Virus-specific cofactor requirement and chimeric hepatitis C virus/GB virus B nonstructural protein 3

Area of Science:

• Virology
• Molecular Biology
• Biochemistry

Background:

• GB virus B (GBV-B) is a close relative of hepatitis C virus (HCV) and serves as a valuable small monkey model for studying hepatitis.
• The nonstructural protein 3 (NS3) serine protease of GBV-B shares substrate specificity with HCV NS3 protease.
• Understanding the cofactor requirements of GBV-B NS3 protease is crucial for developing anti-HCV therapeutics.

Purpose of the Study:

• To characterize the full-length GBV-B NS3 protein's protease activity and cofactor dependency.
• To compare the cofactor requirements of GBV-B and HCV NS3 proteases.
• To identify the essential regions and residues within the GBV-B NS4A cofactor.

Main Methods:

• In vitro translation of GBV-B substrates.
• Protease activity assays using full-length GBV-B NS3 protein and cofactor peptides.
• Alanine substitution analysis to identify critical residues in NS4A.
• Structural modeling of the GBV-B NS3 protease-NS4A cofactor complex.

Main Results:

• GBV-B NS3 protease activity requires a specific cofactor peptide from the central region of GBV-B NS4A.
• HCV NS3 protease can cleave GBV-B substrates, but requires the HCV NS4A cofactor, indicating shared specificity but distinct cofactor requirements.
• The minimal GBV-B NS4A cofactor region (Phe22-Val36) and essential residues (Val27, Trp31) were identified, showing similarities to HCV NS4A.

Conclusions:

• GBV-B NS3 protease exhibits a strict, virus-specific cofactor requirement, despite sharing substrate specificity with HCV NS3 protease.
• GBV-B and HCV may employ similar structural strategies for NS3 protease activation and regulation.
• The findings support the use of GBV-B as a surrogate model for anti-HCV drug development and provide insights into protease-cofactor interactions.