1. Department of Chemistry, Drexel University, Philadelphia, Pennsylvania 19104-2875, United States
2. RCSB Protein Data Bank, Department of Chemistry and Chemical Biology, Rutgers The State University of New Jersey, Piscataway, New Jersey 08854-8087, United States
3. Department of Chemistry, Massachusetts Institute of Technology, Cambridge, Massachusetts 02139-4307, United States
4. The Episcopal Academy, Newtown Square, Pennsylvania 19073, United States
5. Roy and Diana Vagelos Laboratories, Department of Chemistry, University of Pennsylvania, Philadelphia, Pennsylvania 19104-6323 United States