title: Non-Bonded Interactions Drive the Sub-Picosecond Bilin Photoisomerization in the P(fr) State of Phytochrome Cph1.
abstract: Phytochromes are protein-based photoreceptors harboring a bilin-based photoswitch in the active site. The timescale of photosignaling via C15 =C16 E-to-Z photoisomerization has been ambiguous in the far-red-absorbing Pfr state. Here we present a unified view of the structural events in phytochrome Cph1 post excitation with femtosecond precision, obtained via stimulated Raman and polarization-resolved transient IR spectroscopy. We demonstrate that photoproduct formation occurs within 700 fs, determined by a two-step partitioning process initiated by a planarization on the electronic excited state with a 300 fs time scale. The ultrafast isomerization timescale for Pfr -to-Pr conversion highlights the active role of the nonbonding methyl-methyl clash initiating the reaction in the excited state. We envision that our results will motivate the synthesis of new artificial photoswitches with precisely tuned non-bonded interactions for ultrafast response.
authors.affiliation: Department of Physics, Freie Universitat Berlin, Arnimallee 14, 14195, Berlin, Germany.
authors.forename: Yang
authors.initials: Y
authors.lastname: Yang
authors.affiliation: Department of Physics, Freie Universitat Berlin, Arnimallee 14, 14195, Berlin, Germany. karsten.heyne@fu-berlin.de.
authors.forename: Karsten
authors.initials: K
authors.lastname: Heyne
authors.affiliation: Department of Chemistry, University of California, Berkeley, CA, 94720, USA. ramathies@berkeley.edu.
authors.forename: Richard A
authors.initials: RA
authors.lastname: Mathies
authors.affiliation: Department of Chemical Sciences, Tata Institute of Fundamental Research, 1 Homi Bhabha Road, Mumbai, 400005, India. dasgupta@tifr.res.in.
authors.forename: Jyotishman
authors.initials: J
authors.lastname: Dasgupta
mesh_terms: D001426:Bacterial Proteins / Q000737:chemistry* / Q000528:radiation effects*; D001654:Bile Pigments / Q000737:chemistry* / Q000528:radiation effects*; D055668:Photochemical Processes; D020283:Photoreceptors, Microbial; D010834:Phytochrome / Q000737:chemistry* / Q000528:radiation effects*; D011494:Protein Kinases / Q000737:chemistry* / Q000528:radiation effects*; D013237:Stereoisomerism; D013997:Time Factors
chemical_list: D001426:Bacterial Proteins; D001654:Bile Pigments; D020283:Photoreceptors, Microbial; D010834:Phytochrome; D011494:Protein Kinases; C413623:Cph1 phytochrome protein, bacteria
keywords: IR spectroscopy; Raman spectroscopy; bilin; photoreceptors; phytochrome