P03165 · X_HBVD3

Function

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.

Caution

Transcriptional activities should be taken with a grain of salt. As of 2007, all studies demonstrating in vivo interaction between protein X and transcriptional components were performed with significant overexpression of both proteins and in the absence of viral infection.

GO annotations

AspectTerm
Cellular Componenthost cell mitochondrion
Cellular Componenthost cell nucleus
Biological Processapoptotic process
Biological ProcessDNA-templated transcription
Biological Processsymbiont-mediated activation of host NF-kappaB cascade
Biological Processsymbiont-mediated arrest of host cell cycle during G2/M transition
Biological Processviral genome replication

Keywords

Names & Taxonomy

Protein names

  • Recommended name
    Protein X
  • Alternative names
    • HBx
    • Peptide X
    • pX

Gene names

    • Name
      X

Organism names

Accessions

  • Primary accession
    P03165

Proteomes

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.

Keywords

Phenotypes & Variants

Features

Showing features for natural variant, mutagenesis.

TypeIDPosition(s)Description
Natural variant26in strain: Switzerland/Strubin/1999
Natural variant33in strain: Switzerland/Strubin/1999
Natural variant36in strain: Switzerland/Strubin/1999
Natural variant40-43in strain: Switzerland/Strubin/1999
Natural variant46in strain: Latvia
Natural variant47-48in strain: Switzerland/Strubin/1999
Mutagenesis77-78No effect on interaction with human DDB1.
Natural variant84-88in strain: Latvia
Mutagenesis91No effect on interaction with human DDB1.
Mutagenesis95No effect on interaction with human DDB1.
Mutagenesis96Complete loss of interaction with human DDB1.
Mutagenesis98Complete loss of interaction with human DDB1.
Natural variant102in strain: Latvia
Mutagenesis107No effect on interaction with human DDB1.
Mutagenesis113-114No effect on interaction with human DDB1.

Variants

We now provide the "Disease & Variants" viewer in its own tab.

The viewer provides 8 variants from UniProt as well as other sources including ClinVar and dbSNP.

Go to variant viewer

PTM/Processing

Features

Showing features for chain.

TypeIDPosition(s)Description
ChainPRO_00002223611-154Protein X

Post-translational modification

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.

PTM databases

Interaction

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. Interacts with host TRPC4AP; leading to prevent ubiquitination of TRPC4AP. Interacts with host PLSCR1; this interaction promotes ubiquitination and degradation of HBx and impairs HBx-mediated cell proliferation.

Binary interactions

TypeEntry 1Entry 2Number of experimentsIntact
XENO P03165AKT1 P317493EBI-7683985, EBI-296087
XENO P03165Akt1 P317502EBI-7683985, EBI-298707

Protein-protein interaction databases

Structure

3D structure databases

Family & Domains

Features

Showing features for region.

TypeIDPosition(s)Description
Region68-117Mitochondrial targeting sequence

Sequence similarities

Belongs to the orthohepadnavirus protein X family.

Family and domain databases

Sequence

  • Sequence status
    Complete
  • Length
    154
  • Mass (Da)
    16,618
  • Last updated
    1990-04-01 v2
  • Checksum
    29FD1CC9E09A34B5
MAARLCCQLDPARDVLCLRPVGAESRGRPFSGSLGTLSSPSPSAVPTDHGAHLSLRGLPVCAFSSAGPCALRFTSARRMETTVNAHQILPKVLHKRTLGLSAMSTTDLEAYFKDCLFKDWEELGEEIRLKVFVLGGCRHKLVCAPAPCNFFTSA

Keywords

Sequence databases

Nucleotide SequenceProtein SequenceMolecule TypeStatus
V01460
EMBL· GenBank· DDBJ
-Genomic DNA No translation available.
X02496
EMBL· GenBank· DDBJ
CAB41697.1
EMBL· GenBank· DDBJ
Genomic DNA

Similar Proteins

Disclaimer

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