Vlahakis Niko, Clauss Arden, Rodriguez Jose A
Department of Chemistry and Biochemistry, UCLA-DOE Institute for Genomics and Proteomics; STROBE, NSF Science and Technology Center, University of California, Los Angeles, 611 Charles E. Young Dr East, Los Angeles, CA 90095, USA.
IUCrJ. 2025 Mar 1;12(Pt 2):223-238. doi: 10.1107/S2052252524012132.
High-energy electrons induce sample damage and motion at the nanoscale to fundamentally limit the determination of molecular structures by electron diffraction. Using a fast event-based electron counting (EBEC) detector, we characterize beam-induced, dynamic, molecular crystal lattice reorientations (BIRs). These changes are sufficiently large to bring reciprocal lattice points entirely in or out of intersection with the sphere of reflection, occur as early events in the decay of diffracted signal due to radiolytic damage, and coincide with beam-induced migrations of crystal bend contours within the same fluence regime and at the same illuminated location on a crystal. These effects are observed in crystals of biotin, a series of amino acid metal chelates, and a six-residue peptide, suggesting that incident electrons inevitably warp molecular lattices. The precise orientation changes experienced by a given microcrystal are unpredictable but are measurable by indexing individual diffraction patterns during beam-induced decay. Reorientations can often tilt a crystal lattice several degrees away from its initial position before irradiation, and for an especially beam-sensitive Zn(II)-methionine chelate, are associated with dramatic crystal quakes prior to 1 e Å electron beam fluence accumulates. Since BIR coincides with the early stages of beam-induced damage, it echoes the beam-induced motion observed in single-particle cryoEM. As with motion correction for cryoEM imaging experiments, accounting for BIR-induced errors during data processing could improve the accuracy of MicroED data.
高能电子在纳米尺度上会引发样品损伤和运动，从根本上限制了通过电子衍射确定分子结构的能力。我们使用基于事件的快速电子计数（EBEC）探测器，对束流诱导的动态分子晶格重排（BIRs）进行了表征。这些变化足够大，足以使倒易晶格点完全进入或离开反射球的相交区域，是由于辐射损伤导致衍射信号衰减过程中的早期事件，并且与在相同注量范围和晶体上相同照明位置处束流诱导的晶体弯曲轮廓迁移相一致。在生物素晶体、一系列氨基酸金属螯合物晶体和一个六残基肽晶体中都观察到了这些效应，这表明入射电子不可避免地会使分子晶格发生扭曲。给定微晶所经历的精确取向变化是不可预测的，但可以通过在束流诱导衰减过程中对各个衍射图案进行索引来测量。重排常常会使晶格从辐照前的初始位置倾斜几度，对于一种对束流特别敏感的Zn（II）-甲硫氨酸螯合物，在累积1 e Å电子束注量之前会伴随着剧烈的晶体震动。由于BIR与束流诱导损伤的早期阶段相吻合，它与单颗粒冷冻电镜中观察到的束流诱导运动相呼应。与冷冻电镜成像实验的运动校正一样，在数据处理过程中考虑BIR引起的误差可以提高MicroED数据的准确性。
