Structural Basis for Alternative Self-Assembly Pathways Leading to Different Human Immunodeficiency Virus Capsid-Like...

Area of Science:

• Biophysics
• Structural Biology
• Nanotechnology

Background:

• Virus particle assembly mechanisms inspire the design of self-assembling protein nanostructures.
• The human immunodeficiency virus type 1 (HIV-1) capsid protein (CA) is a model for studying nanoparticle assembly.
• Achieving specific nanoparticle architectures in vitro, like cone-shaped HIV-1 capsids, remains challenging, often resulting in aberrant tubular structures.

Purpose of the Study:

• To investigate the molecular determinants governing the in vitro self-assembly of specific protein nanoparticle architectures.
• To understand why HIV-1 CA typically forms tubes instead of the desired cone-shaped capsid structures.
• To identify strategies for directing the assembly of HIV-1 CA into authentic capsid-like nanoparticles.

Main Methods:

• Utilizing specific amino acid substitutions at CA-CA interfaces to alter protein interactions.
• Employing all-atom molecular dynamics (MD) simulations to analyze the stability of assembly intermediates.
• Comparing the in vitro assembly outcomes of wild-type (wt) CA and mutant variants.

Main Results:

• Certain amino acid substitutions favored the assembly of cone-shaped nanoparticles resembling authentic HIV-1 capsids.
• All-atom MD simulations revealed that the trimer of CA dimers (ToD) intermediate is destabilized in mutants forming cone-shaped particles.
• ToD destabilization was linked to conformational changes at CA-CA interfaces, reducing interprotein interactions.

Conclusions:

• Reducing the stability of the ToD intermediate promotes the formation of cone-shaped HIV-1 capsid-like nanoparticles in vitro.
• Destabilization of the ToD intermediate facilitates the incorporation of CA pentamers, crucial for cone formation.
• This study provides a model for controlling protein nanoparticle assembly by tuning the stability of key intermediates.