Q8JMZ5 · X_HBVH3

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
    Q8JMZ5

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

PTM/Processing

Features

Showing features for chain.

TypeIDPosition(s)Description
ChainPRO_00003199241-154Protein 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.

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.

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)
    16,627
  • Last updated
    2002-10-01 v1
  • Checksum
    2EE1D8019B2839F2
MAARLCCQLDPARDVLCLRPVGAESCGRPLSWSPGALPPPSPPSVPADDGSHLSLRGLPACAFSSAGPCALRFTSARRMETTVNAPQSLPTTLHKRTLGLSPRSTTWIEEYIKDCVFKDWEESGEELRLKVFVLGGCRHKLVCSPAPCNFFTSA

Sequence databases

Nucleotide SequenceProtein SequenceMolecule TypeStatus
AY090457
EMBL· GenBank· DDBJ
AAM09050.1
EMBL· GenBank· DDBJ
Genomic DNA

Similar Proteins

Disclaimer

Any medical or genetic information present in this entry is provided for research, educational and informational purposes only. It is not in any way intended to be used as a substitute for professional medical advice, diagnosis, treatment or care. Our staff consists of biologists and biochemists that are not trained to give medical advice.
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