There is a lot of working currently being done in this field outside of channels.

The main competitors are:
LOV domains
Phytochromes
Cryptochromes

Currently phytochromes and cryptochromes seem to have to best light/dark switching but they come at the cost of the proteins being huge(> 100kDa) and the need to add exogenous chromophore (billins).

Personally I work on LOV domains which are small(<15kDa) and contain an FMN chromophore found in most every cell but we do not quite understand how they work and how to make the conformational switching better. We are becoming more knowledgeable though. However, LOV domains have been used to do cool stuff like make cells move, and colocalize substrates.

My Ph.D. thesis is on characterizing the biophysical phenomena regarding LOV domains and apply that to make good photoswitchable proteins. Currently anyone can make two proteins colocalize or turn on a gene. I think what everyone wants or is trying to do is to make most "any" protein function activatable by light. Something cryptochromes and phytochromes will not be able to do this easily because of their size and need to for exogenous chromophore. However, even in the context of LOV domains making something like the well characterized KcsA potassium channel light activated is no easy task.


I can easily provide plasmids for engineered LOV domains if requested.


On Friday, January 4, 2013 6:25:19 PM UTC-6, Nathan McCorkle wrote:

So it seems adding a photoswitch isn't terribly hard, but it's an in-vitro operation as far as I've been reading... at least we haven't figured out the synBio way to do it yet.

This is the seemingly simplest photo-isomerizable group:

http://en.wikipedia.org/wiki/Azobenzene

goes from trans to cis when you illuminate it, so if you add this between areas of a protein in the right way, you can twist the protein into or out of a working conformation via a pulse of light. 

The way to engineer a protein to receive the current in-vitro treatment is to identify all the surface exposed amino acids, find two that are about the distance relaxed or excited photoswitch, then try to engineer them to be cysteines and try to engineer away any other surface cysteines. Then express the engineered protein with your specially placed cysteine pair, purify the protein, add maleimide linker by using this cross-linker

http://en.wikipedia.org/wiki/Maleimide

then hope that it works, and if not try again. Here's a good slideshow of the concept:

Molecular Photoswitches – Properties and Applications 

Shishi Lin, Organic Student Seminar, Yoon Group

http://www.chem.wisc.edu/areas/organic/studsemin/lin_shishi/lin-sem.pdf

It looks like we're getting close to understanding the chemistry of natural systems a bit better...

Reversible Photocontrol of Peptide Conformation with a Rhodopsin-like Photoswitch

http://pubs.acs.org/doi/abs/10.1021/ja301868p

Sooo, what are some existing biological light switches that people have seen hacked or are ripe to be?

I'm wondering if one could make a channel that spits out single nucleotides when illuminated, or maybe use a neuron that blebs out a vesicle with just one nucleotide in it. (in effort of directed DNA synthesis)

--
-Nathan

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