1. Verna and Marrs McLean Department of Biochemistry and Molecular Biology, Baylor College of Medicine, Houston, TX 77030, USA.
2. Department of Molecular Virology and Microbiology, Baylor College of Medicine, Houston, TX 77030, USA.
3. CryoEM Core, Baylor College of Medicine, Houston, TX 77030, USA.
4. Molecular Biophysics and Integrated Bioimaging, Berkeley Center for Structural Biology, Lawrence Berkeley National Laboratory, Berkeley, CA 94720, USA.
5. Department of Medicine, Baylor College of Medicine, Houston, TX 77030, USA.
6. Department of Molecular and Cellular Biology, Baylor College of Medicine, Houston, TX 77030, USA.