1. Department
of Physics and Beckman Institute, University of Illinois at Urbana−Champaign, Urbana, Illinois 61801, United States
2. Department
of Structural Biology, University of Pittsburgh School of Medicine, Pittsburgh, Pennsylvania 15260, United States
3. Pittsburgh
Center for HIV Protein Interactions, University of Pittsburgh School of Medicine, Pittsburgh, Pennsylvania 15260, United States
4. Department
of Chemistry and Biochemistry, University of Delaware, Newark, Delaware 19716, United States
5. Division
of Structural Biology, University of Oxford, The Henry Wellcome Building for Genomic Medicine, Headington, Oxford OX3 7BN, U.K.
6. Electron
Bio-Imaging Centre, Diamond Light Sources, Harwell Science and Innovation Campus, Didcot OX11 0DE, U.K.