title: An active-like structure in the unphosphorylated StyR response regulator suggests a phosphorylation- dependent allosteric activation mechanism.
abstract: StyR belongs to the FixJ subfamily of signal transduction response regulators; it controls transcription of the styABCD operon coding for styrene catabolism in Pseudomonas fluorescens ST. The crystal structure of unphosphorylated StyR is reported at 2.2 A resolution. StyR is composed of an N-terminal regulatory domain (StyR-N) and a C-terminal DNA binding domain (StyR-C). The two domains are separated by an elongated linker alpha helix (34 residues), a new feature in known response regulator structures. StyR-C is structured similarly to the DNA binding domain of the response regulator NarL. StyR-N shows structural reorganization of the phosphate receiving region involved in activation/homodimerization: specific residues adopt an "active-like" conformation, and the alpha4 helix, involved in dimerization of the homologous FixJ response regulator, is trimmed to just one helical turn. Overall, structural considerations suggest that phosphorylation may act as an allosteric switch, shifting a preexisting StyR equilibrium toward the active, dimeric, DNA binding form.
authors.affiliation: Giannina Gaslini Institute and INFM, Largo G. Gaslini 5, I-16147 Genova, Italy.
authors.forename: Mario
authors.initials: M
authors.lastname: Milani
authors.forename: Livia
authors.initials: L
authors.lastname: Leoni
authors.forename: Giordano
authors.initials: G
authors.lastname: Rampioni
authors.forename: Elisabetta
authors.initials: E
authors.lastname: Zennaro
authors.forename: Paolo
authors.initials: P
authors.lastname: Ascenzi
authors.forename: Martino
authors.initials: M
authors.lastname: Bolognesi
mesh_terms: D000494:Allosteric Regulation; D001426:Bacterial Proteins / Q000737:chemistry*; D003461:Crystallography; D004268:DNA-Binding Proteins / Q000737:chemistry*; D019281:Dimerization; D010766:Phosphorylation; D017433:Protein Structure, Secondary; D017434:Protein Structure, Tertiary
chemical_list: D001426:Bacterial Proteins; D004268:DNA-Binding Proteins; C110964:StyR protein, Pseudomonas