Structure of the TolR periplasmic domain

TolR是一种五元跨膜多蛋白复合物，在革兰氏阴性菌中是保守的。 Tol/Tol系统有助于维持外膜的完整性，并已被提出参与其他几个细胞过程，包括细胞分裂。获得TolR的结构不仅有助于解释许多提出的功能，而且有助于了解TolR同系物ExbD和MotB，并为抗菌治疗提供更多靶点。此外，该结构可以提供关于大肠杆菌素和噬菌体如何能够进入细胞的见解。 因此，我们已经确定了溶液结构的同源二聚体周质结构域的TolR从流感嗜血杆菌，确定与传统的，基于NOE的NMR光谱，辅以广泛的残留偶极耦合测量。 一种新的方法，用于组装的二聚体从小角X射线散射数据的开发，并确认NMR衍生结构的准确性。 为了便于NMR光谱分析，创建了含有139个残基蛋白质的残基59-130的TolR构建体。TolR的周质结构域形成由强烈弯曲的八链β-折叠组成的C2对称二聚体，在一侧产生大的深沟，而四个螺旋覆盖折叠的另一面。TolR二聚体的结构以及来自文献的数据表明，TolR的周质结构域最有可能相对于细胞质膜取向，以及它如何与α-淀粉酶/Tol系统的其他组分相互作用，特别是TolQ。

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.