Dissecting Receptor-Induced Activation of HIV-1 Env
Infection by the virus HIV-1 is initiated by interactions between host cell receptors (CD4 and a chemokine coreceptor) and the trimeric, viral envelope glycoprotein, Env (gp120/gp41). These binding events trigger Env to transition from a native state to an extended intermediate, which bridges the viral and target cell membranes, and ultimately into a fusogenic state which allows for fusion of the two membranes. Because traditional approaches at blocking Env function have failed to deliver an effective monotherapy or vaccine, a more rigorous understanding of Env structure and function will yield better results. As a first step towards this goal, this work focused on understanding of the structural changes within each Env protomer upon activation with cellular receptors. In the first portion of these studies, two functional complementation strategies were developed to assess the impact of multiple cellular receptor binding events on Env trimer structure. Titrations using attachment inhibitors, agents which block Env interactions with host cell receptors, revealed nuanced details of the reciprocal relationship between CD4 and coreceptor binding. Attachment inhibitors were also used to generate infectivity profiles over a range of cellular receptor levels. These infectivity profiles report on CD4 and coreceptor usage Env can only perform minimal receptor binding events. The next portion utilized another functional complementation strategy to explore the global structural changes in Env as it evolves into extended intermediate state. Titrations with fusion inhibitors, peptides that target the gp41 subunits in Env after it has been triggered, revealed that the transition occurs in an asymmetric manner such that individual subunits of gp41 are exposed one at a time upon interactions between Env and CD4. In the final portion of this work, the crystal structure of an Env resistance mutant with an asymmetric N-HR coiled coil is reported. Fusion inhibitor titrations of this mutant Env were multiphasic only in the region of structural asymmetry. Taken together with data from the previous portion, the results suggest that the spatial and temporal exposure of gp41 can proceed in nonconcerted, asymmetric manner depending on the number of CD4s that engage the Env trimer.
Khasnis, Mukta Dilip, "Dissecting Receptor-Induced Activation of HIV-1 Env" (2017). ProQuest ETD Collection - Thomas Jefferson University. AAI10284090.