The MHC-binding and gp120-binding functions of CD4 are separable

Area of Science:

• Immunology
• Virology
• Molecular Biology

Background:

• CD4 is a cell surface glycoprotein involved in immune responses and serves as the receptor for Human Immunodeficiency Virus (HIV).
• CD4 interacts with class II Major Histocompatibility (MHC) molecules, crucial for immune system communication.
• HIV-1's gp120 envelope glycoprotein binds to CD4, initiating viral entry.

Purpose of the Study:

• To identify CD4 regions critical for class II MHC binding.
• To determine if CD4 binding sites for gp120 and class II MHC are related.
• To explore the possibility of separating these binding functions.

Main Methods:

• Utilized homolog-scanning mutagenesis to alter CD4 protein regions.
• Assessed the impact of mutations on both class II MHC binding and gp120 binding.
• Analyzed mutations affecting one binding function without altering the other.

Main Results:

• Mutations in the first three immunoglobulin-like domains of CD4 abolished class II MHC binding.
• gp120 binding could be abolished independently of class II MHC binding.
• One mutation significantly reduced binding for both gp120 and class II MHC, suggesting some overlap.

Conclusions:

• The binding sites for gp120 (HIV) and class II MHC on CD4 are distinct and separable.
• It is feasible to engineer CD4 analogs that block HIV infection.
• Such analogs could potentially avoid interfering with normal immune responses mediated by class II MHC interactions.