Molecular Understanding of the Photophysics and Photochemistry of the Cyanobacteriochrome Slr1393g3
Final Report Abstract
Phytochrome-like photoreceptor proteins are promising candidates for biotechnological applications like in optogenetics and bioimaging. In particular, cyanobacteriochromes (CBCRs) require only a single GAF domain for chromophore attachment and complete photochemistry. In addition, they exhibit a large spectral diversity with lowest energy absorbance maxima from nearultraviolet to near-infrared. This project was dedicated to the investigation of the prototypical red/green CBCR Slr1393g3. This photoreceptor harbors phycocyanobilin (PCB) as a chromophore and it exhibits a red light-absorbing dark state (Pr) and a green light-absorbing photoproduct (Pg). Starting with the crystal structures of both forms, this difference in absorption between the two forms, denoted photoproduct tuning, could be modelled qualitatively. This was the first time that this tuning could be simulated and it unraveled the origin of the difference in absorption between the two forms: The effective conjugation lengths of the Pg form is shorter than that of the Pr form resulting in the blue shifted absorption. In contrast to this, direct electrostatic interactions of PCB with the binding pocket lead to similar shifts in both forms. In addition to this central finding, a benchmark study was published to elucidate critical components in our computational protocol. As shown in further investigations, this approach can also be employed to model the photoproduct tuning of further phytochrome-like photoreceptors, for which crystal structures of both forms are available. Finally, potential energy surface scans along certain dihedral angles of the PCB chromophore in vacuo and in protein were calculated to obtain insights into the excited state reactivity. For this purpose, the pure QM calculations and the QM region of the QM/MM simulations consisted of the same atoms to obtain direct insights into how far the protein environment can influence the photochemistry of the chromophore. All in all, this research resulted in a molecular understanding of the differences in the photophysics between the Pr and Pg forms of Slr1393g3, gave first insights into the photochemistry of the PCB chromophore inside the protein and will serve as a foundation for further investigations on the photophysics and photochemistry of phytochrome-like photoreceptor proteins.
Publications
- A QM/MM study of the initial excited state dynamics of green-absorbing proteorhodopsin. Faraday Discuss. 207, 137-152 (2018)
V. Borin, C. Wiebeler, and I. Schapiro
(See online at https://doi.org/10.1039/c7fd00198c) - QM/MM Benchmark of Cyanobacteriochrome Slr1393g3 Absorption Spectra. Molecules 24, 9, 1720 (2019)
C. Wiebeler and I. Schapiro
(See online at https://doi.org/10.3390/molecules24091720) - The Effective Conjugation Length is responsible for the Red/Green Spectral Tuning in the Cyanobacteriochrome Slr1393g3. Angew. Chem. Int. Ed. 58, 7, 1934-1938 (2019)
C. Wiebeler, A. G. Rao, W. Gärtner, and I. Schapiro
(See online at https://doi.org/10.1002/anie.201810266)
