99 research outputs found
Weak splittings of quotients of Drinfeld and Heisenberg doubles
We investigate the fine structure of the simplectic foliations of Poisson
homogeneous spaces. Two general results are proved for weak splittings of
surjective Poisson submersions from Heisenberg and Drinfeld doubles. The
implications of these results are that the torus orbits of symplectic leaves of
the quotients can be explicitly realized as Poisson-Dirac submanifolds of the
torus orbits of the doubles. The results have a wide range of applications to
many families of real and complex Poisson structures on flag varieties. Their
torus orbits of leaves recover important families of varieties such as the open
Richardson varieties.Comment: 20 pages, AMS Late
Generalizing Tanisaki's ideal via ideals of truncated symmetric functions
We define a family of ideals in the polynomial ring
that are parametrized by Hessenberg functions
(equivalently Dyck paths or ample partitions). The ideals generalize
algebraically a family of ideals called the Tanisaki ideal, which is used in a
geometric construction of permutation representations called Springer theory.
To define , we use polynomials in a proper subset of the variables
that are symmetric under the corresponding permutation
subgroup. We call these polynomials {\em truncated symmetric functions} and
show combinatorial identities relating different kinds of truncated symmetric
polynomials. We then prove several key properties of , including that if
in the natural partial order on Dyck paths then ,
and explicitly construct a Gr\"{o}bner basis for . We use a second family
of ideals for which some of the claims are easier to see, and prove that
. The ideals arise in work of Ding, Develin-Martin-Reiner, and
Gasharov-Reiner on a family of Schubert varieties called partition varieties.
Using earlier work of the first author, the current manuscript proves that the
ideals generalize the Tanisaki ideals both algebraically and
geometrically, from Springer varieties to a family of nilpotent Hessenberg
varieties.Comment: v1 had 27 pages. v2 is 29 pages and adds Appendix B, where we include
a recent proof by Federico Galetto of a conjecture given in the previous
version. We also add some connections between our work and earlier results of
Ding, Gasharov-Reiner, and Develin-Martin-Reiner. v3 corrects a typo in
Valibouze's citation in the bibliography. To appear in Journal of Algebraic
Combinatoric
Depletion of Plasmodium berghei Plasmoredoxin Reveals a Non-Essential Role for Life Cycle Progression of the Malaria Parasite
Proliferation of the pathogenic Plasmodium asexual blood stages in host erythrocytes requires an exquisite capacity to protect the malaria parasite against oxidative stress. This function is achieved by a complex antioxidant defence system composed of redox-active proteins and low MW antioxidants. Here, we disrupted the P. berghei plasmoredoxin gene that encodes a parasite-specific 22 kDa member of the thioredoxin superfamily. The successful generation of plasmoredoxin knockout mutants in the rodent model malaria parasite and phenotypic analysis during life cycle progression revealed a non-vital role in vivo. Our findings suggest that plasmoredoxin fulfils a specialized and dispensable role for Plasmodium and highlights the need for target validation to inform drug development strategies
The Type III Secreted Protein BspR Regulates the Virulence Genes in Bordetella bronchiseptica
Bordetella bronchiseptica is closely related with B. pertussis and B. parapertussis, the causative agents of whooping cough. These pathogenic species share a number of virulence genes, including the gene locus for the type III secretion system (T3SS) that delivers effector proteins. To identify unknown type III effectors in Bordetella, secreted proteins in the bacterial culture supernatants of wild-type B. bronchiseptica and an isogenic T3SS-deficient mutant were compared with iTRAQ-based, quantitative proteomic analysis method. BB1639, annotated as a hypothetical protein, was identified as a novel type III secreted protein and was designated BspR (Bordetella
secreted protein regulator). The virulence of a BspR mutant (ΞbspR) in B. bronchiseptica was significantly attenuated in a mouse infection model. BspR was also highly conserved in B. pertussis and B. parapertussis, suggesting that BspR is an essential virulence factor in these three Bordetella species. Interestingly, the BspR-deficient strain showed hyper-secretion of T3SS-related proteins. Furthermore, T3SS-dependent host cell cytotoxicity and hemolytic activity were also enhanced in the absence of BspR. By contrast, the expression of filamentous hemagglutinin, pertactin, and adenylate cyclase toxin was completely abolished in the BspR-deficient strain. Finally, we demonstrated that BspR is involved in the iron-responsive regulation of T3SS. Thus, Bordetella virulence factors are coordinately but inversely controlled by BspR, which functions as a regulator in response to iron starvation
The Pathogenic Properties of a Novel and Conserved Gene Product, KerV, in Proteobacteria
Identification of novel virulence factors is essential for understanding bacterial pathogenesis and designing antibacterial strategies. In this study, we uncover such a factor, termed KerV, in Proteobacteria. Experiments carried out in a variety of eukaryotic host infection models revealed that the virulence of a Pseudomonas aeruginosa kerV null mutant was compromised when it interacted with amoebae, plants, flies, and mice. Bioinformatics analyses indicated that KerV is a hypothetical methyltransferase and is well-conserved across numerous Proteobacteria, including both well-known and emerging pathogens (e.g., virulent Burkholderia, Escherichia, Shigella, Vibrio, Salmonella, Yersinia and Brucella species). Furthermore, among the 197 kerV orthologs analyzed in this study, about 89% reside in a defined genomic neighborhood, which also possesses essential DNA replication and repair genes and detoxification gene. Finally, infection of Drosophila melanogaster with null mutants demonstrated that KerV orthologs are also crucial in Vibrio cholerae and Yersinia pseudotuberculosis pathogenesis. Our findings suggested that KerV has a novel and broad significance as a virulence factor in pathogenic Proteobacteria and it might serve as a new target for antibiotic drug design
Structural Basis for Type VI Secretion Effector Recognition by a Cognate Immunity Protein
The type VI secretion system (T6SS) has emerged as an important mediator of interbacterial interactions. A T6SS from Pseudomonas aeruginosa targets at least three effector proteins, type VI secretion exported 1β3 (Tse1β3), to recipient Gram-negative cells. The Tse2 protein is a cytoplasmic effector that acts as a potent inhibitor of target cell proliferation, thus providing a pronounced fitness advantage for P. aeruginosa donor cells. P. aeruginosa utilizes a dedicated immunity protein, type VI secretion immunity 2 (Tsi2), to protect against endogenous and intercellularly-transferred Tse2. Here we show that Tse2 delivered by the T6SS efficiently induces quiescence, not death, within recipient cells. We demonstrate that despite direct interaction of Tsi2 and Tse2 in the cytoplasm, Tsi2 is dispensable for targeting the toxin to the secretory apparatus. To gain insights into the molecular basis of Tse2 immunity, we solved the 1.00 Γ
X-ray crystal structure of Tsi2. The structure shows that Tsi2 assembles as a dimer that does not resemble previously characterized immunity or antitoxin proteins. A genetic screen for Tsi2 mutants deficient in Tse2 interaction revealed an acidic patch distal to the Tsi2 homodimer interface that mediates toxin interaction and immunity. Consistent with this finding, we observed that destabilization of the Tsi2 dimer does not impact Tse2 interaction. The molecular insights into Tsi2 structure and function garnered from this study shed light on the mechanisms of T6 effector secretion, and indicate that the Tse2βTsi2 effectorβimmunity pair has features distinguishing it from previously characterized toxinβimmunity and toxinβantitoxin systems
Identification of Chromosomal Genes in Yersinia pestis that Influence Type III Secretion and Delivery of Yops into Target Cells
Pathogenic Yersinia species possess a type III secretion system, which is required for the delivery of effector Yop proteins into target cells during infection. Genes encoding the type III secretion machinery, its substrates, and several regulatory proteins all reside on a 70-Kb virulence plasmid. Genes encoded in the chromosome of yersiniae are thought to play important roles in bacterial perception of host environments and in the coordinated activation of the type III secretion pathway. Here, we investigate the contribution of chromosomal genes to the complex regulatory process controlling type III secretion in Yersinia pestis. Using transposon mutagenesis, we identified five chromosomal genes required for expression or secretion of Yops in laboratory media. Four out of the five chromosomal mutants were defective to various extents at injecting Yops into tissue culture cells. Interestingly, we found one mutant that was not able to secrete in vitro but was fully competent for injecting Yops into host cells, suggesting independent mechanisms for activation of the secretion apparatus. When tested in a mouse model of plague disease, three mutants were avirulent, whereas two strains were severely attenuated. Together these results demonstrate the importance of Y. pestis chromosomal genes in the proper function of type III secretion and in the pathogenesis of plague
The Cost of Virulence: Retarded Growth of Salmonella Typhimurium Cells Expressing Type III Secretion System 1
Virulence factors generally enhance a pathogen's fitness and thereby foster transmission. However, most studies of pathogen fitness have been performed by averaging the phenotypes over large populations. Here, we have analyzed the fitness costs of virulence factor expression by Salmonella enterica subspecies I serovar Typhimurium in simple culture experiments. The type III secretion system ttss-1, a cardinal virulence factor for eliciting Salmonella diarrhea, is expressed by just a fraction of the S. Typhimurium population, yielding a mixture of cells that either express ttss-1 (TTSS-1+ phenotype) or not (TTSS-1β phenotype). Here, we studied in vitro the TTSS-1+ phenotype at the single cell level using fluorescent protein reporters. The regulator hilA controlled the fraction of TTSS-1+ individuals and their ttss-1 expression level. Strikingly, cells of the TTSS-1+ phenotype grew slower than cells of the TTSS-1β phenotype. The growth retardation was at least partially attributable to the expression of TTSS-1 effector and/or translocon proteins. In spite of this growth penalty, the TTSS-1+ subpopulation increased from <10% to approx. 60% during the late logarithmic growth phase of an LB batch culture. This was attributable to an increasing initiation rate of ttss-1 expression, in response to environmental cues accumulating during this growth phase, as shown by experimental data and mathematical modeling. Finally, hilA and hilD mutants, which form only fast-growing TTSS-1β cells, outcompeted wild type S. Typhimurium in mixed cultures. Our data demonstrated that virulence factor expression imposes a growth penalty in a non-host environment. This raises important questions about compensating mechanisms during host infection which ensure successful propagation of the genotype
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