Genetics of osmoregulation in<i>Escherichia coli</i>: Uptake and biosynthesis of organic osmolytes

Strøm, Arne R.; Falkenberg, Pål; Landfald, Bjarne

doi:10.1111/j.1574-6968.1986.tb01846.x

Cited by 125 publications

(73 citation statements)

References 27 publications

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“…This osmoprotector accumulates in large amounts in the cytoplasm, which allows cells to maintain appropriate osmotic strength and thus prevents dehydration. Glycine betaine is only one of several cellular osmolytes used by E. coli, but its accumulation allows this microbe to achieve its highest level of osmotic tolerance (199,373). To accumulate glycine betaine, E. coli needs an external supply of this compound or its precursors choline and betaine aldehyde.…”

Section: Beti Controls the Choline-glycine Betaine Pathway Of E Colimentioning

confidence: 99%

The TetR Family of Transcriptional Repressors

Ramos

Martínez-Bueno

Molina‐Henares

et al. 2005

Microbiol Mol Biol Rev

976

1,133

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We have developed a general profile for the proteins of the TetR family of repressors. The stretch that best defines the profile of this family is made up of 47 amino acid residues that correspond to the helix-turn-helix DNA binding motif and adjacent regions in the three-dimensional structures of TetR, QacR, CprB, and EthR, four family members for which the function and three-dimensional structure are known. We have detected a set of 2,353 nonredundant proteins belonging to this family by screening genome and protein databases with the TetR profile. Proteins of the TetR family have been found in 115 genera of gram-positive, α-, β-, and γ-proteobacteria, cyanobacteria, and archaea. The set of genes they regulate is known for 85 out of the 2,353 members of the family. These proteins are involved in the transcriptional control of multidrug efflux pumps, pathways for the biosynthesis of antibiotics, response to osmotic stress and toxic chemicals, control of catabolic pathways, differentiation processes, and pathogenicity. The regulatory network in which the family member is involved can be simple, as in TetR (i.e., TetR bound to the target operator represses tetA transcription and is released in the presence of tetracycline), or more complex, involving a series of regulatory cascades in which either the expression of the TetR family member is modulated by another regulator or the TetR family member triggers a cell response to react to environmental insults. Based on what has been learned from the cocrystals of TetR and QacR with their target operators and from their three-dimensional structures in the absence and in the presence of ligands, and based on multialignment analyses of the conserved stretch of 47 amino acids in the 2,353 TetR family members, two groups of residues have been identified. One group includes highly conserved positions involved in the proper orientation of the helix-turn-helix motif and hence seems to play a structural role. The other set of less conserved residues are involved in establishing contacts with the phosphate backbone and target bases in the operator. Information related to the TetR family of regulators has been updated in a database that can be accessed at www.bactregulators.org

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Section: Beti Controls the Choline-glycine Betaine Pathway Of E Colimentioning

confidence: 99%

The TetR Family of Transcriptional Repressors

Ramos

Martínez-Bueno

Molina‐Henares

et al. 2005

Microbiol Mol Biol Rev

976

1,133

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“…Thus, the sugar is nonreducing and has the unique quality of maintaining the fluidity of membranes under conditions of dryness and desiccation (16,17). In Escherichia coli, trehalose is synthesized internally as an answer to osmotic stress (23,45,48). Among other, more prominent osmoprotectants such as glycine betaine or proline (11,36), trehalose can contribute up to 20% of the entire capacity for osmotic protection of the cell (21, 32).…”

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confidence: 99%

Trehalose-6-phosphate hydrolase of Escherichia coli

1994

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The disaccharide trehalose acts as an osmoprotectant as well as a carbon source in Escherichia coli. At high osmolarity of the growth medium, the cells synthesize large amounts of trehalose internally as an osmoprotectant. However, they can also degrade trehalose as the sole source of carbon under both high-and low-osmolarity growth conditions. The modes of trehalose utilization are different under the two conditions and have to be well regulated (W. Boos, U. Ehmann, H. Forkl, W. Klein, M. Rimmele, and P. Postma, J. Bacteriol. 172:3450-3461, 1990). At low osmolarity, trehalose is transported via a trehalose-specific enzyme II of the phosphotransferase system, encoded by treB. The trehalose-6-phosphate formed internally is hydrolyzed to glucose and glucose 6-phosphate by the key enzyme of the system, trehalose-6-phosphate hydrolase, encoded by treC. We have cloned treC, contained in an operon with treB as the promoter-proximal gene. We have overproduced and purified the treC gene product and identified it as a protein consisting of a single polypeptide with an apparent molecular weight of 62,000 as determined by sodium dodecyl sulfate-polyacrylamide gel electrophoresis. The enzyme hydrolyzes trehalose-6-phosphate with a Km of 6 mM and a V.. of at least 5.5iimol of trehalose-6-phosphate hydrolyzed per min per mg of protein. The enzyme also very effectively hydrolyzes p-nitrophenyl-a-D-glucopyranoside, but it does not recognize trehalose, sucrose, maltose, isomaltose, or maltodextrins. treC was sequenced and found to encode a polypeptide with a calculated molecular weight of 63,781. The amino acid sequence deduced from the DNA sequence shows homology (50%6 identity) with those of oligo-1,6-glucosidases (sucrase-isomaltases) of Bacilus spp. but not with those of other disaccharide phosphate hydrolases. This report corrects our previous view on the function of the treC gene product as an amylotrehalase, which was based on the analysis of the metabolic products of trehalose metabolism in whole cells.The disaccharide trehalose serves as an osmoprotectant in many different organisms. Its two glucose molecules are linked 1-1 oa-glycosidically. Thus, the sugar is nonreducing and has the unique quality of maintaining the fluidity of membranes under conditions of dryness and desiccation (16,17). In Escherichia coli, trehalose is synthesized internally as an answer to osmotic stress (23,45,48). Among other, more prominent osmoprotectants such as glycine betaine or proline (11,36), trehalose can contribute up to 20% of the entire capacity for osmotic protection of the cell (21, 32). To synthesize the osmoprotectant trehalose at high osmolarity, UDP-glucose and glucose 6-phosphate are used to form trehalose-6-phosphate, regardless of the carbon source. Trehalose-6-phosphate is subsequently dephosphorylated to give free trehalose. Trehalose-6-phosphate synthase is encoded by otsA (osmotic trehalose synthesis), and trehalose-6-phosphate phosphatase is encoded by otsB. The two genes are localized at 42 min on the chromosome, otsB...

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“…Escherichia coli synthesizes trehalose when exposed to high osmolarity (3)(4)(5). The synthesis of trehalose requires the enzymes trehalose-6-phosphate synthase and trehalose-6-phosphate phosphatase, encoded by otsA and otsB, respectively (6,7).…”

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confidence: 99%

Characterization of TreR, the Major Regulator of theEscherichia coliTrehalose System

Horlacher

Boos

1997

Journal of Biological Chemistry

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The pathway of trehalose utilization in Escherichia coli is different at low and high osmolarity. The low osmolarity system takes up trehalose as trehalose 6-phosphate which is hydrolyzed to glucose and glucose 6-phosphate. treB and treC, the genes for the enzymes involved, form an operon that is controlled by TreR (encoded by treR), the repressor of the system, for which trehalose 6-phosphate is the inducer. We have cloned and sequenced treR. The protein contains 315 amino acids with a molecular weight of 34,508. TreR was purified and shown to bind as a dimer trehalose 6-phosphate and trehalose with a K d of 10 and 280 M, respectively. The conformations of the protein differ from each other with either one or the other substrate-bound. Protease treatment removed the DNA-binding domain from the intact protein leaving the dimerization domain (a 29-kDa carboxyl-terminal fragment) intact. Nuclease protection experiments revealed a palindromic sequence located directly upstream of the ؊35 promoter sequence of treB that functions as the operator of the system.

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Genetics of osmoregulation inEscherichia coli: Uptake and biosynthesis of organic osmolytes

Cited by 125 publications

References 27 publications

The TetR Family of Transcriptional Repressors

The TetR Family of Transcriptional Repressors

Trehalose-6-phosphate hydrolase of Escherichia coli

Characterization of TreR, the Major Regulator of theEscherichia coliTrehalose System

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