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Query: UNIPROT:P06889 (Mol)
 630,302 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

The amounts of cytoplasmic water and of all osmotically significant cytoplasmic solutes were determined for Escherichia coli K-12 grown in 3-(N-morpholino)propane sulfonate (MOPS)-buffered glucose-minimal medium containing 0.5 M NaCl in the presence and absence of the osmoprotectants betaine and proline. The goal of this work is to correlate the effects of osmoprotectants on the composition of the cytoplasm with their ability to increase the growth rate of osmotically stressed cells. At a concentration of 1 mM in the growth medium, betaine increases the growth rate more than does proline; choline, which is converted to betaine by E. coli, appears to have an intermediate effect on growth rate. The accumulation of either betaine or proline reduces the cytoplasmic amounts of K+, glutamate, trehalose, and MOPS (the major cytoplasmic osmolytes accumulated in the absence of osmoprotectants), so that at this external osmolarity the total amount of cytoplasmic solutes is essentially the same in the presence or absence of either osmoprotectant. More betaine than proline is accumulated, so the extent of replacement of cytoplasmic solutes is greater for betaine than for proline. Accumulation of these osmoprotectants is accompanied by a large (20 to 50%) increase in the volume of cytoplasmic water per unit of cell dry weight (Vcyto). This effect, which appears to result from an increase in the volume of free water, Vf (as opposed to water of hydration, or bound water), is greater for betaine than for proline. Taken together, these results indicate that the molar effects of betaine and proline on water activity and on the osmotic pressure of the cytoplasm must be significantly larger than those of the solutes they replace. Cayley et al. (S. Cayley, B. A. Lewis, H. J. Guttman, and M. T. Record, Jr., J. Mol. Biol. 222:281-300, 1991) observed that, in cells grown in the absence of osmoprotectants, both growth rate and Vcyto decreased, whereas the amount of cytoplasmic K+ (nK+) increased, with increasing external osmolarity. We predicted that the observed changes in nK+ and Vcyto would have large and approximately compensating effects on key protein-nucleic acid interactions of gene expression, and we proposed that Vf was the fundamental determinant of growth rate in osmotically stressed cells. The properties of cells cultured in the presence of betaine and proline appear completely consistent with our previous work and proposals. Accumulation of betaine and, to a lesser extent, proline shifts the set of linked physiological parameters (nK+, Vcyto, growth rate) to those characteristic of growth at lower osmolarity in the absence of osmoprotectants. Models for the thermodynamic basis and physiological consequences of the effect of osmoprotectants on Vcyto and Vf are discussed.
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PMID:Origins of the osmoprotective properties of betaine and proline in Escherichia coli K-12. 153 1

Isolated alveolar type II epithelial cells (granular pneumocytes) from rat lung accumulate free choline against a concentration gradient by an energy-dependent saturable transport process with apparent Km approximately 18 microM. In order to evaluate the structural requirements for choline transport by these cells, the inhibition of the initial rate of cellular uptake of [3H]choline (5 microM) by its analogue was measured. There was no significant inhibition of substrate uptake by analogues lacking an amino group while the presence of a quaternary nitrogen was most effective. N,N'-dimethylethanolamine (apparent Ki, 7 microM) and n-decylcholine (apparent Ki, 0.5 microM) were potent competitive inhibitors of choline transport. Substitution of the hydroxyl group in choline greatly diminished the inhibitory effect; fluorocholine, thiocholine, betaine, and betaine aldehyde showed little or no inhibition. This requirement for a hydroxyl group raises the possibility of hydrogen bonding of choline with the transport protein. The choline transport system in granular pneumocytes appears to differ from that in synaptosomes by the lower affinity of the carrier for substrate and for hemicholinium-3 and from that in erythrocytes by the role of the hydroxyl in the substrate molecule. The availability of inhibitory analogues for choline transport will facilitate isolation and study of the granular pneumocyte choline transport protein.
Am J Respir Cell Mol Biol 1992 Apr
PMID:Inhibitors of choline transport in alveolar type II epithelial cells. 155 Jun 88

Phospholipase C has been increasingly recognized as a significant virulence determinant in the pathogenesis of Gram-negative and Gram-positive infections. Pseudomonas aeruginosa carries two, non-tandem genes encoding phospholipase C (PLC) activity. One PLC (PLC-H) haemolyses human and sheep erythrocytes while the other is not haemolytic for these kinds of red blood cells. It was previously determined that the synthesis of both PLCs is regulated by inorganic phosphate (Pi), but little else was known regarding the regulation of these potentially important virulence determinants of P. aeruginosa. In this report, data are presented demonstrating that both PLC genes are regulated at the transcriptional level by Pi and by a P. aeruginosa homologue of the positive regulator of genes in the Pi regulon of Escherichia coli, i.e. PhoB. In addition to Pi, it is also shown in this report that the synthesis of both PLC-H and PLC-N is induced by compounds which are not only derived from the substrate product of both enzymes, i.e. phosphorylcholine, but are also known osmoprotectants in eukaryotic and prokaryotic cells. The osmoprotective derivatives of phosphorylcholine which induce the synthesis of PLC in P. aeruginosa include choline, glycine betaine, and dimethylglycine, but not sarcosine (monomethylglycine) or glycine. By constructing mutants which are deficient in the production of each separate PLC and in the production of PhoB it was determined that induction of PLC-H by the osmoprotective compounds is independent of Pi concentration and PhoB, while induction of PLC-N by these compounds requires Pi-deficient conditions and PhoB.(ABSTRACT TRUNCATED AT 250 WORDS)
Mol Microbiol 1992 Apr
PMID:Osmoprotectants and phosphate regulate expression of phospholipase C in Pseudomonas aeruginosa. 160 66

Members of the Chenopodiaceae, such as sugar beet and spinach, accumulate glycine betaine in response to salinity or drought stress. The last enzyme in the glycine betaine biosynthetic pathway is betaine aldehyde dehydrogenase (BADH). In sugar beet the activity of BADH was found to increase two- to four-fold in both leaves and roots as the NaCl level in the irrigation solution was raised from 0 to 500 mM. This increase in BADH activity was paralleled by an increase in level of translatable BADH mRNA. Several cDNAs encoding BADH were cloned from a lambda gt10 library representing poly(A+) RNA from salinized leaves of sugar beet plants, by hybridization with a spinach BADH cDNA. Three nearly full-length cDNA clones were confirmed to encode BADH by their nucleotide and deduced amino acid sequence identity to spinach BADH; these clones showed minor nucleotide sequence differences consistent with their being of two different BADH alleles. The clones averaged 1.7 kb and contained an open reading frame predicting a polypeptide of 500 amino acids with 83% identity to spinach BADH. RNA gel blot analysis of total RNA showed that salinization to 500 mM NaCl increased BADH mRNA levels four-fold in leaves and three-fold in the taproot. DNA gel blot analyses indicated the presence of at least two copies of BADH in the haploid sugar beet genome.
Plant Mol Biol 1992 Jan
PMID:Salt-inducible betaine aldehyde dehydrogenase from sugar beet: cDNA cloning and expression. 173 61

Rhizobium meliloti is known to use betaines synthesized by its host, Medicago sativa, as osmoprotectants and sources of energy. It is shown in the present report that the symbiotic megaplasmid (pSym) of R. meliloti RCR2011 encodes functions essential to the catabolism of three betaines, trigonelline (nicotinic acid N-methylbetaine), stachydrine (proline betaine or dimethylproline), and carnitine (gamma-trimethyl-beta-hydroxybutyrobetaine). Preliminary evidence is presented showing that functions on pSym also influence the catabolism of choline and its oxidative product, glycine betaine. Genes implicated in betaine catabolism are found in the symbiotic region of pSym. Trigonelline catabolism functions lie between two clusters of symbiotic genes, nifKDH and nok/fixVI'. Stachydrine and carnitine functions lie to the right of trigonelline catabolism functions, immediately to the right of fixVI'. Information necessary to choline and glycine betaine catabolism is probably encoded to the right of stachydrine catabolism functions.
Mol Plant Microbe Interact
PMID:Betaine use by rhizosphere bacteria: genes essential for trigonelline, stachydrine, and carnitine catabolism in Rhizobium meliloti are located on pSym in the symbiotic region. 180 2

The sequence was determined of 6493 nucleotides encompassing the bet genes of Escherichia coli which encode the osmoregulatory choline-glycine betaine pathway. Four open reading frames were identified: betA encoding choline dehydrogenase, a flavoprotein of 61.9kDa; betB encoding betaine aldehyde dehydrogenase (52.8kDa); betT encoding a proton-motive-force-driven, high-affinity transport system for choline (75.8kDa); and betl, capable of encoding a protein of 21.8kDa, implicated as a repressor involved in choline regulation of the bet genes. Identification of the genes was supported by subcloning, physical mapping of lambda placMu53 insertions, amino acid sequence similarity, or N-terminal amino acid sequencing. The bet genes are tightly spaced, with betT located upstream of, and transcribed divergently to, the tandemly linked betIBA genes.
Mol Microbiol 1991 May
PMID:DNA sequence and analysis of the bet genes encoding the osmoregulatory choline-glycine betaine pathway of Escherichia coli. 195 85

Choline, betaine and N,N-dimethylglycine as the sole carbon and nitrogen source induced a periplasmic acid phosphatase activity in Pseudomonas aeruginosa. This enzyme produced the highest rates of hydrolysis in phosphorylcholine and phosphorylethanolamine among the various phosphoric esters tested. At saturating concentrations of Mg2+, the Km values were 0.2 and 0.7 mM for phosphorylcholine and phosphorylethanolamine respectively. At high concentrations both compounds were inhibitors of the enzyme activity. The Ksi values for phosphorylcholine and phosphorylethanolamine were 1.0 and 3.0 mM respectively. The higher catalytic efficiency was that of phosphorylcholine. Considering these results it is possible to suggest that the Pseudomonas aeruginosa acid phosphatase is a phosphorylcholine phosphatase. The existence of this activity which is induced jointly with phospholipase C by different choline metabolites, in a high phosphate medium, suggests that the attack of Pseudomonas aeruginosa on the cell host may also be produced under conditions of high phosphate concentrations, when the alkaline phosphatase is absent.
Mol Cell Biochem 1990 Apr 18
PMID:Identification of the Pseudomonas aeruginosa acid phosphatase as a phosphorylcholine phosphatase activity. 211 92

The Escherichia coli proU operon encodes a high-affinity, binding-protein-dependent transport system for the osmoprotectant glycine betaine. Expression of proU is osmoregulated, and transcription of this operon is greatly increased in cells grown at high osmolarity. Characterization of the proU operon and its promoter provided results similar to those published elsewhere (Gowrishankar, 1989; Stirling et al., 1989). The previously identified proU601 mutation, which leads to increased proU expression both at low- and high osmolarity, is a G to A transition in the Pribnow box of the proU promoter, which increases the homology of the -10 region to the consensus sequence of E. coli promoters. Using an antiserum raised against a ProV-beta-galactosidase hybrid protein, we have identified ProV as a protein associated with the cytoplasmic membrane. This cellular location is consistent with its proposed role as the energy-coupling component of the ProU transport system.
Mol Microbiol 1989 Nov
PMID:Characterization of the osmoregulated Escherichia coli proU promoter and identification of ProV as a membrane-associated protein. 251 17

The proU loci of Salmonella typhimurium and Escherichia coli encode high-affinity glycine betaine transport systems which play an important role in survival under osmotic stress. Transcription of the proU locus is tightly regulated by osmolarity and this regulation appears to be mediated by osmotically induced changes in DNA supercoiling. In order to study the regulatory mechanisms involved we have cloned and characterized the proU locus of S. typhimurium by an in vivo transductional procedure. The locus is shown to consist of at least three genes, designated proVWX, cotranscribed as a single operon. The first gene in the operon encodes a protein sharing considerable sequence identity with ATP-binding proteins from other periplasmic transport systems. Unexpectedly, the highly expressed periplasmic glycine betaine binding protein was found to be encoded by a distal gene, proX, in the operon. The operon has no significant internal promoters but is expressed from a single osmoregulated promoter whose transcription start site has been mapped. The proU promoter of E. coli has also been sequenced and the transcription start site shown to be similar to that of S. typhimurium. Evidence is presented which suggests that, besides de novo glycine betaine uptake, an important function of ProU may be the recapture and recycling of other osmolytes that leak from the cell.
Mol Microbiol 1989 Aug
PMID:Molecular characterization of the proU loci of Salmonella typhimurium and Escherichia coli encoding osmoregulated glycine betaine transport systems. 269 38

The proU locus of Escherichia coli encodes a high-affinity, binding-protein-dependent transport system (ProU) for the osmoprotectant glycine betaine. We cloned this locus into both low-copy-number lambda vectors and multicopy plasmids and demonstrated that these clones restore osmotically controlled synthesis of the periplasmic glycine betaine binding protein (GBBP) and the transport of glycine betaine in a delta (proU) strain. These clones allowed us to investigate the influence of osmolarity on ProU transport activity independent of the osmotically controlled expression of proU. ProU activity was strongly stimulated by a moderate increase in osmolarity and was partially inhibited by high osmolarity. This activity profile differs from the profile of the osmotically regulated proU expression. The proU locus is organized in an operon and the position of the structural gene (proV) for GBBP is defined using a minicell system. We determined that at least three proteins (in addition to GBBP) are encoded by the proU locus. We also investigated the permeation of glycine betaine across the outer membrane. At low substrate concentration (0.7 microM), permeation of glycine betaine was entirely dependent on the OmpF and OmpC porins.
Mol Microbiol 1988 Mar
PMID:Cloned structural genes for the osmotically regulated binding-protein-dependent glycine betaine transport system (ProU) of Escherichia coli K-12. 283 16


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