Grant: Project Grant

Optogenetics is a biological technique that combines optics and genetics to control the activity of neurons and other cells by light. For this purpose, light-sensitive ion channels, pumps, or enzymes are specifically expressed in target cells. Channelrhodopsins (ChRs) were discovered 20 years ago in green algae as photoreceptor proteins consisting of an opsin moiety that serves as ion channel and the chromophore retinal that absorbs light to control channel open and closed states. By genetic means, various ChRs can be expressed in specific neurons. Depending on the ChR ion selectivity, they can excite or inhibit neurons with millisecond temporal precision. ChRs are applied in neuroscience and neurobiology where they help to understand neural circuits and brain activities underlying behavior and diseases. Our collaborators discovered a new ChR, Kalium channelrhodopsin, selective for potassium ions, which can be used for inhibiting neuronal signaling. We were the first to determine the cryo-electron microscopy structure of this new class of ChRs as well as a homologous ChR which is sodium selective. From the structures, electrophysiology and spectroscopy, we learn about the mechanism of ChR. We propose to determine the elusive open-state structures of ChRs and perform time-resolved studies to understand ion selectivity and channel opening and closing. This will enable rational mutagenesis to design the next generation of ChRs with specific properties in terms of spectral absorption and ion conductance. By expanding our cryo-electron microscopy approach we will provide a platform to routinely determine new ChR structures which will guide mutagenesis to design better optogenetics tools. These ChRs will be tested by collaborators at universities and hospitals and made available to the community to study the brain and its complex function, and could potentially be used to treat diseases such as schizophrenia, epilepsy and Parkinson's.