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Intramolecular Proton Transfer Controls Protein Structural Changes in Phytochrome
Citation key Kraskov2020
Author Kraskov, Anastasia and Nguyen, Anh Duc and Goerling, Jan and Buhrke, David and Velazquez Escobar, Francisco and Fernandez Lopez, Maria and Michael, Norbert and Sauthof, Luisa and Schmidt, Andrea and Piwowarski, Patrick and Yang, Yang and Stensitzki, Till and Adam, Suliman and Bartl, Franz and Schapiro, Igor and Heyne, Karsten and Siebert, Friedrich and Scheerer, Patrick and Mroginski, Maria Andrea and Hildebrandt, Peter
Pages 1023-1037
Year 2020
DOI 10.1021/acs.biochem.0c00053
Journal Biochemistry
Volume 59
Number 9
Note PMID: 32073262
Abstract Phytochromes are biological photoswitches that interconvert between two parent states (Pr and Pfr). The transformation is initiated by photoisomerization of the tetrapyrrole chromophore, followed by a sequence of chromophore and protein structural changes. In the last step, a phytochrome-specific peptide segment (tongue) undergoes a secondary structure change, which in prokaryotic phytochromes is associated with the (de)activation of the output module. The focus of this work is the Pfr-to-Pr photoconversion of the bathy bacteriophytochrome Agp2 in which Pfr is the thermodynamically stable state. Using spectroscopic techniques, we studied the structural and functional consequences of substituting Arg211, Tyr165, His278, and Phe192 close to the biliverdin (BV) chromophore. In Pfr, substitutions of these residues do not affect the BV structure. The characteristic Pfr properties of bathy phytochromes, including the protonated propionic side chain of ring C (propC) of BV, are preserved. However, replacing Arg211 or Tyr165 blocks the photoconversion in the Meta-F state, prior to the secondary structure transition of the tongue and without deprotonation of propC. The Meta-F state of these variants displays low photochemical activity, but electronic excitation causes ultrafast alterations of the hydrogen bond network surrounding the chromophore. In all variants studied here, thermal back conversion from the photoproducts to Pfr is decelerated but substitution of His278 or Phe192 is not critical for the Pfr-to-Pr photoconversion. These variants do not impair deprotonation of propC or the α-helix/β-sheet transformation of the tongue during the Meta-F-to-Pr decay. Thus, we conclude that propC deprotonation is essential for restructuring of the tongue.
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