Recent advances in single-particle cryogenic electron microscopy (cryo-EM) have enabled the structural determination of numerous protein assemblies at high resolution, yielding unprecedented insights into their function. However, despite its extraordinary capabilities, cryo-EM remains time-consuming and resource-intensive. It is therefore beneficial to have a means for rapidly assessing and optimizing the quality of samples prior to lengthy cryo-EM analyses. To do this, we have developed a native mass spectrometry (nMS) platform that provides rapid feedback on sample quality and highly streamlined biochemical screening. Because nMS enables accurate mass analysis of protein complexes, it is well suited to routine evaluation of the composition, integrity, and homogeneity of samples prior to their plunge-freezing on EM grids. We demonstrate the utility of our nMS-based platform for facilitating cryo-EM studies using structural characterizations of exemplar bacterial transcription complexes as well as the replication-transcription assembly from the SARS-CoV-2 virus that is responsible for the COVID-19 pandemic.

单颗粒低温电子显微镜 (cryo-EM) 的最新进展使得能够以高分辨率对众多蛋白质组装体进行结构测定，从而对其功能产生前所未有的见解。然而，尽管冷冻电镜具有非凡的功能，但它仍然耗时且资源密集。因此，在进行冗长的冷冻电镜分析之前，拥有一种快速评估和优化样品质量的方法是有益的。为此，我们开发了一个原生质谱 (nMS) 平台，可提供有关样品质量的快速反馈和高度简化的生化筛选。由于 nMS 能够对蛋白质复合物进行精确的质量分析，因此非常适合在 EM 网格上冷冻之前对样品的组成、完整性和均质性进行常规评估。我们展示了基于 nMS 的平台的实用性，可利用示例细菌转录复合物的结构特征以及导致 COVID-19 大流行的 SARS-CoV-2 病毒的复制转录组装来促进冷冻电镜研究。