Single-particle cryo-EM structures from iDPC-STEM at near-atomic resolution
Electron cryo-microscopy (cryo-EM) is becoming one of the routine tools for structure determination of biological macromolecules. Commonly, molecular images are obtained by conventional transmission electron microcopy (CTEM) using underfocus and subsequently computationally combined into a high-resolution 3D structure. Here, we apply scanning transmission electron microscopy (STEM) using the integrated differential phase contrast mode also known as iDPC-STEM to the cryo-EM test specimen of tobacco mosaic virus (TMV). The micrographs show complete contrast transfer to high resolution and enable the cryo-EM structure determination at 3.5 [A] resolution using single-particle based helical reconstruction. A series of cryo-EM TMV maps was resolved at near-atomic resolution taken at different convergence semi-angle (CSA) beams and share identical features with maps obtained by CTEM of a previously acquired same-sized TMV data set. The associated map B-factors from iDPC-STEM match those obtained by CTEM recordings using 2nd generation direct electron detection devices. These data show that STEM imaging in general, and in particular the iDPC-STEM approach, can be applied to vitrified single-particle specimens to determine near-atomic resolution cryo-EM structures of biological macromolecules.