A comparative anatomy of protein crystals
What is it about?
In the 70 year history of macromolecular crystallography (MX) there has never been a wide ranging study of the size and shape of protein crystals or how these properties are related to the data that are collected from them. This is a phenomenal gap in our understanding of the most used method for structure determination and reflects the difficulty in gathering such data. In this paper, we analyse the properties of over 56,000 samples sent to the ESRF beamline MASSIF-1 over the last 4 years. The beamline records volumetric data for each sample as well as the results of scanning, characterisation, indexing and data processing. This has allowed us to test experimentally many assumptions and theories that have been made in the field and make new observations.
Why is it important?
The study is important for structural biologists as it removes the myth of crystal size or shape affecting cryo-cooling, still a major bottleneck in the process, allows measures of intra-crystal variability to be linked to final data quality, shows that crystal volume scales inversely with molecular weight and confirms experimentally the theoretical limits of crystal volumes and experimental setup. The latter is important as this is regularly used to define the limits of new experimental stations at free electron lasers and synchrotrons. Together, the data provide an important resource for method development and provide a framework to direct the development of future beamline facilities, with a particular emphasis of the roles that X-rays will play in the future where cryo-EM can achieve similar resolutions.