title: Capsid Phosphorylation State and Hepadnavirus Virion Secretion.
abstract: The C-terminal domain (CTD) of hepadnavirus core protein is involved in multiple steps of viral replication. In particular, the CTD is initially phosphorylated at multiple sites to facilitate viral RNA packaging into immature nucleocapsids (NCs) and the early stage of viral DNA synthesis. For the avian hepadnavirus duck hepatitis B virus (DHBV), CTD is dephosphorylated subsequently to facilitate the late stage of viral DNA synthesis and to stabilize NCs containing mature viral DNA. The role of CTD phosphorylation in virion secretion, if any, has remained unclear. Here, the CTD from the human hepatitis B virus (HBV) was found to be dephosphorylated in association with NC maturation and secretion of DNA-containing virions, as in DHBV. In contrast, the CTD in empty HBV virions (i.e., enveloped capsids with no RNA or DNA) was found to be phosphorylated. The potential role of CTD dephosphorylation in virion secretion was analyzed through mutagenesis. For secretion of empty HBV virions, which is independent of either viral RNA packaging or DNA synthesis, multiple substitutions in the CTD to mimic either phosphorylation or dephosphorylation showed little detrimental effect. Similarly, phospho-mimetic substitutions in the DHBV CTD did not block the secretion of DNA-containing virions. These results indicate that CTD dephosphorylation, though associated with NC maturation in both HBV and DHBV, is not essential for the subsequent NC-envelope interaction to secrete DNA-containing virions, and the CTD state of phosphorylation also does not play an essential role in the interaction between empty capsids and the envelope for secretion of empty virions.IMPORTANCEThe phosphorylation state of the C-terminal domain (CTD) of hepatitis B virus (HBV) core or capsid protein is highly dynamic and plays multiple roles in the viral life cycle. To study the potential role of the state of phosphorylation of CTD in virion secretion, we have analyzed the CTD phosphorylation state in complete (containing the genomic DNA) versus empty (genome-free) HBV virions. Whereas CTD is unphosphorylated in complete virions, it is phosphorylated in empty virions. Mutational analyses indicate that neither phosphorylation nor dephosphorylation of CTD is required for virion secretion. These results demonstrate that while CTD dephosphorylation is associated with HBV DNA synthesis, the CTD state of phosphorylation may not regulate virion secretion.
authors.affiliation: Department of Microbiology and Immunology, Pennsylvania State University College of Medicine, Hershey, Pennsylvania, USA.
authors.forename: Xiaojun
authors.initials: X
authors.lastname: Ning
authors.affiliation: Department of Microbiology and Immunology, Pennsylvania State University College of Medicine, Hershey, Pennsylvania, USA.
authors.forename: Suresh H
authors.initials: SH
authors.lastname: Basagoudanavar
authors.affiliation: Department of Microbiology and Immunology, Pennsylvania State University College of Medicine, Hershey, Pennsylvania, USA.
authors.forename: Kuancheng
authors.initials: K
authors.lastname: Liu
authors.affiliation: Department of Microbiology and Immunology, Pennsylvania State University College of Medicine, Hershey, Pennsylvania, USA.
authors.forename: Laurie
authors.initials: L
authors.lastname: Luckenbaugh
authors.affiliation: China National Vaccine and Serum Institute, Beijing, China.
authors.forename: Duoqian
authors.initials: D
authors.lastname: Wei
authors.affiliation: China National Vaccine and Serum Institute, Beijing, China.
authors.forename: Chunyan
authors.initials: C
authors.lastname: Wang
authors.affiliation: China National Vaccine and Serum Institute, Beijing, China.
authors.forename: Bo
authors.initials: B
authors.lastname: Wei
authors.affiliation: Department of Infectious Diseases, First Affiliated Hospital, School of Medicine, Xi'an Jiaotong University, Xi'an, Shaanxi, China.
authors.forename: Yingren
authors.initials: Y
authors.lastname: Zhao
authors.affiliation: Department of Infectious Diseases, First Affiliated Hospital, School of Medicine, Xi'an Jiaotong University, Xi'an, Shaanxi, China.
authors.forename: Taotao
authors.initials: T
authors.lastname: Yan
authors.affiliation: Gilead Sciences, Inc., Foster City, California, USA.
authors.forename: William
authors.initials: W
authors.lastname: Delaney
authors.affiliation: Department of Microbiology and Immunology, Pennsylvania State University College of Medicine, Hershey, Pennsylvania, USA juh13@psu.edu.
authors.forename: Jianming
authors.initials: J
authors.lastname: Hu
mesh_terms: D000818:Animals; D002213:Capsid / Q000378:metabolism*; D036022:Capsid Proteins / Q000378:metabolism*; D045744:Cell Line, Tumor; D002645:Chickens; D056945:Hep G2 Cells; D015611:Hepatitis B Virus, Duck / Q000235:genetics / Q000378:metabolism*; D006515:Hepatitis B virus / Q000235:genetics / Q000378:metabolism*; D006801:Humans; D010766:Phosphorylation; D017434:Protein Structure, Tertiary; D012367:RNA, Viral / Q000378:metabolism; D019065:Virus Assembly / Q000235:genetics*; D014779:Virus Replication; D017201:Virus Shedding
chemical_list: D036022:Capsid Proteins; D012367:RNA, Viral
keywords: C-terminal domain; capsid protein; dephosphorylation; duck hepatitis B virus; hepadnavirus; hepatitis B virus; maturation; phosphorylation; virion secretion