CD4 and the immunoglobulin superfamily

Area of Science:

• Immunology
• Structural Biology
• Virology

Background:

• CD4 is a cell surface glycoprotein vital for T lymphocyte recognition of foreign proteins.
• CD4 functions as the primary receptor for the human immunodeficiency virus (HIV).
• The extracellular region of CD4 exhibits sequence similarities to immunoglobulin domains.

Purpose of the Study:

• To elucidate the structural characteristics of CD4 domains 3 and 4.
• To analyze the sequence similarities within the extracellular region of CD4.
• To understand the evolutionary implications of CD4's immunoglobulin-like folds.

Main Methods:

• Monoclonal antibody-based identification of CD4.
• Amino acid sequence analysis of CD4.
• X-ray crystallography for determining the structure of CD4 domains 3 and 4.

Main Results:

• The extracellular region of CD4 comprises four distinct regions with sequence similarities to immunoglobulin domains.
• X-ray crystallography revealed that CD4 domains 3 and 4 possess typical immunoglobulin-like folds.
• These findings are consistent with the previously determined structures of CD4 domains 1 and 2.

Conclusions:

• The structural determination of CD4 domains 3 and 4 further solidifies their immunoglobulin-like nature.
• The identification of multiple immunoglobulin-like folds in CD4 provides insights into its function and evolution.
• This structural information aids in understanding CD4's role in T cell recognition and HIV interaction.