1. Department of Biochemistry and Center for Structural Biology, Vanderbilt University, Nashville, Tennessee 37232-8725,
United States
2. Department of Chemistry
and Biochemistry, Arizona State University, Tempe, Arizona 85287-1604, United States
3. Department
of Molecular Physiology and Biological Physics, University of Virginia, Charlottesville, Virginia 22908, United
States
4. Institute for Organic Chemistry, Christian-Albrechts University of Kiel, D-24118 Kiel, Germany