Structure of the TolR periplasmic domain

TolR是Pal/ toll系统的一部分，该系统形成一个由五成员组成的跨膜多蛋白复合物，在革兰氏阴性菌中保守存在。Pal/Tol系统有助于维持外膜的完整性，并被认为参与包括细胞分裂在内的其他几个细胞过程。获得TolR的结构不仅有助于解释Pal/Tol系统的许多功能，而且有助于了解TolR的同源物ExbD和MotB，并为抗菌治疗提供更多的靶点。此外，该结构可能为了解粘菌素和噬菌体如何进入细胞提供见解。因此，我们确定了流感嗜血杆菌TolR的同型二聚体质周结构域的溶液结构，用传统的、基于no2的核磁共振光谱测定，辅以广泛的残余偶极偶联测量。提出了一种利用小角度x射线散射数据组装二聚体的新方法，并证实了核磁共振衍生结构的准确性。为了便于核磁共振光谱分析，构建了包含139残基蛋白中的59-130残基的TolR结构。TolR的外质域形成一个c2对称的二聚体，由一个强弯曲的八链β -片组成，在一侧产生一个大的深槽，而四个螺旋覆盖片的另一侧。TolR二聚体的结构和文献数据表明，TolR的质周结构域最有可能相对于细胞质膜定向，以及它如何与Pal/Tol系统的其他组分，特别是TolQ相互作用。

TolR is a part of the Pal/Tol system which forms a five member, membrane-spanning, multi-protein complex that is conserved in gram-negative bacteria. The Pal/Tol system helps maintain the integrity of the outer membrane and has been proposed to be involved in several other cellular processes including cell division. Obtaining the structure of TolR is of interest not only to help explain the many proposed functions of the Pal/Tol system, but also to gain an understanding of the TolR homologues ExbD and MotB, and to provide more targets for anti-bacterial treatments. In addition, the structure may provide insights into how colicins and bacteriophages are able to enter the cell. Therefore, we have determined the solution structure of the homodimeric periplasmic domain of TolR from Haemophilus influenzae, determined with conventional, NOE-based NMR spectroscopy, supplemented by extensive residual dipolar coupling measurements. A novel method for assembling the dimer from small angle X-ray scattering data was developed and confirms the accuracy of the NMR-derived structure. To facilitate NMR spectral analysis, a TolR construct containing residues 59-130 of the 139 residue protein was created. The periplasmic domain of TolR forms a C2-symmetric dimer consisting of a strongly curved eight-stranded beta-sheet, generating a large deep groove on one side, while four helices cover the other face of the sheet. The structure of the TolR dimer together with data from the literature suggest how the periplasmic domain of TolR is most likely oriented relative to the cytoplasmic membrane and how it may interact with other components of the Pal/Tol system, particularly TolQ.