthetic, light-gated channels have produced as well.<ref>[http://dx.doi.org/10.1016/S0040-4020(01)86704-1|"Photosensitive artificial membranes based on azobenzene and spirobenzopyran derivatives"] — Tetrahedron
Volume 50, Issue 14, 4 April 1994, Pages 4039-4070</ref><ref>[http://pubs.acs.org/cgi-bin/abstract.cgi/langd5/2004/20/i17/abs/la048942v.html|"Lipid-Mediated Light Activation of a Mechanosensitive Channel of Large Conductance"] — <i>Langmuir</i>, <b>20</b> (17), 6985 -6987, 2004</ref>


== See Also ==
[[Channelrhodopsin]]<br>
[[Ion channels]]<br>
[[Voltage-gated ion channel]]<br>
[[Ligand-gated ion channel]]<br>
[[Photoreceptor protein]]<br>

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== References ==
<references/><br>

[[Category:Ion channels]]
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