Enveloped viruses need to fuse with a host cell membrane in order to deliver their genome into the host cell. CoVs are important pathogens of animals and man with high zoonotic potential as demonstrated by the emergence of SARS- and MERS-CoVs. A recent study investigated the cell entry of coronaviruses (CoVs).
Previous studies resulted in apparently conflicting results with respect to CoV cell entry, particularly regarding the fusion-activating requirements of the CoV S protein. By combining cell-biological, infection, and fusion assays the authors demonstrated that murine hepatitis virus (MHV), a prototypic member of the CoV family, enters cells via clathrin-mediated endocytosis. Moreover, although MHV does not depend on a low pH for fusion, the virus was shown to rely on trafficking to lysosomes for proteolytic cleavage of its spike (S) protein and membrane fusion to occur.
Based on these results they predicted and then demonstrated that MERS- and feline CoV require cleavage by different proteases and escape the endo/lysosomal system from different compartments.