1. Center for Advanced Biotechnology and Medicine, Department of Biochemistry, University of Medicine and Dentistry of New JerseyRobert Wood Johnson Medical School, and Howard Hughes Medical Institute, 679 Hoes Lane, Piscataway, New Jersey 08854, Department of Chemistry and Biochemistry, University of Oklahoma, 620 Parrington Oval, Norman, Oklahoma 73019, and Department of Biochemistry and Molecular Biology, University College London, Gower Street, London WC1E 6BT, United Kingdom