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HBcAg (core antigen) is a
HBcAg (core antigen) is a hepatitis B
Hepatitis B is an infectious disease caused by the '' hepatitis B virus'' (HBV) that affects the liver; it is a type of viral hepatitis. It can cause both acute and chronic infection.
Many people have no symptoms during an initial infection. ...
viral protein. It is an indicator of active viral replication; this means the person infected with Hepatitis B can likely transmit the virus on to another person (i.e. the person is infectious).
Structure and function
HBcAg is anantigen
In immunology, an antigen (Ag) is a molecule, moiety, foreign particulate matter, or an allergen, such as pollen, that can bind to a specific antibody or T-cell receptor. The presence of antigens in the body may trigger an immune response.
...
that can be found on the surface of the nucleocapsid
A capsid is the protein shell of a virus, enclosing its genetic material. It consists of several oligomeric (repeating) structural subunits made of protein called protomers. The observable 3-dimensional morphological subunits, which may or ma ...
core (the inner most layer of the hepatitis B virus
Hepatitis B virus (HBV) is a partially double-stranded DNA virus, a species of the genus '' Orthohepadnavirus'' and a member of the '' Hepadnaviridae'' family of viruses. This virus causes the disease hepatitis B.
Classification
Hepatitis B ...
). While both HBcAg and HBeAg are made from the same open reading frame
In molecular biology, reading frames are defined as spans of DNA sequence between the start and stop codons. Usually, this is considered within a studied region of a prokaryotic DNA sequence, where only one of the six possible reading frames ...
, HBcAg is not secreted as a monomer. HBcAg is considered "particulate" and it does not circulate in the blood, but recent study show it can be detected in serum by Radioimmunoassay
A radioimmunoassay (RIA) is an immunoassay that uses radioactive tracer, radiolabeled molecules in a stepwise formation of immune complexes. A RIA is a very sensitive in vitro assay technique used to measure concentrations of substances, usually m ...
. However, it is readily detected in hepatocyte
A hepatocyte is a cell of the main parenchymal tissue of the liver. Hepatocytes make up 80% of the liver's mass.
These cells are involved in:
* Protein synthesis
* Protein storage
* Transformation of carbohydrates
* Synthesis of cholesterol, bi ...
s after biopsy
A biopsy is a medical test commonly performed by a surgeon, interventional radiologist, an interventional radiologist, or an interventional cardiology, interventional cardiologist. The process involves the extraction of sampling (medicine), sample ...
. When both HBcAg and HBeAg proteins are present, it acts as a marker of viral replication
Viral replication is the formation of biological viruses during the infection process in the target host cells. Viruses must first get into the cell before viral replication can occur. Through the generation of abundant copies of its genome ...
.
HBcAg, also called core protein (Cp), is a 21 kDa protein of 183–185 amino acids, depending on the genotype
The genotype of an organism is its complete set of genetic material. Genotype can also be used to refer to the alleles or variants an individual carries in a particular gene or genetic location. The number of alleles an individual can have in a ...
, and is the result of the second start codon
The start codon is the first codon of a messenger RNA (mRNA) transcript translated by a ribosome. The start codon always codes for methionine in eukaryotes and archaea and a ''N''-formylmethionine (fMet) in bacteria, mitochondria and plastids.
...
in the open reading frame. Once a threshold of HBcAg proteins are translated in the cytoplasm, the viral capsid will spontaneously into a T=3 or T=4 icosahedral capsid. The capsid will usually package the hepatitis B genomic RNA, but some capsids will have cellular RNA or be empty. HBcAg is the target of antiviral compounds, termed capsid assembly modulators (CAMs), that are under clinical investigation for treating chronic hepatitis B.
Interactions
Tapasin can interact with HBcAg18-27 and enhance cytotoxicT-lymphocyte
T cells (also known as T lymphocytes) are an important part of the immune system and play a central role in the adaptive immune response. T cells can be distinguished from other lymphocytes by the presence of a T-cell receptor (TCR) on their ce ...
response against HBV.
See also
* HBeAg *HBsAg
HBsAg (also known as the Australia antigen) is the surface antigen of the hepatitis B virus (HBV). Its presence in blood indicates existing hepatitis B infection.
Structure and function
The viral envelope of an enveloped virus has different su ...
References
{{Viral proteins Viral structural proteins Hepatitis B virus