Setting up and operating a cryo-EM laboratory.

Deryck J Mills

doi:10.1017/s003358352000013x

Abstract

Cryo-electron microscopy (cryo-EM) has become the technique of choice for structural biology of macromolecular assemblies, after the 'resolution revolution' that has occurred in this field since 2012. With a suitable instrument, an appropriate electron detector and, last but not least, a cooperative sample it is now possible to collect images from which macromolecular structures can be determined to better than 2 Å resolution, where reliable atomic models can be built. By electron tomography and sub-tomogram averaging of cryo-samples, it is also possible to reconstruct subcellular structures to sub-nanometre resolution. This review describes the infrastructure that is needed to achieve this goal. Ideally, a cryo-EM lab will have a dedicated 300 kV electron microscope for data recording and a 200 kV instrument for screening cryo-samples, both with direct electron detectors, and at least one 120 kV EM for negative-stain screening at room temperature. Added to this should be ancillary equipment for specimen preparation, including a light microscope, carbon coater, plasma cleaner, glow discharge unit, a device for fast, robotic sample freezing, liquid nitrogen storage Dewars and a ready supply of clean liquid nitrogen. In practice, of course, the available budget will determine the number and types of microscopes and how elaborate the lab can be. The cryo-EM lab should be designed with adequate space for the electron microscopes and ancillary equipment, and should allow for sufficient storage space. Each electron microscope room should be connected to the image-processing computers by fibre-optic cables for the rapid transfer of large datasets. The cryo-EM lab should be overseen by a facility manager whose responsibilities include the day-to-day tasks to ensure that all microscopes are operating perfectly, organising service and repairs to minimise downtime, and controlling the budget. Large facilities will require additional support staff who help to oversee the operation of the facility and instruct new users.

Highlights

In a very short time, cryo-electron microscopy has transformed from a technique practised by a small number of experts producing mostly medium-resolution structures with great effort, into a mainstream method for structural biologists, rivalling X-ray crystallography especially for samples that do not crystallize well, in particular, flexible and dynamic complexes and membrane proteins (Kühlbrandt, 2014; Bai et al, 2015; Armache and Cheng, 2019)
I established my first EM facility at the University of Birmingham UK for the departments of biological sciences and paediatrics in 1980. This was before the age of cryo-electron microscopy (cryo-EM), but it gave me a good understanding of setting up an EM unit with two transmission electron microscopes (TEMs) and one scanning electron microscope (SEM) and all the problems that went with it
The unit has evolved over the years, together with the cryo-EM field, and the original emphasis on electron crystallography has shifted to single-particle EM (Mills et al, 2013; Allegretti et al, 2014; Allegretti et al, 2015; Hahn et al, 2018; Safarian et al, 2019) and cryo-electron tomography (Strauss et al, 2008; Davies et al, 2014; Faelber et al, 2019)