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Author Spotlight: A Pseudotype Virus System for Assessing Omicron Subvariants and Neutralizing Antibodies in SARS-CoV-2 Research
Published on: September 8, 2023
The Unexpected Visibility of the SARS-CoV-2 Nucleocapsid Protein Reveals a Hidden Route of Surface Trafficking
Anthonia Osuagwu1, Jeffrey McCausland1, Christopher L King1,2,3
1Department of Molecular Biology and Microbiology, Case Western Reserve University School of Medicine, Cleveland, Ohio, United States of America.
Abstract:
The SARS-CoV-2 Nucleocapsid (N) protein, long regarded as an internal structural component of the virion, unexpectedly localizes to the plasma membrane of infected cells. Here, we show that N is actively trafficked to the cell surface via a ceramide-dependent unconventional secretory pathway. Live-stained imaging and kinetic analyses revealed that N surface association begins early in infection, before Spike (S) expression and viral release, and persists after enzymatic removal of heparan sulfate. Pharmacological disruption of phosphoinositide or phosphatidylserine interactions had minimal effect, whereas inhibition of neutral sphingomyelinase with GW4869 markedly reduced surface N, identifying a ceramide-regulated route as essential for its export. This mechanism distinguishes N from canonical transmembrane viral proteins and explains how N-specific antibodies mediate potent Fc-effector responses across SARS-CoV-2 variants. Our findings redefine the spatiotemporal dynamics of coronavirus structural proteins and reveal an unanticipated axis of immune visibility within the infected cell.
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