Cell entry by SARS-CoV-2

Severe acute respiratory syndrome virus 2 (SARS-CoV-2) invades host cells by interacting with receptors/coreceptors, as well as with other cofactors, via its spike (S) protein that further mediates fusion between viral and cellular membranes. The host membrane protein, angiotensin-converting enzyme 2 (ACE2), is the major receptor for SARS-CoV-2 and is a crucial determinant for cross-species transmission. In addition, some auxiliary receptors and cofactors are also involved that expand the host/tissue tropism of SARS-CoV-2. After receptor engagement, specific proteases are required that cleave the S protein and trigger its fusogenic activity. Here we discuss the recent advances in understanding the molecular events during SARS-CoV-2 entry which will contribute to developing vaccines and therapeutics. Both severe acute respiratory syndrome virus 2 (SARS-CoV-2) and SARS-CoV mainly invade human lungs, although increasing evidence shows that SARS-CoV-2 can also infect many other tissues to develop systematic infection and multiple organ damage, and can also hijack T cells to directly paralyze host immunity.Angiotensin-converting enzyme 2 (ACE2) is the major receptor for SARS-CoV-2 infection and is a crucial determinant for cross-species transmission of the virus; SARS-CoV-2 can establish infections in a panel of domestic or wild animals via their ACE2 orthologs.Several proteins and non-protein molecules have been found to interact with SARS-CoV-2 S protein and serve as potential alternative/auxiliary attachment receptors/coreceptors to facilitate SARS-CoV-2 entry into specific types of host cells.Membrane fusion of SARS-CoV-2 requires two proteolytic events of S protein by host proteases, and the S1/S2 boundary of SARS-CoV-2 S protein harbors a polybasic insertion that expands the spectrum of available proteases and thus the tropism for different tissues.