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Genetically engineered frameshifted YopN-TyeA chimeras influence type III secretion system function in Yersinia pseudotuberculosis.

ABSTRACT: Type III secretion is a tightly controlled virulence mechanism utilized by many gram negative bacteria to colonize their eukaryotic hosts. To infect their host, human pathogenic Yersinia spp. translocate protein toxins into the host cell cytosol through a preassembled Ysc-Yop type III secretion device. Several of the Ysc-Yop components are known for their roles in controlling substrate secretion and translocation. Particularly important in this role is the YopN and TyeA heterodimer. In this study, we confirm that Y. pseudotuberculosis naturally produce a 42 kDa YopN-TyeA hybrid protein as a result of a +1 frame shift near the 3 prime of yopN mRNA, as has been previously reported for the closely related Y. pestis. To assess the biological role of this YopN-TyeA hybrid in T3SS by Y. pseudotuberculosis, we used in cis site-directed mutagenesis to engineer bacteria to either produce predominately the YopN-TyeA hybrid by introducing +1 frame shifts to yopN after codon 278 or 287, or to produce only singular YopN and TyeA polypeptides by introducing yopN sequence from Y. enterocolitica, which is known not to produce the hybrid. Significantly, the engineered 42 kDa YopN-TyeA fusions were abundantly produced, stable, and were efficiently secreted by bacteria in vitro. Moreover, these bacteria could all maintain functionally competent needle structures and controlled Yops secretion in vitro. In the presence of host cells however, bacteria producing the most genetically altered hybrids (+1 frameshift after 278 codon) had diminished control of polarized Yop translocation. This corresponded to significant attenuation in competitive survival assays in orally infected mice, although not at all to the same extent as Yersinia lacking both YopN and TyeA proteins. Based on these studies with engineered polypeptides, most likely a naturally occurring YopN-TyeA hybrid protein has the potential to influence T3S control and activity when produced during Yersinia-host cell contact.

SUBMITTER: Amer AA

PROVIDER: S-EPMC3789692 | biostudies-literature | 2013

REPOSITORIES: biostudies-literature

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Genetically engineered frameshifted YopN-TyeA chimeras influence type III secretion system function in Yersinia pseudotuberculosis.

Amer Ayad A A AA Costa Tiago R D TR Farag Salah I SI Avican Ummehan U Forsberg Åke Å Francis Matthew S MS

PloS one 20131003 10

Type III secretion is a tightly controlled virulence mechanism utilized by many gram negative bacteria to colonize their eukaryotic hosts. To infect their host, human pathogenic Yersinia spp. translocate protein toxins into the host cell cytosol through a preassembled Ysc-Yop type III secretion device. Several of the Ysc-Yop components are known for their roles in controlling substrate secretion and translocation. Particularly important in this role is the YopN and TyeA heterodimer. In this stud ...[more]

PMID: 24098594

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Project description:One milliliter of triplicate bacterial cultures in both Wild type (WT) and rpoN mutant were immediately pelleted by centrifugation at 9000 rpm at room temperature for 2 minutes after adding phenol:ethanol. The supernatant were removed and the pellets resuspended in 0.5 ml Trizol solution. For Gram-negative bacteria, the cells were homogenized in Trizol solution by pipetting up and down 15 times. For Gram-positive bacteria, culture suspensions in Trizol were transferred to previously cooled bead beater tubes containing 0.1-mm glass beads and treated with Mini-Beadbeater (Biospec Products Inc, USA) twice at a fixed speed for 45 seconds, and then cooled on ice for 1 minute between the treatments. Culture homogenates were incubated at room temperature for 5 minutes and then supplemented with 0.2 ml chloroform, thoroughly mixed by shaking 10 times, and incubated for 3 minutes. After centrifugation at 12 000 g at 4°C for 15 minutes, the aqueous upper phase was carefully transferred to new RNase free tubes. An equal volume of 99% ethanol was added to the transferred aqueous phase and isolation continued using the Direct-Zol RNA Miniprep Plus (Zymo Research, USA) RNA purification kit protocol. Total RNAs were eluted in RNase free water in RNase free tubes. The total RNA concentrations were measured using the Qubit BR RNA Assay Kit (ThermoFisher Scientific, USA) and RNA integrity confirmed on a 0.8% agarose gel in TBE buffer. All rRNA-depleted RNA-seq library preparations were performed according to Shishkin et al.,2015 with minor modifications. RNAtag-Seq allows multiple library preparations in one tube, with initial tagging of total RNA samples with modified (5'P and 3'ddC) DNA barcoded adaptors, each harboring a unique 8 nt sequence used to demultiplex individual libraries after sequencing We combined the library preparation of three biological replicates from WT and ∆rpon preparations in one tube for each bacterial strain. Therefore, 24 unique barcoded adaptors were used to tag the 24 replicates. A total of 100 ng total RNA was used for each biological replicate. The total RNA was fragmented in 2X FastAP Thermosensitive Alkaline Phosphatase buffer for 3 minutes at 94°C, DNase treated, and dephosphorylated with a combination of TURBO DNase and Thermosensitive Alkaline Phosphatase in 1X FastAP buffer for 30 minutes at 37°C. Fragmented, DNase-treated, and dephosphorylated total RNAs were cleaned with a 2X reaction volume of Agencourt RNAClean XP beads. Cleaned total RNAs were incubated with 100 pmol of a unique DNA barcode adaptor at 70°C for 3 minutes, and then ligated with T4 RNA ligase 1 for 90 minutes at 22°C. The ligation was stopped and the enzyme denatured by the addition of RLT buffer. The 36 denatured ligation mixes were then pooled and cleaned in a Zymo Clean & ConcentratorTM-5 column according to the manufacturer's 200 nt cut-off protocol. The RNAs were eluted in 32 ml of RNase free water. The ribosomal RNA was depleted using the Ribo-ZeroTM Magnetic Gold Kit (Bacteria) according to the manufacturer's instructions. The first strand cDNA of each pool was generated using an AffinityScript Multiple Temperature cDNA synthesis kit with 50 pmol of AR2 primer at 55°C for 55 minutes. The RNA was degraded by adding a 10% reaction volume of 1 N NaOH at 70°C for 12 minutes and the reaction neutralized with an 18% reaction volume of 0.5 M acetic acid. After cleaning the reverse transcription primers with a 2X reaction volume of RNAClean XP beads, the 3Tr3 adapter was ligated with T4 RNA ligase 1 at 22°C with overnight incubation. The second ligation was cleaned first with a 2X, and secondly 1.5X, reaction volume of RNAClean XP beads. The cDNA was then used as the template for PCR reaction with FailSafeTM PCR enzyme mix using 12.5 pmol 2P_univP5 as forward primers and 12.5 pmol ScriptSeqTM Index (barcode) PCR primers as reverse primers. The PCR cycles were as follows: 95°C for 3 minutes, followed by 12 cycles at 95°C for 30 seconds, 55°C for 30 seconds, and 68°C for 3 minutes, and then finishing at 68°C for 7 minutes. The PCR product was cleaned first with a 1.5X, and secondly 0.8X, reaction volume of AMPure beads and eluted in RNAse free water. The library concentrations were measured using the QubitTM dsDNA HS Assay Kit and the library insert size determined by the Agilent DNA 1000 Kit in a 2100 Electrophoresis Bioanalyser Instrument (Agilent, USA). The libraries were sequenced by Illumina NovaSeq 6000

Project description:During infection, Yersinia enterocolitica exports Yop proteins via a type III secretion pathway. Secretion is activated when the environmental concentration of calcium ions is below 100 microM (low-calcium response). Yersiniae lacking yopN (lcrE), yscB, sycN, or tyeA do not inactivate the type III pathway even when the concentration of calcium is above 100 microM (calcium-blind phenotype). Purified YscB and SycN proteins form cytoplasmic complexes that bind a region including amino acids 16 to 100 of YopN, whereas TyeA binds YopN residues 101 to 294. Translational fusion of yopN gene sequences to the 5' end of the npt reporter generates hybrid proteins that are transported by the type III pathway. The signal necessary and sufficient for the type III secretion of hybrid proteins is located within the first 15 codons of yopN. Expression of plasmid-borne yopN, but not of yopN(1-294)-npt, complements the calcium-blind phenotype of yopN mutants. Surprisingly, yopN mutants respond to environmental changes in calcium concentration and secrete YopN(1-294)-Npt in the absence but not in the presence of calcium. tyeA is required for the low-calcium regulation of YopN(1-294)-Npt secretion, whereas sycN and yscB mutants fail to secrete YopN(1-294)-Npt in the presence of calcium. Experiments with yopN-npt fusions identified two other signals that regulate the secretion of YopN. yopN codons 16 to 100 prevent the entry of YopN into the type III pathway, a negative regulatory effect that is overcome by expression of yscB and sycN. The portion of YopN encoded by codons 101 to 294 prevents transport of the polypeptide across the bacterial double membrane envelope in the presence of functional tyeA. These data support a model whereby YopN transport may serve as a regulatory mechanism for the activity of the type III pathway. YscB/SycN binding facilitates the initiation of YopN into the type III pathway, whereas TyeA binding prevents transport of the polypeptide across the bacterial envelope. Changes in the environmental calcium concentration relieve the TyeA-mediated regulation, triggering YopN transport and activating the type III pathway.

Project description:Specialized protein translocation systems are used by many bacterial pathogens to deliver effector proteins into host cells that interfere with normal cellular functions. How the host immune system recognizes and responds to this intrusive event is not understood. To address these questions, we determined the mammalian cellular response to the virulence-associated type III secretion system (T3SS) of the human pathogen Yersinia pseudotuberculosis. We found that macrophages devoid of Toll-like receptor (TLR) signaling regulate expression of 266 genes following recognition of the Y. pseudotuberculosis T3SS. This analysis revealed two temporally distinct responses that could be separated into activation of NFkappaB- and type I IFN-regulated genes. Extracellular bacteria were capable of triggering these signaling events, as inhibition of bacterial uptake had no effect on the ensuing innate immune response. The cytosolic peptidoglycan sensors Nod1 and Nod2 and the inflammasome component caspase-1 were not involved in NFkappaB activation following recognition of the Y. pseudotuberculosis T3SS. However, caspase-1 was required for secretion of the inflammatory cytokine IL-1beta in response to T3SS-positive Y. pseudotuberculosis. In order to characterize the bacterial requirements for induction of this novel TLR-, Nod1/2-, and caspase-1-independent response, we used Y. pseudotuberculosis strains lacking specific components of the T3SS. Formation of a functional T3SS pore was required, as bacteria expressing a secretion needle, but lacking the pore-forming proteins YopB or YopD, did not trigger these signaling events. However, nonspecific membrane disruption could not recapitulate the NFkappaB signaling triggered by Y. pseudotuberculosis expressing a functional T3SS pore. Although host cell recognition of the T3SS did not require known translocated substrates, the ensuing response could be modulated by effectors such as YopJ and YopT, as YopT amplified the response, while YopJ dampened it. Collectively, these data suggest that combined recognition of the T3SS pore and YopBD-mediated delivery of immune activating ligands into the host cytosol informs the host cell of pathogenic challenge. This leads to a unique, multifactorial response distinct from the canonical immune response to a bacterium lacking a T3SS.

Dataset Information

Genetically engineered frameshifted YopN-TyeA chimeras influence type III secretion system function in Yersinia pseudotuberculosis.

Publications

Genetically engineered frameshifted YopN-TyeA chimeras influence type III secretion system function in Yersinia pseudotuberculosis.

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