1. Sealy Center for Structural Biology and Molecular Biophysics, University of Texas Medical Branch, Galveston, TX 77555, USA.
2. Department of Mechanical Engineering and Materials Science, Duke University, Durham, NC 27708, USA.
3. Department of Biochemistry and Molecular Biology, University of Texas Medical Branch, Galveston, TX 77555, USA.
4. Department of Diagnostic and Biological Sciences, School of Dentistry, and Institute for Molecular Virology, University of Minnesota, Minneapolis, MN 55455, USA.
5. Characterization Facility, College of Science and Engineering, University of Minnesota, Minneapolis, MN 55455, USA.