title: The helicase activity associated with hepatitis C virus nonstructural protein 3 (NS3).
abstract: To assess the RNA helicase activity of hepatitis C virus (HCV) nonstructural protein 3 (NS3), a polypeptide encompassing amino acids 1175 to 1657, which cover only the putative helicase domain, was expressed in Escherichia coli by a pET expression vector. The protein was purified to near homogeneity and assayed for RNA helicase activity in vitro with double-stranded RNA substrates prepared from a multiple cloning sequence and an HCV 5' nontranslated region (5'-NTR) or 3'-NTR. The enzyme acted successfully on substrates containing both 5' and 3' single-stranded regions (standard) or on substrates containing only the 3' single-stranded regions (3'/3') but failed to act on substrates containing only the 5' single-stranded regions (5'/5') or on substrates lacking the single-stranded regions (blunt). These results thus suggest 3' to 5' directionality for HCV RNA helicase activity. However, a 5'/5' substrate derived from the HCV 5'-NTR was also partially unwound by the enzyme, possibly because of unique properties inherent in the 5' single-stranded regions. Gel mobility shift analyses demonstrated that the HCV NS3 helicase could bind to either 5'- or 3'-tailed substrates but not to substrates lacking a single-stranded region, indicating that the polarity of the RNA strand to which the helicase bound was a more important enzymatic activity determinant. In addition to double-stranded RNA substrates, HCV NS3 helicase activity could displace both RNA and DNA oligonucleotides on a DNA template, suggesting that HCV NS3 too was disposed to DNA helicase activity. This study also demonstrated that RNA helicase activity was dramatically inhibited by the single-stranded polynucleotides. Taken altogether, our results indicate that the HCV NS3 helicase is unique among the RNA helicases characterized so far.
authors.affiliation: Graduate Institute of Microbiology, National Taiwan University, Taipei.
authors.forename: C L
authors.initials: CL
authors.lastname: Tai
authors.forename: W K
authors.initials: WK
authors.lastname: Chi
authors.forename: D S
authors.initials: DS
authors.lastname: Chen
authors.forename: L H
authors.initials: LH
authors.lastname: Hwang
mesh_terms: D000818:Animals; D004791:Enzyme Inhibitors / Q000494:pharmacology; D004926:Escherichia coli / Q000378:metabolism; D016174:Hepacivirus / Q000201:enzymology* / Q000235:genetics; D006801:Humans; D011061:Poly A / Q000494:pharmacology; D011068:Poly G / Q000494:pharmacology; D011072:Poly U / Q000494:pharmacology; D020365:RNA Helicases; D012316:RNA Nucleotidyltransferases / Q000037:antagonists & inhibitors / Q000235:genetics / Q000378:metabolism*; D011817:Rabbits; D011993:Recombinant Fusion Proteins / Q000235:genetics / Q000378:metabolism; D013379:Substrate Specificity; D017361:Viral Nonstructural Proteins / Q000037:antagonists & inhibitors / Q000235:genetics / Q000378:metabolism*; D012697:Serine Endopeptidases; D043583:Nucleoside-Triphosphatase; D053487:DEAD-box RNA Helicases; D000085242:Viral Proteases
chemical_list: D004791:Enzyme Inhibitors; D011061:Poly A; D011068:Poly G; D011072:Poly U; D020365:RNA Helicases; D012316:RNA Nucleotidyltransferases; D011993:Recombinant Fusion Proteins; D017361:Viral Nonstructural Proteins; C084422:NS3 protein, hepatitis C virus; D012697:Serine Endopeptidases; D043583:Nucleoside-Triphosphatase; D053487:DEAD-box RNA Helicases; D000085242:Viral Proteases