ACKNOWLEDGMENTS
We thank the assistance and services provided at the Robert P. Apkarian Integrated Electron Microscopy Core (IEMC) at Emory University. This research was partly supported by the National Cancer Institute’s National Cryo-EM Facility at the Frederick National Laboratory for Cancer Research under contract 75N91019D00024. This project was supported in part by an appointment to the Research Participation Program at the Centers for Disease Control and Prevention, administered by the Oak Ridge Institute for Science and Education through an interagency agreement between the U.S. Department of Energy and CDC. The findings and conclusions in this report are those of the authors and do not necessarily represent the official position of the U.S. Centers for Disease Control and Prevention or the Agency for Toxic Substances and Disease Registry.