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Updated: Jul 4, 2026
Prediction of HIV-1 Coreceptor Usage (Tropism) by Sequence Analysis using a Genotypic Approach
Published on: December 1, 2011
Mapping of the CXCR4 binding site within variable region 3 of the feline immunodeficiency virus surface glycoprotein
Magnus Sundstrom1, Rebecca L White, Aymeric de Parseval
1Department of Molecular Biology, The Scripps Research Institute, La Jolla, CA 92037, USA.
Insights
Feline immunodeficiency virus (FIV) uses the V3 region of its envelope surface unit (SU) to bind to the CXCR4 receptor, similar to HIV-1. Specific amino acids in the V3 loop are crucial for FIV entry into cells.
Area of Science:
- Virology
- Immunology
- Molecular Biology
Background:
- Feline immunodeficiency virus (FIV) utilizes the chemokine receptor CXCR4 for cellular entry, a mechanism shared with human immunodeficiency virus type 1 (HIV-1).
- Understanding the FIV envelope surface unit (SU) interaction with CXCR4 is crucial for developing broad-spectrum antiviral therapies.
Purpose of the Study:
- To precisely map the interaction site between the FIV SU and the CXCR4 receptor.
- To identify specific regions and amino acids within FIV SU critical for CXCR4 binding and viral entry.
Main Methods:
- Production of full-length FIV SU-Fc and deletion constructs in CHO cells.
- Binding studies using modified SU proteins on CXCR4-expressing cells, with and without CXCR4 inhibitors.
- Analysis of synthetic peptides and monoclonal antibodies targeting the FIV V3 region.
- Site-directed mutagenesis to investigate the role of specific amino acids in viral entry.
Main Results:
- The V3 region of FIV SU is essential for binding to CXCR4.
- Antibodies and peptides targeting the FIV V3 loop effectively block SU binding and virus entry.
- A contiguous nine-amino-acid sequence within V3 contains both the neutralizing epitope and the CXCR4 binding site.
- Serine 393 and Tryptophan 394 in the V3 tip are critical for FIV entry via CXCR4.
Conclusions:
- The V3 region of FIV SU is the primary determinant for CXCR4 engagement and viral entry.
- FIV's ability to use both feline and human CXCR4 highlights its potential as a model for studying lentiviral entry.
- This research provides a basis for designing novel, broad-acting entry inhibitors targeting conserved viral-host interactions.
Abstract:
Feline immunodeficiency virus (FIV) shares with T-cell tropic strains of human immunodeficiency virus type 1 (HIV-1) the use of the chemokine receptor CXCR4 for cellular entry. In order to map the interaction of the FIV envelope surface unit (SU) with CXCR4, full-length FIV SU-Fc as well as constructs with deletions of extended loop L2, V3, V4, or V5 were produced in stable CHO cell lines. Binding studies were performed using these proteins on 3201 cells (CXCR4(hi) CD134(-)), with or without the CXCR4 inhibitor AMD3100. The findings established that SU binding to CXCR4 specifically requires the V3 region of SU. Synthetic peptides spanning the V3 region as well as a panel of monoclonal antibodies (MAbs) to SU were used to further map the site of CXCR4 interaction. Both the SU V3-specific antibodies and the full-length V3 peptide potently blocked binding of SU to CXCR4 and virus entry. By using a set of nested peptides overlapping a region of SU specifically recognized by CD134-dependent neutralizing V3 MAbs, we showed that the neutralizing epitope and the region required for CXCR4 binding are within the same contiguous nine-amino-acid sequence of V3. Site-directed mutagenesis was used to reveal that serine 393 and tryptophan 394 at the predicted tip of V3 are required to facilitate entry into the target cell via CXCR4. Although the amino acid sequences are not identical between FIV and HIV, the ability of FIV to bind and utilize both feline and human CXCR4 makes the feline model an attractive venue for development of broad-based entry antagonists.
