DIALS for ED: Adapting X-ray software for electron diffraction integration

In recent years, electron diffraction has arisen as an alternative to X-ray diffraction for structural studies on threedimensional crystals. Promising features of the technique include complete data sets from a few or even singlenanocrystals, sensitivity to the charged state of ions and the relatively low expense of the apparatus. Experimentalprotocols and detector technologies are improving, so that data collection using the rotation method, dominant inX-ray crystallography, is now feasible in a cryoTEM. This convergence of experimental techniques has beenaccompanied by repurposing of analysis tools: robust and sophisticated algorithms developed over decades forX-ray diffraction integration software can be now employed to tackle electron diffraction data. Nevertheless, thegeometry of the electron diffraction experiment incurs specific challenges to address in the analysis. Here, thediffraction integration package DIALS is discussed, highlighting particular adaptations that were made to thesoftware for various example cases of electron diffraction, particularly on protein crystals. The experience gainedindicates that integration of good quality ED data can be straightforward, but the bottleneck remains with collectionof such good data, which relies on careful calibration and understanding of the instrument. Improved apparatus willameliorate this issue and future studies to develop improved models for details including dynamic diffraction andabsorption are anticipated.