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Importin β Can Bind Hepatitis B Virus Core Protein and Empty Core-Like Particles and Induce Structural Changes
Chao Chen1, Joseph Che-Yen Wang1, Elizabeth E Pierson2
1Department of Molecular and Cellular Biochemistry, Indiana University, Bloomington, Indiana, United States of America.
Plos Pathogens
|August 13, 2016
Summary
Hepatitis B virus (HBV) empty capsids and free core proteins can bind importin beta (Impβ) independently. This interaction can destabilize capsids, suggesting new insights into HBV trafficking and chronic infection mechanisms.
Area of Science:
- Virology
- Structural Biology
- Molecular Biology
Background:
- Hepatitis B virus (HBV) capsids exist in various forms, crucial for viral replication.
- Mature HBV capsids are transported to the nucleus via importin alpha (Impα) and importin beta (Impβ) binding to core protein C-terminal domains (CTDs).
Purpose of the Study:
- To investigate the in vitro interactions between HBV core protein and importins.
- To elucidate the mechanism of Impβ binding to HBV capsids and free core protein.
Main Methods:
- In vitro binding assays.
- Cryo-electron microscopy (Cryo-EM) image reconstructions.
- Single molecule charge-detection mass spectrometry.
Main Results:
- Empty HBV capsids and free core protein bind Impβ without requiring Impα.
- Cryo-EM revealed that internal CTDs can extrude through the capsid to bind Impβ.
- Mass spectrometry indicated complexes with over 90 Impβ molecules, and Cryo-EM showed capsid destabilization and internal density upon excess Impβ incubation.
Conclusions:
- HBV capsids and core proteins exhibit an unexpected ability to bind Impβ independently of Impα.
- Impβ can destabilize HBV capsids, suggesting a role in capsid opening and trafficking.
- These findings have implications for understanding the trafficking of empty capsids and free core protein in chronic HBV infection.
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