1. Departments of Medical Biochemistry and Genetics, Biochemistry and Biophysics and Center for Macromolecular Design, Texas A&M University, College Station, Texas 77843-1114; Institute of Molecular Biology of the Slovak Academy of Science, Dubravska cesta 21, 842 51 Bratislava, Slovak Republic, and Department of Chemistry, University of York, Heslington, York YO1 5DD, United Kingdom