Cryo Electron Microscopy Visualizes Coronavirus Structure

Severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) is humans’ third most impactful example of potentially lethal coronavirus infection within the last 20 years. Coronaviruses are positive-stranded RNA (+RNA) viruses that replicate their unusually large genomes in the host cell’s cytoplasm. This process is supported by an elaborate virus-induced network of transformed endoplasmic reticulum (ER) membranes known as the viral replication organelle (RO). Researchers used cryo electron microscopy to visualize these structures.

Coronavirus genome replication is associated with virus-induced cytosolic double-membrane vesicles, which may provide a tailored micro-environment for viral RNA synthesis in the infected cell. However, it is still being determined how newly synthesized genomes and mRNAs can travel from these sealed replication compartments to the cytosol to ensure their translation and the assembly of progeny virions.

Cellular cryo electron microscopy helped visualize a molecular pore complex that spans both membranes of the double-membrane vesicle and would allow the export of RNA to the cytosol. A hexameric assembly of a large viral transmembrane protein was found to form the core of the crown-shaped complex. This coronavirus-specific structure likely plays a critical role in coronavirus replication and thus constitutes a potential drug target.

The findings suggest a pathway for newly made viral genomic RNA from the DMV interior, via the pore channel, to the cytosolic sites of encapsidation. In the model, specific replicase subunits may associate with the pore complex to guide the newly synthesized RNA toward it.

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