ACE2-Independent Interaction of SARS-CoV-2 Spike Protein with Human Epithelial Cells Is Inhibited by Unfractionated Heparin

Coronaviruses such as SARS-CoV-2, which is responsible for COVID-19, depend on virus spike protein binding to host cell receptors cause infection. The SARS-CoV-2 binds primarily ACE2 target cells and then processed by membrane proteases, including TMPRSS2, leading viral internalisation or fusion with the plasma membrane. It has been suggested, however, that other than may be involved in binding. We have investigated interactions of recombinant versions human epithelial lines express low/very low levels TMPRSS2 a proxy assay interaction cells. A tagged form containing S1 S2 regions bound temperature-dependent manner all lines, whereas region alone receptor-binding domain (RBD) interacted only weakly. Spike associated independently while RBD required presence high interaction. As previously shown bind heparin, soluble glycosaminoglycan, we tested effects various heparins ACE2-independent Unfractionated heparin inhibited an IC50 value <0.05 U/mL, two low-molecular-weight were less effective. mutant protein, lacking arginine-rich putative furin cleavage site, weakly had lower affinity unfractionated wild-type protein. This suggests site might also heparin-binding potentially important glycosaminoglycans heparan sulphate dermatan sulphate, but not chondroitin indicating it one both these surface