title: Light-induced chromophore activity and signal transduction in phytochromes observed by 13C and 15N magic-angle spinning NMR.
abstract: Both thermally stable states of phytochrome, Pr and Pfr, have been studied by (13)C and (15)N cross-polarization (CP) magic-angle spinning (MAS) NMR using cyanobacterial (Cph1) and plant (phyA) phytochrome sensory modules containing uniformly (13)C- and (15)N-labeled bilin chromophores. Two-dimensional homo- and heteronuclear experiments allowed most of the (13)C chemical shifts to be assigned in both states. Chemical shift differences reflect changes of the electronic structure of the cofactor at the atomic level as well as its interactions with the chromophore-binding pocket. The chromophore in cyanobacterial and plant phytochromes shows very similar features in the respective Pr and Pfr states. The data are interpreted in terms of a strengthened hydrogen bond at the ring D carbonyl. The red shift in the Pfr state is explained by the increasing length of the conjugation network beyond ring C including the entire ring D. Enhanced conjugation within the pi-system stabilizes the more tensed chromophore in the Pfr state. Concomitant changes at the ring C propionate carboxylate and the ring D carbonyl are explained by a loss of hydrogen bonding to Cph1-His-290 and transmittance of conformational changes to the ring C propionate via a water network. These and other conformational changes may lead to modified surface interactions, e.g., along the tongue region contacting the bilin chromophore.
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: Jon
authors.initials: J
authors.lastname: Hughes
authors.forename: Lars-Oliver
authors.initials: LO
authors.lastname: Essen
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; D001654:Bile Pigments / Q000737:chemistry; D002247:Carbon Isotopes / Q000737:chemistry; D008027:Light; D009682:Magnetic Resonance Spectroscopy; D008958:Models, Molecular; D009587:Nitrogen Isotopes / Q000737:chemistry; D020283:Photoreceptors, Microbial; D052980:Phycobilins / Q000737:chemistry; D010834:Phytochrome / Q000737:chemistry* / Q000378:metabolism; D011487:Protein Conformation; D011494:Protein Kinases / Q000737:chemistry / Q000378:metabolism; D015398:Signal Transduction
chemical_list: D001426:Bacterial Proteins; D001654:Bile Pigments; D002247:Carbon Isotopes; D009587:Nitrogen Isotopes; D020283:Photoreceptors, Microbial; D052980:Phycobilins; D010834:Phytochrome; D011494:Protein Kinases; C413623:Cph1 phytochrome protein, bacteria