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Functional characterization of naturally occurring variants of human hepatitis B virus containing the core internal
1Department of Pathology, Center for Tropical Diseases, University of Texas Medical Branch, Galveston 77555-0609, USA.
Insights
Hepatitis B virus (HBV) core internal deletion (CID) variants are replication defective due to missing core protein. Complementation with wild-type protein rescues HBV replication and particle secretion.
Area of Science:
- Virology
- Hepatology
- Molecular Biology
Background:
- Naturally occurring human hepatitis B virus (HBV) variants with core internal deletion (CID) mutations are prevalent globally.
- Despite frequent detection in patients, the functional characteristics and biological significance of CID variants remain largely unknown.
- Previous studies have focused on sequence analysis, lacking functional characterization of these variants.
Purpose of the Study:
- To functionally characterize two distinct CID variants of HBV identified in patients.
- To elucidate the biological significance of CID mutations in HBV replication and pathogenesis.
- To investigate the potential for complementation of replication-defective CID variants.
Main Methods:
- Identification and isolation of two CID variant strains from HBV-infected patients.
- Replication assays to assess viral propagation.
- Western blot analysis to detect viral proteins (core, precore, e antigen, polymerase).
- Complementation experiments using wild-type HBV core protein.
- Gradient centrifugation to analyze particle assembly and secretion.
Main Results:
- The studied CID variants were replication defective, primarily due to the absence of detectable core protein.
- Precore protein and e antigen were not detected in CID variant infections.
- Polymerase production was unaffected in CID variants.
- The replication defect was successfully rescued by trans-complementation with wild-type core protein.
- Rescued CID variant particles showed proper envelopment and secretion, similar to wild-type HBV Dane particles.
Conclusions:
- CID variants are replication-defective due to a lack of functional core protein, impacting precore and e antigen expression.
- Complementation with wild-type core protein can restore replication and particle formation of CID variants.
- These findings explain the frequent co-occurrence of CID variants with wild-type HBV.
- The study provides insights into the pathogenesis and biological role of CID variants in HBV infection.
Abstract:
Naturally occurring variants of human hepatitis B virus (HBV) containing the core internal deletion (CID) mutation have been found frequently in HBV carriers worldwide. Despite numerous sequence analysis reports of CID variants in patients, in the past decade, CID variants have not been characterized functionally, and thus their biological significance to HBV infection remains unclear. We report here two different CID variants identified from two patients that are replication defective, most likely due to the absence of detectable core protein. In addition, we were unable to detect the presence of the precore protein and e antigen from CID variants. However, the production of polymerase appeared to be normal. The replication defect of the CID variants can be rescued in trans by complementation with wild-type core protein. The rescued CID variant particles, which utilize the wild-type core protein, presumably are enveloped properly since they can be secreted into the medium and band at a position similar to that of mature wild-type Dane particles, as determined by gradient centrifugation analysis. Our results also provide an explanation for the association of CID variants with helper or wild-type HBV in nature. The significance of CID variants in HBV infection and pathogenesis is discussed.