1 Biophysics Program, School of Medicine, Stanford University, Stanford, CA 94305, USA.
2 Direct Electron, LP, San Diego, CA 92128, USA.
3 Division of CryoEM and Bioimaging, SSRL, SLAC National Accelerator Laboratory, Menlo Park, CA 94025, USA.
4 Department of Chemistry, Stanford University, Stanford, CA 94305, USA.
5 Division of CryoEM and Bioimaging, SSRL, SLAC National Accelerator Laboratory, Menlo Park, CA 94025, USA; Department of Bioengineering and Department of Microbiology and Immunology, Stanford University, Stanford, CA 94305, USA. Electronic address: [email protected].