HIV requires multiple gp120 molecules for CD4-mediated infection.

Area of Science:

• Virology
• Immunology
• Biochemistry

Background:

• Human immunodeficiency virus (HIV) infects target cells via binding of its envelope glycoprotein gp120 to the CD4 receptor.
• Inhibiting this gp120-CD4 interaction is a key strategy for blocking HIV infection.
• The precise molecular mechanisms of competitive inhibitors like soluble CD4 (sCD4) remain incompletely understood.

Purpose of the Study:

• To quantitatively investigate the blocking mechanisms of soluble CD4 (sCD4) against HIV infection.
• To gain insights into the complex processes of viral binding, adsorption, and penetration.
• To determine the biological association constants (Kassoc) for gp120-sCD4 interactions across different HIV strains.

Main Methods:

• Quantitative examination of sCD4 blocking activity against three different HIV strains.
• Measurement of biological association constants (Kassoc) from HIV infectivity assays.
• Comparison of biological Kassoc with chemical Kassoc values.

Main Results:

• At low sCD4 concentrations, inhibition is proportional to gp120 binding, with varying Kassoc values for different HIV strains (e.g., HIV-2NIHZ, HIV-1HXB3, HIV-1MN).
• Biological Kassoc from infectivity assays closely matches chemical Kassoc for all tested viral strains.
• At high sCD4 concentrations, synergistic inhibition of infection occurs when approximately 50% of gp120 molecules are occupied, independent of Kassoc differences.

Conclusions:

• sCD4 effectively inhibits HIV infection through binding to gp120.
• The inhibitory action of sCD4 is concentration-dependent and involves synergistic effects at higher concentrations.
• The developed method for measuring viral-receptor Kassoc is broadly applicable to other inhibitors, viruses, and cell types.