J Biol Chem

. 2020 Dec 3;100111.
doi: 10.1074/jbc.RA120.016175. Online ahead of print.
The SARS-CoV-2 Envelope and Membrane proteins modulate maturation and retention of the Spike protein, allowing assembly of virus-like particles

Bertrand Boson 1 , Vincent Legros 2 , Bingjie Zhou 3 , Eglantine Siret 1 , Cyrille Mathieu 1 , François-Loïc Cosset 1 , Dimitri Lavillette 4 , Solène Denolly 5



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 vs. 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 re-localized at endoplasmic reticulum (ER)-Golgi intermediate compartment (ERGIC) or Golgi compartments upon co-expression 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: COVID-19; Glycoprotein; Infectious disease; SARS-CoV; Secretion; Viral protein; Virus assembly.