Department of Molecular Biosciences, The University of Kansas, Lawrence, Kansas, USA.
Biophys J. 2010 Feb 3;98(3):452-61. doi: 10.1016/j.bpj.2009.10.030.
Many Gram-negative bacteria initiate infections by injecting effector proteins into host cells through the type III secretion apparatus, which is comprised of a basal body, a needle, and a tip. The needle channel is formed by the assembly of a single needle protein. To explore the export mechanisms of MxiH needle protein through the needle of Shigella flexneri, an essential step during needle assembly, we have performed steered molecular dynamics simulations in implicit solvent. The trajectories reveal a screwlike rotation motion during the export of nativelike helix-turn-helix conformations. Interestingly, the channel interior with excessive electronegative potential creates an energy barrier for MxiH to enter the channel, whereas the same may facilitate the ejection of the effectors into host cells. Structurally known basal regions and ATPase underneath the basal region also have electronegative interiors. Effector proteins also have considerable electronegative potential patches on their surfaces. From these observations, we propose a repulsive electrostatic mechanism for protein translocation through the type III secretion apparatus. Based on this mechanism, the ATPase activity and/or proton motive force could be used to energize the protein translocation through these nanomachines. A similar mechanism may be applicable to macromolecular channels in other secretion systems or viruses through which proteins or nucleic acids are transported.
许多革兰氏阴性细菌通过 III 型分泌装置将效应蛋白注入宿主细胞，从而引发感染。III 型分泌装置由基底部、针和尖端组成。针通道由单个针蛋白组装而成。为了探索 MxiH 针蛋白通过 Shigella flexneri 针的出口机制，这是针组装过程中的一个重要步骤，我们在隐溶剂中进行了导向分子动力学模拟。轨迹揭示了天然螺旋-转角-螺旋构象在出口过程中的螺旋旋转运动。有趣的是，通道内部的高负电性会为 MxiH 进入通道创造一个能量障碍，而这同样可能有利于将效应蛋白喷射到宿主细胞中。结构上已知的基底区域和基底区域下方的 ATP 酶也具有负电性内部。效应蛋白表面也有相当大的负电性电位斑。从这些观察结果中，我们提出了一种用于 III 型分泌装置中蛋白质转运的排斥静电机制。基于这个机制，ATP 酶活性和/或质子动力势可以用来为这些纳米机器中的蛋白质转运提供能量。类似的机制可能适用于其他分泌系统或病毒中的大分子通道，蛋白质或核酸通过这些通道进行运输。
