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Figure 1. Diversity of target antigen locations in the different areas of the bacterial ghost envelope. (A) (1) RecP acting as a TA; (2) export of TA to sealed periplasmic space as maltose-binding protein (MBP) fusion; (3) protein TA anchored into the inner membrane via E', L', or E'and L'anchor sequences, or attachment of biotinylated TA to E'-membrane-anchored StrepA.
(B) (1) Presentation of TA as a fusion protein on the outer membrane surface with OMP A; (2) export of TA to the sealed periplasmic space as MBP-SbsA or -SbsB S-layer fusion proteins; (3) mcDNA carrying the LacOs anchored to the inner membrane via L'-membrane-anchored LacI or IMP acting as TA.
(C) (1) LPS acting as a TA; (2) export of TA to the sealed periplasmic space using a signal sequence that is cleaved off after transport (e.g., GIII, MBP signal sequence); (3) loading of bacterial lumen with linear and circular DNA plasmids, making BG a carrier for DNA vaccines.
(D) (1) OMP acting as a TA; (2) export of TA to the sealed periplasmic space as SbsA or SbsB S-layer fusion proteins using a signal sequence that is cleaved off after transport (e.g., GIII, MBP signal sequence); (3) DNA carrying the LacOs anchored to the inner membrane via L'-membrane anchored LacI (LacI-L') repressor molecule.
(E) (1) Pilus acting as a TA; (2) the periplasmic space; (3) cytoplasmic space filled up with recombinant S-layer proteins carrying foreign TA. cccDNA: Covalently closed circular DNA; E': Membrane anchor sequence of the N-terminal part of lysis protein E derived from bacteriophage ΦΦX174; IMP: Inner membrane protein; L': Membrane anchor sequence of the C-terminal part of lysis protein L derived from bacteriophage MS2; Lacl: The
lac repressor; LacO: Lac operator sequence; LPS: Lipopolysaccharide; MBP: Maltose-binding protein; mcDNA: Minicircle DNA; OMP: Outer membrane protein; RecP: Recombinant or induced pilus; StrepA: Streptavidine; TA: Target antigen. Adapted from [100].
(Figure omitted. See article PDF.)
Figure 2. Advanced version of self-immobilizing pDNA produces minicircle DNA without the antibiotic-resistance genes anchored to the inner membrane of bacterial ghost envelopes via the LacOs-LacI-L'interaction. (A) Mother plasmid after recombination is divided into the miniplasmid, comprising the antibiotic-resistant gene and one recombination site along with the bacterial backbone, and the minicircle, containing only LacOs necessary for binding...