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HAMAP rule MF_04074

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General rule information [?]

Accession MF_04074
Dates 9-MAY-2017 (Created)
28-JUN-2022 (Last updated, Version 6)
Name HBV_X
Viruses; Orthohepadnavirus
Template Q69027 (X_HBVCJ)

Propagated annotation [?]

Identifier, protein and gene names [?]

Protein name
RecName: Full=Protein X;
AltName: Full=HBx;
AltName: Full=Peptide X;
AltName: Full=pX;
Gene name

Comments [?]

Function Multifunctional protein that plays a role in silencing host antiviral defenses and promoting viral transcription. Does not seem to be essential for HBV infection. May be directly involved in development of cirrhosis and liver cancer (hepatocellular carcinoma). Most of cytosolic activities involve modulation of cytosolic calcium. The effect on apoptosis is controversial depending on the cell types in which the studies have been conducted. May induce apoptosis by localizing in mitochondria and causing loss of mitochondrial membrane potential. May also modulate apoptosis by binding host CFLAR, a key regulator of the death-inducing signaling complex (DISC). Promotes viral transcription by using the host E3 ubiquitin ligase DDB1 to target the SMC5-SMC6 complex to proteasomal degradation. This host complex would otherwise bind to viral episomal DNA, and prevents its transcription. Moderately stimulates transcription of many different viral and cellular transcription elements. Promoters and enhancers stimulated by HBx contain DNA binding sites for NF-kappa-B, AP-1, AP-2, c-EBP, ATF/CREB, or the calcium-activated factor NF-AT.
Subunit May form homodimer. May interact with host CEBPA, CFLAR, CREB1, DDB1, E4F1, HBXIP, HSPD1/HSP60, NFKBIA, POLR2E and SMAD4. Interacts with host SMC5-SMC6 complex and induces its degradation.
Subcellular location Host cytoplasm. Host nucleus. Host mitochondrion. Note=Mainly cytoplasmic as only a fraction is detected in the nucleus. In cytoplasm, a minor fraction associates with mitochondria or proteasomes.
Ptm A fraction may be phosphorylated in insect cells and HepG2 cells, a human hepatoblastoma cell line. Phosphorylated in vitro by host protein kinase C or mitogen-activated protein kinase. N-acetylated in insect cells.
Similarity Belongs to the orthohepadnavirus protein X family.

Keywords [?]

Gene Ontology [?]

GO:0033650; Cellular component: host cell mitochondrion.
GO:0042025; Cellular component: host cell nucleus.
GO:0039652; Biological process: induction by virus of host NF-kappaB cascade.
GO:0039592; Biological process: suppression by virus of G2/M transition of host mitotic cell cycle.
GO:0006351; Biological process: DNA-templated transcription.
GO:0019079; Biological process: viral genome replication.

Cross-references [?]

Pfam PF00739; X; 1;

Features [?]

From: X_HBVCJ (Q69027)
Key     From     To       Description   Tag   Condition   FTGroup
REGION     68     117       Mitochondrial targeting sequence        

Additional information [?]

Size range 134-154 amino acids
Related rules None
Fusion None