| 1. |
- Frost, Stefan, et al.
(författare)
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Autoproteolysis and Intramolecular Dissociation of Yersinia YscU Precedes Secretion of Its C-Terminal Polypeptide YscU CC
- 2012
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Ingår i: PLOS ONE. - : Public Library of Science (PLoS). - 1932-6203. ; 7:11
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Tidskriftsartikel (refereegranskat)abstract
- Type III secretion system mediated secretion and translocation of Yop-effector proteins across the eukaryotic target cell membrane by pathogenic Yersinia is highly organized and is dependent on a switching event from secretion of early structural substrates to late effector substrates (Yops). Substrate switching can be mimicked in vitro by modulating the calcium levels in the growth medium. YscU that is essential for regulation of this switch undergoes autoproteolysis at a conserved N↑PTH motif, resulting in a 10 kDa C-terminal polypeptide fragment denoted YscUCC. Here we show that depletion of calcium induces intramolecular dissociation of YscUCC from YscU followed by secretion of the YscUCC polypeptide. Thus, YscUCC behaved in vivo as a Yop protein with respect to secretion properties. Further, destabilized yscU mutants displayed increased rates of dissociation of YscUCC in vitro resulting in enhanced Yop secretion in vivo at 30°C relative to the wild-type strain.These findings provide strong support to the relevance of YscUCC dissociation for Yop secretion. We propose that YscUCC orchestrates a block in the secretion channel that is eliminated by calcium depletion. Further, the striking homology between different members of the YscU/FlhB family suggests that this protein family possess regulatory functions also in other bacteria using comparable mechanisms.
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| 2. |
- Weise, Christoph F, et al.
(författare)
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Negatively charged lipid membranes promote a disorder-order transition in the Yersinia YscU protein
- 2014
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Ingår i: Biophysical Journal. - : Cell Press. - 0006-3495 .- 1542-0086. ; 107:8, s. 1950-1961
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Tidskriftsartikel (refereegranskat)abstract
- The inner membrane of Gram-negative bacteria is negatively charged, rendering positively charged cytoplasmic proteins in close proximity likely candidates for protein-membrane interactions. YscU is a Yersinia pseudotuberculosis type III secretion system protein crucial for bacterial pathogenesis. The protein contains a highly conserved positively charged linker sequence that separates membrane-spanning and cytoplasmic (YscUC) domains. Although disordered in solution, inspection of the primary sequence of the linker reveals that positively charged residues are separated with a typical helical periodicity. Here, we demonstrate that the linker sequence of YscU undergoes a largely electrostatically driven coil-to-helix transition upon binding to negatively charged membrane interfaces. Using membrane-mimicking sodium dodecyl sulfate micelles, an NMR derived structural model reveals the induction of three helical segments in the linker. The overall linker placement in sodium dodecyl sulfate micelles was identified by NMR experiments including paramagnetic relaxation enhancements. Partitioning of individual residues agrees with their hydrophobicity and supports an interfacial positioning of the helices. Replacement of positively charged linker residues with alanine resulted in YscUC variants displaying attenuated membrane-binding affinities, suggesting that the membrane interaction depends on positive charges within the linker. In vivo experiments with bacteria expressing these YscU replacements resulted in phenotypes displaying significantly reduced effector protein secretion levels. Taken together, our data identify a previously unknown membrane-interacting surface of YscUC that, when perturbed by mutations, disrupts the function of the pathogenic machinery in Yersinia.
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| 3. |
- Beery, T. H., et al.
(författare)
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Nature to place : Rethinking the environmental connectedness perspective
- 2014
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Ingår i: Journal of Environmental Psychology. - Amsterdam : Elsevier BV. - 0272-4944 .- 1522-9610. ; 40, s. 198-205
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Tidskriftsartikel (refereegranskat)abstract
- The environmental connectedness perspective posits that direct encounter with generalized, or non-specific "nature," leads to environmental connectedness and subsequent pro-environmental behavior. This article examines this perspective and proposes a place-based application of the nature encounter-environmental behavior relation. An empirical study using data from a national survey on outdoor recreation and nature-based tourism is presented. Results show a minimal relationship between measures of environmental connectedness and self-reports of environmental behavior. The following examination of the environmental connectedness perspective reveals that environmental connectedness is rooted in a material/objective perspective, neglecting the human domain of perceptions, values, and representations. The environment as "nature" is portrayed as a geographically undefined agent with the inherent power to change human attitudes and behavior. Based on this, the article concludes with a proposed replacement of the elusive concept of nature for the relational concept of place. © 2014 Elsevier Ltd.
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| 4. |
- Engström, Patrik, 1982-, et al.
(författare)
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Mutations in hemG Mediate Resistance to Salicylidene Acylhydrazides, Demonstrating a Novel Link between Protoporphyrinogen Oxidase (HemG) and Chlamydia trachomatis Infectivity
- 2013
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Ingår i: Journal of Bacteriology. - Washington DC, USA : American Society for Microbiology. - 0021-9193 .- 1098-5530. ; 195:18, s. 4221-4230
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Tidskriftsartikel (refereegranskat)abstract
- Salicylidene acylhydrazides (SAHs) inhibit the type III secretion system (T3S) of Yersinia and other Gram-negative bacteria. In addition, SAHs restrict the growth and development of Chlamydia species. However, since the inhibition of Chlamydia growth by SAH is suppressed by the addition of excess iron and since SAHs have an iron-chelating capacity, their role as specific T3S inhibitors is unclear. We investigated here whether SAHs exhibit a function on C. trachomatis that goes beyond iron chelation. We found that the iron-saturated SAH INP0341 (IS-INP0341) specifically affects C. trachomatis infectivity with reduced generation of infectious elementary body (EB) progeny. Selection and isolation of spontaneous SAH-resistant mutant strains revealed that mutations in hemG suppressed the reduced infectivity caused by IS-INP0341 treatment. Structural modeling of C. trachomatis HemG predicts that the acquired mutations are located in the active site of the enzyme, suggesting that IS-INP0341 inhibits this domain of HemG and that protoporphyrinogen oxidase (HemG) and heme metabolism are important for C. trachomatis infectivity.
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| 5. |
- Eriksson, Jonas, et al.
(författare)
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Small Molecule Screening for Inhibitors of the YopH Phosphatase of Yersinia pseudotuberculosis
- 2012
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Ingår i: Advances in Yersinia Research. - New York : Springer. - 9781461435600 - 9781461435617 ; , s. 357-363
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Bokkapitel (refereegranskat)abstract
- Bacterial virulence systems are attractive targets for development of new antibacterial agents. Yersinia spp. utilize the type III secretion (T3S) system to secrete and translocate Yersinia outer proteins (Yop effectors) into the cytosol of the target cell and thereby overcome host defenses to successfully establish an infection. Thus, the Yop effectors constitute attractive targets for drug development. In the present study we apply small molecule screening to identify inhibitors of one of the secreted proteins YopH, a tyrosine phosphatase required for virulence. Characterization of seven inhibitors indicated that both competitive and noncompetitive inhibitors were identified with IC50 values of 6–20 μM.
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