title: Crystal structure of the quorum-sensing protein TraM and its interaction with the transcriptional regulator TraR.
abstract: Transfer of the tumor-inducing plasmid in Agrobacterium tumefaciens is controlled by a quorum-sensing system whose main components are the transcriptional regulator TraR and its autoinducer. This system allows bacteria to synchronize infection of the host plant when a "quorum" of cells has been reached. TraM is an A. tumefaciens protein involved in the regulation of this system because it binds to TraR and prevents it from binding DNA. As a first step to understanding the molecular basis for the regulation of TraR by TraM, we have determined the crystal structure of TraM at 1.65 A resolution. This protein is packed as a dimer, with each monomer consisting mainly of two antiparallel alpha helices. Monomers are tightly associated, with a large hydrophobic area buried upon dimerization. Secondly, we characterized the TraR-TraM complex in vitro. TraM (11.4 kDa, monomer molecular mass) binds tightly TraR (27 kDa, monomer molecular mass) forming a stable oligomeric complex that likely accounts for two TraR and two TraM dimers.
authors.affiliation: Department of Biochemistry, Istituto di Ricerche di Biologia Molecolare Pietro Angeletti, 00040 Pomezia, Rome, Italy.
authors.forename: Alessandro
authors.initials: A
authors.lastname: Vannini
authors.forename: Cinzia
authors.initials: C
authors.lastname: Volpari
authors.forename: Stefania
authors.initials: S
authors.lastname: Di Marco
mesh_terms: D016960:Agrobacterium tumefaciens / Q000378:metabolism; D001426:Bacterial Proteins / Q000737:chemistry*; D002845:Chromatography; D018360:Crystallography, X-Ray; D019281:Dimerization; D004583:Electrons; D007700:Kinetics; D008027:Light; D008958:Models, Molecular; D009154:Mutation; D011485:Protein Binding; D017433:Protein Structure, Secondary; D012542:Scattering, Radiation
chemical_list: D001426:Bacterial Proteins; C080512:TraR protein, Agrobacterium tumefaciens; C074281:TraM protein, bacterial