An Optimized Hepatitis C Virus E2 Glycoprotein Core Adopts a Functional Homodimer That Efficiently Blocks Virus Entry

Area of Science:

• Virology and Immunology
• Structural Biology
• Vaccine Development

Background:

• Hepatitis C virus (HCV) infection is a global health concern with no available vaccine.
• The HCV E2 envelope glycoprotein is a primary target for neutralizing antibodies and vaccine design.
• E2 exhibits significant amino acid variability in hypervariable regions (HVR1, HVR2) and the intergenotypic variable region (igVR), contributing to immune evasion.

Purpose of the Study:

• To investigate the role of the three variable regions (HVR1, HVR2, igVR) in the folding and function of the HCV E2 ectodomain.
• To understand how these variable regions influence the binding of E2 to the host cell receptor CD81.
• To explore the impact of variable regions on the formation of functional E2 homodimers.

Main Methods:

• Characterization of a recombinant E2 ectodomain fragment (rE2) with and without its variable regions.
• Assessment of CD81 binding kinetics following deletion of variable regions.
• Analysis of E2 homodimer formation in the presence and absence of variable motifs.

Main Results:

• Removal of E2 variable regions accelerated binding to the CD81 receptor.
• Simultaneous deletion of HVR2 and igVR was necessary to preserve wild-type CD81-binding characteristics.
• Deletion of variable regions restored the ability of rE2 to form a functional homodimer.

Conclusions:

• The variable regions of HCV E2 modulate the ectodomain's interaction with CD81 and influence higher-order assembly.
• The rE2 core structure provides insights into the role of variable motifs in E2 ectodomain assembly.
• Findings have implications for understanding the E1E2 glycoprotein structure on the virion surface and for universal HCV vaccine design.