3-DIMENSIONAL SOLUTION STRUCTURE OF THE HIV-1 PROTEASE COMPLEXED WITHDMP323, A NOVEL CYCLIC UREA-TYPE INHIBITOR, DETERMINED BY NUCLEAR-MAGNETIC-RESONANCE SPECTROSCOPY

The three-dimensional solution structure of the HIV-1 protease homodim er, MW 22.2 kDa, complexed to a potent, cyclic urea-based inhibitor, D MP323, is reported. This is the first solution structure of an HIV pro tease/inhibitor complex that has been elucidated. Multidimensional het eronuclear NMR spectra were used to assemble more than 4,200 distance and angle constraints. Using the constraints, together with a hybrid d istance geometry/simulated annealing protocol, an ensemble of 28 NMR s tructures was calculated having no distance or angle violations greate r than 0.3 Angstrom or 5 degrees, respectively. Neglecting residues in disordered loops, the RMS deviation (RMSD) for backbone atoms in the family of structures was 0.60 Angstrom relative to the average structu re. The individual NMR structures had excellent covalent geometry and stereochemistry, as did the restrained minimized average structure. Th e latter structure is similar to the 1.8-Angstrom X-ray structure of t he protease/DMP323 complex (Chang CH et al., 1995, Protein Science, su bmitted); the pairwise backbone RMSD calculated for the two structures is 1.22 Angstrom. As expected, the mismatch between the structures is greatest in the loops that are disordered and/or flexible. The flexib ility of residues 37-42 and 50-51 may be important in facilitating sub strate binding and product release, because these residues make up the respective hinges and tips of the protease flaps. Flexibility of resi dues 4-8 may play a role in protease regulation by facilitating autoly sis.