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  • 1
    Language: English
    In: Journal of bacteriology, May 2013, Vol.195(9), pp.1912-9
    Description: The outer membrane is the first line of defense for Gram-negative bacteria and serves as a major barrier for antibiotics and other harmful substances. The biosynthesis of lipopolysaccharides (LPS), the essential component of the outer membrane, must be tightly controlled as both too much and too little LPS are toxic. In Escherichia coli, the cellular level of the key enzyme LpxC, which catalyzes the first committed step in LPS biosynthesis, is adjusted by proteolysis carried out by the essential and membrane-bound protease FtsH. Here, we demonstrate that LpxC is degraded in a growth rate-dependent manner with half-lives between 4 min and 〉2 h. According to the cellular demand for LPS biosynthesis, LpxC is degraded during slow growth but stabilized when cells grow rapidly. Disturbing the balance between LPS and phospholipid biosynthesis in favor of phospholipid production in an E. coli strain encoding a hyperactive FabZ protein abolishes growth rate dependency of LpxC proteolysis. Lack of the alternative sigma factor RpoS or inorganic polyphosphates, which are known to mediate growth rate-dependent gene regulation in E. coli, did not affect proteolysis of LpxC. In contrast, absence of RelA and SpoT, which synthesize the alarmone (p)ppGpp, deregulated LpxC degradation resulting in rapid proteolysis in fast-growing cells and stabilization during slow growth. Our data provide new insights into the essential control of LPS biosynthesis in E. coli.
    Keywords: ATP-Dependent Proteases -- Metabolism ; Escherichia Coli -- Enzymology ; Escherichia Coli Proteins -- Metabolism ; Guanine Nucleotides -- Metabolism ; Lipopolysaccharides -- Biosynthesis
    ISSN: 00219193
    E-ISSN: 1098-5530
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  • 2
    Article
    Article
    In: Nature, 2013, Vol.502(7470), p.178
    Description: The human pathogen Neisseria meningitidis, which can cause septicaemia and meningitis, has evolved various defensive mechanisms including a polysaccharide capsule that aids survival in extracellular fluids. Here Christoph Tang and colleagues demonstrate that capsule expression in N. meningitidis is regulated by an RNA thermosensor located in the 5-untranslated region of the messenger RNA for three genes required for capsule biosynthesis. The authors suggest that the bacteria sense the inflammatory status of the nasopharyngeal mucosa by detecting the temperature rise associated with inflammation and recruitment of immune effectors. The primarily commensal N. meningitidis is then able to bolster its own defences to resist host reactions to coinfecting viral pathogens such as such as influenza.
    Keywords: Sciences (General) ; Physics;
    ISSN: 0028-0836
    E-ISSN: 14764687
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  • 3
    Language: English
    In: Nature, Oct 10, 2013, Vol.502(7470), p.178(2)
    Description: Fascinatingly, Loh and co-workers reveal that RNA thermosensing also regulates the synthesis of two of these factors: factor H binding protein, which regulates the complement pathway of the immune system, and Lst, which modifies the lipopolysaccharide molecules in the outer membrane of the bacterium. [...]in an unprecedented scenario, three independent RNA thermosensors join forces to counteract immune killing in this important human pathogen (Fig. 1c). The concomitant immune response could eradicate the harmless bystander N. meningitidis, and so inducing immune-evasion mechanisms as soon as the host temperature rises seems like a logical survival strategy. [...]the bacterium would benefit from its temperature-induced protective capsule once it gains access to the bloodstream.
    Keywords: RNA – Research ; RNA – Physiological Aspects ; Host-Parasite Relationships – Physiological Aspects ; Host-Parasite Relationships – Genetic Aspects ; Host-Parasite Relationships – Research ; Immune Response – Physiological Aspects ; Immune Response – Genetic Aspects ; Immune Response – Research ; Neisseria Meningitidis – Physiological Aspects ; Neisseria Meningitidis – Genetic Aspects ; Neisseria Meningitidis – Research
    ISSN: 0028-0836
    E-ISSN: 14764687
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  • 4
    Language: English
    In: The Journal of Bacteriology, 2011, Vol. 193(5), p.1090
    Description: Despite the essential function of lipopolysaccharides (LPS) in Gram-negative bacteria, it is largely unknown how the exact amount of this molecule in the outer membrane is controlled. The first committed step in LPS biosynthesis is catalyzed by the LpxC enzyme. In Escherichia coli, the cellular concentration of LpxC is adjusted by the only essential protease in this organism, the membrane-anchored metalloprotease FtsH. Turnover of E. coli LpxC requires a length- and sequence-specific C-terminal degradation signal. LpxC proteins from Salmonella, Yersinia, and Vibrio species carry similar C-terminal ends and, like the E. coli enzyme, were degraded by FtsH. Although LpxC proteins are highly conserved in Gram-negative bacteria, there are striking differences in their C termini. The Aquifex aeolicus enzyme, which is devoid of the C-terminal extension, was stable in E. coli, whereas LpxC from the alphaproteobacteria Agrobacterium tumefaciens and Rhodobacter capsulatus was degraded by the Lon protease. Proteolysis of the A. tumefaciens protein required the C-terminal end of LpxC. High stability of Pseudomonas aeruginosa LpxC in E. coli and P. aeruginosa suggested that Pseudomonas uses a proteolysis-independent strategy to control its LPS content. The differences in LpxC turnover along with previously reported differences in susceptibility against antimicrobial compounds have important implications for the potential of LpxC as a drug target. doi: 10.1128/JB.01043-10
    Keywords: Proteases -- Physiological Aspects ; Proteolysis -- Methods ; Mitogens -- Physiological Aspects ; Gram-negative Bacteria -- Physiological Aspects ; Biosynthesis -- Methods;
    ISSN: 0021-9193
    ISSN: 00219193
    E-ISSN: 10985530
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  • 5
    Language: English
    In: Molecular microbiology, June 2011, Vol.80(5), pp.1313-25
    Description: Post-translational proteolysis-dependent regulation of critical cellular processes is a common feature in bacteria. The Escherichia coli Lon protease is involved in the control of the SOS response, acid tolerance and nutritional deprivation. Moreover, Lon plays a role in the regulation of toxin-antitoxin (TA) systems and thereby is linked to persister cell induction. Persister cells represent a small subpopulation that has reversibly switched to a dormant and non-dividing state without genomic alterations. Formation of persister cells permits viability upon nutritional depletion and severe environmental stresses. CspD is a replication inhibitor, which is induced in stationary phase or upon carbon starvation and increases the production of persister cells. It has remained unknown how CspD activity is counteracted when growth is resumed. Here we report that CspD is subject to proteolysis by the Lon protease both in vivo and in vitro. Turnover of CspD by Lon is strictly adjusted to the growth rate and growth phase of E. coli, reflecting the necessity to control CspD levels according to the physiological conditions.
    Keywords: DNA Replication ; Down-Regulation ; Escherichia Coli -- Growth & Development ; Escherichia Coli Proteins -- Metabolism ; Heat-Shock Proteins -- Metabolism ; Protease La -- Metabolism
    ISSN: 0950382X
    E-ISSN: 1365-2958
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  • 6
    Language: English
    In: The Journal of biological chemistry, 31 July 2015, Vol.290(31), pp.19367-78
    Description: Regulated proteolysis efficiently and rapidly adapts the bacterial proteome to changing environmental conditions. Many protease substrates contain recognition motifs, so-called degrons, that direct them to the appropriate protease. Here we describe an entirely new degron identified in the cytoplasmic N-terminal end of the membrane-anchored protein YfgM of Escherichia coli. YfgM is stable during exponential growth and degraded in stationary phase by the essential FtsH protease. The alarmone (p)ppGpp, but not the previously described YfgM interactors RcsB and PpiD, influence YfgM degradation. By scanning mutagenesis, we define individual amino acids responsible for turnover of YfgM and find that the degron does not at all comply with the known N-end rule pathway. The YfgM degron is a distinct module that facilitates FtsH-mediated degradation when fused to the N terminus of another monotopic membrane protein but not to that of a cytoplasmic protein. Several lines of evidence suggest that stress-induced degradation of YfgM relieves the response regulator RcsB and thereby permits cellular protection by the Rcs phosphorelay system. On the basis of these and other results in the literature, we propose a model for how the membrane-spanning YfgM protein serves as connector between the stress responses in the periplasm and cytoplasm.
    Keywords: ATP-Dependent Protease ; Escherichia Coli (E. Coli) ; Rcs Phosphorelay System ; Protease ; Protein Degradation ; Stress Response ; ATP-Dependent Proteases -- Physiology ; Escherichia Coli Proteins -- Metabolism ; Molecular Chaperones -- Metabolism
    E-ISSN: 1083-351X
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  • 7
    Language: English
    In: Proceedings of the National Academy of Sciences of the United States of America, 30 September 2014, Vol.111(39), pp.14241-6
    Description: Vibrio cholerae is the bacterium that causes the diarrheal disease cholera. The bacteria experience a temperature shift as V. cholerae transition from contaminated water at lower temperatures into the 37 °C human intestine. Within the intestine, V. cholerae express cholera toxin (CT) and toxin-coregulated pilus (TCP), two main virulence factors required for disease. CT and TCP expression is controlled by the transcriptional activator protein ToxT. We identified an RNA thermometer motif in the 5' UTR of toxT, with a fourU anti-Shine-Dalgarno (SD) element that base pairs with the SD sequence to regulate ribosome access to the mRNA. RNA probing experiments demonstrated that the fourU element allowed access to the SD sequence at 37 °C but not at 20 °C. Moreover, mutations within the fourU element (U5C, U7C) that strengthened base-pairing between the anti-SD and SD sequences prevented access to the SD sequence even at 37 °C. Translation of ToxT-FLAG from the native toxT UTR was enhanced at 37 °C, compared with 25 °C in both Escherichia coli and V. cholerae. In contrast, the U5C, U7C UTR prevented translation of ToxT-FLAG even at 37 °C. V. cholerae mutants containing the U5C, U7C UTR variant were unable to colonize the infant mouse small intestine. Our results reveal a previously unknown regulatory mechanism consisting of an RNA thermometer that controls temperature-dependent translation of toxT, facilitating V. cholerae virulence at a relevant environmental condition found in the human intestine.
    Keywords: RNA, Bacterial -- Chemistry ; Vibrio Cholerae -- Genetics ; Virulence Factors -- Genetics
    ISSN: 00278424
    E-ISSN: 1091-6490
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  • 8
    Language: English
    In: Journal of Bacteriology, July, 2011, Vol.193(13-14), p.3473(9)
    Description: The presence of the membrane lipid phosphatidylcholine (PC) in the bacterial membrane is critically important for many host-microbe interactions. The phospholipid N-methyltransferase PmtA from the plant pathogen Agrobacterium tumefaciens catalyzes the formation of PC by a three-step methylation of phosphatidylethanolamine via monomethylphosphatidylethanolamine and dimethylphosphatidylethanolamine. The methyl group is provided by S-adenosylmethionine (SAM), which is converted to S-adenosylhomocysteine (SAH) during transmethylation. Despite the biological importance of bacterial phospholipid N-methyltransferases, little is known about amino acids critical for binding to SAM or phospholipids and catalysis. Alanine substitutions in the predicted SAM-binding residues E58, G60, G62, and E84 in A. tumefaciens PmtA dramatically reduced SAM-binding and enzyme activity. Homology modeling of PmtA satisfactorily explained the mutational results. The enzyme is predicted to exhibit a consensus topology of the SAM-binding fold consistent with cofactor interaction as seen with most structurally characterized SAM-methyltransferases. Nuclear magnetic resonance (NMR) titration experiments and [sup.14]C-SAM-binding studies revealed binding constants for SAM and SAH in the low micromolar range. Our study provides first insights into structural features and SAM binding of a bacterial phospholipid N-methyltransferase. doi:10.1128/JB.01539-10
    Keywords: Enzyme Binding -- Physiological Aspects ; Enzyme Binding -- Genetic Aspects ; Enzyme Binding -- Research ; Methyltransferases -- Physiological Aspects ; Methyltransferases -- Genetic Aspects ; Methyltransferases -- Research ; Phospholipids -- Research ; Phospholipids -- Genetic Aspects ; Phospholipids -- Physiological Aspects
    ISSN: 0021-9193
    Source: Cengage Learning, Inc.
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  • 9
    Language: English
    In: Journal of Bacteriology, 2011, Vol. 193(19), p.5119
    Description: Agrobacterium tumefaciens is a facultative phytopathogen that causes crown gall disease. For successful plant transformation A. tumefaciens requires the membrane lipid phosphatidylcholine (PC), which is produced via the methylation and the PC synthase (Pcs) pathways. The latter route is dependent on choline. Although choline uptake has been demonstrated in A. tumefaciens, the responsible transporter(s) remained elusive. In this study, we identified the first choline transport system in A. tumefaciens. The ABC-type choline transporter is encoded by the chromosomally located choXWVoperon (ChoX, binding protein; ChoW, permease; and ChoV, ATPase). The Cho system is not critical for growth and PC synthesis. However, [[sup.14]C]choline uptake is severely reduced in A. tumefaciens choX mutants. Recombinant ChoX is able to bind choline with high affinity (equilibrium dissociation constant [K.sub.D] of [approximately equal to]2 [micro]M). Since other quaternary amines are bound by ChoX with much lower affinities (acetylcholine, [K.sub.D] of [approximately equal to]80 [micro]M; betaine, [K.sub.D] of [approximately equal to]470 [micro]M), the ChoXWV system functions as a high-affinity transporter with a preference for choline. Two tryptophan residues (W40 and W87) located in the predicted ligand-binding pocket are essential for choline binding. The structural model of ChoX built on Sinorhizobium meliloti ChoX resembles the typical structure of substrate binding proteins with a so-called "Venus flytrap mechanism" of substrate binding. doi:l0.1128/JB.05421-11
    Keywords: Choline -- Physiological Aspects ; Choline -- Research ; Binding Proteins -- Physiological Aspects ; Binding Proteins -- Research ; Agrobacterium Tumefaciens -- Physiological Aspects ; Agrobacterium Tumefaciens -- Research;
    ISSN: 1098-5530
    ISSN: 10985530
    ISSN: 00219193
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  • 10
    Language: English
    In: Nucleic acids research, 20 June 2016, Vol.44(11), pp.5410-23
    Description: Natural regulatory RNAs like riboswitches and RNA thermometers (RNAT) have considerable potential in synthetic biology. They are located in the 5' untranslated region (UTR) of bacterial mRNAs and sense small molecules or changes in temperature, respectively. While riboswitches act on the level of transcription, translation or mRNA stability, all currently known RNATs regulate translation initiation. In this study, we explored the modularity of riboswitches and RNATs and obtained regulatory devices with novel functionalities. In a first approach, we established three riboswitch-RNAT systems conferring dual regulation of transcription and translation depending on the two triggers ligand binding and temperature sensing. These consecutive fusions control gene expression in vivo and can even orchestrate complex cellular behavior. In another approach, we designed two temperature-controlled riboswitches by the integration of an RNAT into a riboswitch aptamer domain. These 'thermoswitches' respond to the cognate ligand at low temperatures and are turned into a continuous on-state by a temperature upshift. They represent the first RNATs taking control of transcription. Overall, this study demonstrates that riboswitches and RNATs are ideal for engineering synthetic RNA regulators due to their modular behavior.
    Keywords: Gene Expression Regulation ; Temperature ; RNA, Messenger -- Genetics ; Riboswitch -- Genetics
    ISSN: 03051048
    E-ISSN: 1362-4962
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