The emergence of drug-resistant variants is a serious side effect assocd. with acquired immune deficiency syndrome therapies based on inhibition of human immunodeficiency virus type 1 protease (HIV-1 PR). In these variants, compensatory mutations, usually located far from the active site, are able to affect the enzymic activity via mol. mechanisms that have been related to differences in the conformational flexibility, although the detailed mechanistic aspects have not been clarified so far. Here, we perform multinanosecond mol. dynamics simulations on L63P HIV-1 PR, corresponding to the wild type, and one of its most frequently occurring compensatory mutations, M46I, complexed with the substrate and an enzymic intermediate. The quality of the calcns. is established by comparison with the available NMR data. Our calcns. indicate that the dynamical fluctuations of the mutated enzyme differ from those in the wild type. These differences in the dynamic properties of the adducts with the substrate and with the gem-diol intermediate might be directly related to variations in the enzymic activity and therefore offer an explanation of the obsd. changes in catalytic rate between wild type and mutated enzyme. We anticipate that this "flexibility-assisted" mechanism might be effective in the vast majority of compensatory mutations, which do not change the electrostatic properties of the enzyme. [on SciFinder (R)]