Host cell factor requirement for hepatitis C virus enzyme maturation

The cellular chaperone, HSP90, is identified here as an essential factor fo r the activity of NS2/3 protease of hepatitis C virus. The cleavage activit y of NS2/3 protease synthesized in reticulocyte lysate is ATP-dependent, as evidenced by ATP depletion experiments and inhibition with nonhydrolyzable ATP analogs. Geldanamycin and radicicol, ATP-competitive inhibitors of the chaperone HSP90, also inhibit the cleavage of in vitro-synthesized NS2/3. Furthermore, these HSP90 inhibitors prevent NS2/3 cleavage when the proteas e is expressed in mammalian cells. The physical association of NS2/3 with H SP90 is demonstrated by immunoprecipitation. Thus, by way of a chaperone/fo lding activity, an HSP90-containing complex is required for maturation of t he polyprotein that encodes the enzymes essential for hepatitis C virus rep lication.