1. Center for Bio/Molecular Science and Engineering, U.S. Naval Research Laboratories, Washington, DC 20375, USA.
2. United States Army Medical Research Institute of Infectious Diseases, Frederick, MD 21702, USA.
3. Department of Chemistry, Biochemistry and Molecular Medicine, University of California, Davis, Davis, CA 95616, USA.
4. Department of Biochemistry, University of Washington, Seattle, WA 98195, USA.
5. Department of Medicine, Uniformed Services University of Health Sciences, Bethesda, MD 20814, USA.