Related Experiment Video
Updated: Aug 10, 2026
Imaging of HIV-1 Envelope-induced Virological Synapse and Signaling on Synthetic Lipid Bilayers
Published on: March 8, 2012
Distinct functional sites for human immunodeficiency virus type 1 and stromal cell-derived factor 1alpha on CXCR4
Shaomin Tian1, Won-Tak Choi, Dongxiang Liu
1Departments of Biochemistry, University of Illnois at Urbana-Champaign, 61801, USA.
Insights
Researchers identified specific transmembrane regions of CXCR4 crucial for HIV-1 entry, distinct from SDF-1alpha binding sites. This finding offers a new strategy for developing selective anti-HIV therapies targeting viral entry mechanisms.
Area of Science:
- Virology
- Cell Biology
- Structural Biology
Background:
- Human immunodeficiency virus type 1 (HIV-1) entry relies on interactions with CD4 and chemokine coreceptors like CXCR4.
- While extracellular interactions are known, the role of CXCR4's transmembrane (TM) domains in HIV-1 entry and SDF-1alpha binding remains unclear.
Purpose of the Study:
- To investigate the functional roles of CXCR4 transmembrane helices in HIV-1 entry and SDF-1alpha binding.
- To determine if these roles are overlapping or distinct for physiological and pathological functions.
Main Methods:
- Alanine-scanning mutagenesis of CXCR4.
- Competition binding assays with radiolabeled SDF-1alpha.
- Calcium (Ca2+) mobilization assays.
- Cell-cell fusion assays to measure HIV-1 entry.
Main Results:
- Mutations in several CXCR4 TM residues selectively impaired HIV-1-mediated cell fusion without affecting SDF-1alpha binding.
- Specific residues (Phe87, Phe292) involved in SDF-1alpha binding did not significantly impact CXCR4 coreceptor activity for HIV-1.
- Mutations in the second extracellular loop also reduced HIV-1 entry without affecting ligand binding or signaling.
Conclusions:
- CXCR4 transmembrane domains possess distinct functional sites for HIV-1 entry and SDF-1alpha binding.
- These findings provide a mechanistic basis for developing novel, selective anti-HIV agents targeting viral entry.
Abstract:
The entry of human immunodeficiency virus type 1 (HIV-1) into the cell is initiated by the interaction of the viral surface envelope protein with two cell surface components of the target cell, CD4 and a chemokine coreceptor, usually CXCR4 or CCR5. The natural ligand of CXCR4 is stromal cell-derived factor 1alpha (SDF-1alpha). Whereas the overlap between HIV-1 and SDF-1alpha functional sites on the extracellular domains of CXCR4 has been well documented, it has yet to be determined whether there are sites in the transmembrane (TM) helices of CXCR4 important for HIV-1 and/or SDF-1alpha functions, and if such sites do exist, whether they are overlapping or distinctive for the separate functions of CXCR4. For this study, by employing alanine-scanning mutagenesis, (125)I-SDF-1alpha competition binding, Ca(2+) mobilization, and cell-cell fusion assays, we found that the mutation of many CXCR4 TM residues, including Tyr(45), His(79), Asp(97), Pro(163), Trp(252), Tyr(255), Asp(262), Glu(288), His(294), and Asn(298), could selectively decrease HIV-1-mediated cell fusion but not the binding activity of SDF-1alpha. Phe(87) and Phe(292), which were involved in SDF-1alpha binding, did not play a significant role in the coreceptor activity of CXCR4, further demonstrating the disconnection between physiological and pathological activities of CXCR4 TM domains. Our data also show that four mutations of the second extracellular loop, D182A, D187A, F189A, and P191A, could reduce HIV-1 entry without impairing either ligand binding or signaling. Taken together, our first detailed characterization of the different functional roles of CXCR4 TM domains may suggest a mechanistic basis for the discovery of new selective anti-HIV agents.
More Related Videos
Related Concept Videos
01:22T Cell Activation and Clonal Selection
Naive T cells that have not yet encountered an antigen express two primary CD...
01:19Inhibitors of Virion Maturation and Assembly