Glycine Decarboxylase Mediates a Postbinding Step in Duck Hepatitis B Virus Infection

ABSTRACT Envelope protein precursors of many viruses are processed by a basic endopeptidase to generate two molecules, one for receptor binding and the other for membrane fusion. Such a cleavage event has not been demonstrated for the hepatitis B virus family. Two binding partners for duck hepatitis B virus (DHBV) pre-S envelope protein have been identified. Duck carboxypeptidase D (DCPD) interacts with the full-length pre-S protein and is the DHBV docking receptor, while duck glycine decarboxylase (DGD) has the potential to bind several deletion constructs of the pre-S protein in vitro. Interestingly, DGD but not DCPD expression was diminished following prolonged culture of primary duck hepatocytes (PDH), which impaired productive DHBV infection. Introduction of exogenous DGD promoted formation of protein-free viral genome, suggesting restoration of several early events in viral life cycle. Conversely, blocking DGD expression in fresh PDH by antisense RNA abolished DHBV infection. Moreover, addition of DGD antibodies soon after virus binding reduced endogenous DGD protein levels and impaired production of covalently closed circular DNA, the template for DHBV gene expression and genome replication. Our findings implicate this second pre-S binding protein as a critical cellular factor for productive DHBV infection. We hypothesize that DCPD, a molecule cycling between the cell surface and the trans-Golgi network, targets DHBV particles to the secretary pathway for proteolytic cleavage of viral envelope protein. DGD represents the functional equivalent of other virus receptors in its interaction with processed viral particles.

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St, a Truncated Envelope Protein Derived from the S Protein of Duck Hepatitis B Virus, Acts as a Chaperone for the Folding of the Large Envelope Protein

Journal of Virology ◽

10.1128/jvi.79.9.5346-5352.2005 ◽

2005 ◽

Vol 79 (9) ◽

pp. 5346-5352 ◽

Cited By ~ 8

Author(s):

Elizabeth V. L. Grgacic ◽

David A. Anderson

Keyword(s):

Hepatitis B Virus ◽

Hepatitis B ◽

Envelope Protein ◽

Cellular Localization ◽

Transmembrane Domain ◽

Molar Ratio ◽

Duck Hepatitis B Virus ◽

S Protein ◽

Duck Hepatitis ◽

B Virus

ABSTRACT Envelope proteins of hepadnaviruses undergo a unique folding mechanism which results in the posttranslational translocation of 50% of the large envelope protein (L) chains across the endoplasmic reticulum. This mechanism is essential for the eventual positioning of the receptor-binding domain on the surface of the virus particle and in duck hepatitis B virus (DHBV) is dependent on the small (S) envelope protein as part of the assembly process. In this study, we report the identification of a third envelope protein, St, derived from the S protein and carrying functions previously attributed to S. Antibody mapping and mutagenesis studies indicated St to be C terminally truncated, spanning the N-terminal transmembrane domain (TM1) plus the adjacent cysteine loop. We have previously shown that the mutation of two conserved polar residues in TM1 of S (SAA) eliminates L translocation and assembly. A plasmid expressing a functional equivalent of St was able to rescue assembly, demonstrating that this assembly defect is due to mutations of the corresponding residues in St and not in S per se. Immunofluorescence analysis showed that St directly affects L protein cellular localization. These results indicate that St acts as a viral chaperone for L folding, remaining associated with the DHBV envelope upon secretion. The presence of St at a molar ratio of half that of L suggests that it is St which regulates L translocation to 50%.

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Fine Mapping of Neutralization Epitopes on Duck Hepatitis B Virus (DHBV) pre-S Protein Using Monoclonal Antibodies and Overlapping Peptides

Virology ◽

10.1006/viro.1993.1024 ◽

1993 ◽

Vol 192 (1) ◽

pp. 217-223 ◽

Cited By ~ 23

Author(s):

Sylvie Chassot ◽

Véronique Lambert ◽

Alan Kay ◽

Catherine Godinot ◽

Bernard Roux ◽

...

Keyword(s):

Monoclonal Antibodies ◽

Hepatitis B Virus ◽

Hepatitis B ◽

Fine Mapping ◽

Duck Hepatitis B Virus ◽

S Protein ◽

Duck Hepatitis ◽

B Virus

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Myristylation of a duck hepatitis B virus envelope protein is essential for infectivity but not for virus assembly

Virology ◽

10.1016/0042-6822(91)90503-4 ◽

1991 ◽

Vol 181 (1) ◽

pp. 359-363 ◽

Cited By ~ 47

Author(s):

Donald R. Macrae ◽

Volker Bruss ◽

Don Ganem

Keyword(s):

Hepatitis B Virus ◽

Hepatitis B ◽

Envelope Protein ◽

Virus Assembly ◽

Virus Envelope ◽

Duck Hepatitis B Virus ◽

Duck Hepatitis ◽

B Virus ◽

Virus Envelope Protein

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Domains of the Hepatitis B Virus Small Surface Protein S Mediating Oligomerization

Journal of Virology ◽

10.1128/jvi.02232-17 ◽

2018 ◽

Vol 92 (11) ◽

Cited By ~ 9

Author(s):

Sascha Suffner ◽

Nadine Gerstenberg ◽

Maria Patra ◽

Paula Ruibal ◽

Ahmed Orabi ◽

...

Keyword(s):

Amino Acids ◽

Hepatitis B Virus ◽

Hepatitis B ◽

Envelope Protein ◽

Mammalian Cells ◽

Protein S ◽

Viral Envelope ◽

Small Surface ◽

S Protein ◽

B Virus

ABSTRACTDuring hepatitis B virus (HBV) infections, subviral particles (SVP) consisting only of viral envelope proteins and lipids are secreted. Heterologous expression of the small envelope protein S in mammalian cells is sufficient for SVP generation. S is synthesized as a transmembrane protein with N-terminal (TM1), central (TM2), and hydrophobic C-terminal (HCR) transmembrane domains. The loops between TM1 and TM2 (the cytosolic loop [CL]) and between TM2 and the HCR (the luminal loop [LL]) are located in the cytosol and the endoplasmic reticulum (ER) lumen, respectively. To define the domains of S mediating oligomerization during SVP morphogenesis, S mutants were characterized by expression in transiently transfected cells. Mutation of 12 out of 15 amino acids of TM1 to alanines, as well as the deletion of HCR, still allowed SVP formation, demonstrating that these two domains are not essential for contacts between S proteins. Furthermore, the oligomerization of S was measured with a fluorescence-activated cell sorter (FACS)-based Förster resonance energy transfer (FRET) assay. This approach demonstrated that the CL, TM2, and the LL independently contributed to S oligomerization, while TM1 and the HCR played minor roles. Apparently, intermolecular homo-oligomerization of the CL, TM2, and the LL drives S protein aggregation. Detailed analyses revealed that the point mutation C65S in the CL, the mutation of 13 out of 19 amino acids of TM2 to alanine residues, and the simultaneous replacement of all 8 cysteine residues in the LL by serine residues blocked the abilities of these domains to support S protein interactions. Altogether, specific domains and residues in the HBV S protein that are required for oligomerization and SVP generation were defined.IMPORTANCEThe small hepatitis B virus envelope protein S has the intrinsic ability to direct the morphogenesis of spherical 20-nm subviral lipoprotein particles. Such particles expressed in yeast or mammalian cells represent the antigenic component of current hepatitis B vaccines. Our knowledge about the steps leading from the initial, monomeric, transmembrane translation product of S to SVP is very limited, as is our information on the structure of the complex main epitope of SVP that induces the formation of protective antibodies after vaccination. This study contributes to our understanding of the oligomerization process of S chains during SVP formation and shows that the cytoplasmic loop, one membrane-embedded domain, and the luminal loop of S independently drive S-S oligomerization.

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