Finding proteases that make cells go viral.

The activation of influenza virus hemagglutinin (HA) glycoprotein via cleavage by host cell proteases is essential for viral infectivity, and understanding the mechanisms for HA protein cleavage and how they may differ depending on the biological context is important for the development of flu treatments. However, the HA proteases involved in the activation of many viral strains remain unidentified. In this issue, Harbig et al. identify a repertoire of proteases that cleave HA and determine the proteases' functionality against specific HA glycoproteins.