1. Molecular Pharmacology Group, Division of Biochemistry and Molecular Biology, Institute of Biomedical and Life Sciences, University of Glasgow, Glasgow G12 8QQ, U.K.
2. Department of Chemistry, School of Engineering and Physical Sciences, Heriot-Watt University, Riccarton Campus, Edinburgh EH14 4AS, U.K.
3. Max-Delbrück-Centrum für Molekulare Medizin (MDC), Berlin-Buch, Robert-Rössle-Strasse 10, 13125 Berlin, Germany