Trapping the HIV-1 V3 loop in a helical conformation enables broad neutralization

Area of Science:

• Virology
• Immunology
• Structural Biology

Background:

• The V3 loop of HIV-1 envelope glycoprotein is crucial for viral entry.
• Current broadly neutralizing antibodies often target conserved epitopes on the prefusion trimer, but V3 loop accessibility is limited.
• Antibodies targeting the V3 loop on open trimers after CD4 binding are less common but highly sought after.

Purpose of the Study:

• To develop novel V3 loop-specific inhibitors targeting the CD4-bound state of HIV-1.
• To characterize the binding site and neutralization mechanism of these new inhibitors.
• To explore the potential of postattachment inhibition strategies for HIV-1 therapy.

Main Methods:

• Designed ankyrin repeat protein (DARPin) technology was employed to create V3-specific inhibitors.
• Binding assays were performed to determine the interaction of DARPins with open HIV-1 envelope trimers.
• Molecular dynamics simulations and escape mutation analyses were used to understand the functional relevance of the target epitope.

Main Results:

• A distinct category of V3-specific DARPins demonstrated broad neutralization breadth (>90%) against HIV-1.
• These broadly neutralizing DARPins (bnDs) specifically recognized an α-helical region (αV3C) within the V3 loop of open envelope trimers.
• The αV3C epitope was found to be highly conserved, comparable to the CD4 binding site.

Conclusions:

• Designed ankyrin repeat proteins targeting the αV3C region of the V3 loop represent a promising new class of HIV-1 inhibitors.
• These inhibitors effectively target the postattachment, CD4-bound state of the virus, overcoming limitations of current antibody therapies.
• The findings highlight the potential of αV3C-based inhibitors and postattachment inhibition strategies for developing effective HIV-1 therapeutics.