Alphaviral Capsid Proteins Inhibit Stress Granule Assembly via Competitive RNA Binding With G3BP1

Area of Science:

• Virology
• Cell Biology
• Biochemistry

Background:

• Viral infections trigger cellular stress granule (SG) formation as a defense mechanism.
• Viruses employ strategies to inhibit SGs, but mechanisms remain unclear.
• Nucleocapsid proteins are key viral factors in replication and host interactions.

Purpose of the Study:

• To investigate the role of alphavirus nucleocapsid proteins in inhibiting stress granule formation.
• To elucidate the molecular mechanisms by which viral nucleocapsids modulate SGs.

Main Methods:

• Utilized Semliki Forest Virus (SFV) as a model system.
• Investigated nucleocapsid protein oligomerization and RNA-binding properties.
• Assessed disruption of G3BP1-RNA liquid-liquid phase separation (LLPS) in vitro and SG assembly in cells.

Main Results:

• SFV nucleocapsid inhibits SG formation through N-terminal helix-mediated oligomerization and an intrinsically disordered region (IDR).
• SFV capsid directly competes with G3BP1 for RNA binding, disrupting SG assembly.
• This inhibitory mechanism is conserved in alphaviruses but not in SARS-CoV-2 or other examined viruses.

Conclusions:

• Viral nucleocapsid proteins can actively inhibit host cell stress granule formation.
• SFV capsid's disruption of G3BP1-RNA LLPS is a key mechanism for SG inhibition.
• SFV capsid peptides show potential for therapeutic applications in SG-related diseases like ALS.