Hepatitis C virus nonstructural protein 3 (NS3), nonstructural protein 4 (NS4), and nonstructural protein 5B (NS5B) (NS3, NS4, NS5B)

NS3, NS4, and NS5B are nonstructural proteins of the hepatitis C virus, derived from the processing of the viral polyprotein. NS3 is a multifunctional enzyme with both serine protease activity (required for cleavage of the viral polyprotein at specific sites) and ATP-dependent RNA helicase activity (essential for viral RNA replication). NS4A serves as a critical cofactor that activates NS3’s protease function; NS4B is integral to the formation of the membranous web that acts as the site for RNA replication. NS5B functions as HCV’s RNA-dependent RNA polymerase, catalyzing the synthesis of new viral genomes. These NS proteins interact to form the viral replication complex, localizing to modified endoplasmic reticulum membranes. All three proteins are prominent targets for direct-acting antiviral drugs due to their indispensable roles in the HCV lifecycle and are central to the design of combination therapies for chronic HCV infection.

Other names

NS3 serine protease/helicaseNS4 (typically NS4A and NS4B are distinguished, but NS4A is the major cofactor for NS3; NS4B has separate functions)NS5B RNA-dependent RNA polymeraseHCV NS3HCV NS4AHCV NS4BHCV NS5BHepatitis C nonstructural protein 3/4/5B

Protease inhibition: blocks NS3/4A-mediated cleavage of viral polyprotein, halting viral maturation; Polymerase inhibition: NS5B inhibitors block RNA-dependent RNA polymerase, preventing viral RNA replication; Formation of nonfunctional replication complexes (targeting NS4B and NS3/4A interactions)