1 Emerging Infectious Diseases, Duke-NUS Medical School, 169857, Singapore; Department of Biological Science, National University of Singapore, 117558, Singapore. Electronic address: sheemei.lok@duke-nus.edu.sg.
2 Department of Bioengineering and James H. Clark Center, Stanford University, Stanford, CA, 94305, USA; Division of CryoEM and Bioimaging, SSRL, SLAC National Accelerator Laboratory, Menlo Park, CA, 94025, USA.