Vannini Alessandro, Volpari Cinzia, Di Marco Stefania
Department of Biochemistry, Istituto di Ricerche di Biologia Molecolare Pietro Angeletti, 00040 Pomezia, Rome, Italy.
J Biol Chem. 2004 Jun 4;279(23):24291-6. doi: 10.1074/jbc.M401855200. Epub 2004 Mar 24.
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.
根癌土壤杆菌中致瘤质粒的转移由一种群体感应系统控制，该系统的主要成分是转录调节因子TraR及其自诱导物。当达到细胞“群体数量”时，该系统使细菌能够同步感染宿主植物。TraM是一种根癌土壤杆菌蛋白，参与该系统的调节，因为它与TraR结合并阻止其与DNA结合。作为了解TraM对TraR调节的分子基础的第一步，我们已确定TraM在1.65埃分辨率下的晶体结构。该蛋白以二聚体形式堆积，每个单体主要由两个反平行的α螺旋组成。单体紧密结合，二聚化时掩埋了一个大的疏水区域。其次，我们在体外对TraR-TraM复合物进行了表征。TraM（单体分子量11.4 kDa）与TraR（单体分子量27 kDa）紧密结合，形成一个稳定的寡聚复合物，该复合物可能由两个TraR二聚体和两个TraM二聚体组成。
