Plastic-embedded protein crystals

Rapid vitrification followed by the replacement of the vitrified water by a solvent (freeze substitution) and then resin is a widely used procedure for preparing biological samples for electron microscopy. The resulting plastic‐embedded samples permit convenient room‐temperature sectioning (micro­tomy) and can yield well preserved cellular structures. Here this procedure has been applied to crystalline protein samples, and it is shown that it is possible to freeze‐substitute vitrified crystals while preserving some of their original diffraction properties. The plastic‐embedded crystals were used to collect a series of complete room‐temperature data sets at a powerful macromolecular crystallography synchrotron beamline. Whereas one normally observes specific damage to disulfide bonds upon X‐ray radiation, no such damage was seen for the plastic‐embedded sample. The X‐ray diffraction data allowed an initial atomic analysis to be made of the effects of freeze‐substitution and plastic embedding on biological samples.