title: Biochemical and physiological characterization of a BLUF protein-EAL protein complex involved in blue light-dependent degradation of cyclic diguanylate in the purple bacterium Rhodopseudomonas palustris.
abstract: Organisms adapt their physiologies in response to the quality and quantity of environmental light. Members of a recently identified photoreceptor protein family, BLUF domain proteins, use a flavin chromophore to sense blue light. Herein, we report that PapB, which contains a BLUF domain, controls the biofilm formation of the purple photosynthetic bacterium Rhodopseudomonas palustris. Purified PapB undergoes a typical BLUF-type photocycle, and light-excited PapB enhances the phosphodiesterase activity of the EAL domain protein, PapA, which degrades the second messenger, cyclic dimeric GMP (c-di-GMP). PapB directly interacts with PapA in vitro in a light-independent manner and induces a conformational change in the preformed PapA-PapB complex. A PapA-PapB docking simulation, as well as a site-directed mutagenesis study, identified amino acids partially responsible for the interaction between the PapA EAL domain and the two C-terminal α-helices of the PapB BLUF domain. Thus, the conformational change, which involves the C-terminal α-helices, transfers the flavin-sensed blue light signal to PapA. Deletion of papB in R. palustris enhances biofilm formation under high-intensity blue light conditions, indicating that PapB functions as a blue light sensor, which negatively regulates biofilm formation. These results demonstrate that R. palustris can control biofilm formation via a blue light-dependent modulation of its c-di-GMP level by the BLUF domain protein, PapB.
authors.affiliation: Graduate School of Bioscience and Biotechnology, Tokyo Institute ofTechnology, Yokohama 226-8501, Japan.
authors.forename: Takuya
authors.initials: T
authors.lastname: Kanazawa
authors.forename: Shukun
authors.initials: S
authors.lastname: Ren
authors.forename: Mikika
authors.initials: M
authors.lastname: Maekawa
authors.forename: Koji
authors.initials: K
authors.lastname: Hasegawa
authors.forename: Fumio
authors.initials: F
authors.lastname: Arisaka
authors.forename: Mamoru
authors.initials: M
authors.lastname: Hyodo
authors.forename: Yoshihiro
authors.initials: Y
authors.lastname: Hayakawa
authors.forename: Hiroyuki
authors.initials: H
authors.lastname: Ohta
authors.forename: Shinji
authors.initials: S
authors.lastname: Masuda
mesh_terms: D001426:Bacterial Proteins / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism*; D018441:Biofilms / Q000254:growth & development; D002851:Chromatography, High Pressure Liquid; D006152:Cyclic GMP / Q000031:analogs & derivatives* / Q000378:metabolism; D008027:Light; D008954:Models, Biological; D008958:Models, Molecular; D010727:Phosphoric Diester Hydrolases / Q000235:genetics / Q000378:metabolism; D017433:Protein Structure, Secondary; D012241:Rhodopseudomonas / Q000254:growth & development / Q000378:metabolism* / Q000528:radiation effects*
chemical_list: D001426:Bacterial Proteins; C062025:bis(3',5')-cyclic diguanylic acid; D010727:Phosphoric Diester Hydrolases; D006152:Cyclic GMP