Development of Light-Gated Ion Channels With Red-Shifted Action Spectra

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The aim of this project is to reprogram naturally occurring “blind” receptors in such a way that they become sensitive toward light. Using a combination of chemical synthesis and protein engineering, we have been able to convert ionotropic receptors, i.e. ion channels, into photoreceptors. These can be used to control neural activity and behavior in living organisms. Herein, we propose to investigate our most successful system, the light-actuated ionotropic glutamate receptor (LiGluR), at the atomic level using X-ray crystallography (in collaboration with I. Schlichting) and with molecular dynamics simulations. LiGluR is based on kainate receptors (iGluR6), whose extracellular ligand-binding domain is conjugated to an azobenzene that terminates in a glutamate ligand. Photochemical switching between the extended and bent form of this molecule changes the effective concentration of the ligand, allowing for optical control of the receptor. We believe that this concept is very general and could be easily applied to metabotropic glutamate receptors as well. Together with A. Gottschalk, we will also apply it to pentameric ligand gated ion channels, such as certain nicotinic acetylcholine receptors found in C. elegans. Detailed biophysical investigations of this system will be subsequently carried out in collaboration with J. Heberle. The optimized lightgated glutamate and acetylcholine receptors will be used by our collaborators S. Ryu and A. Gottschalk to address neurobiological questions in zebrafish and nematodes (C. elegans).