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Proteolytic activation of influenza viruses and coronaviruses by host cell proteases

The aim of our research is the identification and characterization of virus-activating proteases in the human respiratory tract. Among other things, we investigate the distribution of relevant proteases along the upper respiratory tract, the entry portal of viruses, to the lower airways. We are also interested in the molecular mechanisms underlying the differences in subcellular localization and timing of viral envelope protein activation by TMPRSS2. Influenza virus hemagglutinin is cleaved during its transport to the cell surface, resulting in the release of viral particles containing cleaved hemagglutinin. The spike protein of SARS-CoV-2 is activated by TMPRSS2 at the cell surface during cell entry. In contrast, TMPRSS2 does not appear to cleave hemagglutinin during virus entry.