title: Phytochrome as molecular machine: revealing chromophore action during the Pfr --> Pr photoconversion by magic-angle spinning NMR spectroscopy.
abstract: The cyanobacterial phytochrome Cph1 can be photoconverted between two thermally stable states, Pr and Pfr. The photochemically induced Pfr --> Pr back-reaction has been followed at low temperature by magic-angle spinning (MAS) NMR spectroscopy, allowing two intermediates, Lumi-F and Meta-F, to be trapped. Employing uniformly (13)C- and (15)N-labeled open-chain tetrapyrrole chromophores, all four states-Pfr, Lumi-F, Meta-F, and Pr-have been structurally characterized. In the first step, the double bond photoisomerization forming Lumi-F occurs. The second step, the transformation to Meta-F, is driven by the release of the mechanical tension. This process leads to the break of the hydrogen bond of the ring D nitrogen to Asp-207 and triggers signaling. The third step is protonically driven allowing the hydrogen-bonding interaction of the ring D nitrogen to be restored. Compared to the forward reaction, the order of events is changed, probably caused by the different properties of the hydrogen bonding partners of N24, leading to the directionality of the photocycle.
authors.affiliation: Leiden Institute of Chemistry, Leiden University, P.O. Box 9502, 2300 RA Leiden, The Netherlands.
authors.forename: Thierry
authors.initials: T
authors.lastname: Rohmer
authors.forename: Christina
authors.initials: C
authors.lastname: Lang
authors.forename: Christian
authors.initials: C
authors.lastname: Bongards
authors.forename: Karthick Babu Sai Sankar
authors.initials: KB
authors.lastname: Gupta
authors.forename: Johannes
authors.initials: J
authors.lastname: Neugebauer
authors.forename: Jon
authors.initials: J
authors.lastname: Hughes
authors.forename: Wolfgang
authors.initials: W
authors.lastname: Gärtner
authors.forename: Jörg
authors.initials: J
authors.lastname: Matysik
mesh_terms: D001426:Bacterial Proteins / Q000737:chemistry / Q000378:metabolism; D001665:Binding Sites; D003080:Cold Temperature; D000458:Cyanobacteria / Q000737:chemistry / Q000378:metabolism*; D009682:Magnetic Resonance Spectroscopy; D008958:Models, Molecular; D010084:Oxidation-Reduction; D010777:Photochemistry; D020283:Photoreceptors, Microbial; D010834:Phytochrome / Q000737:chemistry / Q000145:classification / Q000378:metabolism*; D011485:Protein Binding; D011494:Protein Kinases / Q000737:chemistry / Q000378:metabolism; D013696:Temperature
chemical_list: D001426:Bacterial Proteins; D020283:Photoreceptors, Microbial; D010834:Phytochrome; D011494:Protein Kinases; C413623:Cph1 phytochrome protein, bacteria