| 61. |
- Buts, L, et al.
(författare)
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The fimbrial adhesin F17-G of enterotoxigenic Escherichia coli has an immunoglobulin-like lectin domain that binds N-acetylglucosamine
- 2003
-
Ingår i: Molecular Microbiology. - : Wiley. - 0950-382X .- 1365-2958. ; 49:3, s. 705-715
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Tidskriftsartikel (refereegranskat)abstract
- The F17-G adhesin at the tip of flexible F17 fimbriae of enterotoxigenic Escherichia coli mediates binding to N-acetyl-beta-D-glucosamine-presenting receptors on the microvilli of the intestinal epithelium of ruminants. We report the 1.7 Angstrom resolution crystal structure of the lectin domain of F17-G, both free and in complex with N-acetylglucosamine. The monosaccharide is bound on the side of the ellipsoid-shaped protein in a conserved site around which all natural variations of F17-G are clustered. A model is proposed for the interaction between F17-fimbriated E. coli and microvilli with enhanced affinity compared with the binding constant we determined for F17-G binding to N-acetylglucosamine (0.85 mM(-1)). Unexpectedly, the F17-G structure reveals that the lectin domains of the F17-G, PapGII and FimH fimbrial adhesins all share the immunoglobulin-like fold of the structural components (pilins) of their fimbriae, despite lack of any sequence identity. Fold comparisons with pilin and chaperone structures of the chaperone/usher pathway highlight the central role of the C-terminal beta-strand G of the immunoglobulin-like fold and provides new insights into pilus assembly, function and adhesion.
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| 62. |
- Cava, Felipe, et al.
(författare)
-
A cytochrome c containing nitrate reductase plays a role in electron transport for denitrification in Thermus thermophilus without involvement of the bc respiratory complex
- 2008
-
Ingår i: Molecular Microbiology. - : Wiley. - 0950-382X .- 1365-2958. ; 70:2, s. 507-518
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Tidskriftsartikel (refereegranskat)abstract
- The bc(1) respiratory complex III constitutes a key energy-conserving respiratory electron transporter between complex I (type I NADH dehydrogenase) and II (succinate dehydrogenase) and the final nitrogen oxide reductases (Nir, Nor and Nos) in most denitrifying bacteria. However, we show that the expression of complex III from Thermus thermophilus is repressed under denitrification, and that its role as electron transporter is replaced by an unusual nitrate reductase (Nar) that contains a periplasmic cytochrome c (NarC). Several lines of evidence support this conclusion: (i) nitrite and NO are as effective signals as nitrate for the induction of Nar; (ii) narC mutants are defective in anaerobic growth with nitrite, NO and N2O; (iii) such mutants present decreased NADH oxidation coupled to these electron acceptors; and (iv) complementation assays of the mutants reveal that the membrane-distal heme c of NarC was necessary for anaerobic growth with nitrite, whereas the membrane-proximal heme c was not. Finally, we show evidence to support that Nrc, the main NADH oxidative activity in denitrification, interacts with Nar through their respective membrane subunits. Thus, we propose the existence of a Nrc-Nar respiratory super-complex that is required for the development of the whole denitrification pathway in T. thermophilus.
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| 63. |
- Cava, Felipe, et al.
(författare)
-
Binding to pyruvylated compounds as an ancestral mechanism to anchor the outer envelope in primitive bacteria
- 2004
-
Ingår i: Molecular Microbiology. - : Wiley. - 0950-382X .- 1365-2958. ; 52:3, s. 677-690
-
Tidskriftsartikel (refereegranskat)abstract
- Electron microscopy of isolated cell walls of the ancient bacterium Thermus thermophilus revealed that most of the peptidoglycan (PG) surface, apart from the septal region, was shielded against specific alphaPG antibodies. On the other hand, an antiserum raised against S-layer-attached cell wall fragments (alphaSAC) bound to most of the surface except for the septal regions. Treatments with alpha-amylase and pronase E made the entire cell wall surface uniformly accessible to alphaPG and severely decreased the binding of alphaSAC. We concluded that a layer of strongly bound secondary cell wall polymers (SCWPs) covers most of the cell wall surface in this ancient bacterium. A preliminary analysis revealed that such SCWPs constitute 14% of the cell wall and are essentially composed of sugars. Enzyme treatments of the cell walls revealed that SCWP was required in vitro for the binding of the S-layer protein through the S-layer homology (SLH) motif. The csaB gene was necessary for the attachment of the S-layer-outer membrane (OM) complex to the cell wall in growing cells of T. thermophilus. In vitro experiments confirmed that cell walls from a csaB mutant bound to the S-layer with a much lower affinity ( approximately 1/10) than that of the wild type. CsaB was found to be required for pyruvylation of components of the SCWP and for immunodetection with alpha-SAC antiserum. Therefore, the S-layer-OM complex of T. thermophilus binds to the cell wall through the SLH motif of the S-layer protein via a strong interaction with a highly immunogenic pyruvylated component of the SCWP. Immuno-cross-reactive compounds were detected with alphaSAC on cell walls of other Thermus spp. and in the phylogenetically related microorganism Deinococcus radiodurans. These results imply that the interaction between the SLH motif and pyruvylated components of the cell wall arose early during bacterial evolution as an ancestral mechanism for anchoring proteins and outer membranes to the cell walls of primitive bacteria.
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| 64. |
- Cava, Felipe, et al.
(författare)
-
Control of the respiratory metabolism of Thermus thermophilus by the nitrate respiration conjugative element NCE
- 2007
-
Ingår i: Molecular Microbiology. - : Wiley. - 0950-382X .- 1365-2958. ; 64:3, s. 630-646
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Tidskriftsartikel (refereegranskat)abstract
- The strains of Thermus thermophilus that contain the nitrate respiration conjugative element (NCE) replace their aerobic respiratory chain by an anaerobic counterpart made of the Nrc-NADH dehydrogenase and the Nar-nitrate reductase in response to nitrate and oxygen depletion. This replacement depends on DnrS and DnrT, two homologues to sensory transcription factors encoded in a bicistronic operon by the NCE. DnrS is an oxygen-sensitive protein required in vivo to activate transcription on its own dnr promoter and on that of the nar operon, but not required for the expression of the nrc operon. In contrast, DnrT is required for the transcription of these three operons and also for the repression of nqo, the operon that encodes the major respiratory NADH dehydrogenase expressed during aerobic growth. Thermophilic in vitro assays revealed that low DnrT concentrations allows the recruitment of the T. thermophilus RNA polymerase sigma(A) holoenzyme to the nrc promoter and its transcription, whereas higher DnrT concentrations are required to repress transcription on the nqo promoter. In conclusion, our data show a complex autoinducible mechanism by which DnrT functions as the transcriptional switch that allows the NCE to take the control of the respiratory metabolism of its host during adaptation to anaerobic growth.
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| 65. |
- Croxatto, Antony, et al.
(författare)
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A distinctive dual-channel quorum-sensing system operates in Vibrio anguillarum
- 2004
-
Ingår i: Molecular Microbiology. - : Wiley-Blackwell. - 0950-382X .- 1365-2958. ; 52:6, s. 1677-1689
-
Tidskriftsartikel (refereegranskat)abstract
- Many bacterial cells communicate using diffusible signal molecules to monitor cell population density via a process termed quorum sensing. In marine Vibrio species, the Vibrio harveyi-type LuxR protein is a key player in a quorum-sensing phosphorelay cascade, which controls the expression of virulence, symbiotic and survival genes. Previously, we characterized Vibrio anguillarum homologues of LuxR (VanT) and LuxMN (VanMN) and, in this study, we have identified homologues of LuxPQ (VanPQ) and LuxOU (VanOU). In contrast to other Vibrio species, vanT was expressed at low cell density and showed no significant induction as the cell number increased. In addition, although the loss of VanO increased vanT expression, the loss of VanU, unexpectedly, decreased it. Both VanN and VanQ were required for repression of vanT even in a vanU mutant, suggesting an alternative route for VanNQ signal transduction other than via VanU. VanT negatively regulated its own expression by binding and repressing the vanT promoter and by binding and activating the vanOU promoter. The signal relay results in a cellular response as expression of the metalloprotease, empA, was altered similar to that of vanT in all the mutants. Consequently, the V. anguillarum quorum-sensing phosphorelay systems work differently from those of V. harveyi and may be used to limit rather than induce vanT expression.
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| 66. |
- del Peso-Santos, Teresa, et al.
(författare)
-
The styrene-responsive StyS/StyR regulation system controls expression of an auxiliary phenylacetyl-coenzyme A ligase : implications for rapid metabolic coupling of the styrene upper- and lower-degradative pathways.
- 2008
-
Ingår i: Molecular microbiology. - : Wiley. - 1365-2958 .- 0950-382X. ; 69:2, s. 317-30
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Tidskriftsartikel (refereegranskat)abstract
- Pseudomonas sp. strain Y2 degrades styrene through oxidation to phenylacetic acid via the styABCD operon-encoded enzymes, whose expression is induced in response to styrene by the StyS/StyR two-component regulatory system. Further transformation of phenylacetic acid to tricarboxylic acid cycle intermediates is mediated by the enzymes of paa catabolic genes, whose expression is regulated by the PaaX repressor. The first step of this paa degradation pathway is catalysed by paaF-encoded phenylacetyl-coenzyme A ligases that produce phenylacetyl-coenzyme A. This metabolic intermediate, upon being bound by PaaX, inactivates PaaX-mediated repression of both the paa genes and the styABCD operon. Strain Y2 is unique in having three paaF genes located within two complete copies of the paa gene clusters. Expression of both paaF and paaF3 is controlled by the PaaX repressor. Here we use specific mutants in combination with in vivo and in vitro assays to demonstrate that paaF2, adjacent to the StyS/StyR regulatory genes, belongs to the StyR regulon and is not subject to repression by PaaX. We propose that this unexpected styrene-responsive regulatory strategy for the otherwise metabolically redundant PaaF2 auxiliary enzyme provides a system for rapid co-ordinate de-repression of the two sets of catabolic genes required for styrene degradation.
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| 67. |
- Edqvist, Petra J, et al.
(författare)
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Tetratricopeptide repeats in the type III secretion chaperone, LcrH : their role in substrate binding and secretion.
- 2006
-
Ingår i: Molecular Microbiology. - : Wiley. - 0950-382X .- 1365-2958. ; 59:1, s. 31-44
-
Tidskriftsartikel (refereegranskat)abstract
- Non-flagellar type III secretion systems (T3SSs) transport proteins across the bacterial cell and into eukaryotic cells. Targeting of proteins into host cells requires a dedicated translocation apparatus. Efficient secretion of the translocator proteins that make up this apparatus depends on molecular chaperones. Chaperones of the translocators (also called class-II chaperones) are characterized by the possession of three tandem tetratricopeptide repeats (TPRs). We wished to dissect the relations between chaperone structure and function and to validate a structural model using site-directed mutagenesis. Drawing on a number of experimental approaches and focusing on LcrH, a class-II chaperone from the Yersinia Ysc-Yop T3SS, we examined the contributions of different residues, residue classes and regions of the protein to chaperone stability, chaperone-substrate binding, substrate stability and secretion and regulation of Yop protein synthesis. We confirmed the expected role of the conserved canonical residues from the TPRs to chaperone stability and function. Eleven mutations specifically abrogated YopB binding or secretion while three mutations led to a specific loss of YopD secretion. These are the first mutations described for any class-II chaperone that allow interactions with one translocator to be dissociated from interactions with the other. Strikingly, all mutations affecting the interaction with YopB mapped to residues with side chains projecting from the inner, concave surface of the modelled TPR structure, defining a YopB interaction site. Conversely, all mutations preventing YopD secretion affect residues that lie on the outer, convex surface of the triple-TPR cluster in our model, suggesting that this region of the molecule represents a distinct interaction site for YopD. Intriguingly, one of the LcrH double mutants, Y40A/F44A, was able to maintain stable substrates inside bacteria, but unable to secrete them, suggesting that these two residues might influence delivery of substrates to the secretion apparatus.
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| 68. |
- Ettema, Thijs J. G., et al.
(författare)
-
An actin-based cytoskeleton in archaea
- 2011
-
Ingår i: Molecular Microbiology. - : Wiley. - 0950-382X .- 1365-2958. ; 80:4, s. 1052-1061
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Tidskriftsartikel (refereegranskat)abstract
- In eukaryotic and bacterial cells, spatial organization is dependent upon cytoskeletal filaments. Actin is a main eukaryotic cytoskeletal element, involved in key processes such as cell shape determination, mechanical force generation and cytokinesis. We describe an archaeal cytoskeleton which forms helical structures within Pyrobaculum calidifontis cells, as shown by in situ immunostaining. The core components include an archaeal actin homologue, Crenactin, closely related to the eukaryotic counterpart. The crenactin gene belongs to a conserved gene cluster denoted Arcade (actin-related cytoskeleton in Archaea involved in shape determination). The phylogenetic distribution of arcade genes is restricted to the crenarchaeal Thermoproteales lineage, and to Korarchaeota, and correlates with rod-shaped and filamentous cell morphologies. Whereas Arcadin-1, -3 and -4 form helical structures, suggesting cytoskeleton-associated functions, Arcadin-2 was found to be localized between segregated nucleoids in a cell subpopulation, in agreement with possible involvement in cytokinesis. The results support a crenarchaeal origin of the eukaryotic actin cytoskeleton and, as such, have implications for theories concerning the origin of the eukaryotic cell.
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| 69. |
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| 70. |
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