Ebolavirus VP35 coats the backbone of double-stranded RNA for interferon antagonism

Abstract

Recognition of viral double-stranded RNA (dsRNA) activates interferon production and immune signaling in host cells. Crystal structures of ebolavirus VP35 show that it caps dsRNA ends to prevent sensing by pattern recognition receptors such as RIG-I. In contrast, structures of marburgvirus VP35 show that it primarily coats the dsRNA backbone. Here, we demonstrate that ebolavirus VP35 also coats the dsRNA backbone in solution, although binding to the dsRNA ends probably constitutes the initial binding event.

Fig 1

Isotherms for binding of RESTV VP35 RBD molecules to 18-bp dsRNA with blunt ends, 18-bp dsRNA with a 3′ overhang, and 12-bp dsRNA with blunt ends. The top of each panel shows enthalpic heat released during titration, and the bottom panel shows integrated binding isotherms with the proposed fitted model of binding. Binding events A and B are labeled in the leftmost isotherm.

Fig 2

dsRNA recognition events observed in different filovirus VP35-dsRNA complexes. (A) Crystal structure of the RESTV VP35 RBD in complex with a 12-bp dsRNA. The end-capping monomer (number 1 in panel C) is shown in yellow, and the backbone-binding member of the dimer (number 2 in panel C) is shown in teal. (B) Previous crystal structure of the RESTV VP35 RBD in complex with an 18-bp dsRNA (PDB accession no. 3KS8). (C) Continuous-coating crystal structure of the MARV VP35 RBD determined in complex with a 12-bp dsRNA (PDB accession no. 4GHA). Only backbone binding interactions are observed in the crystal structure (numbered 2 to 5, different shades of blue and green). An end-capping interaction (yellow), modeled from RESTV structures by the superimposition of the dsRNA and backbone-binding copy number 2 indicates that no steric clash would occur if MARV also bound an RBD on the dsRNA end (1).