The color-transitions of bilin photoreceptors

• Applicants: Professor Dr. Jörg Matysik; Professor Dr. Daniel Sebastiani
• Subject Area: Structural Biology ; Analytical Chemistry ; Biochemistry ; Plant Biochemistry and Biophysics ; Biological and Biomimetic Chemistry ; Biophysics ; Physical Chemistry of Molecules, Liquids and Interfaces, Biophysical Chemistry ; Theoretical Chemistry: Molecules, Materials, Surfaces
• Term: from 2015 to 2021
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 282144690

• Final Report Year: 2021

Final Report Abstract

The project has been aiming to answer the question why the photoisomerization of Pr can either lead to Pfr (red shift as in canonical phytochromes) or to Pg (blue shift as in AnPixJ2g). Working hypothesis has been the “orbital-lift model” describing opposite charge effects on the two LUMO orbitals. While in Pfr, charges stabilize the LUMO, in Pg the opposite happens. To this end, the charge architecture has to be experimentally explored and the orbital structure theoretically reconstructed. On that pathway, we have obtained theses data in high quality and are still in the process of analyzing experimental data. The delay has been caused by the difficulties to introduce the labelled cofactor and to control heterogeneities. Furthermore, the unexpected theoretical prediction of the Y302F mutant, showing sub-state III and the spectroscopic discovery of the appropriate PIII state was a sidepath worth to be taken: We demonstrated the reliability of our methods and proposed a new explanation for the satellite absorption band. The study of sub-states, their dynamics and their structural differences is old. In particular the first experimental observation of the two isoforms Pr-I und Pr-II sparked the question whether both isoforms are interchanging and, if they do, on which time scale. Here we identified by means of molecular dynamics simulations the two sub-states I and II, their exchange kinetics and their specific molecular features. Theory also recognized that on the basis of these structural difference, the split of the Q band cannot be explained. It was the prediction of sub-state III and the discovery of the fittingly spectroscopic PIII state which provided a hint for the interpretation of the Q-band split. It turned out that PIII is selectively created on the costs of sub-state II which also was theoretically predicted. This implies that the satellite band with its enormous line-width has a cause which is not yet implemented into the spectral calculations. We propose here that the positive charge moves under conditions which are not yet understood to the conjugated carbon network forming a defect. If this defect is mobile, the enormous linewidth would be immediately become understood. Future work will be: (i) MAS-DNP NMR to localize the position of the positive charge on the cofactor in Pr state. (ii) Reconstruction of charge architecture in Pg, molecular orbital structure, comparison of orbital structures of Pfr and Pg. (iii) Understanding spectral properties of a charge defect in the conjugated system.

Publications

• “Structural heterogeneity in parent ground-state structure in AnPixJg2 revealed by spectroscopy and theory” Physical Chemistry Chemical Physics 19, 13882-13894 (2017)
  Laura Katharina Scarbath-Evers, Sascha Jähnigen, Hossam Elgabarty, Chen Song, Rei Narikawa, Jörg Matysik, Daniel Sebastiani
  
• “3D structures of plant phytochrome A as Pr and Pfr from solid-state NMR: implications for molecular function” Frontiers in Plant Science 9, 498 (2018)
  Chen Song, Maria-Andrea Mroginski, Christina Lang, Jakub Kopycki, Wolfgang Gärtner, Jörg Matysik, Jon Hughes
  
• "Lyophilization reveals a multitude of structural conformations in the chromophore of a Cph2-like phytochrome”. J. Phys. Chem. B, 124, 7115-7125 (2020)
  Yunmi Kim, Qian-Zhao Xu, Kai-Hong Zhao, Wolfgang Gärtner, Jörg Matysik, Chen Song
  
• “Carbon Atoms Speaking Out: How the Geometric Sensitivity of 13C Chemical Shifts Leads to Understanding the Colour Tuning of Phycocyanobilin in Cph1 and AnPixJ” Molecules 25, 5505 (2020)
  S. Jähnigen, D. Sebastiani
  
• “The Hydrogen Bond of a Tyrosine Residue to the C Ring Propionate has a Direct Influence on Absorption and Conformation of the Bilin Cofactor in Red/Green Cyanobacteriochromes” J. Phys. Chem. B, 125, 1331-1342 (2021)
  Susanne Altmayer, Lisa Köhler, Sascha Jähnigen, Christian Wiebeler, Chen Song, Daniel Sebastiani, Jörg Matysik