Restrained molecular dynamics simulations of HIV-1 protease: the first step in validating a new target for drug design

To test the anticorrelated relationship that was recently displayed in conventional molecular dynamics (MD) simulations, several different restrained MD simulations on a wild type and on the V82F/I84V drug-resistant mutant of HIV-1 protease were performed. This anticorrelated relationship refers to the observation that compression of the peripheral ear-to-cheek region of HIV protease (i.e., the elbow of the flap to the fulcrum and the cantilever) occurred as the active site flaps were opening, and, conversely, expansion of that ear-to-cheek region occurred as both flaps were closing. An additional examination of this anticorrelated relationship was necessary to determine whether it can be harnessed in a useful manner. Consequently, six different MD experiments were performed that incorporated pairwise distance restraints in that ear-to-cheek region (i.e., the distance between the alpha-carbons of Gly40 and Gln61 was restrained to either 7.7 or 10.5 A, in both monomers). Pushing the backbones of the ear and the cheek regions away from each other slightly did force the flaps that guard the active site to remain closed in both the wild type and the mutant systems-even though there were no ligands in the active sites. Thus, these restrained MD simulations provided evidence that the anticorrelated relationship can be exploited to affect the dynamic behavior of the flaps that guard the active site of HIV-1 protease. These simulations supported our hypothesis of the mechanism governing flap motion, and they are the first step towards validating that peripheral surface as a new target for drug design.