The covalent attachment of synthetic
photoswitches is a general
approach to impart light sensitivity onto native receptors. It mimics
the logic of natural photoreceptors and significantly expands the
reach of optogenetics. Here we describe a novel photoswitch design—the
photoswitchable orthogonal remotely tethered ligand (PORTL)—that
combines the genetically encoded SNAP-tag with photochromic ligands
connected to a benzylguanine via a long flexible linker. We use the
method to convert the G protein-coupled receptor mGluR2, a metabotropic
glutamate receptor, into a photoreceptor (SNAG-mGluR2) that provides
efficient optical control over the neuronal functions of mGluR2: presynaptic
inhibition and control of excitability. The PORTL approach enables
multiplexed optical control of different native receptors using distinct
bioconjugation methods. It should be broadly applicable since SNAP-tags
have proven to be reliable, many SNAP-tagged receptors are already
available, and photochromic ligands on a long leash are readily designed
and synthesized.
Photochromic blockers of voltage gated ion channels are powerful tools for the control of neuronal systems with high spatial and temporal precision. We now introduce fotocaine, a new type of photochromic channel blocker based on the long-lasting anesthetic fomocaine. Fotocaine is readily taken up by neurons in brain slices and enables the optical control of action potential firing by switching between 350 and 450 nm light. It also provides an instructive example for "azologization", that is, the systematic conversion of an established drug into a photoswitchable one.
Nicotinic acetylcholine receptors (nAChRs) are essential for cellular communication in higher organisms. Even though a vast pharmacological toolset to study cholinergic systems has been developed, control of endogenous neuronal nAChRs with high spatiotemporal precision has been lacking. To address this issue, we have generated photoswitchable nAChR agonists and re-evaluated the known photochromic ligand, BisQ. Using electrophysiology, we found that one of our new compounds, AzoCholine, is an excellent photoswitchable agonist for neuronal α7 nAChRs, whereas BisQ was confirmed to be an agonist for the muscle-type nAChR. AzoCholine could be used to modulate cholinergic activity in a brain slice and in dorsal root ganglion neurons. In addition, we demonstrate light-dependent perturbation of behavior in the nematode, Caenorhabditis elegans.
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