电子衍射 | MicroED | Thermo Fisher Scientific

What is microcrystal electron diffraction?

微晶电子衍射 (MicroED) 技术可以快速、高分辨率的测定小分子化合物和生物大分子的 3D 结构。赛默飞世尔科技现在提供完整的 MicroED 微晶电子衍射解决方案，可选配在新的电镜上，也可在现有设备上升级。

使用电子作为入射光束，在冷冻透射电镜 (cryo-TEM) 上获得 MicroED 微晶电子衍射数据。由于它是衍射技术，像 X 射线晶体衍射一样，样品需要经过结晶。

结晶过程与 X 射线晶体学基本相同。然而，由于晶体与电子的相互作用远远强于与 X 射线的相互作用，因而可分析小很多的晶体。可以轻松地分析远小于 100 nm 的晶体。这可以显著地缩短样品制备过程，并且可以分析由于太小而不能用其他衍射方法分析的晶体。

数据收集时间仅几分钟，可以得到原子分辨率的 3D 结构。

您现有的赛默飞世尔科技冷冻电镜可以添加我们 MicroED 整体解决方案，完美实现对各种大小结构的分析！

Sample requirements for MicroED

The unique requirements of MicroED set it apart, not just from other cryo-electron microscopy (cryo-EM) techniques, but from traditional crystallography as well. MicroED necessitates small crystals (<50 µm) but samples can be cut (or milled) from larger crystals using a focused ion beam (FIB), if necessary. (Note that crystals >200 nm have increased secondary scattering, which convolutes the data.)

Sample preparation also varies between small molecule and protein samples. Small molecule crystals are usually dry and can often be analyzed at room temperature. Mechanical grinding can easily be used to reduce the size of large crystals, or the molecules can simply be crystallized spontaneously out of solution using evaporation.

Proteinase structure determined with microcrystal electron diffraction.

蛋白酶 K 结构。Gonen 实验室 HHMI/UCLA 提供的 MicroED 数据。

Protein crystals, however, are typically kept in water to retain their hydrated, native states. These samples are subsequently flash-frozen (vitrified) in order to avoid sample damage due to crystalline ice formation. Vitrified samples are sensitive to changes in humidity or to the buffer and may disintegrate at the slightest touch. Therefore, cryo-FIB milling is used to reduce the size of large protein crystals.

What are they key benefits of MicroED?

MicroED fills a gap in structural biology, since X-ray crystallography requires large crystals that can be difficult to obtain whereas synchrotron X-ray free-electron lasers (XFELs) necessitates hundreds, if not thousands, of small crystals for the structural analysis of a single protein or small molecule. Time on a synchrotron is also expensive and access is limited. MicroED uniquely offers fast, high-resolution analysis that requires only a few small crystals.

Fast, atomic-resolution 3D structural information

Obtain diffraction data from nanocrystals in minutes.

Instant productivity

Nanocrystals as small as 100 nm can readily be analyzed, removing the burden of large crystal growth (as needed in X-ray crystallography). This also reduces the amount of sample material required. Mixtures of different polymorphs and compounds can be analyzed.

Complete turnkey solution

Obtain hardware, software, and support from one single vendor. Acquired data can be processed using established reconstruction packages for X-ray crystallography.

2-in-1 solution

MicroED and single particle analysis can be performed on the same cryo-electron microscope. This solution is compatible with new microscopes but can also be retrofitted onto existing cryo-EM instruments.

MicroED and drug discovery

MicroED is becoming increasingly popular in drug discovery as it can be used to determine the structure of protein-drug complexes and small molecules. Critically, MicroED alleviates the need for long and complicated large-crystal growth, a significant benefit in the fast-paced pharmaceutical industry.

To highlight some of the key benefits of MicroED, we determined the structure of acetaminophen from a commercial sample. Only ~10^-12 grams of the sample were required to obtain the structure shown; the nanocrystal was also extracted from a mixture consisting of filler and other compound constituents. The entire 70-degree range of data was collected in a matter of minutes.

MicroED structure determination of paracetamol.

Example of MicroED structure determination performed in-house on Thermo Scientific instrumentation.

Data processing was performed in the open-source Diffraction Integration for Advanced Light Sources (DIALS) software, as outlined below. It is important to note that while the full structure could be determined from a dataset that was only 43% complete, additional data from other crystals could be used to further enhance these results.

General outline of MicroED data processing performed with open-source Diffraction Integration for Advanced Light Sources (DIALS) Software.

MicroED solutions

With the addition of our complete MicroED solution, your Thermo Scientific cryo-TEM becomes your own in-house beam line for structure determination!

Single particle analysis and MicroED capability in one instrument
MicroED package:	Thermo Scientific EPU-D Software Modified beam stop, optimized for MicroED Optimized C2/SA aperture set Micro-ED lens series 90° rotation projection system Thermo Scientific Ceta-D Camera Optimized for diffraction application: increased accuracy and sensitivity Compatible with single-particle-analysis screening requirements Compatible with bottom-mount filter (retractable)
Compatible with:	Thermo Scientific Glacios Cryo-TEM Thermo Scientific Krios Cryo-TEM Thermo Scientific Talos Arctica Cryo-TEM Thermo Scientific Talos L120C and Talos L200C TEMs with side-entry holder