A protonation-coupled feedback mechanism controls the signalling process in bathy phytochromes

Photoswitching of phytochromes is based on the isomerization of the tetrapyrrole chromophore, and eventually leads to the (de)activation of an enzymatic output module. Now it has been shown that both the structural changes associated with photoswitching and the thermal decay of the light-activated state are coupled to proton translocations in the chromophore pocket.