title: A protonation-coupled feedback mechanism controls the signalling process in bathy phytochromes.
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.
authors.affiliation: Institut für Chemie, Technische Universität Berlin, Sekr. PC 14, Straße des 17. Juni 135, Berlin D-10623, Germany.
authors.forename: Francisco
authors.initials: F
authors.lastname: Velazquez Escobar
authors.affiliation: Institut für Medizinische Physik und Biophysik, AG Spektroskopie, Charité - Universitätsmedizin Berlin, Charitéplatz 1, D-10117 Berlin, Germany.
authors.forename: Patrick
authors.initials: P
authors.lastname: Piwowarski
authors.affiliation: Institut für Chemie, Technische Universität Berlin, Sekr. PC 14, Straße des 17. Juni 135, Berlin D-10623, Germany.
authors.forename: Johannes
authors.initials: J
authors.lastname: Salewski
authors.affiliation: Institut für Chemie, Technische Universität Berlin, Sekr. PC 14, Straße des 17. Juni 135, Berlin D-10623, Germany.
authors.forename: Norbert
authors.initials: N
authors.lastname: Michael
authors.affiliation: Institut für Chemie, Technische Universität Berlin, Sekr. PC 14, Straße des 17. Juni 135, Berlin D-10623, Germany.
authors.forename: Maria
authors.initials: M
authors.lastname: Fernandez Lopez
authors.affiliation: Institut für Medizinische Physik und Biophysik, AG Spektroskopie, Charité - Universitätsmedizin Berlin, Charitéplatz 1, D-10117 Berlin, Germany.
authors.forename: Anna
authors.initials: A
authors.lastname: Rupp
authors.affiliation: Institut für Medizinische Physik und Biophysik, AG Protein X-ray Crystallography and Signal Transduction, Charité - Universitätsmedizin Berlin, Charitéplatz 1, D-10117, Berlin, Germany.
authors.forename: Bilal Muhammad
authors.initials: BM
authors.lastname: Qureshi
authors.affiliation: Institut für Medizinische Physik und Biophysik, AG Protein X-ray Crystallography and Signal Transduction, Charité - Universitätsmedizin Berlin, Charitéplatz 1, D-10117, Berlin, Germany.
authors.forename: Patrick
authors.initials: P
authors.lastname: Scheerer
authors.affiliation: Institut für Medizinische Physik und Biophysik, AG Spektroskopie, Charité - Universitätsmedizin Berlin, Charitéplatz 1, D-10117 Berlin, Germany.
authors.forename: Franz
authors.initials: F
authors.lastname: Bartl
authors.affiliation: Fachbereich Biologie, Abteilung Mikrobiologie, Technische Universität Kaiserslautern, Paul-Ehrlich-Straße 23, Kaiserslautern D-67663, Germany.
authors.forename: Nicole
authors.initials: N
authors.lastname: Frankenberg-Dinkel
authors.affiliation: Institut für Molekulare Medizin und Zellforschung, Sektion Biophysik, Albert-Ludwigs-Universität, Freiburg, Hermann-Herderstraße 9, Freiburg D-79104, Germany.
authors.forename: Friedrich
authors.initials: F
authors.lastname: Siebert
authors.affiliation: Institut für Chemie, Technische Universität Berlin, Sekr. PC 14, Straße des 17. Juni 135, Berlin D-10623, Germany.
authors.forename: Maria
authors.initials: M
authors.lastname: Andrea Mroginski
authors.affiliation: Institut für Chemie, Technische Universität Berlin, Sekr. PC 14, Straße des 17. Juni 135, Berlin D-10623, Germany.
authors.forename: Peter
authors.initials: P
authors.lastname: Hildebrandt
mesh_terms: D005246:Feedback; D008958:Models, Molecular; D010834:Phytochrome / Q000378:metabolism*; D011522:Protons; D015398:Signal Transduction
chemical_list: D011522:Protons; D010834:Phytochrome