Hepatitis C virus NS3 serine protease interacts with the serpin C1 inhibitor

Both NS3 protein (1007-1657) and its protease moiety (NS3p, 1027-1207) were able to interact in vitro with C1 Inhibitor (C1Inh) to give a 95-kDa Mr C1Inh cleavage product similar to that obtained upon proteolysis by complement protease C1s. High-Mr reaction products were also detected after incubation of C1Inh with NS3 but not with NS3p; they correspond to ester-bonded complexes from their hydroxylamine lability. Similar reactivity of NS3 was observed upon incubation with alpha2-antiplasmin. Serpin cleavage was prevented by treatment of NS3 with synthetic serine protease inhibitors. This interaction between viral NS3 and host serpins suggests that NS3 is likely to be controlled by infected cell protease inhibitors.