Journal of Biological Chemistry
Volume 296, January–June 2021, 100111
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Research Article
The SARS-CoV-2 envelope and membrane proteins modulate maturation and retention of the spike protein, allowing assembly of virus-like particles

https://doi.org/10.1074/jbc.RA120.016175Get rights and content
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The severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2), a β-coronavirus, is the causative agent of the COVID-19 pandemic. Like for other coronaviruses, its particles are composed of four structural proteins: spike (S), envelope (E), membrane (M), and nucleoprotein (N) proteins. The involvement of each of these proteins and their interactions are critical for assembly and production of β-coronavirus particles. Here, we sought to characterize the interplay of SARS-CoV-2 structural proteins during the viral assembly process. By combining biochemical and imaging assays in infected versus transfected cells, we show that E and M regulate intracellular trafficking of S as well as its intracellular processing. Indeed, the imaging data reveal that S is relocalized at endoplasmic reticulum (ER)–Golgi intermediate compartment (ERGIC) or Golgi compartments upon coexpression of E or M, as observed in SARS-CoV-2-infected cells, which prevents syncytia formation. We show that a C-terminal retrieval motif in the cytoplasmic tail of S is required for its M-mediated retention in the ERGIC, whereas E induces S retention by modulating the cell secretory pathway. We also highlight that E and M induce a specific maturation of N-glycosylation of S, independently of the regulation of its localization, with a profile that is observed both in infected cells and in purified viral particles. Finally, we show that E, M, and N are required for optimal production of virus-like-particles. Altogether, these results highlight how E and M proteins may influence the properties of S proteins and promote the assembly of SARS-CoV-2 viral particles.

Keywords

virus assembly
viral protein
glycoprotein
secretion
infectious disease
COVID-19
SARS-CoV

Abbreviations

DMEM
Dulbecco’s modified minimal essential medium
E
envelope
ERGIC
endoplasmic reticulum (ER)–Golgi intermediate compartment
IBV
infectious bronchitis virus
IF
immunofluorescence
M
membrane
MERS-CoV
Middle East Respiratory Virus
N
nucleoprotein
SARS-CoV-2
severe acute respiratory syndrome coronavirus 2
S
spike
VLPs
virus-like particles
vRNP
viral ribonucleoprotein

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