“Beam-Induced Motion: Videos of Particles on a Cryo-EM Grid”

“Beam-Induced Motion: Videos of Particles on a Cryo-EM Grid”

Niko Grigorieff, Ph.D. – Professor of Biochemistry, Brandeis University

The contrast observed in images of frozen-hydrated biological specimens prepared for electron cryo-microscopy falls significantly short of theoretical predictions. It is widely acknowledged that motion of the specimen during its exposure to the electron beam leads to significant blurring in the recorded images. We have studied the amount and direction of motion of virus particles suspended in thin vitrified ice layers across holes in perforated carbon films using exposure series. Our data shows that the particle motion is correlated within patches of 0.3 – 0.5 micrometers, indicating that the whole ice layer is moving in a drum-like motion, leading to particle rotations of up to a few degrees. Furthermore, analysis of movies showing changes in the specimen during beam exposure show that the specimen moves significantly more at the start of an exposure than towards its end. The movies offer the possibility of frame alignment and averaging to significantly reduce the blurring in the images and restore the high-resolution signal.