title: Small-angle X-ray scattering reveals the solution structure of a bacteriophytochrome in the catalytically active Pr state.
abstract: Phytochromes are light-sensing macromolecules that are part of a two component phosphorelay system controlling gene expression. Photoconversion between the Pr and Pfr forms facilitates autophosphorylation of a histidine in the dimerization domain (DHp). We report the low-resolution structure of a bacteriophytochrome (Bph) in the catalytic (CA) Pr form in solution determined by small-angle X-ray scattering (SAXS). Ab initio modeling reveals, for the first time, the domain organization in a typical bacteriophytochrome, comprising an chromophore binding and phytochrome (PHY) N terminal domain followed by a C terminal histidine kinase domain. Homologous high-resolution structures of the light-sensing chromophore binding domain (CBD) and the cytoplasmic part of a histidine kinase sensor allows us to model 75% of the structure with the remainder comprising the phytochrome domain which has no 3D representative in the structural database. The SAXS data reveal a dimeric Y shaped macromolecule and the relative positions of the chromophores (biliverdin), autophosphorylating histidine residues and the ATP molecules in the kinase domain. SAXS data were collected from a sample in the autophosphorylating Pr form and reveal alternate conformational states for the kinase domain that can be modeled in an open (no-catalytic) and closed (catalytic) state. This model suggests how light-induced signal transduction can stimulate autophosphorylation followed by phosphotransfer to a response regulator (RR) in the two-component system.
authors.affiliation: CCLRC Daresbury Laboratory, Keckwick Lane, Warrington, Cheshire, WA4 4AD, UK.
authors.forename: Katie
authors.initials: K
authors.lastname: Evans
authors.forename: J Günter
authors.initials: JG
authors.lastname: Grossmann
authors.forename: Anthony P
authors.initials: AP
authors.lastname: Fordham-Skelton
authors.forename: Miroslav Z
authors.initials: MZ
authors.lastname: Papiz
mesh_terms: D000255:Adenosine Triphosphate / Q000378:metabolism; D001426:Bacterial Proteins / Q000737:chemistry / Q000378:metabolism; D001664:Biliverdine / Q000737:chemistry / Q000378:metabolism; D002384:Catalysis; D008958:Models, Molecular; D008968:Molecular Conformation; D015394:Molecular Structure; D010766:Phosphorylation; D010834:Phytochrome / Q000737:chemistry* / Q000378:metabolism; D012996:Solutions; D014785:Vision, Ocular; D014961:X-Ray Diffraction
chemical_list: D001426:Bacterial Proteins; D012996:Solutions; D010834:Phytochrome; D000255:Adenosine Triphosphate; D001664:Biliverdine