Inhibitor-induced structural change in the HCV IRES domain IIa RNA

Area of Science:

• Biochemistry
• Structural Biology
• Virology

Background:

• Hepatitis C virus (HCV) RNA translation initiates via a structured internal ribosomal entry site (IRES).
• A critical feature is a helical bend in domain IIa, positioning domain IIb for efficient ribosome assembly.
• This process involves eIF2-GDP release and 80S ribosome formation.

Purpose of the Study:

• To determine the NMR structure of the IRES domain IIa in complex with a small-molecule inhibitor.
• To elucidate the mechanism by which the inhibitor affects HCV RNA structure and replication.

Main Methods:

• Nuclear Magnetic Resonance (NMR) spectroscopy to determine the structure of the IRES domain IIa-inhibitor complex.
• Molecular dynamics simulations in explicit solvent for refinement and energetic analysis.
• Fluorescence-based binding assays to quantify inhibitor binding affinity.

Main Results:

• The inhibitor binds to domain IIa with comparable affinity for both stereoisomers.
• Inhibitor binding induces a major conformational change, displacing key nucleotides in the bulge region.
• This conformational change eliminates the native helical bend in the IRES RNA.

Conclusions:

• The small-molecule inhibitor disrupts the essential helical structure of the HCV IRES domain IIa.
• This structural disruption provides a clear mechanism for the observed antiviral activity against HCV.
• The findings support the development of IRES-targeting inhibitors for HCV therapy.