Structural basis of double-stranded RNA recognition by the RIG-I like receptor MDA5

Area of Science:

• Immunology
• Structural Biology
• Virology

Background:

• RIG-I, MDA5, and LGP2 are key cytosolic pattern recognition receptors involved in detecting viral RNA.
• Activation of RIG-I and MDA5 triggers type I interferon secretion, essential for antiviral immunity.
• While RIG-I and LGP2 C-terminal domains (CTDs) are known for RNA binding, MDA5's mechanism remained unclear.

Purpose of the Study:

• To elucidate the structural basis of double-stranded RNA (dsRNA) recognition by the MDA5 C-terminal domain (CTD).
• To understand how MDA5 discriminates between different forms of dsRNA.

Main Methods:

• Determined the 1.45Å resolution crystal structure of the human MDA5 CTD.
• Utilized NMR titration with dsRNA to identify binding surfaces.
• Performed mutagenesis and RNA binding assays to confirm interaction mechanisms.
• Conducted molecular modeling of the MDA5 CTD/dsRNA complex.

Main Results:

• The MDA5 CTD shares a conserved fold with RIG-I and LGP2 CTDs.
• A positively charged surface on MDA5 CTD is critical for dsRNA binding.
• Electrostatic interactions are the primary drivers of dsRNA recognition by MDA5.
• MDA5 CTD preferentially binds blunt-ended dsRNA, similar to LGP2, and avoids dsRNA with overhangs.

Conclusions:

• The structure and binding studies reveal the molecular mechanism of dsRNA recognition by MDA5 CTD.
• MDA5 CTD employs electrostatic interactions to bind blunt-ended dsRNA, contributing to innate antiviral immunity.
• Findings provide insights into the structural similarities and functional roles of RIG-I-like receptors in RNA sensing.