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Updated: Jun 24, 2026
Monitoring Activation of the Antiviral Pattern Recognition Receptors RIG-I And PKR By Limited Protease Digestion and Native PAGE
Published on: July 29, 2014
The RIG-I-like receptor LGP2 recognizes the termini of double-stranded RNA
Xiaojun Li1, C T Ranjith-Kumar2, Monica T Brooks3
1Department of Biochemistry and Biophysics, Texas A & M University, College Station, Texas 77843-2128.
Abstract:
The RIG-I-like receptors (RLRs), RIG-I and MDA5, recognize single-stranded RNA with 5' triphosphates and double-stranded RNA (dsRNA) to initiate innate antiviral immune responses. LGP2, a homolog of RIG-I and MDA5 that lacks signaling capability, regulates the signaling of the RLRs. To establish the structural basis of dsRNA recognition by the RLRs, we have determined the 2.0-A resolution crystal structure of human LGP2 C-terminal domain bound to an 8-bp dsRNA. Two LGP2 C-terminal domain molecules bind to the termini of dsRNA with minimal contacts between the protein molecules. Gel filtration chromatography and analytical ultracentrifugation demonstrated that LGP2 binds blunt-ended dsRNA of different lengths, forming complexes with 2:1 stoichiometry. dsRNA with protruding termini bind LGP2 and RIG-I weakly and do not stimulate the activation of RIG-I efficiently in cells. Surprisingly, full-length LGP2 containing mutations that abolish dsRNA binding retained the ability to inhibit RIG-I signaling.
Insights
Harnessing the innate immune system, researchers explored how LGP2 protein interacts with double-stranded RNA (dsRNA). This structural study reveals LGP2
Area of Science:
- Immunology
- Structural Biology
- Virology
Background:
- RIG-I-like receptors (RLRs), including RIG-I and MDA5, are crucial for initiating innate antiviral immune responses by detecting viral RNA.
- LGP2, a non-signaling RLR homolog, plays a regulatory role in RLR-mediated signaling pathways.
- Understanding the structural basis of RNA recognition by RLRs is essential for developing novel antiviral strategies.
Purpose of the Study:
- To elucidate the structural mechanisms of double-stranded RNA (dsRNA) recognition by LGP2.
- To investigate the binding stoichiometry and characteristics of LGP2 with dsRNA.
- To explore the functional implications of LGP2-dsRNA interactions on RIG-I signaling.
Main Methods:
- X-ray crystallography was employed to determine the high-resolution structure of the LGP2 C-terminal domain bound to dsRNA.
- Gel filtration chromatography and analytical ultracentrifugation were used to analyze LGP2-dsRNA complex formation and stoichiometry.
- Cell-based assays were performed to assess the impact of dsRNA structure and LGP2 mutations on RIG-I activation.
Main Results:
- The 2.0-Å crystal structure revealed two LGP2 C-terminal domains binding to the termini of an 8-bp dsRNA molecule.
- LGP2 was shown to bind blunt-ended dsRNA of varying lengths with a 2:1 protein-to-dsRNA stoichiometry.
- dsRNA with protruding termini exhibited weak binding to LGP2 and RIG-I, leading to inefficient RIG-I activation.
- Mutations in full-length LGP2 that abolished dsRNA binding did not impair its ability to inhibit RIG-I signaling, suggesting alternative regulatory mechanisms.
Conclusions:
- LGP2 recognizes dsRNA through its C-terminal domain, with specific binding modes dictated by dsRNA termini.
- The stoichiometry and binding characteristics of LGP2-dsRNA complexes provide insights into RLR regulation.
- Unexpectedly, LGP2 can inhibit RIG-I signaling independently of direct dsRNA binding, highlighting a complex regulatory role in innate immunity.
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