Journal: Structure / Year: 2023 Title: Addressing compressive deformation of proteins embedded in crystalline ice. Authors: Huigang Shi / Chunling Wu / Xinzheng Zhang / Abstract: For cryoelectron microscopy (cryo-EM), high cooling rates have been required for preparation of protein samples to vitrify the surrounding water and avoid formation of damaging crystalline ice. ...For cryoelectron microscopy (cryo-EM), high cooling rates have been required for preparation of protein samples to vitrify the surrounding water and avoid formation of damaging crystalline ice. Whether and how crystalline ice affects single-particle cryo-EM is still unclear. Here, single-particle cryo-EM was used to analyze three-dimensional structures of various proteins and viruses embedded in crystalline ice formed at various cooling rates. Low cooling rates led to shrinkage deformation and density distortions on samples having loose structures. Higher cooling rates reduced deformations. Deformation-free proteins in crystalline ice were obtained by modifying the freezing conditions, and reconstructions from these samples revealed a marked improvement over vitreous ice. This procedure also increased the efficiency of cryo-EM structure determinations and was essential for high-resolution reconstructions.
The EM map of Coxsackie A10 virus embedded in vitreous ice frozen at -183 celsius degree using standard procedure. The resolution of EM map is 3.6 angstrom.
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