The intrinsically disordered CARDs-Helicase linker in RIG-I is a molecular gate for RNA proofreading

Area of Science:

• Immunology
• Molecular Biology
• Virology

Background:

• The innate immune receptor RIG-I is crucial for detecting viral RNA and initiating immune responses.
• RNA recognition by RIG-I's C-terminal domain (CTD) is necessary, but RNA must then engage the helicase domain to activate signaling.
• The helicase domain lacks intrinsic RNA specificity, necessitating a proofreading mechanism.

Purpose of the Study:

• To identify and characterize the previously unknown RNA proofreading mechanisms of RIG-I.
• To elucidate the role of the CARDs-Helicase Linker (CHL) in RIG-I's RNA engagement and specificity.
• To understand how RIG-I distinguishes viral RNA from non-specific RNAs.

Main Methods:

• Biochemical assays to study protein-RNA interactions.
• Structural analysis of RIG-I domains and their interactions.
• Mutational analysis of the CHL and CARD2:Hel2i interface.

Main Results:

• A novel RNA proofreading mechanism involving the CHL was identified.
• The CHL acts as an RNA gate, using electrostatic repulsion to block non-specific RNAs.
• The CHL stabilizes the CARD2:Hel2i interface, crucial for autoinhibition.
• A tunable gating mechanism involving CHL and CARD2:Hel2i ensures selective RNA binding to the helicase domain.

Conclusions:

• RIG-I employs a sophisticated gating mechanism mediated by the CHL and CARD2:Hel2i interface to ensure specific viral RNA recognition.
• This mechanism prevents aberrant immune activation by non-specific RNAs.
• The CHL represents a potential therapeutic target for modulating RIG-I activity.