Figure 5.

Omicron spike-driven cell entry is less dependent on TMPRSS2 than Beta. (A) Simplified representation of the two putative entry routes for SARS-CoV-2 via plasma membrane fusion or via the endosomal pathway. In both routes, SARS-CoV-2 is recognized by ACE2 and either proteolytically cleaved in the presence of TMPRSS2 to enter the cell via membrane fusion. In the absence of TMPRSS2, the virus is engulfed endosomally and, after proteolytic cleavage by cathepsin L, membrane fusion of the host endosome with the viral membrane is induced. Ammonium chloride (NH₄Cl) prevents endosomal acidification, making the endosomal entry pathway inefficient for the virus entry. BHK21 cells transiently expressing murine (m)ACE2 and/or (m)TMPRSS2 were treated for 2 h with DMSO as control (grey bar) or 50 mM NH₄Cl (green bar). Furthermore, they were inoculated with particles pseudotyped with (B) the glycoprotein, (C) SARS-2-S of wild-type B.1 (D) Beta B 1.351-S and (E) Omicron BA.1-S. At 16 h after inoculation, the SARS-2-S-related cell entry of the viral pseudotypes was analyzed by measuring the activity of luciferase activity encoded by the virus in cell lysates. (F) The calculated rescue efficiency represented by the fold difference in NH₄Cl-mediated entry inhibition between mACE2/(−) and mACE2/mTMPRSS2 groups. (Figure 5A Created with BioRender.com).