Proteolytic Activation of SARS-CoV-2 Spike at the S1/S2 Boundary: Potential Role of Proteases beyond Furin

ACS Infect Dis. 2021 Feb 12;7(2):264-272. doi: 10.1021/acsinfecdis.0c00701. Epub 2021 Jan 12.

Abstract

The severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) uses its spike (S) protein to mediate viral entry into host cells. Cleavage of the S protein at the S1/S2 and/or S2' site(s) is associated with viral entry, which can occur at either the cell plasma membrane (early pathway) or the endosomal membrane (late pathway), depending on the cell type. Previous studies show that SARS-CoV-2 has a unique insert at the S1/S2 site that can be cleaved by furin, which appears to expand viral tropism to cells with suitable protease and receptor expression. Here, we utilize viral pseudoparticles and protease inhibitors to study the impact of the S1/S2 cleavage on infectivity. Our results demonstrate that S1/S2 cleavage is essential for early pathway entry into Calu-3 cells, a model lung epithelial cell line, but not for late pathway entry into Vero E6 cells, a model cell line. The S1/S2 cleavage was found to be processed by other proteases beyond furin. Using bioinformatic tools, we also analyze the presence of a furin S1/S2 site in related CoVs and offer thoughts on the origin of the insertion of the furin-like cleavage site in SARS-CoV-2.

Keywords: S1/S2 site; SARS-CoV-2; cleavage; furin; viral entry.

Publication types

  • Research Support, N.I.H., Extramural
  • Research Support, Non-U.S. Gov't

MeSH terms

  • Animals
  • COVID-19 / virology*
  • Cell Line
  • Chlorocebus aethiops
  • Furin / metabolism*
  • HEK293 Cells
  • Humans
  • Models, Molecular
  • Peptide Hydrolases / chemistry
  • Peptide Hydrolases / metabolism*
  • Proteolysis
  • SARS-CoV-2 / chemistry
  • SARS-CoV-2 / metabolism*
  • Spike Glycoprotein, Coronavirus / metabolism*
  • Vero Cells
  • Virus Internalization

Substances

  • Spike Glycoprotein, Coronavirus
  • spike protein, SARS-CoV-2
  • Peptide Hydrolases
  • Furin