background:
Hepatitis B Virus (HBV) infection induces a disease state characterised by liver damage, inflammation and viral persistence. Infection also increases the risk of hepatocellular carcinoma. HBV belongs to the Hepadnaviridae family of viruses. Its genome consists of partially double stranded circular DNA. The DNA is enclosed in a nucleocapsid, or core antigen (HBcAg), which is surrounded by a spherical envelope (surface antigen or HBsAg). The core antigen shares its sequences with the e antigen (HBeAg) but no cross reactivity between the two proteins has been observed. The HBV genome also encodes a DNA polymerase that also acts as a reverse transcriptase. Hepatitis B infection is normally diagnosed from serological tests that detect HBsAg but as the disease progresses this antigen may no longer be present in the blood and tests for HBcAg are used. If HBsAg can be detected in the blood for longer than six months, chronic hepatitis B is diagnosed. The antigenic determinant of the protein moiety of the HBsAg determines specific characteristics of different serotypes and provides the basis of immunodetection. HBsAg has antigenic heterogeneity, specifically, two pairs of sub specific determinants, d/y and w/r allow the following combinations: adw, ayw, adr, ayr.
Function:
The large envelope protein exists in two topological conformations, one which is termed 'external' or Le-HBsAg and the other 'internal' or Li-HBsAg. In its external conformation the protein attaches the virus to cell receptors and thereby initiating infection. This interaction determines the species specificity and liver tropism. This attachment induces virion internalization predominantly through caveolin-mediated endocytosis. The large envelope protein also assumes fusion between virion membrane and endosomal membrane (Probable). In its internal conformation the protein plays a role in virion morphogenesis and mediates the contact with the nucleocapsid like a matrix protein.
The middle envelope protein plays an important role in the budding of the virion. It is involved in the induction of budding in a nucleocapsid independent way. In this process the majority of envelope proteins bud to form subviral lipoprotein particles of 22 nm of diameter that do not contain a nucleocapsid.
Subunit:
Li-HBsAg interacts with capsid protein and with HDV Large delta antigen. Isoform M associates with host chaperone CANX through its pre-S2 N glycan. This association may be essential for M proper secretion.
Subcellular Location:
Virion membrane.
Post-translational modifications:
Isoform M is N-terminaly acetylated at a ratio of 90%, and N-glycosylated at the pre-S2 region.
Myristoylated.
Similarity:
Belongs to the orthohepadnavirus major surface antigen family.
Database links:
Entrez Gene: 2828293 Hepatitis B virus
Entrez Gene: 944569 Hepatitis B virus
SwissProt: P03138 Hepatitis B virus
SwissProt: P03140 Hepatitis B virus
SwissProt: P03141 Hepatitis B virus
SwissProt: Q81157 Hepatitis B virus
SwissProt: Q81158 Hepatitis B virus
SwissProt: Q81159 Hepatitis B virus
SwissProt: Q81160 Hepatitis B virus
Important Note:
This product as supplied is intended for research use only, not for use in human, therapeutic or diagnostic applications.
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