ABSTRACT
We developed a new class of vaccines, based on killed but metabolically active (KBMA) bacteria, that simultaneously takes advantage of the potency of live vaccines and the safety of killed vaccines. We removed genes required for nucleotide excision repair (uvrAB), rendering microbial-based vaccines exquisitely sensitive to photochemical inactivation with psoralen and long-wavelength ultraviolet light. Colony formation of the nucleotide excision repair mutants was blocked by infrequent, randomly distributed psoralen crosslinks, but the bacterial population was able to express its genes, synthesize and secrete proteins. Using the intracellular pathogen Listeria monocytogenes as a model platform, recombinant psoralen-inactivated Lm DeltauvrAB vaccines induced potent CD4(+) and CD8(+) T-cell responses and protected mice against virus challenge in an infectious disease model and provided therapeutic benefit in a mouse cancer model. Microbial KBMA vaccines used either as a recombinant vaccine platform or as a modified form of the pathogen itself may have broad use for the treatment of infectious disease and cancer.
Subject(s)
Bacterial Vaccines/immunology , Immunity, Cellular/immunology , Listeria monocytogenes/immunology , Vaccination/methods , Animals , Carbon Radioisotopes , DNA Repair/genetics , Dendritic Cells , Endodeoxyribonucleases/genetics , Escherichia coli Proteins/genetics , Ficusin , Flow Cytometry , Listeria monocytogenes/genetics , Mice , Mice, Inbred C57BL , Ultraviolet RaysABSTRACT
Recent studies have indicated that FtsY, the signal recognition particle receptor of Escherichia coli, plays a central role in membrane protein biogenesis. For proper function, FtsY must be targeted to the membrane, but its membrane-targeting pathway is unknown. We investigated the relationship between targeting and function of FtsY in vivo, by separating its catalytic domain (NG) from its putative targeting domain (A) by three means: expression of split ftsY, insertion of various spacers between A and NG, and separation of A and NG by in vivo proteolysis. Proteolytic separation of A and NG does not abolish function, whereas separation by long linkers or expression of split ftsY is detrimental. We propose that proteolytic cleavage of FtsY occurs after completion of co-translational targeting and assembly of NG. In contrast, separation by other means may interrupt proper synchronization of co-translational targeting and membrane assembly of NG. The co-translational interaction of FtsY with the membrane was confirmed by in vitro experiments.
Subject(s)
Bacterial Proteins/metabolism , Cell Membrane/metabolism , Receptors, Cytoplasmic and Nuclear/metabolism , Signal Recognition Particle/metabolism , Blotting, Western , Catalytic Domain , Cell Fractionation , Escherichia coli/metabolism , Models, Biological , Mutation , Plasmids/metabolism , Protein Binding , Protein Biosynthesis , Protein Structure, TertiarySubject(s)
Actinomycetales/metabolism , Bacterial Proteins/metabolism , Cell Membrane/metabolism , Receptors, Cytoplasmic and Nuclear/metabolism , Signal Recognition Particle/metabolism , Amino Acid Sequence , Bacterial Proteins/genetics , Escherichia coli/metabolism , Molecular Sequence Data , Mycobacterium/metabolism , Receptors, Cytoplasmic and Nuclear/genetics , Sequence Homology, Amino Acid , Streptomyces/metabolismABSTRACT
In vivo and in vitro studies have suggested that the bacterial version of the mammalian signal recognition particle (SRP) system plays an essential and selective role in protein biogenesis. The bacterial SRP system consists of at least two proteins and an RNA molecule (termed Ffh, FtsY and 4.5S RNA, respectively, in Escherichia coli). Recent evidence suggests that other putative bacterial-specific SRP components may also exist. In vitro experiments confirmed the expected basic features of the bacterial SRP system by demonstrating interactions among the SRP components themselves, between them and ribosomes, ribosome-linked hydrophobic nascent polypeptides or inner membranes. The availability of a conserved (and essential) bacterial SRP version has facilitated the implementation of powerful genetic and biochemical approaches for studying the cascade of events during the SRP-mediated targeting process in vivo and in vitro as well as the three-dimensional structures and the properties of each SRP component and complex.
Subject(s)
Bacterial Proteins/metabolism , Escherichia coli/metabolismABSTRACT
In mammalian cells, as well as Escherichia coli, ribosomes translating membrane proteins interact cotranslationally with translocons in the membrane, and this interaction is essential for proper insertion of nascent polypeptides into the membrane. Both the signal recognition particle (SRP) and its receptor (SR) are required for functional association of ribosomes translating integral membrane proteins with the translocon. Herein, we confirm that membrane targeting of E. coli ribosomes requires the prokaryotic SRalpha homolog FtsY in vivo. Surprisingly, however, depletion of the E. coli SRP54 homolog (Ffh) has no significant effect on binding of ribosomes to the membrane, although Ffh depletion is detrimental to growth. These and other observations suggest that, in E. coli, SRP may operate downstream of SR-mediated targeting of ribosomes to the plasma membrane.