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Leucine-specific, functional interactions between human immunodeficiency virus type 1 Nef and adaptor protein
Scott H Coleman1, Nanette Van Damme, John R Day
1Department of Medicine, University of California, San Diego, La Jolla, CA 92093-0679, USA.
Journal of Virology
|February 1, 2005
Summary
The human immunodeficiency virus type 1 Nef protein requires a specific leucine motif for function, not just binding to adaptor protein (AP) complexes. This interaction with AP hemicomplexes is crucial for Nef
Area of Science:
- Virology
- Cell Biology
- Molecular Interactions
Background:
- The human immunodeficiency virus type 1 (HIV-1) virulence protein Nef interacts with cellular endosomal sorting machinery.
- Leucine-based motifs in cellular proteins bind adaptor protein (AP) complexes to regulate protein trafficking, but the precise mechanism is debated.
Purpose of the Study:
- To elucidate the molecular basis of the interaction between the Nef leucine motif and AP complexes.
- To determine which specific interactions are essential for Nef's functional activities.
Main Methods:
- Mutational analysis of the Nef leucine motif, replacing it with known leucine- or tyrosine-based AP-binding sequences from cellular proteins.
- Correlation of altered Nef-AP subunit interactions with functional outcomes, including CD4 downregulation and viral replication.
- Assessment of AP complex localization to endosomal membranes in cells expressing modified Nef proteins.
Main Results:
- Tyrosine motifs modulated Nef interaction with AP mu subunits, while leucine motifs did not significantly alter this interaction.
- Leucine motifs, but not tyrosine motifs, mediated a ternary interaction between Nef and AP hemicomplexes (AP-1 or AP-3).
- Only leucine motifs supported Nef-mediated AP complex association with endosomal membranes and were required for CD4 downregulation and enhanced viral replication.
Conclusions:
- Interaction with AP mu subunits alone is insufficient for Nef function.
- A leucine-specific interaction involving AP hemicomplexes is essential for Nef's biological activity.
- Cooperative binding involving both mu and hemicomplex interactions likely enhances AP complex avidity to Nef, stabilizing them on endosomal membranes and promoting viral replication.