Large Envelope Protein (S) Recombinant Protein

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

By similarity.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

By similarity.

Subunit structure: 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

By similarity.

Subcellular location: Virion membrane

By similarity.

Domain: The large envelope protein is synthesized with the pre-S region at the cytosolic side of the endoplasmic reticulum and, hence will be within the virion after budding. Therefore the pre-S region is not N-glycosylated. Later a post-translational translocation of N-terminal pre-S and TM1 domains occur in about 50% of proteins at the virion surface. These molecules change their topology by an unknown mechanism, resulting in exposure of pre-S region at virion surface. For isoform M in contrast, the pre-S2 region is translocated cotranslationally to the endoplasmic reticulum lumen and is N-glycosylated.

Post-translational modification: Isoform M is N-terminally acetylated at a ratio of 90%, and N-glycosylated at the pre-S2 region

By similarity.Myristoylated

By similarity.

Biotechnological use: Systematic vaccination of individuals at risk of exposure to the virus has been the main method of controlling the morbidity and mortality associated with hepatitis B. The first hepatitis B vaccine was manufactured by the purification and inactivation of HBsAg obtained from the plasma of chronic hepatitis B virus carriers. The vaccine is now produced by recombinant DNA techniques and expression of the S isoform in yeast cells. The pre-S region do not seem to induce strong enough antigenic response.

Sequence similarities: Belongs to the orthohepadnavirus major surface antigen family.

Sequence caution: The sequence AAA45518.1 differs from that shown. Reason: Erroneous initiation.