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Evaluation of Salmonella enterica type III secretion system effector proteins as carriers for heterologous vaccine antigens.

ABSTRACT: Live attenuated strains of Salmonella enterica have a high potential as carriers of recombinant vaccines. The type III secretion system (T3SS)-dependent translocation of S. enterica can be deployed for delivery of heterologous antigens to antigen-presenting cells. Here we investigated the efficacy of various effector proteins of the Salmonella pathogenicity island (SPI2)-encoded T3SS for the translocation of model antigens and elicitation of immune responses. The SPI2 T3SS effector proteins SifA, SteC, SseL, SseJ, and SseF share an endosomal membrane-associated subcellular localization after translocation. We observed that all effector proteins could be used to translocate fusion proteins with the model antigens ovalbumin and listeriolysin into the cytosol of host cells. Under in vitro conditions, fusion proteins with SseJ and SteC stimulated T-cell responses that were superior to those triggered by fusion proteins with SseF. However, in mice vaccinated with Salmonella carrier strains, only fusion proteins based on SseJ or SifA elicited potent T-cell responses. These data demonstrate that the selection of an optimal SPI2 effector protein for T3SS-mediated translocation is a critical parameter for the rational design of effective Salmonella-based recombinant vaccines.

SUBMITTER: Hegazy WA

PROVIDER: S-EPMC3294654 | biostudies-literature | 2012 Mar

REPOSITORIES: biostudies-literature

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Evaluation of Salmonella enterica type III secretion system effector proteins as carriers for heterologous vaccine antigens.

Hegazy Wael Abdel Halim WA Xu Xin X Metelitsa Leonid L Hensel Michael M

Infection and immunity 20120117 3

Live attenuated strains of Salmonella enterica have a high potential as carriers of recombinant vaccines. The type III secretion system (T3SS)-dependent translocation of S. enterica can be deployed for delivery of heterologous antigens to antigen-presenting cells. Here we investigated the efficacy of various effector proteins of the Salmonella pathogenicity island (SPI2)-encoded T3SS for the translocation of model antigens and elicitation of immune responses. The SPI2 T3SS effector proteins SifA ...[more]

PMID: 22252866

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Project description:Strains of the various Salmonella enterica serovars cause gastroenteritis or typhoid fever in humans, with virulence depending on the action of two type III secretion systems (Salmonella pathogenicity island 1 [SPI-1] and SPI-2). SptP is a Salmonella SPI-1 effector, involved in mediating recovery of the host cytoskeleton postinfection. SptP requires a chaperone, SicP, for stability and secretion. SptP has 94% identity between S. enterica serovar Typhimurium and S Typhi; direct comparison of the protein sequences revealed that S Typhi SptP has numerous amino acid changes within its chaperone-binding domain. Subsequent comparison of ΔsptP S Typhi and S. Typhimurium strains demonstrated that, unlike SptP in S. Typhimurium, SptP in S Typhi was not involved in invasion or cytoskeletal recovery postinfection. Investigation of whether the observed amino acid changes within SptP of S Typhi affected its function revealed that S Typhi SptP was unable to complement S. Typhimurium ΔsptP due to an absence of secretion. We further demonstrated that while S. Typhimurium SptP is stable intracellularly within S Typhi, S Typhi SptP is unstable, although stability could be recovered following replacement of the chaperone-binding domain with that of S. Typhimurium. Direct assessment of the strength of the interaction between SptP and SicP of both serovars via bacterial two-hybrid analysis demonstrated that S Typhi SptP has a significantly weaker interaction with SicP than the equivalent proteins in S. Typhimurium. Taken together, our results suggest that changes within the chaperone-binding domain of SptP in S Typhi hinder binding to its chaperone, resulting in instability, preventing translocation, and therefore restricting the intracellular activity of this effector. Studies investigating Salmonella pathogenesis typically rely on Salmonella Typhimurium, even though Salmonella Typhi causes the more severe disease in humans. As such, an understanding of S. Typhi pathogenesis is lacking. Differences within the type III secretion system effector SptP between typhoidal and nontyphoidal serovars led us to characterize this effector within S Typhi. Our results suggest that SptP is not translocated from typhoidal serovars, even though the loss of sptP results in virulence defects in S. Typhimurium. Although SptP is just one effector, our results exemplify that the behavior of these serovars is significantly different and genes identified to be important for S. Typhimurium virulence may not translate to S Typhi.

Project description:Many pathogenic Gram-negative bacteria use a type III secretion system (T3SS) to deliver effector proteins into the host cell where they reprogram host defenses and facilitate pathogenesis. The first 20-30 N-terminal residues usually contain the 'secretion signal' that targets effector proteins for translocation, however, a consensus sequence motif has never been discerned. Recent machine-learning approaches, such as support vector machine (SVM)-based Identification and Evaluation of Virulence Effectors (SIEVE), have improved the ability to identify effector proteins from genomics sequence information. While these methods all suggest that the T3SS secretion signal has a characteristic amino acid composition bias, it is still unclear if the amino acid pattern is important and if there are any unifying structural properties that direct recognition. To address these issues a peptide corresponding to the secretion signal for Salmonella enterica serovar Typhimurium effector SseJ was synthesized (residues 1-30, SseJ) along with scrambled peptides of the same amino acid composition that produced high (SseJ-H) and low (SseJ-L) SIEVE scores. The secretion properties of these three peptides were tested using a secretion signal-CyaA fusion assay and their structural properties probed using circular dichroism, nuclear magnetic resonance, and ion mobility spectrometry-mass spectrometry. The secretion predictions from SIEVE matched signal-CyaA fusion experimental results with J774 macrophages suggesting that the SseJ secretion signal has some sequence order dependence. The structural studies showed that the SseJ, SseJ-H, and SseJ-L peptides were intrinsically disordered in aqueous solution with a small predisposition to adopt nascent helical structure only in the presence of structure stabilizing agents such as 1,1,1,3,3,3-hexafluoroisopropanol. Intrinsic disorder may be a universal feature of effector secretion signals as similar conclusions were reached following structural characterization of peptides corresponding to the N-terminal regions of the S. Typhimurium effectors SptP, SopD-2, GtgE, and the Yersinia pestis effector YopH.

Dataset Information

Evaluation of Salmonella enterica type III secretion system effector proteins as carriers for heterologous vaccine antigens.

Publications

Evaluation of Salmonella enterica type III secretion system effector proteins as carriers for heterologous vaccine antigens.

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