Optogenetic Channels & Receptors
Targeting Specific Channels and Receptors for Photocontrol
We have developed a strategy for photocontrol of particular ion channels and receptors with “photoswitchable tethered ligands” (PTLs). These are molecules containing a) an agonist or antagonists of the targeted receptor or channel protein, b) an azobenzene, a photoisomerizable linker that changes length with different wavelengths of light, and c) a maleimide, a reactive group that covalently attaches the molecule to the cysteine-substituted channel or receptor of interest. Starting with the Shaker K+ channel protein, we used this approach to develop the first light-regulated ion channel that could be used for controlling neural activity (Banghart et al., Nature Neurosceince, 2004). Over the past few years we have expanded this “toolkit” to include many other type of light-regulated K+ channels, including voltage-gated, neurotransmitter-regulated, and Ca2+-activated K+ channels (Fortin et al., Journal of Neurophysiology 2011). We have also generated aseveral types of llight regulated nicotinic acetylcholine receptors using both tethered agonists and antagonists (Tochitsky et al., Nature Chemistry, 2012).
For many of the channels and receptors we have studied, there is a lack of specific pharmacological tools for functional manipulation and analysis. The primary importance of the PTL approach is that it allows the physiological and pathological roles of particular ion channels and receptors to be understood with great clarity. Hence, we can now ask what a specific channel “does for a living” with unprecedented spatial, temporal, and biochemical precision, a transformative advance in molecular neuroscience.
We are currently developing a family of light regulated GABAA receptors, with different GABA-binding α-subunits modified to possess the photoswitch attachment site. Once again, because light sensitivity is targeted to a particular GABAA receptor subtype, these tools will reveal the exact function of different receptor subtypes with unprecedent accuracy and resolution. In addition, these tools enable optical manipulation of synaptic inhibition and tonic inhibition in neural circuits throughout the brain, a powerful new capability that will be of great value to neuroscience. A paper describing the “first generation” light regulated GABAA receptors is currently under review.