Cryo-EM of a viral RNA and RNA-protein complex reveals how structural dynamics and novel tRNA mimicry combine to hijack host machinery

Bonilla, Steve L.; Sherlock, Madeline E.; MacFadden, Andrea; Kieft, Jeffrey S.

Viruses require multifunctional structured RNAs to hijack their host’s biochemistry, but their mechanisms can be obscured by the difficulty of solving conformationally dynamic RNA structures. Using cryo-EM, we visualized the structure of the mysterious viral tRNA-like structure (TLS) from brome mosaic virus (BMV), which affects replication, translation, and genome encapsidation. Structures in isolation and bound to tyrosyl-tRNA synthetase (TyrRS) show that this ∼55 kDa purported tRNA mimic undergoes large conformational rearrangements to bind TyrRS in a form that differs dramatically from tRNA. Our studies reveal how viral RNAs can use a combination of static and dynamic RNA structures to bind host machinery through highly noncanonical interactions and highlights the utility of cryo-EM for visualizing small conformationally dynamic structured RNAs.