Ultrathin liquid cells for microsecond time-resolved cryo-EM.

Microsecond time-resolved cryo-electron microscopy promises to significantly advance our understanding of protein function by rendering cryo-electron microscopy (cryo-EM) fast enough to observe proteins at work. This emerging technique involves flash melting a cryo sample with a laser beam to provide a brief time window during which dynamics are initiated. When the laser is switched off, the sample revitrifies, arresting the proteins in their transient configurations. However, observations have so far been limited to tens of microseconds only, due to the instability of the thin liquid film under laser irradiation. Here, we seal samples between two ultrathin, vapor-deposited silicon dioxide membranes to extend the observation window by an order of magnitude. These membranes not only allow for reconstructions with near-atomic spatial resolution, but can also be used to eliminate preferred particle orientation. We showcase our technology by performing a time-resolved temperature jump experiment on the 50S ribosomal subunit that provides new insights into the conformational landscape of the L1 stalk. Our experiments significantly expand the capabilities of microsecond time-resolved cryo-EM and promise to bridge the gap to the millisecond timescale, which can already be addressed with traditional approaches.