Neutron Reflectometry and Molecular Simulations Demonstrate HIV-1 Nef Homodimer Formation on Model Lipid Bilayers

Area of Science:

• Structural Biology
• Virology
• Biophysics

Background:

• The Human Immunodeficiency Virus type 1 (HIV-1) Nef protein is essential for viral infectivity, replication, and immune evasion.
• Nef functions through interactions with host cell proteins and pathways, with homodimerization at the plasma membrane being critical for its activities.

Purpose of the Study:

• To elucidate the structural basis of HIV-1 Nef homodimerization at lipid bilayers.
• To understand how Nef homodimers interact with model cell membranes and facilitate host protein engagement.

Main Methods:

• Combined neutron reflectometry of myristoylated Nef on model lipid bilayers with molecular simulations.
• Utilized X-ray crystallography to study wild-type Nef and a dimerization-defective mutant (Nef-L112D) in complex with host protein SH3 domains.

Main Results:

• Provided direct evidence that HIV-1 Nef binds to lipid bilayers as a homodimer, with its structured core held away from the membrane.
• Demonstrated that the helical dimerization interface stabilizes the membrane-bound Nef dimer.
• Showed that a dimerization-defective mutant (Nef-L112D) forms monomeric complexes, confirming the role of the interface in dimerization.

Conclusions:

• HIV-1 Nef homodimerization at lipid bilayers is intrinsically driven by structural features observed in dimeric complexes.
• The membrane-associated Nef homodimer is poised for interaction with host cell signaling partners.