Data from: Characterization of C-ring component assembly in flagellar motors from amino acid coevolution

Bacterial flagellar motility, an important virulence factor, is energized by a rotary motor localized within the flagellar basal body. The rotor module consists of a large framework (C-ring), composed of the FliG, FliM and FliN proteins. FliN and FliM contacts the FliG torque ring to control the direction of flagellar rotation. We report that structure-based models constrained only by residue coevolution can recover the binding interface of atomic X-ray dimer complexes with remarkable accuracy (ca. 1 Å RMSD). We propose a model for FliM-FliN heterodimerization, which agrees accurately with homologous interfaces as well as in-situ cross-linking experiments, and hence supports a proposed architecture for the lower portion of the C-ring. Furthermore, this approach allowed the identification of two discrete and interchangeable homodimerization interfaces between FliM middle domains that agree with experimental measurements and might be associated with C-ring directional switching dynamics triggered upon binding of CheY signal protein. Our findings provide structural details of complex formation at the C-ring that have been difficult to obtain with previous methodologies and clarify the architectural principle that underpins the ultra-sensitive allostery exhibited by this ring assembly that controls the clockwise (CW) or counterclockwise (CCW) rotation of flagella.细菌鞭毛运动作为一类重要的毒力因子，其由定位于鞭毛基体内部的旋转马达提供能量。转子模块由以FliG、FliM与FliN蛋白构成的大型骨架——C环（C-ring）组成。FliN与FliM可结合于FliG扭矩环，以此调控鞭毛旋转的方向。本研究表明，仅以残基共进化作为约束条件的基于结构的模型，能够以极高精度复现原子级分辨率X射线晶体衍射解析的二聚体复合物的结合界面，其均方根偏差（RMSD）约为1埃。我们提出了FliM-FliN异二聚化模型，该模型与同源结合界面及原位交联（in-situ cross-linking）实验结果高度吻合，进而为C环下部的已提出组装结构提供了有力支撑。此外，该方法还成功鉴定出FliM中间结构域之间存在两种独立且可互换的同二聚化界面，该结果与实验测量结果一致，且可能与CheY信号蛋白（CheY signal protein）结合后触发的C环方向切换动力学密切相关。本研究阐明了此前难以通过传统实验方法获取的C环复合物形成的结构细节，并明确了支撑该环组装体展现超灵敏别构效应的结构原理——该别构效应可精准调控鞭毛的顺时针（CW）与逆时针（CCW）旋转。