In light of the fact that a β-turn conformation at the C-terminus of endothelin-1 (ET-1) could be responsible for activity at the ETB receptor, the incorporation of (3S, 6S, 9S)-2-oxo-3-amino-1-azabicyclo[4.3.0]nonane-9-carboxylic acid (IAA) should provide an elegant method to establish whether a formyl group on Trp21 plays a role in stabilizing a β-turn. Eight linear ET-1 analogs, four formylated and four nonformylated, ET-1-(Leu17-Asp18-IAA-Trp21); ET-1-(Leu17-IAA-Ile20-Trp21); ET-1-(Leu17-Asp18-Pro19-Ile20-Trp21) and ET-1-(Leu17-Asp18-Ile19-Pro20-Trp21) have been analyzed by high-resolution nuclear magnetic resonance (NMR) spectroscopy and molecular modeling. Two-dimensional double quantum filtered correlation spectroscopy (DQFCOSY), total correlation spectroscopy (TOCSY) and nuclear Overhausen enhancement spectroscopy (NOESY) were resolved and analyzed for each molecule. Interspatial distance constraints were derived from the intensity of the NOESY connectivities. The formation of hydrogen bonding was monitored from the temperature-dependence of the NH chemical shifts. Molecular models calculated by means of distance geometry, simulated annealing and energy minimization, suggested a global elongated structure for the formylated analogs and a folded arrangement for the nonformylated derivatives, but no hydrogen bonding was detected at the C-terminus of ET-1 analogs.
*Department of Radiology, Hôpital St-Luc, CHUM, Montréal, †INRS/Armand-Frappier Institute, University of Québec, Pointe-Claire, ‡Departement of Chimie, University of Montréal, Montréal, Québec, Canada
Address correspondence and reprint requests to Dr Alain Fournier, INRS/Institut Armand-Frappier, Université du Québec, 245, boulevard Hymus, Pointe-Claire, Québec, Canada H9R 1G6.
© 2000 Lippincott Williams & Wilkins, Inc.