1. Department of Chemistry, Portland State University , Portland , OR 97201, USA
2. Department of Chemistry and Biochemistry, San Diego State University , San Diego , CA, USA
3. Singapore-MIT Alliance for Research and Technology , 138602, Singapore
4. The Viral Information Institute, San Diego State University , San Diego , CA, USA
5. Department of Microbiology and Cell Science, University of Florida , Gainesville , FL 32611, USA
6. Department of Biological Engineering, MIT , Cambridge , MA 02139, USA