ELUCIDATION OF THE MOLECULAR MECHANISM DRIVING DUPLICATION OF THE HIV-1 PTAP LATE DOMAIN.

HIV-1 uses cellular machinery to bud from infected cells. This cellular machinery is comprised of several multiprotein complexes known as endosomal sorting complexes required for transport (ESCRTs). A conserved late domain motif, Pro-Thr-Ala-Pro (PTAP), located in the p6 region of Gag (p6(Gag)), plays a central role in ESCRT recruitment to the site of virus budding. Previous studies have demonstrated that PTAP duplications are selected in HIV-1-infected patients during antiretroviral therapy; however, the consequences of these duplications for HIV-1 biology and drug resistance are unclear. To address these questions, we constructed viruses carrying a patient-derived PTAP duplication with and without drug resistance mutations in the viral protease. We evaluated the effect of the PTAP duplication on viral release efficiency, viral infectivity, replication capacity, drug susceptibility, and Gag processing. In the presence of protease inhibitors, we observed that the PTAP duplication in p6Gag significantly increased the infectivity and replication capacity of the virus compared to those of viruses bearing only resistance mutations in protease. Our biochemical analysis showed that the PTAP duplication, in combination with mutations in protease, enhances processing between the nucleocapsid and p6 domains of Gag, resulting in more complete Gag cleavage in the presence of protease inhibitors. These results demonstrate that duplication of the PTAP motif in p6Gag confers a selective advantage in viral replication by increasing Gag processing efficiency in the context of protease inhibitor treatment, thereby enhancing the drug resistance of the virus. These findings highlight the interconnected role of PTAP duplications and protease mutations in the development of resistance to antiretroviral therapy. IMPORTANCE Resistance to current drug therapy limits treatment options in many HIV-1-infected patients. Duplications in a Pro-Thr-Ala-Pro (PTAP) motif in the p6 domain of Gag are frequently observed in viruses derived from patients on protease inhibitor (PI) therapy. However, the reason that these duplications arise and their consequences for virus replication remain to be established. In this study, we examined the effect of PTAP duplication on PI resistance in the context of wild-type protease or protease bearing PI resistance mutations. We observe that PTAP duplication markedly enhances resistance to a panel of PIs. Biochemical analysis reveals that the PTAP duplication reverses a Gag processing defect imposed by the PI resistance mutations in the context of PI treatment. The results provide a long-sought explanation for why PTAP duplications arise in PI-treated patients.