Characterization of SARS-CoV-2 nucleocapsid protein oligomers

Area of Science:

• Virology
• Structural Biology
• Biochemistry

Background:

• Oligomers of the SARS-CoV-2 nucleocapsid (N) protein exhibit significant instability and rapid degradation in vivo.
• This instability is crucial for the N protein's dual role in viral genome stabilization and release during the infection cycle.
• The N protein forms high molecular mass complexes with the viral genome in vivo.

Purpose of the Study:

• To investigate the instability and degradation profiles of the SARS-CoV-2 nucleocapsid (N) protein.
• To elucidate the factors influencing N protein stability and self-cleavage.
• To determine the 3D structure of a stable N protein oligomeric complex.

Main Methods:

• Analysis of degradation profiles using size-exclusion chromatography.
• Characterization of protein samples via mass spectrometry and cryo-electron microscopy.
• Investigation of Proprotein convertase activities and the role of chloride ions (Cl⁻).

Main Results:

• Identified self-cleavage properties of the N protein linked to Proprotein convertase activity.
• Determined that chloride ions (Cl⁻) play a key role in modulating N protein stability and degradation.
• Successfully isolated a stable oligomeric complex of the N protein and determined its 3D structure at ~6.8 Å resolution.

Conclusions:

• The instability of SARS-CoV-2 N protein oligomers is modulated by self-cleavage and chloride ion concentration.
• The structural and mechanistic insights into N protein stability contribute to understanding the coronavirus infection cycle.
• The determined structure of the stable N protein oligomer provides a basis for further functional studies.