Molecular mechanism of the bacterial flagellar axial coupling joint

1.鞭毛轴蛋白及其复合物的X射线晶体学研究（1）HAP 3的26 kDa片段的晶体结构在1.9 nm分辨率下解析（PDB ID：2D 4X）。(2)HAP 1的49 kDa片段的晶体结构以2.1 nm分辨率解析（PDB ID：2D 4 Y）。(3)我们发现了HAP 2-HAP 3-FlgN的稳定复合物，并建立了该复合物的纯化程序。(4)我们获得了HAP 1-FlgN复合物的小晶体。鞭毛从钩到丝的轴向结构分析。(1)钩的结构通过将FlgE的31 kDa片段的X射线结构拟合到从电子冷冻显微镜获得的密度图中来构建钩的原子模型。该模型及后续的模拟研究揭示了分子万向节的机理。(2)钩丝连接的结构我们根据HAP 1和HAP 3的晶体结构、丝和钩模型，建立了钩丝连接的部分结构模型。该结构清楚地表明了如何将机械上不同的两种结构耦合并平滑地传递扭矩的分子机制。(3)轴向结构的分子动力学模拟在鞭毛丝模型上进行了两种不同类型的分子动力学模拟研究。开关相互作用控制的能量挫折和多态性的转变，确定了从一个大规模的MD模拟。通过粗粒化的分子动力学模拟，证明了溶剂对多态性转变的影响。3.杆和杆-钩复合物的结构分析（1）利用纯化的FlgG蛋白和短钩片段，从钩上重建了远端杆。(2)我们从多杆突变株中纯化了基体，并通过电子冷冻显微镜在8.1 nm分辨率下分析了多杆的结构。

1.X-ray crystallographic studies of the flagellar axial proteins and their complexes(1) Crystal structure of a 26 kDa fragment of HAP3 was solved at 1.9 Å resolution (PDB ID:2D4X).(2) Crystal structure of a 49 kDa fragment of HAP1 was solved at 2.1 Å resolution (PDB ID:2D4Y).(3) We found a stable complex of HAP2-HAP3-FlgN and established a purification procedure of the complex.(4) We obtained small crystals of the HAP1-FlgN complex.2. Analyses of the flagellar axial structure from the hook to the filament.(1) Structure of the hookAn atomic model of the hook was constructed by fitting the X-ray structure of a 31 kDa fragment of FlgE into the density map obtained from electron cryo-microscopy. The model and following simulation studies revealed the molecular universal joint mechanism.(2) Structure of the hook-filament junctionWe built the partial structural model of the hook-filament junction, based on the crystal structures of HAP1 and HAP3, the filament and the hook model. The structure clearly indicated the molecular mechanism of how to couple the mechanically distinct two structures and to transmit torque smoothly.(3) Molecular dynamics simulation of the axial structureTwo different types of molecular dynamics simulation studies were conducted on the flagellar filament model. Switch interactions which control the energy frustration and polymorphic transition were identified from a massive MD simulation. Solvent effects on the'polymorphic transition were demonstrated from the coarse-grained MD simulations.3.Structure analysis of the rod and the rod-hook complex(1) We have reconstructed the distal rod from the hook using purified FlgG proteins and the short hook fragments.(2) We purified the basal body from a poly rod mutant strain and analyzed the structure of the poly rod at 8.1 Å resolution by electron cryo-microscopy.