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Extensive mutagenesis of the hepatitis B virus core gene and mapping of mutations that allow capsid formation
M Koschel1, R Thomssen, V Bruss
1Department of Medical Microbiology, University of Göttingen, D-37075 Göttingen, Germany.
Abstract:
We generated a large number of mutations in the hepatitis B virus (HBV) core gene inserted into a bacterial expression vector. The new mutagenesis procedure generated deletions and insertions (as sequence repeats) of various lengths at random positions between M1 and E145 but not substitutions. The R-rich 30-amino-acid C-terminal domain was not analyzed. A total of 50,000 colonies were tested with a polyclonal human serum for the expression of hepatitis B core or e antigen. A total of 110 mutants randomly chosen from 1,500 positive colonies were genotyped. Deletions and insertions were clustered in four regions: D2 to E14, corresponding to the N-terminal loop in a model for the core protein fold (B. Bottcher, S. A. Wynne, and R. A. Crowther, Nature 386:88-91, 1997); V27 to P50 (second loop); L60 to V86 (upper half of the alpha helix forming the N-terminal part of the spike and the tip of the spike); and V124 to L140 (C-terminal part of the C-terminal helix and downstream loop). Deletions or insertions in the remaining parts of the molecule forming the compact center of the fold seemed to destabilize the protein. Of the 110 mutations, 38 allowed capsid formation in Escherichia coli. They mapped exclusively to nonhelical regions of the proposed fold. The mutations form a basis for subsequent analysis of further functions of the HBV core protein in the viral life cycle.
Insights
Researchers created numerous mutations in the hepatitis B virus (HBV) core gene, identifying specific regions prone to deletions and insertions. These mutations are crucial for understanding HBV core protein function and capsid formation.
Area of Science:
- Virology
- Molecular Biology
- Protein Engineering
Background:
- The hepatitis B virus (HBV) core protein plays a vital role in viral replication and capsid assembly.
- Understanding the structural and functional domains of the HBV core protein is essential for developing antiviral strategies.
Purpose of the Study:
- To generate and characterize mutations in the HBV core gene to identify regions critical for protein stability and function.
- To investigate the impact of deletions and insertions on HBV core protein capsid formation in Escherichia coli.
Main Methods:
- Utilized a novel mutagenesis procedure to introduce random deletions and insertions into the HBV core gene.
- Screened 50,000 bacterial colonies for antigen expression and genotyped 110 selected mutants.
- Analyzed mutation locations and their correlation with capsid formation in E. coli.
Main Results:
- Mutations, primarily deletions and insertions, clustered in four specific regions of the HBV core protein.
- Destabilizing effects were observed for mutations in the compact central regions of the protein fold.
- 38 out of 110 mutations facilitated capsid formation, exclusively in nonhelical regions.
Conclusions:
- The identified mutation hotspots provide a foundation for further functional analysis of the HBV core protein.
- Nonhelical regions appear crucial for maintaining protein stability and enabling capsid assembly.
- This study offers insights into the structure-function relationships of the HBV core protein.