title: Serine protease of hepatitis C virus expressed in insect cells as the NS3/4A complex.
abstract: Hepatitis C virus (HCV) protease NS3 and its protein activator NS4A participate in the processing of the viral polyprotein into its constituent nonstructural proteins. The NS3/4A complex is thus an attractive target for antiviral therapy against HCV. We expressed the full-length NS3 and NS4A in insect cells as a soluble fusion protein with an N-terminal polyhistidine tag and purified the two proteins to homogeneity. Cleavage at the junction between HisNS3 and NS4A occurs during expression, producing a noncovalent complex between HisNS3 and NS4A with a subnanomolar dissociation constant. We purified the HisNS3/4A complex by detergent extraction of cell lysate and by metal chelate chromatography. We removed the His tag by thrombin cleavage and then further purified the complex by gel filtration. The purified NS3/4A complex is active in a protease assay using a synthetic peptide substrate derived from the NS5A-NS5B junction, with kcat/K(m) of 3700 (+/- 600) M-1 s-1, an order of magnitude above those previously reported for NS3 expressed by other strategies. This high protease activity implies that the full-length sequences of NS3 and NS4A are required for optimal activity of the NS3 protease domain. We examined the dependence of the NS3/4A protease activity on buffer conditions, temperature, and the presence of detergents. We find that, under most conditions, NS3 protease activity is dependent on the aggregation state of the NS3/4A complex. The monodisperse, soluble form of the NS3/4A complex is associated with the highest protease activity.
authors.affiliation: Department of Structural Chemistry, Schering-Plough Research Institute, Kenilworth, New Jersey 07033, USA.
authors.forename: D L
authors.initials: DL
authors.lastname: Sali
authors.forename: R
authors.initials: R
authors.lastname: Ingram
authors.forename: M
authors.initials: M
authors.lastname: Wendel
authors.forename: D
authors.initials: D
authors.lastname: Gupta
authors.forename: C
authors.initials: C
authors.lastname: McNemar
authors.forename: A
authors.initials: A
authors.lastname: Tsarbopoulos
authors.forename: J W
authors.initials: JW
authors.lastname: Chen
authors.forename: Z
authors.initials: Z
authors.lastname: Hong
authors.forename: R
authors.initials: R
authors.lastname: Chase
authors.forename: C
authors.initials: C
authors.lastname: Risano
authors.forename: R
authors.initials: R
authors.lastname: Zhang
authors.forename: N
authors.initials: N
authors.lastname: Yao
authors.forename: A D
authors.initials: AD
authors.lastname: Kwong
authors.forename: L
authors.initials: L
authors.lastname: Ramanathan
authors.forename: H V
authors.initials: HV
authors.lastname: Le
authors.forename: P C
authors.initials: PC
authors.lastname: Weber
mesh_terms: D000251:Adenosine Triphosphatases / Q000378:metabolism; D000595:Amino Acid Sequence; D000818:Animals; D016367:Baculoviridae / Q000235:genetics; D002460:Cell Line; D003001:Cloning, Molecular; D004265:DNA Helicases / Q000378:metabolism; D015870:Gene Expression; D005814:Genes, Viral; D016174:Hepacivirus / Q000201:enzymology* / Q000235:genetics*; D007700:Kinetics; D008969:Molecular Sequence Data; D017433:Protein Structure, Secondary; D011993:Recombinant Fusion Proteins / Q000235:genetics / Q000302:isolation & purification / Q000378:metabolism; D012697:Serine Endopeptidases / Q000235:genetics* / Q000302:isolation & purification / Q000378:metabolism; D018411:Spodoptera; D017361:Viral Nonstructural Proteins / Q000235:genetics* / Q000302:isolation & purification / Q000378:metabolism; D043583:Nucleoside-Triphosphatase; D053487:DEAD-box RNA Helicases; D000085242:Viral Proteases
chemical_list: D000251:Adenosine Triphosphatases; D004265:DNA Helicases; D011993:Recombinant Fusion Proteins; D012697:Serine Endopeptidases; D017361:Viral Nonstructural Proteins; C084422:NS3 protein, hepatitis C virus; D043583:Nucleoside-Triphosphatase; D053487:DEAD-box RNA Helicases; D000085242:Viral Proteases; C093542:NS4 protein, hepatitis C virus