The hepatitis C viral NS3 protein is a processive DNA helicase with cofactor enhanced RNA unwinding.
The RNA helicase/protease NS3 plays a central role in the RNA replication of hepatitis C virus (HCV), a cytoplasmic RNA virus that represents a major worldwide health problem. NS3 is, therefore, an important drug target in the effort to combat HCV. Most work has focused on the protease, rather than the helicase, activities of the enzyme. In order to further characterize NS3 helicase activity, we evaluated individual stages of duplex unwinding by NS3 alone and in complex with cofactor NS4A. Despite a putative replicative role in RNA unwinding, we found that NS3 alone is a surprisingly poor helicase on RNA, but that RNA activity is promoted by cofactor NS4A. In contrast, NS3 alone is a highly processive helicase on DNA. Phylogenetic analysis suggests that this robust DNA helicase activity is not vestigial and may have specifically evolved in HCV. Given that HCV has no replicative DNA intermediate, these findings suggest that NS3 may have the capacity to affect host DNA.
Pang
Phillip S
PS
Department of Biochemistry and Molecular Biophysics, Columbia University, New York, NY 10032, USA.
Jankowsky
Eckhard
E
Planet
Paul J
PJ
Pyle
Anna Marie
AM
D001483:Base Sequence; D004247:DNA / Q000378:metabolism*; D004265:DNA Helicases / Q000502:physiology*; D019143:Evolution, Molecular; D016174:Hepacivirus / Q000201:enzymology* / Q000235:genetics; D006801:Humans; D046911:Macromolecular Substances; D008969:Molecular Sequence Data; D010802:Phylogeny; D012367:RNA, Viral / Q000378:metabolism*; D013379:Substrate Specificity; D017361:Viral Nonstructural Proteins / Q000502:physiology*; D012697:Serine Endopeptidases; D043583:Nucleoside-Triphosphatase; D053487:DEAD-box RNA Helicases; D000085242:Viral Proteases
D004247:DNA; D004265:DNA Helicases; D046911:Macromolecular Substances; D012367:RNA, Viral; D017361:Viral Nonstructural Proteins; C084422:NS3 protein, hepatitis C virus; D012697:Serine Endopeptidases; D043583:Nucleoside-Triphosphatase; D053487:DEAD-box RNA Helicases; D000085242:Viral Proteases; C093542:NS4 protein, hepatitis C virus