Fig. 1.

SARS-CoV-2 structure and host cell entry mechanisms. The single stranded (ss) RNA viral genome encodes four structural proteins including the nucleocapsid, membrane, envelope and spike protein (A). Binding of S1 of the viral spike protein to the ACE-2 receptor on host cells induces 1) spike protein cleavage by TMPRSS2, followed by activation of S2 and viral internalization via direct fusion of the viral envelope and the host cell plasma membrane or 2) viral internalization via endocytic entry, followed by fusion between the viral envelope and the endosomal membrane (B). Abbreviations: SARS-CoV-2; severe acute respiratory syndrome coronavirus-2, ACE-2; angiotensin-converting enzyme-2, TMPRSS2; transmembrane protease serine 2, S1; subunit 1, S2; subunit 2. Adapted from ‘Mechanisms of SARS-CoV-2 Viral Entry’, by BioRender.com (2021). Retrieved from https://app.biorender.com/biorender-templates