High resolution cryo-EM structure of the helical RNA-bound Hantaan virus nucleocapsid reveals its assembly mechanisms
- Université Grenoble Alpes, CNRS, CEA, Institute for Structural Biology (IBS), France
- Aix-Marseille Université, CNRS, INSERM, AFMB UMR 7257, 13288, France
Abstract
Negative-strand RNA viruses condense their genome into helical nucleocapsids that constitute essential templates for viral replication and transcription. The intrinsic flexibility of nucleocapsids usually prevents their full-length structural characterization at high resolution. Here we describe purification of full-length recombinant metastable helical nucleocapsid of Hantaan virus (Hantaviridae family, Bunyavirales order) and determine its structure at 3.3 Å resolution by cryo-electron microscopy. The structure reveals the mechanisms of helical multimerization via sub-domain exchanges between protomers and highlights nucleotide positions in a continuous positively charged groove compatible with viral genome binding. It uncovers key sites for future structure-based design of antivirals that are currently lacking to counteract life-threatening hantavirus infections. The structure also suggests a model of nucleoprotein-polymerase interaction that would enable replication and transcription solely upon local disruption of the nucleocapsid.
Data availability
The cryo-EM has been deposited in EMDB under the accession code EMD-0333.The atomic coordinates have been deposited in PDB under the accession code 6I2N.
Article and author information
Author details
Funding
IDEX IRS grant University of Grenoble (G7H-IRS17H50)
- Hélène Malet
The funders had no role in study design, data collection and interpretation, or the decision to submit the work for publication.
Copyright
© 2019, Arragain et al.
This article is distributed under the terms of the Creative Commons Attribution License permitting unrestricted use and redistribution provided that the original author and source are credited.
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High resolution cryo-EM structure of the helical RNA-bound Hantaan virus nucleocapsid reveals its assembly mechanisms
eLife 8:e43075.
https://doi.org/10.7554/eLife.43075
Further reading
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- Structural Biology and Molecular Biophysics
In eukaryotes, RNAs transcribed by RNA Pol II are modified at the 5′ end with a 7-methylguanosine (m7G) cap, which is recognized by the nuclear cap binding complex (CBC). The CBC plays multiple important roles in mRNA metabolism, including transcription, splicing, polyadenylation, and export. It promotes mRNA export through direct interaction with a key mRNA export factor, ALYREF, which in turn links the TRanscription and EXport (TREX) complex to the 5′ end of mRNA. However, the molecular mechanism for CBC-mediated recruitment of the mRNA export machinery is not well understood. Here, we present the first structure of the CBC in complex with an mRNA export factor, ALYREF. The cryo-EM structure of CBC-ALYREF reveals that the RRM domain of ALYREF makes direct contact with both the NCBP1 and NCBP2 subunits of the CBC. Comparing CBC-ALYREF with other cellular complexes containing CBC and/or ALYREF components provides insights into the coordinated events during mRNA transcription, splicing, and export.
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- Structural Biology and Molecular Biophysics
Under physiological conditions, proteins continuously undergo structural fluctuations on different timescales. Some conformations are only sparsely populated, but still play a key role in protein function. Thus, meaningful structure–function frameworks must include structural ensembles rather than only the most populated protein conformations. To detail protein plasticity, modern structural biology combines complementary experimental and computational approaches. In this review, we survey available computational approaches that integrate sparse experimental data from electron paramagnetic resonance spectroscopy with molecular modeling techniques to derive all-atom structural models of rare protein conformations. We also propose strategies to increase the reliability and improve efficiency using deep learning approaches, thus advancing the field of integrative structural biology.
