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A protonation-coupled feedback mechanism controls the signalling process in bathy phytochromes
Citation key Escobar2015
Author Escobar, F. V. and Piwowarski, P. and Salewski, J. and Michael, N. and Lopez, M. F. and Rupp, A. and Qureshi, B. M. and Scheerer, P. and Bartl, F. and Frankenberg-Dinkel, N. and Siebert, F. and Mroginski, M. A. and Hildebrandt, P.
Pages 423–430
Year 2015
DOI 10.1038/NCHEM.2225
Journal Nature Chemistry
Volume 7
Number 5
Publisher Nature Publishing Group
Abstract Phytochromes are bimodal photoswitches composed of a photosensor and an output module. Photoactivation of the sensor is initiated by a double bond isomerization of the tetrapyrrole chromophore and eventually leads to protein conformational changes. Recently determined structural models of phytochromes identify differences between the inactive and the signalling state but do not reveal the mechanism of photosensor activation or deactivation. Here, we report a vibrational spectroscopic study on bathy phytochromes that demonstrates that the formation of the photoactivated state and thus (de) activation of the output module is based on proton translocations in the chromophore pocket coupling chromophore and protein structural changes. These proton transfer steps, involving the tetrapyrrole and a nearby histidine, also enable thermal back-isomerization of the chromophore via keto-enol tautomerization to afford the initial dark state. Thus, the same proton re-arrangements inducing the (de) activation of the output module simultaneously initiate the reversal of this process, corresponding to a negative feedback mechanism.
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