title: Two ground state isoforms and a chromophore D-ring photoflip triggering extensive intramolecular changes in a canonical phytochrome.
abstract: Phytochrome photoreceptors mediate light responses in plants and in many microorganisms. Here we report studies using (1)H-(13)C magic-angle spinning NMR spectroscopy of the sensor module of cyanobacterial phytochrome Cph1. Two isoforms of the red-light absorbing Pr ground state are identified. Conclusive evidence that photoisomerization occurs at the C15-methine bridge leading to a β-facial disposition of the ring D is presented. In the far-red-light absorbing Pfr state, strong hydrogen-bonding interactions of the D-ring carbonyl group to Tyr-263 and of N24 to Asp-207 hold the chromophore in a tensed conformation. Signaling is triggered when Asp-207 is released from its salt bridge to Arg-472, probably inducing conformational changes in the tongue region. A second signal route is initiated by partner swapping of the B-ring propionate between Arg-254 and Arg-222.
authors.affiliation: Leids Instituut voor Chemisch Onderzoek, Universiteit Leiden, P.O. Box 9502, 2300 RA Leiden, The Netherlands.
authors.forename: Chen
authors.initials: C
authors.lastname: Song
authors.forename: Georgios
authors.initials: G
authors.lastname: Psakis
authors.forename: Christina
authors.initials: C
authors.lastname: Lang
authors.forename: Jo
authors.initials: J
authors.lastname: Mailliet
authors.forename: Wolfgang
authors.initials: W
authors.lastname: Gärtner
authors.forename: Jon
authors.initials: J
authors.lastname: Hughes
authors.forename: Jörg
authors.initials: J
authors.lastname: Matysik
mesh_terms: D006860:Hydrogen Bonding; D009682:Magnetic Resonance Spectroscopy; D008958:Models, Molecular; D010777:Photochemistry; D010834:Phytochrome / Q000737:chemistry*; D020033:Protein Isoforms / Q000737:chemistry*; D011789:Quantum Theory
chemical_list: D020033:Protein Isoforms; D010834:Phytochrome