title: Dimerization properties of the RpBphP2 chromophore-binding domain crystallized by homologue-directed mutagenesis.
abstract: Bacteriophytochromes (BphPs) are biliverdin IXα-containing photoreceptors that photoconvert between red (Pr) and far-red (Pfr) absorbing states. BphPs are one half of a two-component system that transmits a light signal to a histidine kinase domain and then to a gene-response regulator. In Rhodopseudomonas palustris, synthesis of a light-harvesting complex (LH4) is controlled by two BphPs (RpBphP2 and RpBphP3). Despite their high sequence identity (52%), their absorption spectra are very different. The spectra of RpBphP2 exhibit classic Pr-to-Pfr photoconversion, whereas RpBphP3 quenches and a high-energy Pnr state emerges [Giraud et al. (2005), J. Biol. Chem. 280, 32389-32397]. Crystallization of the chromophore-binding domain (CBD) of RpBphP2 (RpBphP2-CBD) proved to be difficult and the structure of RpBphP3-CBD was used to crystallize RpBphP2-CBD* using homologue-directed mutagenesis. The structure shows that dimerization is an important factor in successful crystallization of RpBphP2-CBD* and arises from an N136R mutation. Mutations at this site correlate with an ability to dimerize in other truncated BphPs and may also be important for full-length dimer formation. Comparison of the RpBphP3-CBD and RpBphP2-CBD* biliverdin IXα pockets revealed that the former has additional hydrogen bonding around the B and D pyrrole rings that may constrain photoconversion to Pfr, resulting in a strained photoexcited Pnr state.
authors.affiliation: Institute of Integrative Biology, Liverpool University, Biosciences Building, Crown Street, Liverpool L69 7ZB, England.
authors.forename: Dom
authors.initials: D
authors.lastname: Bellini
authors.forename: Miroslav Z
authors.initials: MZ
authors.lastname: Papiz
mesh_terms: D001426:Bacterial Proteins / Q000737:chemistry*; D002850:Chromatography, Gel; D002856:Chromatophores / Q000737:chemistry*; D003001:Cloning, Molecular; D003460:Crystallization; D018360:Crystallography, X-Ray / Q000379:methods; D019281:Dimerization; D045342:Light-Harvesting Protein Complexes / Q000737:chemistry*; D008956:Models, Chemical; D008968:Molecular Conformation; D016296:Mutagenesis; D009154:Mutation; D010834:Phytochrome / Q000737:chemistry*; D017434:Protein Structure, Tertiary; D012241:Rhodopseudomonas / Q000378:metabolism; D013056:Spectrophotometry, Ultraviolet / Q000379:methods
chemical_list: D001426:Bacterial Proteins; D045342:Light-Harvesting Protein Complexes; D010834:Phytochrome