Kinetics of proton release and uptake by channelrhodopsin-2

► Transient proton translocation by channelrhodopsin-2 was detected by an optical pH indicator. ► Proton release and uptake proceed with time constants of 1.7ms and 11ms, respectively. ► The response time of the pH indicator is not limited by surface-to-bulk diffusion. ► Residues E123 and S245 do no...

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Bibliographic Details
Published in:FEBS letters 2012-05, Vol.586 (9), p.1344-1348
Main Authors: Nack, Melanie, Radu, Ionela, Schultz, Bernd-Joachim, Resler, Tom, Schlesinger, Ramona, Bondar, Ana-Nicoleta, del Val, Coral, Abbruzzetti, Stefania, Viappiani, Cristiano, Bamann, Christian, Bamberg, Ernst, Heberle, Joachim
Format: Article
Language:English
Subjects:
Bacteriorhodopsin
Biological Transport
Hydrogen-Ion Concentration
Ion channel
Kinetics
Models, Molecular
Optogenetics
Protein Structure, Secondary
Proton Pumps - chemistry
Proton Pumps - metabolism
Proton transfer
Protons
Rhodopsin
Rhodopsin - chemistry
Rhodopsin - metabolism
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Summary:► Transient proton translocation by channelrhodopsin-2 was detected by an optical pH indicator. ► Proton release and uptake proceed with time constants of 1.7ms and 11ms, respectively. ► The response time of the pH indicator is not limited by surface-to-bulk diffusion. ► Residues E123 and S245 do not participate in proton release. ► The concurrence of proton release and ion channeling points to a mechanistic link. Electrophysiological experiments showed that the light-activated cation channel channelrhodopsin-2 (ChR2) pumps protons in the absence of a membrane potential. We determined here the kinetics of transient pH change using a water-soluble pH-indicator. It is shown that ChR2 released protons prior to uptake with a stoichiometry of 0.3 protons per ChR2. Comparison to the photocycle kinetics revealed that proton release and uptake match rise and decay of the P3520 intermediate. As the P3520 state also represents the conductive state of cation channeling, the concurrence of proton pumping and channel gating implies an intimate mechanistic link of the two functional modes. Studies on the E123T and S245E mutants show that these residues are not critically involved in proton translocation.
ISSN:0014-5793
1873-3468
DOI:10.1016/j.febslet.2012.03.047