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Hepatitis C virus NS3 ATPases/helicases from different genotypes exhibit variations in enzymatic properties
Angela M I Lam1, David Keeney, Patrick Q Eckert
1Department of Biochemistry and Molecular Biology, New York Medical College, Valhalla, New York 10595, USA.
Abstract:
The NS3 ATPase/helicase was isolated and characterized from three different infectious clones of hepatitis C virus (HCV). One helicase was from a genotype that normally responds to therapy (Hel-2a), and the other two were from more resistant genotypes, 1a (Hel-1a) and 1b (Hel-1b). Although the differences among these helicases are generally minor, all three enzymes have distinct properties. Hel-1a is less selective for nucleoside triphosphates, Hel-1b hydrolyzes nucleoside triphosphates less rapidly, and Hel-2a unwinds DNA more rapidly and binds DNA more tightly than the other two enzymes. Unlike related proteins, different nucleic acid sequences stimulate ATP hydrolysis by HCV helicase at different maximum rates and with different apparent efficiencies. This nucleic acid stimulation profile is conserved among the enzymes, but it does not result entirely from differential DNA-binding affinities. Although the amino acid sequences of the three proteins differ by up to 15%, one variant amino acid that is critical for helicase action was identified. NS3 residue 450 is a threonine in Hel-1a and Hel-1b and is an isoleucine in Hel-2a. A mutant Hel-1a with an isoleucine substituted for threonine 450 unwinds DNA more rapidly and binds DNA more tightly than the parent protein.
Insights
Hepatitis C virus (HCV) NS3 ATPase/helicase variants exhibit distinct biochemical properties influencing therapy response. A key amino acid substitution at residue 450 significantly impacts helicase activity and DNA binding.
Area of Science:
- Biochemistry
- Virology
- Molecular Biology
Background:
- The NS3 protein of Hepatitis C virus (HCV) possesses ATPase and helicase activities crucial for viral replication.
- Understanding the biochemical properties of NS3 helicase from different HCV genotypes is important for developing effective antiviral therapies, especially against resistant strains.
Purpose of the Study:
- To isolate and characterize the NS3 ATPase/helicase from three distinct HCV infectious clones representing different genotypes.
- To compare the enzymatic properties of helicases from therapy-responsive and therapy-resistant HCV genotypes.
- To identify specific amino acid residues responsible for functional differences in NS3 helicase activity.
Main Methods:
- Isolation and biochemical characterization of NS3 ATPase/helicase from three HCV infectious clones (genotypes 1a, 1b, and a therapy-responsive genotype).
- Enzyme assays measuring nucleoside triphosphate hydrolysis, DNA unwinding, and DNA binding affinities.
- Site-directed mutagenesis to investigate the role of specific amino acid residues in helicase function.
Main Results:
- Three NS3 helicases (Hel-2a, Hel-1a, Hel-1b) exhibited distinct biochemical properties, including differences in nucleoside triphosphate selectivity and hydrolysis rates.
- Hel-2a showed more rapid DNA unwinding and tighter DNA binding compared to Hel-1a and Hel-1b.
- Different nucleic acid sequences differentially stimulated ATP hydrolysis, with a conserved profile across the enzymes.
- A single amino acid substitution at NS3 residue 450 (Threonine to Isoleucine) in Hel-1a significantly enhanced its DNA unwinding rate and DNA binding affinity.
Conclusions:
- HCV NS3 helicase variants possess unique biochemical characteristics that may contribute to differential responses to antiviral therapy.
- NS3 residue 450 is a critical determinant of helicase activity and DNA binding, offering a potential target for therapeutic intervention.
- The identified functional differences highlight the complexity of HCV NS3 helicase and its interaction with nucleic acids.