Light-gated ion channel
Encyclopedia
Light-gated ion channels 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. Photoreceptor protein
s, which act in a similar manner to light-gated ion channels are generally G protein-coupled receptors and not actually gated ion channels.
and 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.
In 1980, the first ion channel to be adapted for study with a light-gated mechanism was the nicotinic acetylcholine receptor
. 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.
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.
Channelrhodopsin
Channelrhodopsins are a subfamily of opsin proteins that function as light-gated ion channels. They serve as sensory photoreceptors in unicellular green algae, controlling phototaxis, i.e. movement in response to light. Expressed in cells of other organisms, they enable the use of light to control...
, is currently known. Photoreceptor protein
Photoreceptor protein
Photoreceptors are light-sensitive proteins involved in the sensing and response to light in a variety of organisms. Some examples are rhodopsin in the photoreceptor cells of the vertebrate retina, phytochrome in plants, and bacteriorhodopsin and bacteriophytochromes in some bacteria...
s, which act in a similar manner to light-gated ion channels are generally G protein-coupled receptors and not actually gated ion channels.
Synthetic Purpose
Other types of gated ion channels, ligand-gatedLigand-gated ion channel
Ligand-gated ion channels are one type of ionotropic receptor or channel-linked receptor. They are a group of transmembrane ion channels that are opened or closed in response to the binding of a chemical messenger , such as a neurotransmitter.The binding site of endogenous ligands on LGICs...
and voltage-gated
Voltage-gated ion channel
Voltage-gated ion channels are a class of transmembrane ion channels that are activated by changes in electrical potential difference near the channel; these types of ion channels are especially critical in neurons, but are common in many types of cells....
, 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.
In 1980, the first ion channel to be adapted for study with a light-gated mechanism was the nicotinic acetylcholine receptor
Nicotinic acetylcholine receptor
Nicotinic acetylcholine receptors, or nAChRs, are cholinergic receptors that form ligand-gated ion channels in the plasma membranes of certain neurons and on the postsynaptic side of the neuromuscular junction...
. 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 conformationalTertiary structure
In biochemistry and molecular biology, the tertiary structure of a protein or any other macromolecule is its three-dimensional structure, as defined by the atomic coordinates.-Relationship to primary structure:...
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
Photoswitch
A photoswitch is a kind of sensor that detects the presence of light, generally in a certain wavelength. Photoswitches are used for numerous scientific and manufacturing applications. They are also commonly used in residential areas to turn lights on and off based on the time of day...
. Retinal
Retinal
Retinal, also called retinaldehyde or vitamin A aldehyde, is one of the many forms of vitamin A . Retinal is a polyene chromophore, and bound to proteins called opsins, is the chemical basis of animal vision...
is a good example of a molecular photoswitch and is found in the naturally occurring Channelrhodopsins. The photoswitch absorbs a specific photon
Photon
In physics, a photon is an elementary particle, the quantum of the electromagnetic interaction and the basic unit of light and all other forms of electromagnetic radiation. It is also the force carrier for the electromagnetic force...
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
- ChannelrhodopsinChannelrhodopsinChannelrhodopsins are a subfamily of opsin proteins that function as light-gated ion channels. They serve as sensory photoreceptors in unicellular green algae, controlling phototaxis, i.e. movement in response to light. Expressed in cells of other organisms, they enable the use of light to control...
s were the first discovered family of light-gated ion channels.- Channelrhodopsin-1
- Channelrhodopsin-2
Synthetically Adapted
- nicotinic acetylcholine receptorNicotinic acetylcholine receptorNicotinic acetylcholine receptors, or nAChRs, are cholinergic receptors that form ligand-gated ion channels in the plasma membranes of certain neurons and on the postsynaptic side of the neuromuscular junction...
was the first ion channel to be synthetically adapted with a light-gated mechanism. - Many other fully synthetic, light-gated channels have produced as well.
See also
- ChannelrhodopsinChannelrhodopsinChannelrhodopsins are a subfamily of opsin proteins that function as light-gated ion channels. They serve as sensory photoreceptors in unicellular green algae, controlling phototaxis, i.e. movement in response to light. Expressed in cells of other organisms, they enable the use of light to control...
- Ion channels
- Voltage-gated ion channelVoltage-gated ion channelVoltage-gated ion channels are a class of transmembrane ion channels that are activated by changes in electrical potential difference near the channel; these types of ion channels are especially critical in neurons, but are common in many types of cells....
- Ligand-gated ion channelLigand-gated ion channelLigand-gated ion channels are one type of ionotropic receptor or channel-linked receptor. They are a group of transmembrane ion channels that are opened or closed in response to the binding of a chemical messenger , such as a neurotransmitter.The binding site of endogenous ligands on LGICs...
- Photoreceptor proteinPhotoreceptor proteinPhotoreceptors are light-sensitive proteins involved in the sensing and response to light in a variety of organisms. Some examples are rhodopsin in the photoreceptor cells of the vertebrate retina, phytochrome in plants, and bacteriorhodopsin and bacteriophytochromes in some bacteria...
- OptogeneticsOptogeneticsOptogenetics is the combination of genetic and optical methods to control specific events in targeted cells of living tissue, even within freely moving mammals and other animals, with the temporal precision needed to keep pace with functioning intact biological systems.In 2010, optogenetics was...