Dynamical Network of HIV-1 Protease Mutants Reveals the Mechanism of Drug Resistance and Unhindered Activity.

HIV-1 protease variants resist drugs by active and non-active-site mutations. The active-site mutations, which are the primary or first set of mutations, hamper the stability of the enzyme and resist the drugs minimally. As a result, secondary mutations that not only increase protein stability for unhindered catalytic activity but also resist drugs very effectively arise. While the mechanism of drug resistance of the active-site mutations is through modulating the active-site pocket volume, the mechanism of drug resistance of the non-active-site mutations is unclear. Moreover, how these allosteric mutations, which are 8-21 Å distant, communicate to the active site for drug efflux is completely unexplored. Results from molecular dynamics simulations suggest that the primary mechanism of drug resistance of the secondary mutations involves opening of the flexible protease flaps. Results from both residue- and community-based network analyses reveal that this precise action of protease is accomplished by the presence of robust communication paths between the mutational sites and the functionally relevant regions: active site and flaps. While the communication is more direct in the wild type, it traverses across multiple intermediate residues in mutants, leading to weak signaling and unregulated motions of flaps. The global integrity of the protease network is, however, maintained through the neighboring residues, which exhibit high degrees of conservation, consistent with clinical data and mutagenesis studies.