A V3 loop-dependent gp120 element disrupted by CD4 binding stabilizes the human immunodeficiency virus envelope...

Area of Science:

• Virology
• Structural Biology
• Molecular Biology

Background:

• Human immunodeficiency virus type 1 (HIV-1) entry relies on the gp120/gp41 envelope glycoprotein complex.
• gp120 binding to CD4 and chemokine receptors (CCR5/CXCR4) triggers conformational changes essential for viral fusion.

Purpose of the Study:

• To investigate the role of the gp120 V3 loop and adjacent regions in stabilizing the HIV-1 envelope trimer and mediating receptor interactions.
• To understand how mutations in these regions affect gp120-gp41 association and subsequent viral entry.

Main Methods:

• Analysis of mutations within the gp120 V3 loop and adjacent beta strands.
• Assessment of gp120-gp41 subunit association in unliganded and CD4-bound states.
• Evaluation of chemokine receptor binding affinity and syncytium-forming ability of modified HIV-1 envelope glycoproteins.

Main Results:

• Insertions or polar substitutions in the V3 loop decreased gp120-gp41 association and chemokine receptor binding.
• Mutations in gp120 beta strands (beta2, beta19-21) proximal to the V3 loop also reduced gp120-gp41 association.
• These V3 loop and beta strand modifications had a more significant impact on primary HIV-1 isolates compared to laboratory-adapted strains.

Conclusions:

• The V3 loop and adjacent beta strands form a critical element for stabilizing the unliganded HIV-1 envelope trimer.
• CD4 binding disrupts this element, facilitating chemokine receptor engagement and viral entry.
• These findings highlight the structural importance of the V3 loop in HIV-1 envelope glycoprotein function and viral infectivity.