Optical control of metabotropic glutamate receptors

Abstract

G-protein coupled receptors (GPCRs), the largest family of membrane signaling proteins, respond to neurotransmitters, hormones and small environmental molecules. The neuronal function of many GPCRs has been difficult to resolve because of an inability to gate them with subtype-specificity, spatial precision, speed and reversibility. To address this, we developed an approach for opto-chemical engineering native GPCRs. We applied this to the metabotropic glutamate receptors (mGluRs) to generate light-agonized and light-antagonized “LimGluRs”. The light-agonized “LimGluR2”, on which we focused, is fast, bistable, and supports multiple rounds of on/off switching. Light gates two of the primary neuronal functions of mGluR2: suppression of excitability and inhibition of neurotransmitter release. The light-antagonized “LimGluR2block” can be used to manipulate negative feedback of synaptically released glutamate on transmitter release. We generalize the optical control to two additional family members: mGluR3 and 6. The system works in rodent brain slice and in zebrafish in vivo, where we find that mGluR2 modulates the threshold for escape behavior. These light-gated mGluRs pave the way for determining the roles of mGluRs in synaptic plasticity, memory and disease.

Two-photon brightness of azobenzene photoswitches designed for glutamate receptor optogenetics

“…This combination of optical tools facilitates fast, multicellular stimulation and recording, an important benchmark for the utility of PTLs for in vivo optogenetic studies. Finally, we synthesized a new compound with altered stereochemistry, and show that the resulting PTL, D-MAG0 460 , enables 2P control of an engineered G protein-coupled receptor (GPCR), LimGluR3 (30). We discuss why the 2P optical properties of MAGs generalize to a larger range of ligand substitutions, which could broaden the palette of PTLs for optogenetic neural circuit analysis in tissue.…”

“…We turned to the recently described LimGluR2 and LimGluR3, which are based on the group II mGluRs, mGluR2 and mGluR3 (30). LimGluRs allow for photoactivation of the G i/o signaling cascade (Fig.…”

“…MAGs have been used to study neurotransmission and neuroplasticity in a variety of preparations (26)(27)(28)(29). Two families of MAGs have been synthesized to date: First generation MAGs have a symmetrically-substituted azobenzene core, e.g., L-MAG0 (21) and D-MAG0 (30). Second generation MAGs have an asymmetrically-substituted azobenzene core, e.g., L-MAG0 460 (31) and MAG 2p (32).…”

Restoration of visual function by expression of a light-gated mammalian ion channel in retinal ganglion cells or ON-bipolar cells

“…One promising alternative to microbial opsins is an optopharmacological strategy that uses synthetic azobenzene-based photoswitches to endow light sensitivity either to native ion channels of neurons (17,18) or to engineered mammalian receptors and channels that, like the microbial opsins, allow for genetic targeting to specific cells (19)(20)(21)(22). We previously showed that an engineered light-gated ionotropic glutamate receptor (LiGluR) restores light responses to blind retina degeneration (rd1) mice (23).…”

Flipping the Photoswitch: Ion Channels Under Light Control

“…Unlike QBr, which was not targeted by genetic manipulation, recent PTLs were designed to act as an agonist (Mal-ABacylcholine (MAACh)) or antagonist (Mal-AB-homocholine (MAHoCh)) on genetically engineered nAChRs ( Figure 5) . The basis for the development of light-activated nAChRs was, similarly to the development of LiGluR and recent light-activated metabotropic Glu receptors (Levitz et al 2013), a combination of Cys-scanning mutagenesis and molecular modelling.…”