Abstract
The major immunodominant region (MIR) and N-terminus of the hepatitis B virus (HBV) core (HBc) protein were used to expose foreign insertions on the outer surface of HBc virus-like particles (VLPs). The additions to the HBc positively charged arginine-rich C-terminal (CT) domain are usually not exposed on the VLP surface. Here, we constructed a set of recombinant HBcG vectors in which CT arginine stretches were substituted by glycine residues. In contrast to natural HBc VLPs and recombinant HBc VLP variants carrying native CT domain, the HBcG VLPs demonstrated a lowered capability to pack bacterial RNA during expression in Escherichia coli cells. The C-terminal addition of a model foreign epitope from the HBV preS1 sequence to the HBcG vectors resulted in the exposure of the inserted epitope on the VLP surface, whereas the same preS1 sequences added to the native CT of the natural HBc protein remained buried within the HBc VLPs. Based on the immunisation of mice, the preS1 epitope added to the HBcG vectors as a part of preS1(20–47) and preS1phil sequences demonstrated remarkable immunogenicity. The same epitope added to the original C-terminus of the HBc protein did not induce a notable level of anti-preS1 antibodies. HBcG vectors may contribute to the further development of versatile HBc VLP-based vaccine and gene therapy applications.
Highlights
Hepatitis B virus (HBV) core (HBc) virus-like particles (VLPs) are one of the oldest [1,2,3] and the most powerful protein engineering tools utilised to (i) expose immunological epitopes and/or cell-targeting signals and (ii) package poly- and oligonucleotides as genes and immune stimulatory sequences
The C-terminal addition of a model foreign epitope from the hepatitis B virus (HBV) preS1 sequence to the HBcG vectors resulted in the exposure of the inserted epitope on the VLP surface, whereas the same preS1 sequences added to the native CT of the natural HBc protein remained buried within the HBc VLPs
The HBcG vectors can be divided into four categories: (i) all four C-terminal arginine stretches are replaced by glycine residues, (ii) the first arginine stretch is preserved, (iii) the two first arginine stretches are preserved, or (iv) the natural C-terminus is prolonged by the C-terminal sequence with fully replaced arginine stretches
Summary
Hepatitis B virus (HBV) core (HBc) virus-like particles (VLPs) are one of the oldest [1,2,3] and the most powerful protein engineering tools utilised to (i) expose immunological epitopes and/or cell-targeting signals and (ii) package poly- and oligonucleotides as genes and immune stimulatory sequences (for review see [3,4,5,6,7,8]). HBc VLPs and their numerous derivatives are efficiently produced in bacterial and yeast expression systems (for references see [5,6,7,8]). Novel advanced purification and packaging protocols permit the highly technological production and efficient quality control of recombinant HBc-derived VLPs [9]. Analogous HBc VLP structures have been produced in other efficient heterologous expression systems, including yeast S. cerevisiae [13, 14] and P. pastoris [15, 16]
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