1. Structural Biology and NMR Laboratory, Institute of Molecular Biology and Physiology, University of Copenhagen, Øster Farimagsgade 2A, DK-1353 Copenhagen K, Denmark, Laboratory for Molecular Pharmacology, Department of Pharmacology, The Panum Institute, University of Copenhagen, DK-2200 Copenhagen, Denmark, and 7TM Pharma A/S Hørsholm, Denmark