SARS-CoV-2 structure and replication characterized by in situ cryo-electron tomography

Area of Science:

• Virology
• Structural Biology
• Cell Biology

Background:

• Severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) is a pathogenic beta-coronavirus responsible for the COVID-19 pandemic.
• Viral replication and assembly occur within host cells, involving intricate interactions between viral components and cellular membranes.

Purpose of the Study:

• To structurally characterize the SARS-CoV-2 replication compartment.
• To elucidate the mechanism of viral budding and the structure of extracellular virions.
• To understand the role of viral RNA and ribonucleoprotein complexes in assembly.

Main Methods:

• In situ cryo-electron tomography
• Subtomogram averaging
• High-resolution structural analysis of viral components and replication sites.

Main Results:

• Direct visualization of double-stranded RNA filaments within replication compartments.
• Identification of viral ribonucleoprotein complexes (vRNPs) accumulating at curved budding sites, suggesting curvature-enhanced recruitment.
• Demonstration that S-protein trimers reorganize on the envelope during assembly, not solely inducing membrane bending.
• Characterization of vRNPs as distinct cylindrical assemblies, proposing a model for packaging the large coronavirus genome.

Conclusions:

• The study provides critical structural insights into SARS-CoV-2 replication and assembly.
• Viral genome packaging involves multiple vRNPs, allowing flexibility for the large genome.
• Understanding these mechanisms is crucial for developing antiviral strategies against SARS-CoV-2.