Abstract
Hepatitis delta virus (HDV) is a defective virus that requires the supply of hepatitis B virus surface antigen (HBsAg) for replication and transmission. We have previously demonstrated that co-transduction of BHK cells with Bac- GD, a recombinant baculovirus expressing large hepatitis delta antigen (L-HDAg), and Bac-GS2, another recombinant baculovirus expressing HBsAg, gives rise to the assembly and secretion of 22 nm HBsAg subviral particles and 35-37 nm HDV-like particles (HDV VLP). In this study we uncovered oversize particles (>50 nm in diameter) comprised of HBsAg and L-HDAg and the particle properties varied with the relative dosages of Bac-GD and Bac-GS2, as demonstrated by Western blot, transmission electron microscopy and immunogold labeling. At a given Bac-GS2 dosage, decreasing the Bac-GD dosage resulted in the expression of more HBsAg, elevated secretion of HBsAg subviral particles, incorporation of more HBsAg into the HDV VLP, narrower particle size distribution and lower particle density. These data collectively demonstrated that the composition, and hence the properties, of HDV VLPs could be manipulated by altering the relative expression levels of structure proteins.
Highlights
Hepatitis delta virus (HDV) is a satellite virus of hepatitis B virus (HBV) and requires the supply of HBV surface antigen (HBsAg) for replication and transmission [1]
To examine whether all the HDV VLPs assembled inside the cells were effectively secreted, the co-transduced cell lysates were subject to Western blot using anti-HBsAg and anti-HDAg antibodies
Since HBsAg is incorporated into HBsAg subviral particles or HDV VLP [22], the data indicated that the majority, if not all, of the expressed HBsAg and all HDV VLPs, secreted out of the cells
Summary
Hepatitis delta virus (HDV) is a satellite virus of hepatitis B virus (HBV) and requires the supply of HBV surface antigen (HBsAg) for replication and transmission [1]. The HDV virion includes an outer envelope comprising lipids and HBsAg [2] and an inner ribonucleoprotein complex composed of a circular RNA genome as well as large and small forms of hepatitis delta antigens (L-HDAg and S-HDAg). HBsAg exists as large- (L), middle- (M) and small (S) forms in the HDV virion. These 3 isoforms are encoded in a single open reading frame and translated from different in-frame initiation codons, sharing a common C-terminal domain. The SHDAg and L-HDAg are identical in sequence except that LHDAg contains a C-terminal extension that allows for the isoprenylation of L-HDAg, which is crucial for HDV assembly and inhibition of HDV replication [3, 4]
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