Structural basis for dsRNA recognition and interferon antagonism by Ebola VP35

Area of Science:

• Virology
• Structural Biology
• Immunology

Background:

• Ebola virus protein 35 (VP35) is crucial for viral pathogenesis.
• VP35 antagonizes host antiviral signaling pathways, including RIG-I-like receptor pathways, to evade immune detection.
• Understanding VP35-RNA interactions is key to developing antiviral strategies.

Purpose of the Study:

• To determine the structural basis of Ebola VP35's interaction with double-stranded RNA (dsRNA).
• To elucidate how VP35-dsRNA binding contributes to the evasion of host antiviral responses.
• To investigate the functional significance of specific VP35 residues in RNA binding and immune inhibition.

Main Methods:

• X-ray crystallography was used to determine the structure of the VP35 interferon inhibitory domain (IID) bound to dsRNA.
• In vivo experiments were conducted to assess the impact of VP35-dsRNA interactions on immune signaling.
• Site-directed mutagenesis was employed to identify critical residues for RNA binding and function.

Main Results:

• The crystal structure reveals conserved basic residues in VP35 IID binding the dsRNA backbone.
• A hydrophobic pocket in VP35 mimics RIG-I-like receptor recognition of dsRNA blunt ends, effectively 'end-capping' the dsRNA.
• Residues essential for dsRNA binding are critical for VP35's interferon inhibitory activity in vivo.

Conclusions:

• Ebola VP35 utilizes a dual mechanism to bind dsRNA, engaging both the backbone and blunt ends.
• This specific dsRNA recognition strategy allows VP35 to antagonize host pattern recognition receptors and suppress antiviral immunity.
• VP35's immune evasion function is distinct from its role as a cofactor for the viral polymerase.