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Updated: May 17, 2026
Conformational Evaluation of HIV-1 Trimeric Envelope Glycoproteins Using a Cell-based ELISA Assay
Published on: September 14, 2014
Efficiency of bridging-sheet recruitment explains HIV-1 R5 envelope glycoprotein sensitivity to soluble CD4 and
Olivia O'Connell1, Alexander Repik, Jacqueline D Reeves
1Program in Molecular Medicine and Department of Microbiology and Physiological Systems, University of Massachusetts Medical School, Worcester, Massachusetts, USA.
Abstract:
HIV-1 R5 viruses vary extensively in their capacity to infect macrophages. R5 viruses that confer efficient infection of macrophages are able to exploit low levels of CD4 for infection and predominate in brain tissue, where macrophages are a major target for infection. HIV-1 R5 founder viruses that are transmitted were reported to be non-macrophage-tropic. Here, we investigated the sensitivities of macrophage-tropic and non-macrophage-tropic R5 envelopes to neutralizing antibodies. We observed striking differences in the sensitivities of Env(+) pseudovirions to soluble CD4 (sCD4) and to neutralizing monoclonal antibodies (MAbs) that target the CD4 binding site. Macrophage-tropic R5 Envs were sensitive to sCD4, while non-macrophage-tropic Envs were significantly more resistant. In contrast, all Envs were sensitive to VRC01 regardless of tropism, while MAb b12 conferred an intermediate neutralization pattern where all the macrophage-tropic and about half of the non-macrophage-tropic Envs were sensitive. CD4, b12, and VRC01 share binding specificities on the outer domain of gp120. However, these antibodies differ in their ability to induce conformational changes on the trimeric envelope and in specificity for residues on the V1V2 loop stem and β20-21 junction that are targets for CD4 in recruiting the bridging sheet. These distinct specificities of CD4, b12, and VRC01 likely explain the observed differences in Env sensitivity to inhibition by these reagents and provide an insight into the envelope mechanisms that control macrophage tropism. We present a model where the efficiency of bridging-sheet recruitment by CD4 is a major determinant of HIV-1 R5 envelope sensitivity to soluble CD4 and macrophage tropism.
Insights
HIV-1 R5 viruses infecting macrophages differ in their sensitivity to soluble CD4 (sCD4) and neutralizing antibodies. Macrophage-tropic viruses are more sensitive to sCD4, suggesting bridging-sheet recruitment impacts tropism and antibody neutralization.
Area of Science:
- Virology
- Immunology
Background:
- HIV-1 R5 viruses exhibit variable macrophage tropism, with efficient macrophage infectors predominating in brain tissue.
- Transmitted HIV-1 R5 founder viruses are typically non-macrophage-tropic.
- Understanding envelope (Env) protein variations is crucial for targeting HIV-1 infection.
Purpose of the Study:
- To investigate the differential sensitivities of macrophage-tropic and non-macrophage-tropic HIV-1 R5 envelopes to neutralizing antibodies.
- To explore the role of CD4 binding and conformational changes in HIV-1 macrophage tropism.
Main Methods:
- Comparison of Env(+) pseudovirion sensitivities to soluble CD4 (sCD4) and neutralizing monoclonal antibodies (MAbs) targeting the CD4 binding site.
- Analysis of Env binding specificities and conformational changes induced by CD4, MAb b12, and VRC01.
Main Results:
- Macrophage-tropic R5 Envs showed higher sensitivity to sCD4 compared to non-macrophage-tropic Envs.
- All Envs were sensitive to VRC01, while MAb b12 showed intermediate neutralization patterns.
- Differences in Env sensitivity correlate with distinct binding specificities and conformational effects of CD4, b12, and VRC01.
Conclusions:
- The efficiency of bridging-sheet recruitment by CD4 is a key determinant of HIV-1 R5 envelope sensitivity to sCD4 and macrophage tropism.
- Distinct antibody binding specificities provide insights into the mechanisms governing HIV-1 macrophage tropism.
