Zernike Phase Contrast Cryo-Electron Microscopy and Tomography for Structure Determination at Nanometer and Subnanometer Resolutions

SummaryZernike phase contrast cryo-electron microscopy (ZPC-cryoEM) is an emerging technique that is capable of producing higher image contrast than conventional cryoEM. By combining this technique with advanced image processing methods, we achieved subnanometer resolution for two biological specimens: 2D bacteriorhodopsin crystal and epsilon15 bacteriophage. For an asymmetric reconstruction of epsilon15 bacteriophage, ZPC-cryoEM can reduce the required amount of data by a factor of ∼3, compared with conventional cryoEM. The reconstruction was carried out to 13 Å resolution without the need to correct the contrast transfer function. New structural features at the portal vertex of the epsilon15 bacteriophage are revealed in this reconstruction. Using ZPC cryo-electron tomography (ZPC-cryoET), a similar level of data reduction and higher resolution structures of epsilon15 bacteriophage can be obtained relative to conventional cryoET. These results show quantitatively the benefits of ZPC-cryoEM and ZPC-cryoET for structural determinations of macromolecular machines at nanometer and subnanometer resolutions.

Graphical AbstractFigure optionsDownload high-quality image (474 K)Download as PowerPoint slideHighlights
► ZPC-cryoEM resolves a better structure with one-third the data of conventional cryoEM
► α helices seen in maps obtained from ZPC-cryoEM of ɛ15 phage and bacteriorhodopsin
► 100 ZPC-cryoEM particle images resolve nonicosahedral portal vertex of ɛ15 phage
► Asymmetric map of ɛ15 phage computed from 50 subtomograms in a single ZPC-tomogram