SOLUTION STRUCTURE OF THE HIV PROTEASE INHIBITOR ACETYL-PEPSTATIN AS DETERMINED BY NMR AND MOLECULAR MODELING

The structure of acetyl-pepstatin has been investigated in solution by two-dimensional NMR spectroscopy and molecular modeling. The analysis of DQFCOSY, TOCSY and NOESY spectra lead to a full assignment of the NMR signals both in DMSO-d(6) and in TFE-d(3):H2O 1:1. Interproton dis tances, dihedral angles and exchange regimes of NH or OH protons were derived from ROESY connectivities, coupling constants and temperature dependences of the chemical shifts, respectively. Molecular modeling u sing the NMR distance and dihedral angle constraints obtained in DMSO- d(6) yielded a model showing a well-defined structure for the N-termin al segment Ac-1 to Sta-4, but a flexible structure for the C-terminal segment. The structure was less defined in TFE-d(6):H2O 1:1 and C-13 T -1 measurements are indicative of higher mobility Comparison of the NM R-determined solution structure of acetyl-pepstatin with its crystal s tructure when bound to HIV-1 protease shows that the conformation is m ore extended in the complex as a result of intermolecular interactions .