The nonstructural protein 3 protease/helicase requires an intact protease domain to unwind duplex RNA efficiently.
The nonstructural 3 (NS3) protein encoded by the hepatitis C virus possesses both an N-terminal serine protease activity and a C-terminal 3'-5' helicase activity. This study examines the effects of the protease on the helicase by comparing the enzymatic properties of the full-length NS3 protein with truncated versions in which the protease is either deleted or replaced by a polyhistidine (His tag) or a glutathione S-transferase fusion protein (GST tag). When the NS3 protein lacks the protease domain it unwinds RNA more slowly and does not unwind RNA in the presence of excess nucleic acid that acts as an enzyme trap. Some but not all of the RNA helicase activity can be restored by adding a His tag or GST tag to the N terminus of the truncated helicase, suggesting that the effects of the protease are both specific and nonspecific. Similar but smaller effects are also seen in DNA helicase and translocation assays. While translocating on RNA (or DNA) the full-length protein hydrolyzes ATP more slowly than the truncated protein, suggesting that the protease allows for more efficient ATP usage. Binding assays reveal that the full-length protein assembles on single-stranded DNA as a higher order oligomer than the truncated fragment, and the binding appears to be more cooperative. The data suggest that hepatitis C virus RNA helicase, and therefore viral replication, could be influenced by the rotations of the protease domain which likely occur during polyprotein processing.
Frick
David N
DN
Department of Biochemistry and Molecular Biology, New York Medical College, Valhalla, New York 10595, USA. David_Frick@NYMC.edu
Rypma
Ryan S
RS
Lam
Angela M I
AM
Gu
Baohua
B
D000251:Adenosine Triphosphatases / Q000737:chemistry; D000255:Adenosine Triphosphate / Q000737:chemistry; D000595:Amino Acid Sequence; D004277:DNA, Single-Stranded / Q000737:chemistry; D010450:Endopeptidases / Q000737:chemistry; D017353:Gene Deletion; D005982:Glutathione Transferase / Q000378:metabolism; D006868:Hydrolysis; D007700:Kinetics; D008958:Models, Molecular; D008969:Molecular Sequence Data; D009691:Nucleic Acid Denaturation; D009841:Oligonucleotides / Q000737:chemistry; D011485:Protein Binding; D017434:Protein Structure, Tertiary; D021381:Protein Transport; D012313:RNA / Q000737:chemistry; D020365:RNA Helicases / Q000494:pharmacology; D012330:RNA, Double-Stranded / Q000737:chemistry*; D011993:Recombinant Fusion Proteins / Q000378:metabolism; D011994:Recombinant Proteins / Q000737:chemistry; D012260:Ribonucleases / Q000737:chemistry; D013050:Spectrometry, Fluorescence; D013696:Temperature; D013997:Time Factors; D017361:Viral Nonstructural Proteins / Q000737:chemistry* / Q000378:metabolism; D012697:Serine Endopeptidases; D043583:Nucleoside-Triphosphatase; D053487:DEAD-box RNA Helicases; D000085242:Viral Proteases
D000251:Adenosine Triphosphatases; D000255:Adenosine Triphosphate; D004277:DNA, Single-Stranded; D010450:Endopeptidases; D005982:Glutathione Transferase; D009841:Oligonucleotides; D012313:RNA; D020365:RNA Helicases; D012330:RNA, Double-Stranded; D011993:Recombinant Fusion Proteins; D011994:Recombinant Proteins; D012260:Ribonucleases; D017361:Viral Nonstructural Proteins; C084422:NS3 protein, hepatitis C virus; D012697:Serine Endopeptidases; D043583:Nucleoside-Triphosphatase; D053487:DEAD-box RNA Helicases; D000085242:Viral Proteases