Human hepatitis B virus (figure 3) is the prototype virus of the hepadnavirus family and causes serum hepatitis. HBV has a diameter of about 40nm.
It infects humans and chimpanzees but there are closely related members of this family that infect other mammals and birds. HBV is a DNA virus and is enveloped.
The DNA is only partly double stranded and forms a circle of around 3,200 bases. Although surrounded by a host cell-derived envelope, HBV is remarkably stable to organic solvents. It is also heat- and pH-resistant. The genome is associated with the P (polymerase) protein and this complex is, in turn, surrounded by the core antigens (HBcAg and HBeAg). These two proteins have most of their sequence in common and most of the HBeAg is secreted since it is processed differently from the HBcAg and thus not assembled into progeny virus. Embedded in the surface lipid bilayer is the surface antigen (HBsAg).
The HBsAg (Australia antigen) is made up of three glycoproteins that are encoded by the same gene. The proteins are translated in the same reading frame but start at a different AUG start codon; thus, all have the same C-terminus. The largest protein is the L protein (42kd) and contained within this is the M glycoprotein. The S glycoprotein (27kD) is contained within the M protein. The HBsAg protein is also secreted into the patient’s serum where it can be seen as spherical (mostly self-associated S protein) or filamentous particles (also mostly S protein but with some L and M). The former are smaller than the true virus but the filaments can be quite large (several hundred nanometers).
This large amount of free HBsAg accounts for the inability to detect antibodies against the protein early during infection (the so-called "window" between the presence HBsAg (indicative of the presence of virus) and the presence of anti-HBsAg).
The glycoproteins on the virus surface contain antigenic determinants that are group specific and type specific. Using these determinants, epidemiologists identify eight subtypes of HBV.
HBV virions are also known as Dane particles.
tags:hepatitis B virus,DNA,