1. Institute for Medicine and Engineering, University of Pennsylvania, 1170 Vagelos Research Labs, 3340 Smith Walk, Philadelphia, Pennsylvania 19104-6383, Department of Biological Sciences and Department of Chemistry, University of Wollongong, Northfields Avenue, Wollongong, NSW 2522, Australia, School of Molecular and Microbial Biosciences, University of Sydney, Sydney, NSW 2006, Australia, and Department of Biological Sciences, University of Notre Dame, Notre Dame, Indiana 46556-0369