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Biogenesis of Yersinia pestis PsaA in recombinant attenuated Salmonella Typhimurium vaccine (RASV) strain.

ABSTRACT: Yersinia pestis PsaA is an adhesin important for the establishment of bacterial infection. PsaA synthesis requires the products of the psaEFABC genes. Here, by prediction analysis, we identified a PsaA signal sequence with two signal peptidase (SPase) cleavage sites, type-I and type-II (SPase-I and SPase-II). By Edman degradation and site-directed mutagenesis, the precise site for one of these Spase-I PsaA cleavage sites was located between alanine and serine at positions 31 and 32, respectively. Yersinia pestis psaA expression and the role of the PsaB and PsaC proteins were evaluated in recombinant attenuated Salmonella Typhimurium vaccine strains. PsaA was detected in total extracts as a major 15-kDa (mature) and 18-kDa (unprocessed) protein bands. PsaA synthesis was not altered by a DeltaA31-DeltaS32 double-deletion mutation. In contrast, the synthesis of PsaA (DeltaA31-DeltaS32) in Y. pestis and delivery to the supernatant was decreased. Otherwise, substitution of the amino acid cysteine at position 26 by valine involved in the SPase-II cleavage site did not show any effect on the secretion of PsaA in Salmonella and Yersinia. These results help clarify the secretion pathway of PsaA for the possible development of vaccines against Y. pestis.

SUBMITTER: Torres-Escobar A

PROVIDER: S-EPMC2818566 | biostudies-literature | 2010 Jan

REPOSITORIES: biostudies-literature

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Biogenesis of Yersinia pestis PsaA in recombinant attenuated Salmonella Typhimurium vaccine (RASV) strain.

Torres-Escobar Ascención A Juárez-Rodríguez María Dolores MD Curtiss Roy R

FEMS microbiology letters 20091022 2

Yersinia pestis PsaA is an adhesin important for the establishment of bacterial infection. PsaA synthesis requires the products of the psaEFABC genes. Here, by prediction analysis, we identified a PsaA signal sequence with two signal peptidase (SPase) cleavage sites, type-I and type-II (SPase-I and SPase-II). By Edman degradation and site-directed mutagenesis, the precise site for one of these Spase-I PsaA cleavage sites was located between alanine and serine at positions 31 and 32, respectively ...[more]

PMID: 20002189

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Project description:Salmonella enterica serovar Typhimurium genome encodes 13 fimbrial operons. Most of the fimbriae encoded by these operons are not produced under laboratory conditions but are likely to be synthesized in vivo We used an in vivo expression technology (IVET) strategy to identify four fimbrial operons, agf, saf, sti, and stc that are expressed in the spleen. When any three of these operons were deleted, the strain retained wild-type virulence. However, when all four operons were deleted, the resulting strain was completely attenuated, indicating that these four fimbriae play functionally redundant roles critical for virulence. In mice, oral doses of as low as 1 × 105 CFU of the strain with four fimbrial operons deleted provided 100% protection against challenge with 1 × 109 CFU of wild-type S Typhimurium. We also examined the possible effect of these fimbriae on the ability of a Salmonella vaccine strain to deliver a guest antigen. We modified one of our established attenuated vaccine strains, χ9088, to delete three fimbrial operons while the fourth operon was constitutively expressed. Each derivative was modified to express the Streptococcus pneumoniae antigen PspA. Strains that constitutively expressed saf or stc elicited a strong Th1 response with significantly greater levels of anti-PspA serum IgG and greater protective efficacy than strains carrying saf or stc deletions. The isogenic strain in which all four operons were deleted generated the lowest anti-PspA levels and did not protect against challenge with virulent S. pneumoniae Our results indicate that these fimbriae play important roles, as yet not understood, in Salmonella virulence and immunogenicity.IMPORTANCESalmonella enterica is the leading cause of bacterial food-borne infection in the United States. S. Typhimurium is capable of producing up to 13 distinct surface structures called fimbriae that presumably mediate its adherence to surfaces. The roles of most of these fimbriae in disease are unknown. Identifying fimbriae produced during infection will provide important insights into how these bacterial structures contribute to disease and potentially induce protective immunity to Salmonella infection. We identified four fimbriae that are produced during infection. Deletion of all four of these fimbriae results in a significant reduction in virulence. We explored ways in which the expression of these fimbriae may be exploited for use in recombinant Salmonella vaccine strains and found that production of Saf and Stc fimbriae are important for generating a strong immune response against a vectored antigen. This work provides new insight into the role of fimbriae in disease and their potential for improving the efficacy of Salmonella-based vaccines.

Project description:Attenuated Salmonella enterica serovar Typhimurium expressing recombinant antigens from other pathogens elicits primarily a Th1-type dominant immune response to both recombinant and Salmonella antigens. The immunogenicity and appropriate subcellular location of the recombinant antigen in the Salmonella vaccine strain may contribute to augmenting immune responses by facilitating adequate exposure of recombinant antigen to antigen-presenting cells for processing. To allow for secretion from gram-negative bacteria and overexpression of antigen, a DNA fragment encoding a highly antigenic alpha-helical region of PspA (pneumococcal surface protein A) was subcloned downstream from the beta-lactamase signal sequence in the multicopy Asd(+) pYA3493 vector to create pYA3494. pYA3493 was derived from a class of Asd(+) vectors with reduced expression of Asd to minimize selective disadvantage and enhance immunization of expressed recombinant antigens. The S. enterica serovar Typhimurium vaccine strain was constructed by the introduction of deletion mutations Delta crp-28 and Delta asdA16. Approximately 50% of the recombinant PspA (rPspA) expressed in a Salmonella strain harboring pYA3494 was detected in the combined supernatant and periplasmic fractions of broth-grown recombinant Salmonella. After a single oral immunization in BALB/c mice with 10(9) CFU of the recombinant Salmonella vaccine strain carrying pYA3494, immunoglobulin G (IgG) antibody responses were stimulated to both the heterologous antigen rPspA and Salmonella lipopolysaccharide (LPS) and outer membrane proteins (OMPs). About half, and even more at later times after immunization, of the antibodies induced to rPspA were IgG1 (indicating a Th2-type response), whereas 60 to 70% of the antibodies to LPS and 80 to 90% of those to OMPs were IgG2a (indicating a Th1-type response). A sublethal infection with Streptococcus pneumoniae WU2 boosted PspA antibody levels and maintained IgG2a/IgG1 ratios similar to those seen before the challenge. Oral immunization with Salmonella-PspA vaccine protected 60% of immunized mice from death after intraperitoneal challenge with 50 times the 50% lethal dose of virulent S. pneumoniae WU2.

Project description:PsaA, the subunit of the fimbria originally referred to as the "pH 6 antigen," is required for full virulence of Yersinia pestis during bubonic plague. The expression of psaA is dependent upon specific environmental signals, and while the signals (high temperature and acidic pH) are defined, the mechanisms underlying this regulation remain unclear. In the closely related species Yersinia pseudotuberculosis, psaA transcription requires two regulatory genes, psaE and psaF, and it is speculated that posttranscriptional regulation of PsaE and/or PsaF contributes to the regulation of psaA transcription. Few studies have examined the regulation of psaA expression in Y. pestis, and prior to this work, the roles of psaE and psaF in Y. pestis had not been defined. The data presented here show that both psaE and psaF are required for psaA transcription in Y. pestis and that the impact of temperature and pH is mediated through discrete posttranscriptional effects on PsaE and PsaF. By generating antibodies that recognize endogenous PsaE and PsaF, we determined that the levels of both proteins are impacted by temperature and pH. High temperature is required for psaE and psaF translation via discrete mechanisms mediated by the mRNA 5' untranslated region (UTR) upstream of each gene. Additionally, levels of PsaE and PsaF are impacted by pH. We show that PsaF enhances the stability of PsaE, and thus, both PsaE and PsaF are required for psaA transcription. Our data indicate that the environmental signals (temperature and pH) impact the expression of psaA by affecting the translation of psaE and psaF and the stability of PsaE and PsaF.IMPORTANCEY. pestis is a Gram-negative bacterial pathogen that causes bubonic plague. As a vector-borne pathogen, Y. pestis fluctuates between an arthropod vector (flea) and mammalian host. As such, Y. pestis must recognize environmental signals encountered within each host environment and respond by appropriately regulating gene expression. PsaA is a key Y. pestis mammalian virulence determinant that forms fimbriae. Our work provides evidence that Y. pestis utilizes multiple posttranscriptional mechanisms to regulate the levels of two PsaA regulatory proteins in response to both temperature and pH. This study offers insight into mechanisms that bacteria utilize to sense environmental cues and regulate the expression of determinants required for mammalian disease.

Dataset Information

Biogenesis of Yersinia pestis PsaA in recombinant attenuated Salmonella Typhimurium vaccine (RASV) strain.

Publications

Biogenesis of Yersinia pestis PsaA in recombinant attenuated Salmonella Typhimurium vaccine (RASV) strain.

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