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H2020Individual fellowship2015–2017

LIIT-ChR2 · Structural and mechanistic study of ion transport in Channelrhodopsin-2

Horizon 2020 — Marie Skłodowska-Curie Actions

Duration
2015-04-01 → 2017-03-31
EU contribution
€159,461
Participants
1
Scheme
MSCA-IF-EF-ST

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Results in brief

Structural and mechanistic study of ion transport in Channelrhodopsin-2

Channelrhodopsin-2 (ChR2) is a light sensitive ion channel found in green algae. ChR2 is now widely used in optogenetics. Neurons expressing ChR2 can be depolarized rapidly and reversibly by illumination, hence allowing control of the activation/inactivation of neurons in specific locations of the brain. Despite its importance, very little is known about the ChR2 structure, light cycle and mechanism of action. In this project, we studied the mechanism of light activation by elucidating the structure and properties of each of the intermediates of the photocycle by means of theoretical methods. The project objectives were designed to understand the photo-chemical cycle of ChR2 and to target the current technical limitations of the protein. Understanding the structure and biophysical properties of the ChR2 will help in the engineering of new mutants or chemically modified variants with desirable properties. The aim is to expand the range of applicability of ChR2 in optogenetics and in medical devices, as well as to contribute to the basic knowledge of ion transfer in membrane channels. The complete photocycle is defined by at least five photochemically different species. Despite some structural and chemical characteristics of each of the states in the photocycle are known, there is no atomistic structure of any of them. Using classical and quantum mechanics molecular dynamics simulations, we intended to model the intermediates and the transition mechanisms between them, validate the structures using the experimental data and aid our experimental collaborators in designing new variants of ChR2.

Data: CORDIS, © European Union

Project objective

Channelrhodopsins are type-I rhodopsin proteins found in green algae that function as sensory photoreceptors and turn into ion channels under illumination. Upon light absorbance, the retinal moiety induces a conformational change on the protein that opens a channel through which ions can pass.Neurons expressing channelrhodopsin-2 (ChR2) can be depolarized rapidly and reversibly by illumination, hence allowing control of the activation/inactivation of neurons in specific locations of the brain. For this reason, ChR2 has been used widely in optogenetics to study neuronal circuits and disorders in the brain, and to restore light sensitivity and visual capabilities in damaged retinas. However, in contrast to closely related bacteriorhodopsins or halorhodopsins, very little is known about their structure, light cycle and mechanism of action. The current structural evidences of ChR2 is limited to 1) the 6 Å projection map obtained by cryo-electron microscopy that contains a mixture of light (open channel) and dark (closed channel) states; and 2) the 2.3 Å X-ray structure of the dark state of a ChR1/ChR2 chimera. In the present proposal, we aim at elucidating the structure, properties and mechanism of action of the transient species of ChR2 during its photochemical cycle by means of theoretical methods and in close collaboration with the experimental biophysics groups of the host institute.The mechanisms of ion transport and channel opening will be simulated by enhanced sampling and free energy methods. Specific quantum-mechanics/molecular-mechanics (QM/MM) force matching force field will be generated ad hoc for the retinal moiety in the ChR2 environment. The model structures generated for the closed, open, and desensitized states will be validated 1) by comparison of the QM/MM spectroscopic properties of the model with experimental observations; and 2) by comparison to electron microscopy structures using a Bayesian analysis method recently developed in the host group.

Original text from CORDIS.

Participants

  • MAX-PLANCK-GESELLSCHAFT ZUR FORDERUNG DER WISSENSCHAFTEN EV · MUNCHENCoordinatorGermany

Links

Data: CORDIS, © European Union