1. Department of Pharmacology, University of Pennsylvania, 433 South University Avenue, 304G Lynch Laboratories, Philadelphia, Pennsylvania 19104-6018, United States
2. Department of Biochemistry, Virginia Polytechnic Institute and State University, 306 Engel Hall, Blacksburg, Virginia 24061, United States
3. Department of Biochemistry and Molecular Biology and Australian Research Council Centre of Excellence in Structural and Functional Microbial Genomics, Monash University, Clayton, VIC 3800, Australia