Hepatitis C virus nonstructural protein 3–4A protease complex (HCV NS3/4A protease)

The hepatitis C virus nonstructural protein 3–4A protease complex is a membrane-associated serine protease formed by the NS3 protein and its cofactor NS4A. NS3 provides the catalytic protease domain, while NS4A stabilizes the enzyme's tertiary structure and is essential for full protease activity. The complex is critical for proteolytic cleavage of the viral polyprotein at four sites, resulting in production of mature nonstructural proteins necessary for viral replication. In addition to processing viral proteins, NS3/4A cleaves and inactivates key host cell signaling proteins (e.g., MAVS, TRIF), which blocks innate immune antiviral responses and enables viral persistence. Its unique structure and centrality in the viral life cycle make NS3/4A a prime target for direct-acting antivirals; multiple inhibitor classes have been developed that specifically block the protease active site, halting HCV replication and facilitating the cure of chronic HCV. Resistance mutations are a major therapeutic challenge, requiring careful selection and monitoring of drug regimens.

Other names

HCV NS3-4A proteaseHCV NS3/4A proteinHepatitis C virus serine proteaseNS3 protease (in complex with NS4A)HCV protease/helicase (when referring to the full NS3 protein)

Reversible or irreversible inhibition of the active site serine in NS3 protease, blocking viral polyprotein processing and thus HCV replication. Some inhibitors form a covalent bond with the active site serine, others bind via stabilizing interactions on the protein surface. Prevent immune evasion by restoring normal host interferon signaling blocked by NS3/4A-mediated cleavage of MAVS/TRIF.