Dissecting the Complex Mechanisms Behind the Combinatorial Activities of HIV-1 Entry Inhibitors

Koree Wee Ahn, Thomas Jefferson University


For HIV-1 surface glycoprotein Envelope (Env) to mediate the viral entry process, it must interact with two receptors on the target cell, CD4 and coreceptor (CoR). These receptors trigger a series of conformational changes that result in the fusion of viral and target cell membranes. How receptor binding triggers these conformational changes is not fully understood. While there are three binding sites for each receptor in an Env trimer, neither the minimal receptor binding requirement for entry, nor the role of multivalent binding is known. To address these gaps in knowledge, we examined the combinatorial activity of three classes of HIV-1 entry inhibitors. The first two classes are CD4 (CD4A) and CoR antagonists (CoRA). These antagonists bind the cellular receptors and occlude them from Env. The third class, fusion inhibitors (FI), binds an intermediate conformation of Env during entry and stops membrane fusion. As FI bind a transient intermediate conformation, potency is dependent on the kinetics of entry. In our first project we examined CoRA and FI combinations. Previous studies have shown that these inhibitors are synergistic with one another and attributed synergy to CoRAs slowing the kinetics of entry. However, other studies have reported only additivity. By dissecting the synergistic process using a variety of FIs and mutant Env, we were able to determine that synergy can be lost through two factors, the affinity of FI, and the stoichiometry of CoR binding. These results explain the discrepancies observed in the literature, provide new understanding of the role of CoR binding stoichiometry in entry, and have implications for the combinatorial use of these inhibitors in the clinic. In a second study, we probed the coupling of CD4 and CoR binding by investigating the combinatorial activity of CD4A and CoRA. Unexpectedly, we observed that these two inhibitors were antagonistic with another. However, the combinatorial activity was highly HIV-1 strain dependent. By comparing the combinatorial activity of these inhibitors across multiple HIV-1 strains and dissecting the mechanism of antagonism, we determined that CD4 and CoR binding can drive competing processes in during HIV-1 entry.

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Recommended Citation

Ahn, Koree Wee, "Dissecting the Complex Mechanisms Behind the Combinatorial Activities of HIV-1 Entry Inhibitors" (2017). ETD Collection for Thomas Jefferson University. AAI10641897.