title: The conserved serine 177 in the delta antigen of hepatitis delta virus is one putative phosphorylation site and is required for efficient viral RNA replication.
abstract: Hepatitis delta virus (HDV) small delta antigen (S-HDAg) plays a critical role in virus replication. We previously demonstrated that the S-HDAg phosphorylation occurs on both serine and threonine residues. However, their biological significance and the exact phosphorylation sites of S-HDAg are still unknown. In this study, phosphorylated S-HDAg was detected only in the intracellular compartment, not in viral particles. In addition, the number of phosphorylated isoforms of S-HDAg significantly increased with the extent of viral replication in transfection system. Site-directed mutagenesis showed that alanine replacement of serine 177, which is conserved among all the known HDV strains, resulted in reduced phosphorylation of S-HDAg, while the mutation of the other two conserved serine residues (2 and 123) had little effect. The S177A mutant dramatically decreased its capability in assisting HDV RNA replication, with a preferential and profound impairment of the antigenomic RNA replication. Furthermore, the viral RNA editing, a step relying upon antigenomic RNA replication, was also abolished by this mutation. These results suggested that phosphorylation of S-HDAg, with serine 177 as a presumable site, plays a critical role in viral RNA replication, especially in augmenting the replication of antigenomic RNA.
authors.affiliation: Graduate Institute of Clinical Medicine, College of Medicine, National Taiwan University, Taipei, Taiwan.
authors.forename: J J
authors.initials: JJ
authors.lastname: Mu
authors.forename: D S
authors.initials: DS
authors.lastname: Chen
authors.forename: P J
authors.initials: PJ
authors.lastname: Chen
mesh_terms: D000595:Amino Acid Sequence; D002460:Cell Line; D017124:Conserved Sequence; D018963:Hepatitis Antigens / Q000502:physiology*; D003699:Hepatitis D / Q000821:virology*; D003698:Hepatitis Delta Virus / Q000502:physiology*; D035923:Hepatitis delta Antigens; D006801:Humans; D008969:Molecular Sequence Data; D016297:Mutagenesis, Site-Directed; D010766:Phosphorylation; D012367:RNA, Viral / Q000502:physiology; D016601:RNA-Binding Proteins / Q000502:physiology; D014779:Virus Replication
chemical_list: D018963:Hepatitis Antigens; D035923:Hepatitis delta Antigens; D012367:RNA, Viral; D016601:RNA-Binding Proteins; C442244:hepatitis delta virus large antigen