Engineering Light-Gated Ion Channels: A Review
Matthew R. Banghart, Matthew Volgraf, Dirk Trauner
Biochemistry [2006]
Summary:
Ion channels found in cellular membranes can be controlled by a variety of stimuli, including ligands, voltage, and in some cases, light. These Ion channels in turn control the electro-chemical properties of the cell, by changing conductance based on the external stimulus. By artificially fabricating or specific placement of these cells, engineered cultures can be better controlled by a predetermined and controlled stimulus. A light-gated reversible ion channel has many practical applications in tissue engineering due to the quick response of a light source compared to delayed reaction times with ligand bonding, as well as the ease of stimulation compared to many of the aforementioned methods.
The switches that control the gates can function in a few specific ways: through changing the local electric field, moving hindering protein subgroups, or by inducing a reversible conformational change within a gating protein. There are a few basic criterions to engineering a gated ion channel to ensure functionality on the cellular level. It is important to make sure the gate functions on a cellular time scale, with activation times on the order of microseconds. Generally, when engineering gated ion channels, it is more important to focus on a complete “off” position than an “on” configuration because a constant partial flow of ions within a cell could be toxic to the cell. The mechanism by which light gating works is by inducing a cis-trans conformational change when a certain wavelength of light is shone upon a protein linked to the ion gate.
When a light is shone upon the system in (A), a conformational change brings the two halves of the ion gate together, allowing ions to pass. In (B), the natural configuration of the protein is such that there is a large steric group that blocks the ion channel, and when light is shone upon the system, the protein opens to a trans configuration, thereby removing the blocking steric group.
Current applications of light-gated ion channels include simple control of neurons by controlling dopamine cells, as well as muscular control. A test with fruit flies showed a correlation between dopamine release and exploration of environment; light-gated ion channels regulated dopamine channels such that when a light was shone on the insects, dopamine release was triggered, resulting in the fruit fly exploring the container in which it was kept. Muscular control using light-gated ion channels works based on the requirement of certain ions to trigger or relax muscles. By using a light gated ion channel in conjunction with a light that causes sodium or potassium ion gates to transport, muscle contraction can be coordinated to a programmed light source.
Significance:
Light gated ion channels have promising applications to tissue engineered materials based on their ability to transport ions that could be used as signaling mechanisms to promote cellular metabolism. If ions could be isolated that cause production of certain proteins or other potentially helpful molecules (like dopamine, for instance) then one could imagine having bunches of light-gated ion channels that respond to different frequencies of light, that release different cellular signals for production of different molecules within one tissue.
5 comments:
I like the applications proposed for the light gated ion channels. It would be very strange to see an organism twitch in response to different wavelengths of light. Do you know how the light-gated ion channels would be/are being made? It sounds like a synthetic biology process in which you find light-gated ion channels that already exist in a certain cell type, isolate the genes that encode for the channel, and then transfect those genes into the cells you want to have light-gated ion channels. Did the paper state if/where light-gated ion channels exist naturally? In which type of organism/cell type? I would imagine that there would be many of these channels in eye cells.
I also find the application of light-gated ion channels to be fascinating, especially using multiple channels to release different signals in response to different light intensities. Do you know if this could actually be done in the body? I mean, it seems like this method would work well in vitro, but once in the body, how would you expose these cells to light?
Very interesting paper. I only know of these types of channels in green algae, where they regulate Ca++ influx and movement in response to light. But, are there naturally occuring light-gated ion channels in the human body? I guess I'm having a hard time imagining how a researcher would insert one of these in a cell. Or would the researcher have to stimulate a cell to make one by modifying genes?
Hey Ben, this is a really interesting paper. I see that Lavanya mentioned that naturally occurring light-activated channels are present in some algae. Do you know if these operate on the cis/trans mechanism you alluded to?
Also do you know if this is the only mechanism used to accomplish this or are there other models that exist in the lab or in nature? Once again very interesting!
Hey, well there were a few good questions that were raised, and so I'll try to answer them to the best of my ability.
Regarding construction and insertion of the gated ion channel, the methods practiced today are exactly as Jen mentioned through a synthetic biology process, basically using cells that are known to produce the light gated ion channel at a known wavelength and inserting the gene into a cell line. The other method the paper described for construction of the ion gate is through a self-assembling nanotube that would be inserted into the cell, which basically would be inserting a segment of DNA that would produce a specific protein that would become an ion channel with a specifically programmed light gate. The way these gates work is based off of a mechanism that was found in the eye, basically a protein that changes conformation at a specific light frequency.
These light gated ion channels could be used in the body, but would require some sort of conjunctive device to function, for example a microchip with a LED on it. It seems to me though that to really make this worthwhile, it the cells that would be needed to expose light to would be in some sort of large centralized mass, as in the heart or a larger programmed mimetic organ or something of that nature.
I have never heard of this algae with a gated channel, but I would imagine it to work in a similar way. I would need to look it up but I believe researchers get the actual gate from an organism like the algae, and synthesize particular cell lines using the gene from the algae.
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