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. Author manuscript; available in PMC: 2015 Oct 1.
Published in final edited form as: Cytokine Growth Factor Rev. 2014 Jul 15;25(5):507–512. doi: 10.1016/j.cytogfr.2014.07.006

Figure 2. Comparison of RNA filament assembly by RLR proteins.

Figure 2

Panels illustrate features of RLR assembly onto RNA templates. Each RLR protein is illustrated as a colored module, and inset box demonstrates positions of CARD, Helicase and CTD regions. Black lines indicate dsRNA.

A) RIG-I (red) is auto-repressed at steady state by CARD-Hel2i interactions. Recognition of a 5′-triphosphorylated dsRNA terminus (5′-PPP) by the CTD results in CARD de-repression. The helicase domain mediates ATP-dependent translocation away from the RNA terminus with limited processivity, and leads to packaging of RIG-I into short, end-directed filaments.

B) MDA5 (magenta) has a low monomeric RNA binding affinity that is insensitive to terminal structures and characterized by a slow on-rate. ATP-mediated destabilization prevents MDA5 accumulation on dsRNA, but cooperative interactions between monomers can enhance processive filament assembly. Long MDA5 filaments are observed in vitro.

C) LGP2 (blue) has a high affinity for dsRNA and uses ATP hydrolysis to enable high-efficiency binding to diverse RNA species. LGP2 is able to facilitate and stabilize MDA5-dsRNA interactions leading to increased filament nucleation, producing a greater number of shorter MDA5 filaments.