“Using Cryo-EM to Solve the Structures of Conformationally Dynamic RNAs”
Speaker: Steve L. Bonilla, Ph.D., HHMI Hanna H. Gray Postdoctoral Fellow, University of Colorado Anschutz Medical Campus
RNAs fold into complex, dynamic three-dimensional structures to function in essential cellular and viral processes. As such, a full mechanistic understanding of RNA function requires knowledge of the 3D structure and conformational dynamics of the RNAs involved. However, only a small number of RNA structures have been solved to date relative to the vast number of functional RNAs found in nature. In part, this is because RNA structures are challenging targets for structural biology due to their dynamic nature. Because of its ability to resolve multiple conformational states, cryo-EM promises dissection of RNA dynamic structural landscapes in a way not previously possible. To demonstrate its application to conformationally dynamic RNAs, we are using cryo-EM to study a diverse set of functional RNA structures in isolation and in complex with protein partners. First, we used cryo-EM to visualize a mysterious 55kDa tRNA-like structure (TLS) at the 3‘ end of the brome mosaic virus (BMV) genome that is recognized and aminoacylated by cellular tyrosyl-tRNA synthetase (TyrRS). Cryo-EM structures of the TLS RNA both in isolation and bound to TyrRS showed that the anticodon stem of the TLS is conformationally dynamic and undergoes large conformational changes to bind TyrRS using a non-canonical geometry. More recently, we have applied cryo-EM to the study of exonuclease resistant viral RNA structures and catalytic RNAs. The cryo-EM structures provide new insights into the folding and functions of these RNAs. In addition to answering specific biological questions about RNA structure-function relationships, our studies highlight the emerging power of cryo-EM for investigating dynamic mechanisms involving small structured RNAs and RNA-protein complexes.
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