Nef-CD4 physical interaction sensed with the yeast two-hybrid system

Area of Science:

• Molecular Biology
• Virology
• Immunology

Background:

• Human Immunodeficiency Virus type 1 (HIV-1) Nef protein is known to downregulate the CD4 receptor.
• The precise mechanism and direct physical interaction between Nef and CD4 remain areas of investigation.

Purpose of the Study:

• To investigate the direct physical interaction between HIV-1 Nef protein and the cytoplasmic domain of the CD4 receptor (CD4cd).
• To identify specific regions and residues within CD4cd and Nef essential for this interaction.

Main Methods:

• Yeast two-hybrid system utilizing a Saccharomyces cerevisiae strain with a GAL4-responsive lacZ reporter gene.
• Co-transformation with plasmids expressing fusion proteins of GAL4 DNA-binding (DB) or activation (A) domains with Nef and CD4cd sequences.
• Analysis of reporter gene activation with various Nef and CD4cd constructs, including deletions and point mutations.

Main Results:

• Specific reporter gene activation was observed for both DB-Nef + A-CD4cd and DB-CD4cd + A-Nef combinations, indicating a direct interaction.
• The N-terminal 23 amino acids (aa 1-23) of CD4cd were sufficient for interaction with Nef.
• Mutation of the Leu20-Leu21 motif in CD4cd to Ala20-Ala21 abolished the interaction, highlighting its essential role.
• A largely complete Nef protein was required for specific reporter activation.

Conclusions:

• HIV-1 Nef directly interacts with the cytoplasmic domain of CD4.
• The Leu20-Leu21 motif within the first 23 amino acids of CD4cd is essential for Nef binding.
• This direct interaction and the specific CD4cd motif are critical components of Nef-induced CD4 downmodulation.