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Sikandar M, Shah PT, Xing L. Genetic diversity and phylogeographic dynamics of avihepadnavirus: a comprehensive full-length genomic view. Front Vet Sci 2024; 11:1385033. [PMID: 38756526 PMCID: PMC11096447 DOI: 10.3389/fvets.2024.1385033] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/11/2024] [Accepted: 04/19/2024] [Indexed: 05/18/2024] Open
Abstract
Avihepadnavirus is a genus of the Hepadnaviridae family. It primarily infects birds, including species of duck, geese, cranes, storks, and herons etc. To understand the genetic relatedness and evolutionary diversity among avihepadnavirus strains, a comprehensive analysis of the available 136 full-length viral genomes (n = 136) was conducted. The genomes were classified into two major genotypes, i.e., GI and GII. GI viruses were further classified into 8 sub-genotypes including DHBV-I (duck hepatitis B virus-I), DHBV-II (Snow goose Hepatitis B, SGHBV), DHBV-III, RGHBV (rossgoose hepatitis B virus), CHBV (crane hepatitis B virus), THBV (Tinamou hepatitis B virus), STHBV (stork hepatitis B virus), and HHBV (Heron hepatitis B virus). DHBV-I contains two sub-clades DHBV-Ia and DHBV-Ib. Parrot hepatitis B virus (PHBV) stains fall into GII which appeared as a separate phylogenetic branch/clade. All the subtypes of viruses in GI and GII seem to be genetically connected with viruses of DHBV-I by multiple mutational steps in phylogeographic analysis. Furthermore, 16 potential recombination events among different sub-genotypes in GI and one in GII were identified, but none of which is inter-genotypic between GI and GII. Overall, the results provide a whole picture of the genetic relatedness of avihepadnavirus strains, which may assist in the surveillance of virus spreading.
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Affiliation(s)
| | - Pir Tariq Shah
- Faculty of Medicine, School of Biomedical Engineering, Dalian University of Technology, Dalian, China
- Shandong Laboratory of Yantai Drug Discovery, Bohai Rim Advanced Research Institute for Drug Discovery, Yantai, China
| | - Li Xing
- Institute of Biomedical Sciences, Shanxi University, Taiyuan, China
- Shanxi Provincial Key Laboratory of Medical Molecular Cell Biology, Shanxi University, Taiyuan, China
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2
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Pfister S, Rabl J, Wiegand T, Mattei S, Malär AA, Lecoq L, Seitz S, Bartenschlager R, Böckmann A, Nassal M, Boehringer D, Meier BH. Structural conservation of HBV-like capsid proteins over hundreds of millions of years despite the shift from non-enveloped to enveloped life-style. Nat Commun 2023; 14:1574. [PMID: 36949039 PMCID: PMC10033635 DOI: 10.1038/s41467-023-37068-w] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Grants] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/15/2022] [Accepted: 03/02/2023] [Indexed: 03/24/2023] Open
Abstract
The discovery of nackednaviruses provided new insight into the evolutionary history of the hepatitis B virus (HBV): The common ancestor of HBV and nackednaviruses was non-enveloped and while HBV acquired an envelope during evolution, nackednaviruses remained non-enveloped. We report the capsid structure of the African cichlid nackednavirus (ACNDV), determined by cryo-EM at 3.7 Å resolution. This enables direct comparison with the known capsid structures of HBV and duck HBV, prototypic representatives of the mammalian and avian lineages of the enveloped Hepadnaviridae, respectively. The sequence identity with HBV is 24% and both the ACNDV capsid protein fold and the capsid architecture are very similar to those of the Hepadnaviridae and HBV in particular. Acquisition of the hepadnaviral envelope was thus not accompanied by a major change in capsid structure. Dynamic residues at the spike tip are tentatively assigned by solid-state NMR, while the C-terminal domain is invisible due to dynamics. Solid-state NMR characterization of the capsid structure reveals few conformational differences between the quasi-equivalent subunits of the ACNDV capsid and an overall higher capsid structural disorder compared to HBV. Despite these differences, the capsids of ACNDV and HBV are structurally highly similar despite the 400 million years since their separation.
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Affiliation(s)
- Sara Pfister
- Physical Chemistry, ETH Zurich, 8093, Zurich, Switzerland
| | - Julius Rabl
- Cryo-EM Knowledge hub, ETH Zurich, 8093, Zurich, Switzerland
| | - Thomas Wiegand
- Physical Chemistry, ETH Zurich, 8093, Zurich, Switzerland
- Max-Planck-Institute for Chemical Energy Conversion, Stiftstr. 34-36, 45470, Mülheim an der Ruhr, Germany
- Institute of Technical and Macromolecular Chemistry, RWTH Aachen University, Worringerweg 2, 52074, Aachen, Germany
| | - Simone Mattei
- EMBL Imaging Centre, European Molecular Biology Laboratory, EMBL Heidelberg, 69117, Heidelberg, Germany
| | | | - Lauriane Lecoq
- Molecular Microbiology and Structural Biochemistry, UMR 5086 CNRS, Université de Lyon, 69367, Lyon, France
| | - Stefan Seitz
- Division of Virus-Associated Carcinogenesis (F170), German Cancer Research Center (DKFZ), 69120, Heidelberg, Germany
- Department of Infectious Diseases, Molecular Virology, University of Heidelberg, 69120, Heidelberg, Germany
| | - Ralf Bartenschlager
- Division of Virus-Associated Carcinogenesis (F170), German Cancer Research Center (DKFZ), 69120, Heidelberg, Germany
- Department of Infectious Diseases, Molecular Virology, University of Heidelberg, 69120, Heidelberg, Germany
| | - Anja Böckmann
- Molecular Microbiology and Structural Biochemistry, UMR 5086 CNRS, Université de Lyon, 69367, Lyon, France.
| | - Michael Nassal
- Department of Medicine II / Molecular Biology, University of Freiburg, Freiburg im Breisgau, Germany.
| | | | - Beat H Meier
- Physical Chemistry, ETH Zurich, 8093, Zurich, Switzerland.
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3
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Xi J, Cui X, Liu K, Liu H, Wang J, Hu J. Region-Specific Hepatitis B Virus Genome Exposure from Nucleocapsid Modulated by Capsid Linker Sequence and Inhibitor: Implications for Uncoating. J Virol 2022; 96:e0039922. [PMID: 35389266 PMCID: PMC9044944 DOI: 10.1128/jvi.00399-22] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/07/2022] [Accepted: 03/09/2022] [Indexed: 11/20/2022] Open
Abstract
Hepatitis B virus (HBV) contains a partially double-stranded, relaxed circular (RC) DNA genome synthesized within a nucleocapsid (NC) in the host cell cytoplasm. The release of RC DNA from the NC, in an ill-defined process called uncoating, to the nucleus is required for its conversion to the covalently closed circular (CCC) DNA, the viral episome serving as the transcriptional template for all viral RNAs necessary for replication and, thus, essential for establishing and sustaining viral infection. In efforts to better understand uncoating, we analyzed HBV core (HBc) mutants that show various levels of nuclear CCC DNA but little to no cytoplasmic RC DNA. We found that RC DNA could be synthesized by these mutants outside the cell, but in contrast to the wild type (wt), the mutant NCs were unable to protect RC DNA from digestion by the endogenous nuclease(s) in cellular lysates or exogenous DNase. Subcellular fractionation suggested that the major RC DNA-degrading activity was membrane associated. Digestion with sequence-specific and nonspecific DNases revealed the exposure of specific regions of RC DNA from the mutant NC. Similarly, treatment of wt NCs with a core inhibitor known to increase CCC DNA by affecting uncoating also led to region-specific exposure of RC DNA. Furthermore, a subpopulation of untreated wild type (wt) mature NCs showed site-specific exposure of RC DNA as well. Competition between RC DNA degradation and its conversion to CCC DNA during NC uncoating thus likely plays an important role in the establishment and persistence of HBV infection and has implications for the development of capsid-targeted antivirals. IMPORTANCE Disassembly of the hepatitis B virus (HBV) nucleocapsid (NC) to release its genomic DNA, in an ill-understood process called uncoating, is required to form the viral nuclear episome in the host cell nucleus, a viral DNA essential for establishing and sustaining HBV infection. The elimination of the HBV nuclear episome remains the holy grail for the development of an HBV cure. We report here that the HBV genomic DNA is exposed in a region-specific manner during uncoating, which is enhanced by mutations of the capsid protein and a capsid-targeted antiviral compound. The exposure of the viral genome can result in its rapid degradation or, alternatively, can enhance the formation of the nuclear episome, thus having a major impact on HBV infection and persistence. These results are thus important for understanding fundamental mechanisms of HBV replication and persistence and for the ongoing pursuit of an HBV cure.
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Affiliation(s)
- Ji Xi
- Department of Microbiology and Immunology, The Pennsylvania State University College of Medicine, Hershey, Pennsylvania, USA
| | - Xiuji Cui
- Department of Microbiology and Immunology, The Pennsylvania State University College of Medicine, Hershey, Pennsylvania, USA
| | - Kuancheng Liu
- Department of Microbiology and Immunology, The Pennsylvania State University College of Medicine, Hershey, Pennsylvania, USA
| | - Haitao Liu
- Department of Microbiology and Immunology, The Pennsylvania State University College of Medicine, Hershey, Pennsylvania, USA
| | - Joseph Wang
- Department of Microbiology and Immunology, The Pennsylvania State University College of Medicine, Hershey, Pennsylvania, USA
| | - Jianming Hu
- Department of Microbiology and Immunology, The Pennsylvania State University College of Medicine, Hershey, Pennsylvania, USA
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4
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Liu K, Luckenbaugh L, Ning X, Xi J, Hu J. Multiple roles of core protein linker in hepatitis B virus replication. PLoS Pathog 2018; 14:e1007085. [PMID: 29782550 PMCID: PMC5983865 DOI: 10.1371/journal.ppat.1007085] [Citation(s) in RCA: 34] [Impact Index Per Article: 5.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/16/2018] [Revised: 06/01/2018] [Accepted: 05/09/2018] [Indexed: 12/16/2022] Open
Abstract
Hepatitis B virus (HBV) core protein (HBc) contains an N-terminal domain (NTD, assembly domain) and a C-terminal domain (CTD), which are linked by a flexible linker region. HBc plays multiple essential roles in viral replication, including capsid assembly, packaging of the viral pregenomic RNA (pgRNA) into nucleocapsids, viral reverse transcription that converts pgRNA to the genomic DNA, and secretion of DNA-containing (complete) virions or genome-free (empty) virions. The HBc linker is generally assumed to act merely as a spacer between NTD and CTD but some results suggest that the linker may affect NTD assembly. To determine its role in viral replication, we have made a number of deletion and substitution mutants in the linker region, in either the presence or absence of CTD, and tested their abilities to support capsid assembly and viral replication in human cells. Our results indicate that the linker could indeed impede NTD assembly in the absence of CTD, which could be partially relieved by partial linker deletion. In contrast, when CTD was present, the linker deletions or substitutions did not affect capsid assembly. Deletion of the entire linker or its C-terminal part resulted in a partial defect in pgRNA packaging and severely impaired viral DNA synthesis. In contrast, deletion of the N-terminal part of the linker, or substitutions of the linker sequence, had little to no effect on RNA packaging or first-strand DNA synthesis. However, the N-terminal linker deletion and two linker substitution mutants were defective in the production of mature double-stranded viral DNA. Secretion of empty virions was blocked by all the linker deletions and substitutions tested. In particular, a conservative linker substitution that allowed mature viral DNA synthesis and secretion of complete virions severely impaired the secretion of empty virions, thus increasing the ratio of complete to empty virions that were secreted. Together, these results demonstrate that the HBc linker region plays critical and complex roles at multiple stages of HBV replication. The hepatitis B virus (HBV) is a major human pathogen that infects hundreds of millions of people worldwide and represents a major cause of viral hepatitis, liver cirrhosis, and liver cancer. The HBV capsid protein (HBc) plays multiple roles in the viral life cycle and has emerged recently as a major target for developing antiviral therapies against HBV infection. HBc is divided into three separate regions, an N-terminal domain (NTD) responsible for capsid assembly, a C-terminal domain (CTD) that plays critical roles in the specific packaging of the viral pregenomic RNA (pgRNA) into replication-competent nucleocapsids and the subsequent reverse transcription of the pgRNA into the viral genomic DNA, and a linker region between the NTD and CTD. In contrast to the prevailing assumption that the linker merely serves to connect the NTD and CTD, we have discovered here that it plays a critical role in almost every stage of HBV replication. The linker likely exerted its pleiotropic effects via affecting the NTD and CTD as well as via direct interactions with other viral factors independent of the NTD or CTD. Our results thus not only deepen understanding of HBc structure and functions but also implicate the linker as a potential novel target for antiviral development against HBV infection.
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Affiliation(s)
- Kuancheng Liu
- Department of Microbiology and Immunology, Penn State University College of Medicine, Hershey, PA, United States of America
- College of Life Sciences, Zhejiang Sci-Tech University, Hangzhou, China
| | - Laurie Luckenbaugh
- Department of Microbiology and Immunology, Penn State University College of Medicine, Hershey, PA, United States of America
| | - Xiaojun Ning
- Department of Microbiology and Immunology, Penn State University College of Medicine, Hershey, PA, United States of America
| | - Ji Xi
- Department of Microbiology and Immunology, Penn State University College of Medicine, Hershey, PA, United States of America
| | - Jianming Hu
- Department of Microbiology and Immunology, Penn State University College of Medicine, Hershey, PA, United States of America
- * E-mail:
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Guo F, Zhao Q, Sheraz M, Cheng J, Qi Y, Su Q, Cuconati A, Wei L, Du Y, Li W, Chang J, Guo JT. HBV core protein allosteric modulators differentially alter cccDNA biosynthesis from de novo infection and intracellular amplification pathways. PLoS Pathog 2017; 13:e1006658. [PMID: 28945802 PMCID: PMC5629035 DOI: 10.1371/journal.ppat.1006658] [Citation(s) in RCA: 89] [Impact Index Per Article: 12.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/27/2017] [Revised: 10/05/2017] [Accepted: 09/19/2017] [Indexed: 02/06/2023] Open
Abstract
Hepatitis B virus (HBV) core protein assembles viral pre-genomic (pg) RNA and DNA polymerase into nucleocapsids for reverse transcriptional DNA replication to take place. Several chemotypes of small molecules, including heteroaryldihydropyrimidines (HAPs) and sulfamoylbenzamides (SBAs), have been discovered to allosterically modulate core protein structure and consequentially alter the kinetics and pathway of core protein assembly, resulting in formation of irregularly-shaped core protein aggregates or “empty” capsids devoid of pre-genomic RNA and viral DNA polymerase. Interestingly, in addition to inhibiting nucleocapsid assembly and subsequent viral genome replication, we have now demonstrated that HAPs and SBAs differentially modulate the biosynthesis of covalently closed circular (ccc) DNA from de novo infection and intracellular amplification pathways by inducing disassembly of nucleocapsids derived from virions as well as double-stranded DNA-containing progeny nucleocapsids in the cytoplasm. Specifically, the mistimed cuing of nucleocapsid uncoating prevents cccDNA formation during de novo infection of hepatocytes, while transiently accelerating cccDNA synthesis from cytoplasmic progeny nucleocapsids. Our studies indicate that elongation of positive-stranded DNA induces structural changes of nucleocapsids, which confers ability of mature nucleocapsids to bind CpAMs and triggers its disassembly. Understanding the molecular mechanism underlying the dual effects of the core protein allosteric modulators on nucleocapsid assembly and disassembly will facilitate the discovery of novel core protein-targeting antiviral agents that can more efficiently suppress cccDNA synthesis and cure chronic hepatitis B. Persistent HBV infection relies on stable maintenance of a nuclear episomal viral genome called covalently closed circular (ccc) DNA, the sole transcriptional template supporting viral replication. The currently available antiviral therapeutics fail to cure chronic HBV infection due to their failure to eradicate or inactivate cccDNA. In addition to packaging viral pregenomic (pg) RNA and DNA polymerase complex into nucleocapsids for reverse transcriptional DNA replication to take place, HBV core protein also participates in and regulates virion particle assembly, capsid uncoating and cccDNA formation. We report herein an intriguing observation that selected core protein allosteric modulators not only inhibit nucleocapsid assembly, but can also act on assembled, nucleus-bound nucleocapsids to promote their uncoating and consequentially interfere with cccDNA biosynthesis. This finding establishes molecular basis for development of novel core protein targeting antiviral agents with improved efficacy of suppressing cccDNA synthesis and curing chronic HBV infection.
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Affiliation(s)
- Fang Guo
- Baruch S. Blumberg Institute, Doylestown, Pennsylvania, United States of America
| | - Qiong Zhao
- Baruch S. Blumberg Institute, Doylestown, Pennsylvania, United States of America
| | - Muhammad Sheraz
- Microbiology and Immunology graduate program, Drexel University College of Medicine, Philadelphia, Pennsylvania, United States of America
| | - Junjun Cheng
- Baruch S. Blumberg Institute, Doylestown, Pennsylvania, United States of America
| | - Yonghe Qi
- National Institute of Biological Sciences, Beijing, China
| | - Qing Su
- Baruch S. Blumberg Institute, Doylestown, Pennsylvania, United States of America
| | - Andrea Cuconati
- Arbutus Biopharma Inc., Doylestown, Pennsylvania, United States of America
| | - Lai Wei
- Hepatology Institute, Peking University People’s Hospital, Beijing, China
| | - Yanming Du
- Baruch S. Blumberg Institute, Doylestown, Pennsylvania, United States of America
| | - Wenhui Li
- National Institute of Biological Sciences, Beijing, China
| | - Jinhong Chang
- Baruch S. Blumberg Institute, Doylestown, Pennsylvania, United States of America
- * E-mail: (JTG); (JC)
| | - Ju-Tao Guo
- Baruch S. Blumberg Institute, Doylestown, Pennsylvania, United States of America
- * E-mail: (JTG); (JC)
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6
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Alteration of Mature Nucleocapsid and Enhancement of Covalently Closed Circular DNA Formation by Hepatitis B Virus Core Mutants Defective in Complete-Virion Formation. J Virol 2015. [PMID: 26202253 DOI: 10.1128/jvi.01481-15] [Citation(s) in RCA: 41] [Impact Index Per Article: 4.6] [Reference Citation Analysis] [Abstract] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/14/2022] Open
Abstract
UNLABELLED Assembly of hepatitis B virus (HBV) begins with packaging of the pregenomic RNA (pgRNA) into immature nucleocapsids (NC), which are converted to mature NCs containing the genomic relaxed circular (RC) DNA as a result of reverse transcription. Mature NCs have two alternative fates: (i) envelopment by viral envelope proteins, leading to secretion extracellularly as virions, or (ii) disassembly (uncoating) to deliver their RC DNA content into the host cell nucleus for conversion to the covalently closed circular (CCC) DNA, the template for viral transcription. How these two alternative fates are regulated remains to be better understood. The NC shell is composed of multiple copies of a single viral protein, the HBV core (HBc) protein. HBc mutations located on the surface of NC have been identified that allow NC maturation but block its envelopment. The potential effects of some of these mutations on NC uncoating and CCC DNA formation have been analyzed by transfecting HBV replication constructs into hepatoma cells. All envelopment-defective HBc mutations tested were competent for CCC DNA formation, indicating that core functions in envelopment and uncoating/nuclear delivery of RC DNA were genetically separable. Some of the envelopment-defective HBc mutations were found to alter specifically the integrity of mature, but not immature, NCs such that RC DNA became susceptible to nuclease digestion. Furthermore, CCC DNA formation could be enhanced by NC surface mutations that did or did not significantly affect mature NC integrity, indicating that the NC surface residues may be closely involved in NC uncoating and/or nuclear delivery of RC DNA. IMPORTANCE Hepatitis B virus (HBV) infection is a major health issue worldwide. HBV assembly begins with the packaging into immature nucleocapsids (NCs) of a viral RNA pregenome, which is converted to the DNA genome in mature NCs. Mature NCs are then selected for envelopment and secretion as complete-virion particles or, alternatively, can deliver their DNA to the host cell nucleus to maintain the viral genome as nuclear episomes, which are the basis for virus persistence. Previous studies have identified mutations on the capsid surface that selectively block NC envelopment without affecting NC maturation. We have now discovered that some of the same mutations result in preferential alteration of mature NCs and increased viral nuclear episomes. These findings provide important new insights into the regulation of the two alternative fates of mature NCs and suggest new ways to perturb viral persistence by manipulating levels of viral nuclear episomes.
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7
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Maturation-associated destabilization of hepatitis B virus nucleocapsid. J Virol 2013; 87:11494-503. [PMID: 23966388 DOI: 10.1128/jvi.01912-13] [Citation(s) in RCA: 65] [Impact Index Per Article: 5.9] [Reference Citation Analysis] [Abstract] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/06/2023] Open
Abstract
The mature nucleocapsid (NC) of hepatitis B virus containing the relaxed circular (RC) DNA genome can be secreted extracellularly as virions after envelopment with the viral surface proteins or, alternatively, can be disassembled to release RC DNA (i.e., uncoating) into the host cell nucleus to form the covalently closed circular (CCC) DNA, which sustains viral replication and persistence. In contrast, immature NCs containing the viral single-stranded DNA or the pregenomic RNA are incompetent for either envelopment or uncoating. Little is currently known about how mature NCs, and not the immature ones, are specifically selected for these processes. Here, we have carried out a biochemical analysis of the different NC populations upon their separation through sucrose gradient centrifugation. We have found that the maturation of NCs is associated with their destabilization, manifested as increased protease and nuclease sensitivity, altered sedimentation during sucrose gradient centrifugation, and retarded mobility during native agarose gel electrophoresis. Also, three distinct populations of intracellular mature NCs could be differentiated based on these characteristics. Furthermore, mature NCs generated in vitro under cell-free conditions acquired similar properties. These results have thus revealed significant structural changes associated with NC maturation that likely play a role in the selective uncoating of the mature NC for CCC DNA formation and/or its preferential envelopment for virion secretion.
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Jung J, Kim HY, Kim T, Shin BH, Park GS, Park S, Chwae YJ, Shin HJ, Kim K. C-terminal substitution of HBV core proteins with those from DHBV reveals that arginine-rich 167RRRSQSPRR175 domain is critical for HBV replication. PLoS One 2012; 7:e41087. [PMID: 22911745 PMCID: PMC3401125 DOI: 10.1371/journal.pone.0041087] [Citation(s) in RCA: 11] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/14/2012] [Accepted: 06/18/2012] [Indexed: 12/21/2022] Open
Abstract
To investigate the contributions of carboxyl-terminal nucleic acid binding domain of HBV core (C) protein for hepatitis B virus (HBV) replication, chimeric HBV C proteins were generated by substituting varying lengths of the carboxyl-terminus of duck hepatitis B virus (DHBV) C protein for the corresponding regions of HBV C protein. All chimeric C proteins formed core particles. A chimeric C protein with 221–262 amino acids of DHBV C protein, in place of 146–185 amino acids of the HBV C protein, supported HBV pregenomic RNA (pgRNA) encapsidation and DNA synthesis: 40% amino acid sequence identity or 45% homology in the nucleic-acid binding domain of HBV C protein was sufficient for pgRNA encapsidation and DNA synthesis, although we predominantly detected spliced DNA. A chimeric C protein with 221–241 and 251–262 amino acids of DHBV C, in place of HBV C 146–166 and 176–185 amino acids, respectively, could rescue full-length DNA synthesis. However, a reciprocal C chimera with 242–250 of DHBV C (242RAGSPLPRS250) introduced in place of 167–175 of HBV C (167RRRSQSPRR175) significantly decreased pgRNA encapsidation and DNA synthesis, and full-length DNA was not detected, demonstrating that the arginine-rich 167RRRSQSPRR175 domain may be critical for efficient viral replication. Five amino acids differing between viral species (underlined above) were tested for replication rescue; R169 and R175 were found to be important.
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Affiliation(s)
- Jaesung Jung
- Department of Microbiology, Ajou University School of Medicine, Woncheon-dong, Suwon, Korea
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9
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Serine phosphoacceptor sites within the core protein of hepatitis B virus contribute to genome replication pleiotropically. PLoS One 2011; 6:e17202. [PMID: 21358805 PMCID: PMC3039676 DOI: 10.1371/journal.pone.0017202] [Citation(s) in RCA: 46] [Impact Index Per Article: 3.5] [Reference Citation Analysis] [Abstract] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/28/2010] [Accepted: 01/25/2011] [Indexed: 01/29/2023] Open
Abstract
The core protein of hepatitis B virus can be phosphorylated at serines 155, 162, and 170. The contribution of these serine residues to DNA synthesis was investigated. Core protein mutants were generated in which each serine was replaced with either alanine or aspartate. Aspartates can mimic constitutively phosphorylated serines while alanines can mimic constitutively dephosphorylated serines. The ability of these mutants to carry out each step of DNA synthesis was determined. Alanine substitutions decreased the efficiency of minus-strand DNA elongation, primer translocation, circularization, and plus-strand DNA elongation. Aspartate substitutions also reduced the efficiency of these steps, but the magnitude of the reduction was less. Our findings suggest that phosphorylated serines are required for multiple steps during DNA synthesis. It has been proposed that generation of mature DNA requires serine dephosphorylation. Our results suggest that completion of rcDNA synthesis requires phosphorylated serines.
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The arginine clusters of the carboxy-terminal domain of the core protein of hepatitis B virus make pleiotropic contributions to genome replication. J Virol 2010; 85:1298-309. [PMID: 21084467 DOI: 10.1128/jvi.01957-10] [Citation(s) in RCA: 63] [Impact Index Per Article: 4.5] [Reference Citation Analysis] [Abstract] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/23/2023] Open
Abstract
The carboxy-terminal domain (CTD) of the core protein of hepatitis B virus is not necessary for capsid assembly. However, the CTD does contribute to encapsidation of pregenomic RNA (pgRNA). The contribution of the CTD to DNA synthesis is less clear. This is the case because some mutations within the CTD increase the proportion of spliced RNA to pgRNA that are encapsidated and reverse transcribed. The CTD contains four clusters of consecutive arginine residues. The contributions of the individual arginine clusters to genome replication are unknown. We analyzed core protein variants in which the individual arginine clusters were substituted with either alanine or lysine residues. We developed assays to analyze these variants at specific steps throughout genome replication. We used a replication template that was not spliced in order to study the replication of only pgRNA. We found that alanine substitutions caused defects at both early and late steps in genome replication. Lysine substitutions also caused defects, but primarily during later steps. These findings demonstrate that the CTD contributes to DNA synthesis pleiotropically and that preserving the charge within the CTD is not sufficient to preserve function.
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Zhou F, Xu Y. cBar: a computer program to distinguish plasmid-derived from chromosome-derived sequence fragments in metagenomics data. ACTA ACUST UNITED AC 2010; 26:2051-2. [PMID: 20538725 PMCID: PMC2916713 DOI: 10.1093/bioinformatics/btq299] [Citation(s) in RCA: 79] [Impact Index Per Article: 5.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/23/2022]
Abstract
Summary: Huge amount of metagenomic sequence data have been produced as a result of the rapidly increasing efforts worldwide in studying microbial communities as a whole. Most, if not all, sequenced metagenomes are complex mixtures of chromosomal and plasmid sequence fragments from multiple organisms, possibly from different kingdoms. Computational methods for prediction of genomic elements such as genes are significantly different for chromosomes and plasmids, hence raising the need for separation of chromosomal from plasmid sequences in a metagenome. We present a program for classification of a metagenome set into chromosomal and plasmid sequences, based on their distinguishing pentamer frequencies. On a large training set consisting of all the sequenced prokaryotic chromosomes and plasmids, the program achieves ∼92% in classification accuracy. On a large set of simulated metagenomes with sequence lengths ranging from 300 bp to 100 kbp, the program has classification accuracy from 64.45% to 88.75%. On a large independent test set, the program achieves 88.29% classification accuracy. Availability: The program has been implemented as a standalone prediction program, cBar, which is available at http://csbl.bmb.uga.edu/∼ffzhou/cBar Contact:xyn@bmb.uga.edu Supplementary information:Supplementary data are available at Bioinformatics online.
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Affiliation(s)
- Fengfeng Zhou
- Department of Biochemistry and Molecular Biology, University of Georgia, Athens, GA 30602, USA
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12
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Testing the balanced electrostatic interaction hypothesis of hepatitis B virus DNA synthesis by using an in vivo charge rebalance approach. J Virol 2009; 84:2340-51. [PMID: 20015989 DOI: 10.1128/jvi.01666-09] [Citation(s) in RCA: 42] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [Abstract] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/04/2023] Open
Abstract
Previously, a charge balance hypothesis was proposed to explain hepatitis B virus (HBV) capsid stability, assembly, RNA encapsidation, and DNA replication. This hypothesis emphasized the importance of a balanced electrostatic interaction between the positive charge from the arginine-rich domain (ARD) of the core protein (HBc) and the negative charge from the encapsidated nucleic acid. It remains unclear if any of the negative charge involved in this electrostatic interaction could come from the HBc protein per se, in addition to the encapsidated nucleic acid. HBc ARD IV mutant 173GG and ARD II mutant 173RR/R157A/R158A are arginine deficient and replication defective. Not surprisingly, the replication defect of ARD IV mutant 173GG can be rescued by restoring positively charged amino acids at the adjacent positions 174 and 175. However, most interestingly, it can be at least partially rescued by reducing negatively charged residues in the assembly domain, such as by glutamic acid-to-alanine (E-to-A) substitutions at position 46 or 117 and to a much lesser extent at position 113. Similar results were obtained for ARD II mutant 173RR/R157A/R158A. These amino acids are located on the inner surfaces of HBc icosahedral particles, and their acidic side chains point toward the capsid interior. For HBV DNA synthesis, the relative amount of positive versus negative charge in the electrostatic interactions is more important than the absolute amount of positive or negative charge. These results support the concept that balanced electrostatic interaction is important during the viral life cycle.
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13
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Testing an electrostatic interaction hypothesis of hepatitis B virus capsid stability by using an in vitro capsid disassembly/reassembly system. J Virol 2009; 83:10616-26. [PMID: 19656897 DOI: 10.1128/jvi.00749-09] [Citation(s) in RCA: 51] [Impact Index Per Article: 3.4] [Reference Citation Analysis] [Abstract] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/08/2023] Open
Abstract
To test a previously coined "charge balance hypothesis" of human hepatitis B virus (HBV) capsid stability, we established an in vitro disassembly and reassembly system using bacterially expressed HBV capsids. Capsid disassembly can be induced by micrococcal nuclease digestion of encapsidated RNA. HBV core protein (HBc) mutants containing various amounts of arginine were constructed by serial truncations at the C terminus. Capsids containing smaller amounts of arginine (HBc 149, 154, and 157) remained intact after micrococcal nuclease digestion by native gel electrophoresis. Capsids containing larger amounts of arginine (HBc 159, 164, 169, and 171) exhibited reduced and more diffuse banding intensity and slightly upshifted mobility (HBc 159 and 164). Capsids containing the largest amounts of arginine (HBc 173, 175, and 183), as well as HBc 167, exhibited no detectable banding signal, indicating loss of capsid integrity or stability. Interestingly, capsid reassembly can be induced by polyanions, including oligonucleotides, poly-glutamic acid, and nonbiological polymer (polyacrylic acid). In contrast, polycations (polylysine and polyethylenimine) and low-molecular-weight anions (inositol triphosphate) induced no capsid reassembly. Results obtained by gel assay were confirmed by electron microscopy. Reassembled capsids comigrated with undigested parental capsids on agarose gels and cosedimented with undigested capsids by sucrose gradient ultracentrifugation. Taken together, the results indicate that HBV capsid assembly and integrity depend on polyanions, which probably can help minimize intersubunit charge repulsion caused mainly by arginine-rich domain III or IV in close contact. The exact structure of polyanions is not important for in vitro capsid reassembly. A large amount of independent experimental evidence for this newly coined "electrostatic interaction hypothesis" is discussed.
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14
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Li K, Zoulim F, Pichoud C, Kwei K, Villet S, Wands J, Li J, Tong S. Critical role of the 36-nucleotide insertion in hepatitis B virus genotype G in core protein expression, genome replication, and virion secretion. J Virol 2007; 81:9202-15. [PMID: 17567705 PMCID: PMC1951435 DOI: 10.1128/jvi.00390-07] [Citation(s) in RCA: 34] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/23/2007] [Accepted: 05/31/2007] [Indexed: 12/21/2022] Open
Abstract
Frequent coinfection of hepatitis B virus genotype G with genotype A suggests that genotype G may require genotype A for replication or transmission. In this regard, genotype G is unique in having a 12-amino-acid extension in the core protein due to a 36-nucleotide insertion near the core gene translation initiation codon. The insertion alters base pairing in the lower stem of the pregenome encapsidation signal, which harbors the core gene initiator, and thus has the potential to affect both core protein translation and pregenomic RNA encapsidation. Genotype G is also unusual for possessing two nonsense mutations in the precore region, which together with the core gene encode a secreted nonstructural protein called hepatitis B e antigen (HBeAg). We found that genotype G clones were indeed incapable of HBeAg expression but were competent in RNA transcription, genome replication, and virion secretion. Interestingly, the 36-nucleotide insertion markedly increased the level of core protein, which was achieved at the level of protein translation but did not involve alteration in the mRNA level. Consequently, the variant core protein was readily detectable in patient blood. The 12-amino-acid insertion also enhanced the genome maturity of secreted virus particles, possibly through less efficient envelopment of core particles. Cotransfection of genotypes G and A did not lead to mutual interference of genome replication or virion secretion. Considering that HBeAg is an immunotolerogen required for the establishment of persistent infection, its lack of expression rather than a replication defect could be the primary determinant for the rare occurrence of genotype G monoinfection.
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Affiliation(s)
- Ke Li
- Liver Research Center, Rhode Island Hospital, Brown University, Providence, Rhode Island 02903, USA
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15
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Basagoudanavar SH, Perlman DH, Hu J. Regulation of hepadnavirus reverse transcription by dynamic nucleocapsid phosphorylation. J Virol 2006; 81:1641-9. [PMID: 17135319 PMCID: PMC1797568 DOI: 10.1128/jvi.01671-06] [Citation(s) in RCA: 72] [Impact Index Per Article: 4.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/11/2022] Open
Abstract
Reverse transcription, an essential step in the life cycle of all retroelements, is a complex, multistep process whose regulation is not yet clearly understood. We have recently shown that reverse transcription in the pararetrovirus duck hepatitis B virus is associated with complete dephosphorylation of the viral core protein, which forms the nucleocapsid wherein reverse transcription takes place. Here we present a genetic study of the role of this dynamic nucleocapsid phosphorylation in regulating viral reverse transcription. Detailed analyses of the reverse transcription products synthesized within nucleocapsids composed of core phosphorylation site mutants revealed that alanine substitutions, mimicking the nonphosphorylated state, completely blocked reverse transcription at a very early stage. In contrast, aspartate substitutions, mimicking the phosphorylated state, allowed complete first-strand DNA synthesis but were severely defective in accumulating mature double-stranded DNA. The latter defect was due to a combination of mutant nucleocapsid instability during maturation and a block in mature second-strand DNA synthesis. Thus, the reversible phosphorylation of the nucleocapsids regulates the ordered progression of reverse transcription.
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Affiliation(s)
- Suresh H Basagoudanavar
- Department of Microbiology and Immunology-H107, The Penn State University College of Medicine, 500 University Dr., Hershey, PA 17033, USA
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16
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Guo H, Aldrich CE, Saputelli J, Xu C, Mason WS. The insertion domain of the duck hepatitis B virus core protein plays a role in nucleocapsid assembly. Virology 2006; 353:443-50. [PMID: 16837020 DOI: 10.1016/j.virol.2006.06.004] [Citation(s) in RCA: 11] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/12/2006] [Revised: 05/11/2006] [Accepted: 06/06/2006] [Indexed: 01/08/2023]
Abstract
Synthesis of hepadnaviral DNA is dependent upon both the viral DNA polymerase and the viral core protein, the subunit of the nucleocapsids in which viral DNA synthesis takes place. In a study of natural isolates of duck hepatitis B virus (DHBV), we cloned full-length viral genomes from a puna teal. One of the clones failed to direct viral DNA replication in transfected cells, apparently as a result of a 3 nt inframe deletion of histidine 107 in the core protein. Histidine 107 is located in the center of a predicted helical region of the "insertion domain", a stretch of 45 amino acids which appears to be at the tip of a spike on the surface of the nucleocapsid. The mutation was introduced into a well-characterized strain of DHBV for further analysis. Core protein accumulated in cells transfected with the mutant DHBV but was partially degraded, suggesting that it was unstable. Assembled nucleocapsids were not detected by capsid gel electrophoresis. Interestingly, the mutant protein appeared to form chimeric nucleocapsids with wild-type core protein. The chimeric nucleocapsids supported viral DNA replication. These results suggest that the insertion domain of the spike may play a role either in assembly of stable nucleocapsids, possibly in formation of the dimer subunits, or in triggering nucleocapsid disintegration, required during initiation of new rounds of infection.
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Affiliation(s)
- Haitao Guo
- Fox Chase Cancer Center, 333 Cottman Avenue, Philadelphia, PA 19111, USA
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17
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Schorr O, Borel C, Trepo C, Zoulim F, Hantz O. Effects of liver growth factors on hepadnavirus replication in chronically infected duck hepatocytes. J Hepatol 2006; 44:842-7. [PMID: 16458387 DOI: 10.1016/j.jhep.2005.09.014] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 05/10/2005] [Revised: 07/28/2005] [Accepted: 09/21/2005] [Indexed: 01/04/2023]
Abstract
BACKGROUND/AIMS Duck hepatitis B virus (DHBV) replication is up-regulated by cell cycle during the early infection of primary duck but the effect of cell cycle on DHBV replication in chronically infected hepatocyte is not known. METHODS Hepatocytes obtained from DHBV congenitally infected embryos were used. Cell proliferation was controlled by addition of liver growth factors and the impact on viral replication analyzed. RESULTS EGF induced cell proliferation is associated with a slight increase in CCC DNA synthesis and a decrease in viral transcription. Conversely, TGFbeta blocked cell cycle progression, diminished CCC DNA synthesis but increased viral transcription. CONCLUSIONS Cell proliferation decreases DHBV transcription but this effect seems to be compensated by an opposite effect on the synthesis of CCC DNA resulting in a global moderate effect on viral replication. Our results also indicate that after division of chronically infected hepatocytes both daughter cells are infected, confirming that liver regeneration is not sufficient to induce CCC DNA eradication as suggested by the lack of effect of some long term anti-HBV therapies.
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MESH Headings
- Animals
- Cell Division
- Chick Embryo
- Chronic Disease
- DNA, Viral/analysis
- Ducks
- Epidermal Growth Factor/pharmacology
- Gene Expression Regulation, Viral/drug effects
- Hepadnaviridae Infections/drug therapy
- Hepadnaviridae Infections/virology
- Hepatitis B Virus, Duck/genetics
- Hepatitis B Virus, Duck/growth & development
- Hepatitis, Viral, Animal/drug therapy
- Hepatitis, Viral, Animal/virology
- Hepatocytes/cytology
- Hepatocytes/virology
- Liver Regeneration
- RNA, Viral/analysis
- Transcription, Genetic/drug effects
- Transforming Growth Factor beta/pharmacology
- Virus Replication/drug effects
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Affiliation(s)
- Olivier Schorr
- INSERM Unit 271, 151 cours Albert Thomas, 69003 Lyon, France.
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18
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Le Pogam S, Chua PK, Newman M, Shih C. Exposure of RNA templates and encapsidation of spliced viral RNA are influenced by the arginine-rich domain of human hepatitis B virus core antigen (HBcAg 165-173). J Virol 2005; 79:1871-87. [PMID: 15650211 PMCID: PMC544126 DOI: 10.1128/jvi.79.3.1871-1887.2005] [Citation(s) in RCA: 74] [Impact Index Per Article: 3.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/21/2022] Open
Abstract
Previously, human hepatitis B virus (HBV) mutant 164, which has a truncation at the C terminus of the HBV core antigen (HBcAg), was speculated to secrete immature genomes. For this study, we further characterized mutant 164 by different approaches. In addition to the 3.5-kb pregenomic RNA (pgRNA), the mutant preferentially encapsidated the 2.2-kb or shorter species of spliced RNA, which can be reverse transcribed into double-stranded DNA before virion secretion. We observed that mutant 164 produced less 2.2-kb spliced RNA than the wild type. Furthermore, it appeared to produce at least two different populations of capsids: one encapsidated a nuclease-sensitive 3.5-kb pgRNA while the other encapsidated a nuclease-resistant 2.2-kb spliced RNA. In contrast, the wild-type core-associated RNA appeared to be resistant to nuclease. When arginines and serines were systematically restored at the truncated C terminus, the core-associated DNA and nuclease-resistant RNA gradually increased in both size and signal intensity. Full protection of encapsidated pgRNA from nuclease was observed for HBcAg 1-171. A full-length positive-strand DNA phenotype requires positive charges at amino acids 172 and 173. Phosphorylation at serine 170 is required for optimal RNA encapsidation and a full-length positive-strand DNA phenotype. RNAs encapsidated in Escherichia coli by capsids of HBcAg 154, 164, and 167, but not HBcAg 183, exhibited nuclease sensitivity; however, capsid instability after nuclease treatment was observed only for HBcAg 164 and 167. A new hypothesis is proposed here to highlight the importance of a balanced charge density for capsid stability and intracapsid anchoring of RNA templates.
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Affiliation(s)
- Sophie Le Pogam
- Department of Pathology, WHO Collaborating Center for Tropical Diseases, and Center for Biodefense and Emerging Infectious Diseases, University of Texas Medical Branch, Galveston, TX 77555-0609, USA
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19
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Köck J, Nassal M, Deres K, Blum HE, von Weizsäcker F. Hepatitis B virus nucleocapsids formed by carboxy-terminally mutated core proteins contain spliced viral genomes but lack full-size DNA. J Virol 2004; 78:13812-8. [PMID: 15564489 PMCID: PMC533894 DOI: 10.1128/jvi.78.24.13812-13818.2004] [Citation(s) in RCA: 79] [Impact Index Per Article: 4.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/08/2023] Open
Abstract
The carboxy-terminal sequence of the hepatitis B virus (HBV) core protein constitutes a nucleic acid binding domain that is rich in arginine residues and contains three serine phosphorylation sites. While dispensable for capsid assembly, this domain is involved in viral replication, as demonstrated by the effects of mutations on RNA packaging and/or reverse transcription; however, the underlying mechanisms are poorly understood. Here we tested a series of core protein mutants in which the three serine phosphorylation sites were replaced by glutamic acid, in parallel with a previously described deletion variant lacking the 19 C-terminal amino acid residues, for their ability to support viral replication in transfected hepatoma cells. Replacement of all serines and the deletion gave rise to nucleocapsids containing a smaller than wild-type DNA genome. Rather than a single-stranded DNA intermediate, as previously thought, this was a 2.0-kbp double-stranded DNA molecule derived from spliced pregenomic RNA (pgRNA). Interestingly, full-length pgRNA was associated with nucleocapsids but was found to be sensitive to nuclease digestion, while encapsidated spliced RNA and 3' truncated RNA species were nuclease resistant. These findings suggest that HBV pgRNA encapsidation is directional and that a packaging limit is determined by the C-terminal portion of the core protein.
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Affiliation(s)
- Josef Köck
- Department of Medicine II, University of Freiburg, Hugstetter Strasse 55, D-79106 Freiburg, Germany
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20
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Kock J, Kann M, Putz G, Blum HE, Von Weizsacker F. Central role of a serine phosphorylation site within duck hepatitis B virus core protein for capsid trafficking and genome release. J Biol Chem 2003; 278:28123-9. [PMID: 12740387 DOI: 10.1074/jbc.m300064200] [Citation(s) in RCA: 40] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
Viral nucleocapsids compartmentalize and protect viral genomes during assembly while they mediate targeted genome release during viral infection. This dual role of the capsid in the viral life cycle must be tightly regulated to ensure efficient virus spread. Here, we used the duck hepatitis B virus (DHBV) infection model to analyze the effects of capsid phosphorylation and hydrogen bond formation. The potential key phosphorylation site at serine 245 within the core protein, the building block of DHBV capsids, was substituted by alanine (S245A), aspartic acid (S245D) and asparagine (S245N), respectively. Mutant capsids were analyzed for replication competence, stability, nuclear transport, and infectivity. All mutants formed DHBV DNA-containing nucleocapsids. Wild-type and S245N but not S245A and S245D fully protected capsid-associated mature viral DNA from nuclease action. A negative ionic charge as contributed by phosphorylated serine or aspartic acid-supported nuclear localization of the viral capsid and generation of nuclear superhelical DNA. Finally, wild-type and S245D but not S245N virions were infectious in primary duck hepatocytes. These results suggest that hydrogen bonds formed by non-phosphorylated serine 245 stabilize the quarterny structure of DHBV nucleocapsids during viral assembly, while serine phosphorylation plays an important role in nuclear targeting and DNA release from capsids during viral infection.
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Affiliation(s)
- Josef Kock
- Department of Medicine II, University Hospital, 79106 Freiburg, Germany
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21
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Abstract
Hepatitis B virus assembly begins with the packaging of an RNA pregenome into intracellular nucleocapsids, with subsequent reverse transcription within these nucleocapsids converting the RNA into a characteristic, partially double-stranded DNA, which, alone, is found in enveloped extracellular virions as the viral genome. Using a synchronized replication system for the duck hepatitis B virus, together with a stringent two-step assay for virion secretion, we demonstrate that this selective genome secretion results from an intrinsic secretion competence gained only by the nucleocapsids at the late stage of reverse transcription.
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Affiliation(s)
- David Perlman
- Department of Microbiology, Boston University School of Medicine, Boston, Massachusetts 02118, USA
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22
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Delaney W, Bartholomeusz A, Locarnini SA. Evolving therapies for the treatment of chronic hepatitis B virus infection. Expert Opin Investig Drugs 2002; 11:169-87. [PMID: 11829711 DOI: 10.1517/13543784.11.2.169] [Citation(s) in RCA: 15] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/16/2022]
Abstract
Despite the availability of prophylactic vaccines lamivudine and IFN-alpha, chronic hepatitis B remains an enormous global health problem. Several promising nucleosides/nucleotides are undergoing clinical trials, including adefovir dipivoxil, the latter of which is active against lamivudine-resistant hepatitis B virus (HBV). In addition to nucleosides/nucleotides, it will be important to develop new agents with different modes of action. Novel small molecule inhibitors, as well as gene therapy approaches, have produced encouraging results in vitro and in animal models. Additional immunomodulatory therapies, including thymosin-alpha 1, IL-12 and several therapeutic vaccines, are also being explored. Combination therapy with multiple nucleosides/nucleotides and other agents will play an important role in the treatment of hepatitis and may help achieve complete viral suppression, host-mediated elimination of infected cells and lasting immunity.
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Affiliation(s)
- William Delaney
- Victorian Infectious Diseases Reference Laboratory, Carlton South, VIC 3053, Australia
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23
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Preikschat P, Kazaks A, Dishlers A, Pumpens P, Krüger DH, Meisel H. Interaction of wild-type and naturally occurring deleted variants of hepatitis B virus core polypeptides leads to formation of mosaic particles. FEBS Lett 2000; 478:127-32. [PMID: 10922483 DOI: 10.1016/s0014-5793(00)01836-6] [Citation(s) in RCA: 12] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022]
Abstract
The simultaneous presence of hepatitis B virus (HBV) genomes carrying wild-type (wt) and in-frame deleted variants of the HBV core gene has been identified as a typical feature of HBV-infected renal transplant patients with severe liver disease. To investigate possible interactions of wt and deleted core polypeptides a two-vector Escherichia coli expression system ensuring their concomitant synthesis has been developed. Co-expression of wt and a mutant core lacking 17 amino acid residues (77-93) within the immunodominant region led to the formation of mosaic particles, whereas the mutant alone was incapable of self-assembly.
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Affiliation(s)
- P Preikschat
- Institute of Virology, Humboldt University School of Medicine, Schumannstr, 20/21, D-10117, Berlin, Germany
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24
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Yuan TT, Tai PC, Shih C. Subtype-independent immature secretion and subtype-dependent replication deficiency of a highly frequent, naturally occurring mutation of human hepatitis B virus core antigen. J Virol 1999; 73:10122-8. [PMID: 10559327 PMCID: PMC113064 DOI: 10.1128/jvi.73.12.10122-10128.1999] [Citation(s) in RCA: 55] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/12/2023] Open
Abstract
The most frequent mutation of the human hepatitis B virus (HBV) core antigen occurs at amino acid 97. Recently, a phenylalanine (F)-to-leucine (L) mutation at this position (mutant F97L) in HBV surface antigen subtype ayw has been shown to result in an immature secretion phenotype, which is characterized by the nonselective export of an excessive amount of virions containing minus-strand, single-stranded HBV DNA. While subtype ayw mutant F97L has been found in Europe, the major reservoir of HBV resides in Asia and Africa. We report here that the immature secretion phenotype indeed can be found in an HBV strain (subtype adr) prevalent in Asia, changing from an isoleucine (I) to a leucine (mutant I97L). Despite its immature secretion phenotype, the adr variant I97L replicates as well as its parental adr wild-type I97I, supporting the conclusion that the extracellular phenotype of immature secretion is not a consequence of the intracellular HBV DNA replication defect. Further studies demonstrated that it is the acquisition of a leucine, rather than the loss of a wild-type amino acid at codon 97, that is important for immature secretion. We conclude that immature secretion is a subtype-independent phenotype and deficiency in intracellular DNA synthesis is a subtype-dependent phenotype. The former is caused by the trans-acting effect of a mutant core protein, while the latter by a cis-acting effect of a mutated nucleotide on the ayw genome. These immature secretion variants provide an important tool for studying the regulation of HBV virion assembly and secretion.
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Affiliation(s)
- T T Yuan
- Center for Tropical Diseases, Department of Pathology, University of Texas Medical Branch, Galveston, Texas 77555-0609, USA
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25
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Hui EKW, Yi YS, Lo SJ. Hepatitis B viral core proteins with an N-terminal extension can assemble into core-like particles but cannot be enveloped. J Gen Virol 1999; 80 ( Pt 10):2647-2659. [PMID: 10573158 DOI: 10.1099/0022-1317-80-10-2647] [Citation(s) in RCA: 12] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/22/2022] Open
Abstract
The structure of hepatitis B virus (HBV) nucleocapsids has been revealed in great detail by cryoelectron microscopy. How nucleocapsids interact with surface antigens to form enveloped virions remains unknown. In this study, core mutants with N-terminal additions were created to address two questions: (1) can these mutant core proteins still form nucleocapsids and (2) if so, can the mutant nucleocapsids interact with surface antigens to form virion-like particles. One plasmid encoding an extra stretch of 23 aa, including six histidine residues, fused to the N terminus of the core protein (designated HisC183) was expressed in Escherichia coli and detected by Western blot. CsCl gradient and electron microscopy analyses indicated that HisC183 could self-assemble into nucleocapsids. When HisC183 or another similar N-terminal fusion core protein (designated FlagC183) was co-expressed with a core-negative plasmid in human hepatoma cells, both mutant core proteins self-assembled into nucleocapsids. These particles also retained kinase activity. Using an endogenous polymerase assay, a fill-in HBV DNA labelled with isotope was obtained from intracellular nucleocapsids formed by mutant cores. In contrast, no such signal was detected from the transfection medium, which was consistent with PCR and Southern blot analyses. Results indicate that core mutants with N-terminal extensions can form nucleocapsids, but are blocked during the envelopment process and cannot form secreted virions. The mutant nucleocapsids generated from this work should facilitate further study on how nucleocapsids interact with surface antigens.
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Affiliation(s)
- Eric Ka-Wai Hui
- Institute of Microbiology and Immunology, School of Life Science, National Yang-Ming University, Taipei, Taiwan 112, Republic of China 1
| | - Yong Shyang Yi
- Institute of Microbiology and Immunology, School of Life Science, National Yang-Ming University, Taipei, Taiwan 112, Republic of China 1
| | - Szecheng J Lo
- Institute of Microbiology and Immunology, School of Life Science, National Yang-Ming University, Taipei, Taiwan 112, Republic of China 1
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26
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Yuan TT, Sahu GK, Whitehead WE, Greenberg R, Shih C. The mechanism of an immature secretion phenotype of a highly frequent naturally occurring missense mutation at codon 97 of human hepatitis B virus core antigen. J Virol 1999; 73:5731-40. [PMID: 10364324 PMCID: PMC112633 DOI: 10.1128/jvi.73.7.5731-5740.1999] [Citation(s) in RCA: 97] [Impact Index Per Article: 3.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/10/1998] [Accepted: 03/29/1999] [Indexed: 01/12/2023] Open
Abstract
A very frequent missense mutation at codon 97 of human hepatitis B virus (HBV) core antigen (HBcAg) has been found in chronic carriers worldwide. Functional characterization of this mutant revealed one intracellular and two extracellular phenotypes in contrast to wild-type HBV: (i) a 6- to 12-fold decrease in the level of the full-length relaxed circular DNA, a 4- to 5-fold decrease in the plus-strand DNA, and an approximately 1.8-fold decrease in the minus-strand and overall DNA levels in the intracellular viral core particles; (ii) a 5.7-fold increase in the immature secretion of Dane particles, containing minus-strand, single-stranded virion DNA; and (iii) a significant reduction of nonenveloped core particles in the medium. The steady-state levels of mutant and wild-type core proteins expressed from the same vector appeared to be similar. Using a complementation assay and gradient centrifugation analysis, we demonstrated that this mutant core protein alone is necessary and sufficient for immature secretion. The decreased level of intracellular HBV DNA is caused by both the cis defect of the mutant genome and the trans defect of the mutant core protein. We have dissected further the relationship between the intracellular and extracellular phenotypes of mutant F97L. The pleiotropic effects of the HBcAg codon 97 mutation were observed consistently in several different experimental settings. The mechanism and biological significance of these findings are discussed.
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Affiliation(s)
- T T Yuan
- Departments of Pathology and of Microbiology and Immunology, Center for Tropical Diseases, University of Texas Medical Branch, Galveston, Texas 77555-0609, USA
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27
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von Weizsäcker F, Köck J, Wieland S, Offensperger WB, Blum HE. Dominant negative mutants of the duck hepatitis B virus core protein interfere with RNA pregenome packaging and viral DNA synthesis. Hepatology 1999; 30:308-15. [PMID: 10385672 DOI: 10.1002/hep.510300139] [Citation(s) in RCA: 17] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 12/16/2022]
Abstract
Dominant negative (DN) mutants of the hepadnaviral core protein are potent inhibitors of viral replication. We have previously shown that fusion of sequences derived from the duck hepatitis B virus (DHBV) polymerase (Pol), DHBV small surface protein (S), bacterial beta-galactosidase (lacZ), or green fluorescent protein (GFP) to the carboxy terminus of the DHBV core protein yields DN mutants that inhibit viral replication at the posttranslational level. To elucidate the mechanism(s) of their antiviral action, we analyzed the effect of the DN mutants on RNA pregenome packaging and nucleocapsid assembly. Core-Pol and core-S, but not core-lacZ or core-GFP, markedly interfered with RNA pregenome packaging. Nucleocapsid formation was not affected by any of the mutants. The DN core-GFP fusion protein formed mixed particles with wild-type core protein in the cytoplasm of cotransfected cells and interfered with reverse transcription of the viral pregenome. A subpopulation of chimeric nucleocapsids, however, was shown to overcome the block in DNA synthesis and produce mature viral DNA. Thus, at least 2 steps within the viral life cycle can be targeted by DN DHBV core proteins: 1) packaging of the viral pregenome; and 2) reverse transcription within mixed particles. The fact that some mixed particles retain replication competence demonstrates a high structural flexibility of nucleocapsids and indicates a possible mechanism of viral escape.
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Affiliation(s)
- F von Weizsäcker
- Department of Medicine II, University of Freiburg, Freiburg, Germany
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