In vivo protein crystallization opens new routes in structural biology

Protein crystallizationin cells has been observed several times in nature. However, owing to their small size these crystals have not yet been used for X-ray crystallographic analysis. We prepared nano-sized in vivo–grown crystals of Trypanosoma bruceienzymes and applied the emerging method of free-electron laser-based serial femtosecond crystallographyto record interpretable diffraction data. This combined approach will open new opportunities in structural systemsbiology.