title: The Crystal Structures of the N-terminal Photosensory Core Module of Agrobacterium Phytochrome Agp1 as Parallel and Anti-parallel Dimers.
abstract: Agp1 is a canonical biliverdin-binding bacteriophytochrome from the soil bacterium Agrobacterium fabrum that acts as a light-regulated histidine kinase. Crystal structures of the photosensory core modules (PCMs) of homologous phytochromes have provided a consistent picture of the structural changes that these proteins undergo during photoconversion between the parent red light-absorbing state (Pr) and the far-red light-absorbing state (Pfr). These changes include secondary structure rearrangements in the so-called tongue of the phytochrome-specific (PHY) domain and structural rearrangements within the long α-helix that connects the cGMP-specific phosphodiesterase, adenylyl cyclase, and FhlA (GAF) and the PHY domains. We present the crystal structures of the PCM of Agp1 at 2.70 Å resolution and of a surface-engineered mutant of this PCM at 1.85 Å resolution in the dark-adapted Pr states. Whereas in the mutant structure the dimer subunits are in anti-parallel orientation, the wild-type structure contains parallel subunits. The relative orientations between the PAS-GAF bidomain and the PHY domain are different in the two structures, due to movement involving two hinge regions in the GAF-PHY connecting α-helix and the tongue, indicating pronounced structural flexibility that may give rise to a dynamic Pr state. The resolution of the mutant structure enabled us to detect a sterically strained conformation of the chromophore at ring A that we attribute to the tight interaction with Pro-461 of the conserved PRXSF motif in the tongue. Based on this observation and on data from mutants where residues in the tongue region were replaced by alanine, we discuss the crucial roles of those residues in Pr-to-Pfr photoconversion.
authors.affiliation: From the School of Biological and Chemical Sciences, Queen Mary University of London, Mile End Road, London E1 4NS, United Kingdom.
authors.forename: Soshichiro
authors.initials: S
authors.lastname: Nagano
authors.affiliation: the Institute of Medical Physics and Biophysics (CC2), Group Protein X-ray Crystallography and Signal Transduction, Charité-Universitätsmedizin Berlin, Charitéplatz 1, D-10117 Berlin, Germany.
authors.forename: Patrick
authors.initials: P
authors.lastname: Scheerer
authors.affiliation: From the School of Biological and Chemical Sciences, Queen Mary University of London, Mile End Road, London E1 4NS, United Kingdom.
authors.forename: Kristina
authors.initials: K
authors.lastname: Zubow
authors.affiliation: the Institut für Chemie, Technische Universität Berlin, Sekretariat PC 14, Straße des 17. Juni 135, D-10623 Berlin, Germany.
authors.forename: Norbert
authors.initials: N
authors.lastname: Michael
authors.affiliation: the Division of Material Sciences, Graduate School of Natural Science and Technology, Kanazawa University, Kakuma, Kanazawa, Ishikawa, 920-1192, Japan, and.
authors.forename: Katsuhiko
authors.initials: K
authors.lastname: Inomata
authors.affiliation: the Botanical Institute, Karlsruhe Institute of Technology (KIT), Kaiserstraße 2, D-76131 Karlsruhe, Germany.
authors.forename: Tilman
authors.initials: T
authors.lastname: Lamparter
authors.affiliation: From the School of Biological and Chemical Sciences, Queen Mary University of London, Mile End Road, London E1 4NS, United Kingdom, the Botanical Institute, Karlsruhe Institute of Technology (KIT), Kaiserstraße 2, D-76131 Karlsruhe, Germany norbert.krauss@kit.edu.
authors.forename: Norbert
authors.initials: N
authors.lastname: Krauß
mesh_terms: D060054:Agrobacterium / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism; D020816:Amino Acid Motifs; D001426:Bacterial Proteins / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism; D018360:Crystallography, X-Ray; D010834:Phytochrome / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism; D000072417:Protein Domains; D055503:Protein Multimerization; D020836:Protein Structure, Quaternary
chemical_list: D001426:Bacterial Proteins; D010834:Phytochrome
keywords: Agrobacterium; conformational change; crystal structure; histidine kinase; photoreceptor; phytochrome; quaternary structure; signal transduction; tertiary structure