Unexpected similarity between the cytosolic West Nile virus NS3 and the secretory furin-like serine proteinases.

Many viral proteins undergo proteolytic processing events that are required for virus infection and virion assembly. In this issue of Biochemical Journal, Strongin and co-workers report that the NS3 protease from West Nile virus unexpectedly cleaves certain substrates at pairs of basic residues, a specificity that resembles that of the furin-like PCs (proprotein convertases). This led to the demonstration that furin/PC inhibitors containing poly(D-arginine) are also potent inhibitors of NS3, and that anthrax toxin protective antigen and myelin basic protein are potential NS3 substrates. Structural modelling based on Dengue virus NS3 provided a possible rationale for the observed cleavage specificity of West Nile virus NS3.