Protein: Protein X (Q69027)
Organism: Hepatitis B virus genotype C subtype ayr (isolate Human/Japan/Okamoto/-)
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
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
Sequence: MAARLCCQLDPARDVLCLRPVGAESRGRPVSGPFGPLPSPSSSAVPADHGAHLSLRGLPVCAFSSAGPCALRFTSARSMETTVNAHQVLPKVLHKRTLGLSAMSTTDLEAYFKDCLFKDWEELGEEIRLKVFVLGGCRHKLVCSPAPCNFFPSA
InterPro domains: - IPR000236: Transactivation protein X (family) [1-145]
Gene Ontology annotations:
Molecular Function (MF): GO:0003674 (molecular function), GO:0005488 (binding), GO:0005515 (protein binding)
Biological Process (BP): GO:0008150 (biological process), GO:0065007 (biological regulation), GO:0050789 (regulation of biological process), GO:0044419 (biological process involved in interspecies interaction between organisms), GO:0048519 (negative regulation of biological process), GO:0016032 (viral process), GO:0044068 (modulation by symbiont of host cellular process), GO:0050794 (regulation of cellular process), GO:0035821 (modulation of process of another organism), GO:0019048 (modulation by virus of host process), GO:0044403 (biological process involved in symbiotic interaction), GO:0048523 (negative regulation of cellular process), GO:0051701 (biological process involved in interaction with host), GO:0031341 (regulation of cell killing), GO:0052040 (modulation by symbiont of host programmed cell death), GO:0060548 (negative regulation of cell death), GO:0010941 (regulation of cell death), GO:0044003 (modulation by symbiont of host process), GO:0052026 (modulation by symbiont of host transcription), GO:0051709 (regulation of killing of cells of another organism), GO:0019054 (modulation by virus of host cellular process), GO:0052150 (modulation by symbiont of host apoptotic process), GO:0043069 (negative regulation of programmed cell death), GO:0043067 (regulation of programmed cell death), GO:0052041 (suppression by symbiont of host programmed cell death), GO:0019056 (modulation by virus of host transcription), GO:0039526 (modulation by virus of host apoptotic process), GO:0052150 (modulation by symbiont of host apoptotic process), GO:0042981 (regulation of apoptotic process), GO:0043066 (negative regulation of apoptotic process), GO:0019050 (suppression by virus of host apoptotic process), GO:0033668 (suppression by symbiont of host apoptotic process)
Cellular Component (CC): GO:0005575 (cellular component), GO:0110165 (cellular anatomical entity), GO:0018995 (host cellular component), GO:0033643 (host cell part), GO:0043657 (host cell), GO:0033646 (host intracellular part), GO:0043656 (host intracellular region), GO:0030430 (host cell cytoplasm)