Structural Analysis of dsRNA Binding to Anti-viral Pattern Recognition Receptors LGP2 and MDA5

Emiko Uchikawa,Mathilde Lethier,Hélène Malet,Joanna Brunel,Denis Gerlier,Stephen Cusack

doi:10.1016/j.molcel.2016.04.021

Abstract

SummaryRIG-I and MDA5 sense virus-derived short 5′ppp blunt-ended or long dsRNA, respectively, causing interferon production. Non-signaling LGP2 appears to positively and negatively regulate MDA5 and RIG-I signaling, respectively. Co-crystal structures of chicken (ch) LGP2 with dsRNA display a fully or semi-closed conformation depending on the presence or absence of nucleotide. LGP2 caps blunt, 3′ or 5′ overhang dsRNA ends with 1 bp longer overall footprint than RIG-I. Structures of 1:1 and 2:1 complexes of chMDA5 with short dsRNA reveal head-to-head packing rather than the polar head-to-tail orientation described for long filaments. chLGP2 and chMDA5 make filaments with a similar axial repeat, although less co-operatively for chLGP2. Overall, LGP2 resembles a chimera combining a MDA5-like helicase domain and RIG-I like CTD supporting both stem and end binding. Functionally, RNA binding is required for LGP2-mediated enhancement of MDA5 activation. We propose that LGP2 end-binding may promote nucleation of MDA5 oligomerization on dsRNA.

Highlights

Homologous double-stranded RNA dependent ATPases RIG-I, MDA5, and LGP2 (RIG-I-like helicases [RLHs]) are key cytosolic pattern recognition receptors in the vertebrate innate immune response against RNA viruses
Co-crystal structures of chicken LGP2 with double-stranded RNA (dsRNA) display a fully or semi-closed conformation depending on the presence or absence of nucleotide
Structures of 1:1 and 2:1 complexes of chMDA5 with short dsRNA reveal headto-head packing rather than the polar head-to-tail orientation described for long filaments. chLGP2 and chMDA5 make filaments with a similar axial repeat, less co-operatively for chLGP2

Summary

Introduction

Homologous double-stranded RNA (dsRNA) dependent ATPases RIG-I, MDA5, and LGP2 (RIG-I-like helicases [RLHs]) are key cytosolic pattern recognition receptors in the vertebrate innate immune response against RNA viruses. RIG-I senses primarily 50ppp blunt-end dsRNA (50ppp-dsRNA), whereas MDA5 is activated by long dsRNA. The two sensors respond to different but overlapping sets of viruses (Yoo et al, 2014). Both activated receptors trigger the same downstream signaling pathway, leading to interferon (IFN) induction (Goubau et al, 2013). RIG-I and MDA5 possess tandem N-terminal caspase activation and recruitment domains (CARDs), a central DECH-box helicase domain (Fairman-Williams et al, 2010), and a C-terminal domain (CTD). LGP2 differs in lacking CARDs (Figure 1A) and independent signaling activity

Results

Discussion

Conclusion