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First Author:  Boson et al.  

Journal/preprint name:  Bioarchives 

Tags: Virology, Cellular biology, Molecular biology 


Boson et al. characterised how the intracellular trafficking and maturation of the SARS-CoV-2 S protein are regulated by the other structural proteins E, M and N. Co-expression of E or M were found to decrease S cleavage, alter the N-glycosylation patterns in the S2 subunit and to retain S protein in the endoplasmic reticulum (ER)-Golgi intermediate compartment (ERGIC) or cis-Golgi, known CoV assembly sites. The S protein expressed alone was found widely distributed within the cell and to promote syncytia, which was prevented with SARS-CoV-2 infection or co-expression with E or M. In contrast, N protein does not appear to have any effect on S maturation or localisation. While E protein was found to influence the level of S expression by inducing a non-specific retention of glycoproteins in the ER and to slow down the cell secretory pathway; M influenced S localisation through direct interaction with S C-terminal moiety. Finally, all structural proteins proved essential for VLP formation.  

Research Highlights 

  1.  SARS-CoV-2 E and M proteins alter S cleavage, maturation and intracellular trafficking.  

  1.  SARS-CoV-2 E and M proteins promote S retention at ERGIC or cis-Golgi compartments by different mechanisms and induce furin-mediated processing independently of its mechanisms of intracellular retention. 

  1. SARS-CoV-2 E protein induces an ER non-specific retention of glycoproteins and slows down the cell secretory pathway 

  1. M-mediated retention at the ERGIC requires the C-terminal motif in the S cytoplasmic tail.  

  1. SARS-CoV-2 M, E and N are required for VLP formation. 

Impact for COVID-19 research:  

  • Understand the virology and cell biology of SARS-CoV2/COVID19 


  • Study Typein vitro 

  • Important cell lines/viral models used:  

Homo sapiens codon optimized SARS-CoV-2 S (Wuhan-Hu-1, GenBank: QHD43419.1) was cloned into pVAX1 vector. The delta 19 truncation of S form was generated by site directed mutagenesis introducing a stop codon after Cys1254. SARS-CoV-2 E, M and N genes 405 (Wuhan-Hu-1, GenBank: QHD43419.1) were synthesized and cloned into pCDNA3.1(+) vectorsVeroE6, 293T, temperature-dependent folding mutant of VSV-G, Huh-7.5 cells, hepatitis C virus (HCV) p7. 

  • Key Techniques: Transfection, Endo-H assessment for intracellular trafficking, western blot, flow cytometry, Immunofluorescence and confocal microscopy, cell-to-cell fusion assay.   


  • There is no housekeeping protein in the western blots (GAPDH, beta-tubulin and beta-actin) in Figure 1 and 2. 

  • In Figure 1, 3B there is no indication of how many times the experiment was performed. 

  • No other marker for any other cell localisation (as for negative control) is shown in the immunofluorescent studies.