Proteins often have nonzero electric dipole moments, making them interact with external electric fields and offering a means for controlling their orientation. One application that is known to benefit from orientation control is single-particle imaging with x-ray free-electron lasers, in which diffraction is recorded from proteins in the gas phase to determine their structures. To this point, theoretical investigations into this phenomenon have assumed that the field experienced by the proteins is constant or a perfect step function, whereas any real-world pulse will be smooth. Here, we explore the possibility of orienting gas-phase proteins using time-dependent electric fields. We performed ab initio simulations to estimate the field strength required to break protein bonds, with 45 V/nm as a breaking point value. We then simulated ubiquitin in time-dependent electric fields using classical molecular dynamics. The minimal field strength required for orientation within 10 ns was on the order of 0.5 V/nm. Although high fields can be destructive for the structure, the structures in our simulations were preserved until orientation was achieved regardless of field strength, a principle we denote “orientation before destruction.”

蛋白质通常具有非零电偶极矩，使它们与外部电场相互作用并提供控制其方向的方法。已知从取向控制中受益的一种应用是使用 X 射线自由电子激光器进行单粒子成像，其中记录气相中蛋白质的衍射以确定它们的结构。到目前为止，对该现象的理论研究假设蛋白质所经历的场是恒定的或完美的阶跃函数，而任何现实世界的脉冲都是平滑的。在这里，我们探索使用时间相关电场定向气相蛋白质的可能性。我们进行了从头算模拟来估计破坏蛋白质键所需的场强，以 45 V/nm 作为断点值。然后，我们使用经典分子动力学模拟了随时间变化的电场中的泛素。在 10 ns 内定向所需的最小场强约为 0.5 V/nm。尽管高场可能对结构造成破坏，但我们模拟中的结构被保留，直到无论场强如何实现定向，我们将这一原则称为“破坏前的定向”。