title: Structural and functional studies of the response regulator HupR.
abstract: HupR is a response regulator that controls the synthesis of the membrane-bound [NiFe]hydrogenase of the photosynthetic bacterium Rhodobacter capsulatus. The protein belongs to the NtrC subfamily of response regulators and is the second protein of a two-component system. We have crystallized the full-length protein HupR in the unphosphorylated state in two dimensions using the lipid monolayer technique. The 3D structure of negatively stained HupR was calculated to a resolution of approximately 23 A from tilted electron microscope images. HupR crystallizes as a dimer, and forms an elongated V-shaped structure with extended arms. The dimensions of the dimer are about 80 A length, 40 A width and 85 A thick. The HupR monomer consists of three domains, N-terminal receiver domain, central domain and C-terminal DNA-binding domain. We have fitted the known 3D structure of the central domain from NtrC1 Aquifex aeolicus protein into our 3D model; we propose that contact between the dimers is through the central domain. The N-terminal domain is in contact with the lipid monolayer and is situated on the top of the V-shaped structure. The central domain alone has been expressed and purified; it forms a pentamer in solution and lacks ATPase activity.
authors.affiliation: Laboratory of Molecular Biophysics, Department of Biochemistry, University of Oxford, South Parks Road, Oxford OX1 3QU, UK.
authors.forename: Karen M
authors.initials: KM
authors.lastname: Davies
authors.forename: Vasiliki
authors.initials: V
authors.lastname: Skamnaki
authors.forename: Louise N
authors.initials: LN
authors.lastname: Johnson
authors.forename: Catherine
authors.initials: C
authors.lastname: Vénien-Bryan
mesh_terms: D000595:Amino Acid Sequence; D001426:Bacterial Proteins / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism*; D018360:Crystallography, X-Ray; D004268:DNA-Binding Proteins / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism*; D019281:Dimerization; D008958:Models, Molecular; D008969:Molecular Sequence Data; D017434:Protein Structure, Tertiary; D016415:Sequence Alignment; D014157:Transcription Factors / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism*
chemical_list: D001426:Bacterial Proteins; D004268:DNA-Binding Proteins; D014157:Transcription Factors; C070743:hupR1 protein, Rhodobacter capsulatus