Over 7,600 people in Wisconsin and 39 million worldwide are currently living with HIV human immunodeficiency virus (HIV). Despite progress in treatment and prevention, there is still a serious need for an HIV vaccine. One promising approach involves targeting the viral envelope glycoprotein (Env), which enables the virus to bind to and infect host cells. This research used a closely related virus in a nonhuman primate model called SIVmac to better understand how the cytoplasmic tail (CT) of Env protein influences immune recognition and viral survival. Using antibody binding experiments and protein-tagging techniques, the research team identified molecular features of the virus that could be targeted by future vaccines and therapies.
The Challenge
HIV is a major health crisis across the globe. HIV infection is lifelong and requires continuous drug therapy to suppress HIV-related disease. Despite progress in treatment and prevention, there is still a serious need for an HIV vaccine. An HIV vaccine would offer sustainable and broadly accessible protection to help end the epidemic. Unfortunately, the virus’s genetic variability makes developing an HIV vaccine biologically complex. While most vaccine development strategies have targeted the virus’s outer surface, this project will investigate the envelope’s intracellular cytoplasmic tail.
Project Goals
The goal of this research was to understand how the intracellular cytoplasmic tail domain of the HIV envelope glycoprotein contributes to the ability of SIVmac to replicate and cause disease.
Results
The researchers tested a panel of antibodies against the SIVmac envelop protein with either a full-length or truncated CT domain. They classified Env binding patterns into three groups. Unexpected findings came from class III, characterized by modest binding dramatically enhanced by soluble CD4 (a glycoprotein on the surface of T cells) preincubation. Removing the CT domain significantly reduced class III antibody binding, suggesting that the CT domain helps the envelop transition from a “closed” to “open” state in response to soluble CD4 ligands.
The research team identified host proteins that interact with Env CT using proximity-dependent biotin labeling. This process involved introducing a molecular tagging enzyme into primary cells alongside three versions of the viral envelope protein – a full-length CT, truncated CT, and truncated CT variant. Their analysis revealed 277 proteins that appear to interact with the CT domain, and a subset of 60 proteins that are associated with Env CT in multiple cellular contexts. Future studies will investigate the role of these host proteins in virus replication.
