A Simple Modification of a Commercial Plunge-Freezer to Allow Time-Resolved Vitrification for Cryo-EM Analyses of...

Plunge-freezing allows the trapping of potentially complex conformer mixtures for subsequent high-resolution structural analysis by cryogenic electron microscopy. The ultrafast nature of the vitrification process, when combined with a defined activation of the sample, can enable time-resolved structural studies. For light-sensitive samples, this activation can be achieved by controlled illumination of the sample during the plunge-freezing process. Here, we describe a simple approach that enables users to modify commercially available plunge-freezers with a light-emitting diode (LED)-based illumination system, and describe a straightforward protocol for its application to the study of red-light-sensitive phytochromes.