Cryo-EM Structures of MDA5-dsRNA Filaments at Different Stages of ATP Hydrolysis

Area of Science:

• Immunology
• Structural Biology
• Virology

Background:

• Double-stranded RNA (dsRNA) is a key indicator of viral infections, triggering inflammatory responses.
• Cytosolic dsRNA is primarily recognized by the MDA5 receptor.
• MDA5 filament assembly on dsRNA is crucial for initiating type I interferon signaling.

Purpose of the Study:

• To determine the cryoelectron microscopy (cryo-EM) structures of MDA5-dsRNA filaments.
• To elucidate the atomic details of MDA5 filament formation and dsRNA recognition.
• To understand the role of nucleotide analogs and helical twist in MDA5 signaling.

Main Methods:

• Cryoelectron microscopy (cryo-EM) was used to obtain high-resolution structures.
• Atomic models of MDA5-dsRNA filaments were built and refined.
• Mutational analysis of key residues was performed to assess signaling activity.

Main Results:

• Cryo-EM structures revealed MDA5 filaments with varying helical twists bound to dsRNA and nucleotide analogs.
• Filament-forming interfaces were identified, explaining MDA5's cooperativity and length specificity.
• Variations in helical twist correlated with nucleotide occupancy and type, offering insights into ATP hydrolysis's role.

Conclusions:

• The structural and mutational data provide a mechanistic understanding of MDA5's dsRNA sensing and signaling initiation.
• MDA5 filament flexibility, driven by hydrophobic interfaces, allows for adaptation to different dsRNA lengths.
• Understanding MDA5 structure-function relationships is critical for developing therapies against viral infections and autoimmune diseases.