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At least 289 records · Page 16Linked to original sources
PubMed1997

Osmostress response in Bacillus subtilis: characterization of a proline uptake system (OpuE) regulated by high osmolarity and the alternative transcription factor sigma B.

Exogenously provided proline has been shown to serve as an osmoprotectant in Bacillus subtilis. Uptake of proline is under osmotic control and functions independently of the known transport systems for the osmoprotectant glycine betaine. We cloned the structural gene (opuE) for this proline transport system and constructed a chromosomal opuE mutant by marker replacement. The resulting B. subtilis strain was entirely deficient in osmoregulated proline transport activity and was no longer protected by exogenously provided proline, attesting to the central importance of OpuE for proline uptake in high-osmolarity environments. The transport characteristics and growth properties of the opuE mutant revealed the presence of a second proline transport activity in B. subtilis. DNA sequence analysis of the opuE region showed that the OpuE transporter (492 residues) consists of a single integral membrane protein. Database searches indicated that OpuE is a member of the sodium/solute symporter family, comprising proteins from both prokaryotes and eukaryotes that obligatorily couple substrate uptake to Na+ symport. The highest similarity was detected to the PutP proline permeases, which are used in Escherichia coli, Salmonella typhimurium and Staphylococcus aureus for the acquisition of proline as a carbon and nitrogen source, but not for osmoprotective purposes. An elevation of the osmolarity of the growth medium by either ionic or non-ionic osmolytes resulted in a strong increase in the OpuE-mediated proline uptake. This osmoregulated proline transport activity was entirely dependent on de novo protein synthesis, suggesting a transcriptional control mechanism. Primer extension analysis revealed the presence of two osmoregulated and tightly spaced opuE promoters. The activity of one of these promoters was dependent on sigma A and the second promoter was controlled by the general stress transcription factor sigma B.

Amino Acid Sequence↗
PubMed1997

A cryptic proline permease in Salmonella typhimurium.

Wild-type Salmonella typhimurium expresses three proline transport systems: a high-affinity proline transport system encoded by the putP gene, and two glycine betaine transport systems with a lower affinity for proline encoded by the proP and proU genes. Although proline uptake by the ProP and ProU transport systems is sufficient to supplement a proline auxotroph, it is not efficient enough to allow proline utilization as a sole source of carbon or nitrogen. Thus, the PutP transport system is required for utilization of proline as a carbon or nitrogen source. In this study, an overexpression suppressor, designated proY, which allows proline utilization in a putP genetic background and does not require the function of any of the known proline transport systems, was cloned and characterized. The suppressor gene, designated proY, maps at 8 min on the S. typhimurium linkage map, distant from any of the other characterized proline transport genes. The DNA sequence of the proY gene predicts that it encodes a hydrophobic integral membrane protein, with strong similarity to a family of amino acid transporters. The suppressor phenotype requires either a multicopy done of the proY+ gene or both a single copy of the proY+ gene and a proZ mutation. These results indicate that the proY gene is the structural gene for a cryptic proline transporter that is silent unless overexpressed on a multicopy plasmid or activated by a proZ mutation.

Amino Acid Transport Systems↗
PubMed2004

L-proline is essential for the intracellular differentiation of Trypanosoma cruzi.

Using as the host cell, a proline-requiring mutant of Chinese hamster ovary cell (CHO-K1), it was possible to arrest the differentiation of amastigote forms of Trypanosoma cruzi at the intermediate intracellular epimastigote-like stage. Complete differentiation to the trypomastigote stage was obtained by addition of L-proline to the medium. This effect was more pronounced using the T. cruzi CL-14 clone that differentiates fully at 33 degrees C (permissive temperature) and poorly at 37 degrees C (restrictive temperature). A synchronous differentiation of T. cruzi inside the host-cell is then possible by temperature switching in the presence of proline. It was found that differentiation of intracellular epimastigotes and trypomastigote bursting were proline concentration dependent. The intracellular concentration of proline was measured as well as the transport capacity of proline by each stage of the parasite. Amastigotes have the highest concentration of free proline (8.09 +/- 1.46 mM) when compared to trypomastigotes (3.81 +/- 1.55) or intracellular epimastigote-like forms (0.45 +/- 0.06 mM). In spite of having the lowest content of intracellular free proline, intracellular epimastigotes maintained the highest levels of L-proline transport compared to trypomastigotes and intracellular amastigotes, providing evidence for a high turnover for the L-proline pool in that parasite stage. This is the first report to establish a relationship between proline concentration and intracellular differentiation of Trypanosoma cruzi in the mammalian host.

Animals↗
PubMedDate not supplied

A chemostat study on proline uptake and metabolism of Leishmania donovani.

Leishmania donovani grew in the chemostat on proline as its sole carbon and energy source at a maximum growth rate of 1.39 divisions per day. The efficiency of proline metabolism decreased with increasing external proline concentration. The internal concentration of proline and its intracellular metabolites was low when proline was the growth rate limiting substrate and high when proline was available in excess. In time-course experiments proline uptake leveled off after 30 min, independent of the culture conditions prior to the experiment. Proline uptake depended on the external proline concentration in a manner that is best described as the combination of an enzymatic and a diffusion component. Adaptation to different proline concentrations did not occur and no evidence was found that proline is actively transported by L. donovani.

Adaptation, Physiological↗
PubMed1974

Proline excretion and indirect suppression in Escherichia coli and Salmonella typhimurium.

The last step in proline biosynthesis in Escherichia coli K-12, Salmonella typhimurium LT7, and a number of other enterobacterial isolates is regulated so that no proline is excreted, even if excess Delta(1)-pyrroline-5-carboxylate, the immediate precursor of proline, is added to a culture. In proline auxotrophs blocked at an early step in proline biosynthesis (proA or proB), reversion to prototrophy is often due to a mutation in the arginine pathway which diverts N-acetyl glutamate gamma-semialdehyde to proline synthesis, thus bypassing the proA or proB block. In such double mutants (proAB, argD), the last step in proline synthesis appears to be unregulated, since proline is excreted. Feedback inhibition and repression of the arginine pathway overcomes indirect suppression (restoring the Pro(-) phenotype), but proline regulation is not restored; double mutants still excrete proline when fed Delta(1)-pyrroline-5-carboxylate exogeneously. A new class of proline analogue-resistant mutant, due to mutation at argD, is also described.

Arginine↗
PubMed1982

A third L-proline permease in Salmonella typhimurium which functions in media of elevated osmotic strength.

Exogenous proline specifically stimulates the growth rate of enteric bacteria in media of inhibitory osmotic strength (J. H. B. Christian, Aust. J. Biol. Sci. 8:490-497, 1955). I observed that Salmonella typhimurium mutants which lack both of the previously known proline permeases (putP proP) are stimulated by proline in media of inhibitory osmolarity. I propose that there is a third proline permease which functions only in media of elevated osmolarity. This conclusion is based on the observations that, in media of elevated osmolarity, (i) the sensitivity of putP proP mutants to toxic proline analogs increases, (ii) proline requirements for maximal growth of proline auxotrophic putP proP mutants decreases, and (iii) the specific rate of incorporation of radioactive proline into protein of growing cells increases. I obtained a Tn10-induced mutation in a gene (proU) required for the functioning of the third proline permease and determined the map location to be at 59 map units of the chromosome, between srlA and tct, 66% linked to nalB in P22 transduction. My results suggest that the function of the third, osmotically stimulated permease might be to accumulate high intracellular proline levels during osmotic stress. Possible mechanisms by which proline might cause growth stimulation are discussed.

Amino Acid Transport Systems, Neutral↗
PubMed1990

Activation of a new proline transport system in Salmonella typhimurium.

Proline uptake can be mediated by three different transport systems in wild-type Salmonella typhimurium: a high-affinity proline transport system encoded by the putP gene and two glycine-betaine transport systems with a low affinity for proline encoded by the proP and proU genes. However, only the PutP permease transports proline well enough t allow growth on proline as a sole carbon or nitrogen source. By selecting for mutations that allow a putP mutant to grow on proline as a sole nitrogen source, we isolated mutants (designated proZ) that appeared to activate a cryptic proline transport system. These mutants enhanced the transport of proline and proline analogs but did not require the function of any of the known proline transport genes. The mutations mapped between 75 and 77.5 min on the S. typhimurium linkage map. Proline transport by the proZ mutants was competitively inhibited by isoleucine and leucine, which suggests that the ProZ phenotype may be due to unusual mutations that alter the substrate specificity of the branched-chain amino acid transport system encoded by the liv genes.

Biological Transport↗
PubMed1993

Characteristics and osmoregulatory roles of uptake systems for proline and glycine betaine in Lactococcus lactis.

Lactococcus lactis subsp. lactis ML3 contains high pools of proline or betaine when grown under conditions of high osmotic strength. These pools are created by specific transport systems. A high-affinity uptake system for glycine betaine (betaine) with a Km of 1.5 microM is expressed constitutively. The activity of this system is not stimulated by high osmolarities of the growth or assay medium but varies strongly with the medium pH. A low-affinity proline uptake system (Km, > 5 mM) is expressed at high levels only in chemically defined medium (CDM) with high osmolarity. This transport system is also stimulated by high osmolarity. The expression of this proline uptake system is repressed in rich broth with low or high osmolarity and in CDM with low osmolarity. The accumulated proline can be exchanged for betaine. Proline uptake is also effectively inhibited by betaine (Ki of between 50 and 100 microM). The proline transport system therefore probably also transports betaine. The inhibition of proline transport by betaine results in low proline pools in cells grown in high-osmotic-strength, betaine-containing CDM. The energy and pH dependency and the influence of ionophores on the activity of both transport systems suggest that these systems are not proton motive force driven. At low osmolarities, proline uptake is low but significant. This low proline uptake is also inhibited by betaine, although to a lesser extent than in cells grown in high-osmotic-strength CDM. These data indicate that proline uptake in L. lactis is enzyme mediated and is not dependent on passive diffusion, as was previously believed.

Betaine↗
PubMed1976

Nutritional and metabolic interrelationships of arginine, glutamic acid and proline in the chicken.

Proline satisfies by a narrow margin the criterion for dietary essentially for the chick. It is estimated that the chick may synthesize 80-90% of the total proline needed for growth. Although the metabolism of arginine, ornithine and glutamic acid is expected to give rise to proline, dietary supplements to these amino acids are relatively ineffective in reducing the proline requirement of chicks. Studies of the efficacy of dietary ornithine for growth, and tracer studies using L-(5-3H)arginine indicate that the conversion of ornithine to proline in vivo is limited, and the amount of proline synthesized from arginine is but a small fraction of that needed for growth. The limiting processes in proline synthesis from glutamic acid and ornithine are not known. In Escherichia coli, where the biosynthetic pathway from glutamate to proline has been elucidated, a glutamate kinase, NADP-dependent delta1-pyrroline-5-carboxylic acid (P5C) dehydrogenase and P5C reductase catalyze proline synthesis. P5C reductase is present in the soluble fraction of chicken liver and kidney. An NADP-dependent P5C dehydrogenase activity has also been observed in this fraction of liver. Further studies are required to assess the importance of these enzymes in proline biosynthesis and to determine the limiting process in proline formation in the chicken.

Animal Nutritional Physiological Phenomena↗
PubMed1992

L-proline activates glutamate and glycine receptors in cultured rat dorsal horn neurons.

The pharmacological actions of L-proline on excitatory and inhibitory amino acid receptors have been characterized under voltage-clamp conditions, using cultured dissociated neurons from the dorsal horn of the rat spinal cord. At a holding potential of -62 mV, millimolar concentrations of L-proline elicited an inward current that was partially antagonized by D-(-)-2-amino-5-phosphonopentanoic acid (APV), 6-cyano-7-nitroquinoxaline-2,3-dione (CNQX), and strychnine and was virtually abolished (97% block) by a combination of all three antagonists. Currents evoked by D-proline were abolished by strychnine alone. APV-, CNQX-, and strychnine-sensitive components of L-proline-evoked currents were isolated using various combinations of the three antagonists. These currents were identical to currents elicited by N-methyl-D-aspartate (NMDA), kainate, and glycine, respectively, with respect to antagonist specificity, reversal potential, and ionic permeability. The APV- and strychnine-sensitive currents also showed a time dependence similar to that of the currents elicited by NMDA and glycine. EC50 values could not be calculated, because the response did not saturate within the tested range of L-proline concentrations (0.3-50 mM). Estimates of relative potency were obtained, however, by comparison with responses elicited by selective agonists. The APV-sensitive, CNQX-sensitive, and strychnine-sensitive currents evoked by 10 mM L-proline were comparable in size to currents elicited by 15 microM NMDA, 5 microM kainate, and 30 microM glycine, respectively. L-Proline was found to elicit an increase in intracellular [Ca2+] that was dependent upon Ca2+ entry into the cell. These Ca2+ responses were enhanced by strychnine and partially antagonized by APV, CNQX, or Mg2+. Our results using dorsal horn neurons grown in culture indicate that L-proline is a weak agonist at strychnine-sensitive glycine receptors and at both NMDA and non-NMDA glutamate receptors. These observations should help in interpreting the confusing array of L-proline actions that have been described using more intact nervous system preparations. Furthermore, the ability of L-proline to stimulate Ca2+ entry after activation of excitatory amino acid receptors implicates L-proline as a potential endogenous excitotoxin.

2-Amino-5-phosphonovalerate↗
PubMed1964

PROLINE OXIDASES IN HANSENULA SUBPELLICULOSA.

Ling, Chung-Mei (Illinois Institute of Technology, Chicago), and L. R. Hedrick. Proline oxidases in Hansenula subpelliculosa. J. Bacteriol. 87:1462-1470. 1964-Cells of Hansenula subpelliculosa can use l-proline as a carbon and a nitrogen source after a 6- to 8-hr induction period. However, they cannot use l-glutamate as both nitrogen and carbon sources unless the induction period is of several days' duration. Two l-proline oxidases were demonstrated in the mitochondrial preparation of this yeast. One forms the product Delta'-pyrroline-2-carboxylic acid (P2C), which is in equilibrium with alpha-keto-delta-amino-valeric acid; the other forms the product Delta'-pyrroline-5-carboxylic acid (P5C), which is in equilibrium with glutamic-gamma-semialdehyde. The first-mentioned enzyme is induced when l-proline is the carbon source; the second appears to be constitutive, and is probably associated with the use of l-proline as a nitrogen source. The P2C-forming enzyme is specific for the l isomer of proline, and is inactive against l-hydroxyproline. The enzyme activity is at its peak when the mitochondria are prepared from logarithmically grown cells, and is rapidly reduced after cells reach the stationary phase of growth. Kinetic studies with varying concentrations of substrate indicate a Michaelis-Menten constant of 2.45 x 10(-2)m. Paper chromatographic studies, chemical tests with H(2)O(2), sensitivity to freezing, and spectral measurements indicate that proline oxidase from H. subpelliculosa mitochondria forms a product from l-proline which is like, if not identical to, P2C formed by the action of sheep kidney d-proline oxidase upon dl-proline. The soluble portion of the cell extract contains NAD(+) enzymes which use either P2C (alpha-keto-delta-amino-valeric acid) or P5C (glutamic-gamma-semialdehyde) as substrates. No glutamic dehydrogenase activity could be detected when l-glutamic acid and the nicotinamide adenine dinucleotide (NAD(+)) cofactor were added to the supernatant solution with the yeast enzymes. The presence of a dehydrogenase NAD(+) enzyme for activity with P2C (alpha-keto-delta-amino-valeric acid) has not been previously reported.

Amino Acid Oxidoreductases↗
PubMed2001

Regulation of proline accumulation in detached rice leaves exposed to excess copper.

Accumulation of proline in response to excess Cu was studied in detached leaves of rice (Oryza sativa). CuSO(4) was effective in inducing proline accumulation in detached rice leaves under both light and dark conditions. CuSO(4) and CuCl(2) were equally effective in inducing proline accumulation, indicating that proline accumulation is induced by Cu. Sulfate salts of Mg, Mn, and Fe were ineffective in inducing proline accumulation in detached rice leaves. Excess Cu had no effect on relative water content of detached rice leaves, suggesting that Cu-induced proline accumulation is unlikely due to water deficit. Proline accumulation induced by excess Cu was related to proteolysis and an increase in Delta(1)-pyrroline-5-carboxylate reductase or ornithine-delta-aminotransferase activity and could not be explained by proline utilization or stress-induced modifications in proline dehydrogenase or Delta(1)-pyrroline-5-carboxylate dehydrogenase. The content of glutamic acid decreased by excess Cu. The increase in arginine but not ornithine was found to be associated with the increase in proline content in Cu-stressed detached rice leaves. CuSO(4) treatment resulted in an increase in abscisic acid content in detached rice leaves. The possibility that proline accumulation induced by excess Cu is mediated through abscisic acid is discussed.

Journal Article↗
PubMed2003

Novel proline hydroxylase activities in the pneumocandin-producing fungus Glarea lozoyensis responsible for the formation of trans 3- and trans 4-hydroxyproline.

Novel proline 3-hydroxylase (P3H) and proline 4-hydroxylase (P4H) activities that convert free l-proline to both trans 3- and trans 4-hydroxy- l-proline were detected in protein extracts of the anamorphic fungus Glarea lozoyensis. The enzymatic conversion of l-proline to trans 3- and trans 4-hydroxy- l-proline was strictly dependent on alpha-ketoglutarate, ascorbate, and dithiothreitol. Ferrous iron was required for optimal P3H and P4H activity. These substrate and co-factor requirements indicate these enzyme activities belong to the class of 2-oxoglutarate-dependent dioxygenases. Both P3H and P4H were inhibited by zinc and other trace metals. The addition of proline to the fermentation medium resulted in an increase in the specific activity of P4H and a decrease in the synthesis of pneumocandin C(0). Additionally, the synthesis of trans 3- and trans 4-hydroxy- l-proline in vivo was affected differently by the proline concentration in the medium. This result suggested that two enzymes may be responsible for the regio- and stereospecific hydroxylation of l-proline.

Anti-Bacterial Agents↗
PubMed1989

Nonspecific inhibition of proline dehydrogenase synthesis in Escherichia coli during osmotic stress.

L-Proline, which is accumulated by Escherichia coli during growth in media of high osmolality, also induces the synthesis of the enzyme degrading it to glutamate. To determine if proline catabolism is inhibited during osmotic stress, proline utilization and the formation of proline dehydrogenase were examined in varying concentrations of NaCl and sucrose. Although the specific growth rate of E. coli with proline as the sole nitrogen source diminished as the solute osmolality increased, a comparable reduction in growth rate occurred with ammonium as the primary nitrogen source. Proline catabolism, as measured in whole cells by the conversion of [14C]proline to [14C]glutamate, was only slightly inhibited by solute osmolalities up to 1.0 osmol/kg; more than 50% of the initial activity was still found at 2.0 osmol/kg. By contrast, the specific activity of proline dehydrogenase in bacteria grown in the presence of added solutes decreased to less than 20% of the control level. This reduction was related to a lower rate of synthesis, but was independent of genes currently known to be involved in osmoregulation or proline metabolism. The specific activities of tryptophanase, beta-galactosidase, and histidinol dehydrogenase were also reduced under similar growth conditions. These results indicate that while proline catabolism is not directly inhibited by high solute concentrations, prolonged exposure to osmotic stress leads to its reduction as part of a more general metabolic response.

Escherichia coli↗
PubMed1997

Synthesis of citrulline and arginine from proline in enterocytes of postnatal pigs.

The synthesis of ornithine, citrulline, and arginine from proline was quantified in enterocytes of newborn (0-day-old) pigs, 2- to 21-day-old suckling pigs, and 29- to 58-day-old pigs weaned at 21 days of age. Mitochondria were prepared from enterocytes for measurement of proline oxidase activity. For metabolic studies, cells were incubated at 37 degrees C for 30 min in Krebs bicarbonate buffer (pH 7.4) containing 5 mM D-glucose and 0.0-5.0 mM L-[U-14C]proline with or without 2.0 mM L-glutamine. Proline oxidase activity and rates of synthesis of citrulline and arginine from proline were high in enterocytes of newborn pigs and markedly decreased in 7-day-old pigs. With increasing piglet age from 7 to 21 days, enterocyte proline oxidase activity and rate of conversion of proline into citrulline progressively increased, but the values in 21-day-old pigs remained much lower than in newborn pigs. The synthesis of ornithine, citrulline, and arginine from 0.5-5 mM proline was concentration dependent and required the addition of glutamine. About 80-90% of utilized proline carbons were recovered in ornithine plus citrulline plus arginine, with CO2 being a minor product. These results demonstrate a hitherto unrecognized pathway for the synthesis of ornithine, citrulline, and arginine via proline oxidase in enterocytes and challenge the current concept that pyrroline-5-carboxylate (P5C) is synthesized in the small intestine only from glutamine/glutamate via P5C synthase on the basis of previous work with postnatal rats.

Aging↗
PubMed1982

Cell-free translations of proline-rich protein mRNAs.

Treatment of rats with the beta-agonist isoproterenol causes a dramatic increase in a series of proteins rich in proline (proline-rich proteins) in the parotid glands (Muenzer, J., Bildstein, C., Gleason, M., and Carlson, D. M. (1979) J. Biol. Chem. 254, 5623, 5629). These proteins which contain about 43% proline, comprise more than 50% of the total soluble protein of glands of rats treated with isoproterenol for 10 days. Further studies by in vitro translation analysis using the reticulocyte lysate system and labeling with [3H]proline or [35S]methionine show definitive changes in patterns of protein synthesis and proline-rich protein mRNAs are highly elevated in treated animals. Analysis of translation products by sodium dodecyl sulfate-polyacrylamide gel electrophoresis showed (1) very little synthesis of proline-rich proteins from poly(A+) RNA of glands of normal rats, (2) poly(A+) RNA from glands of treated animals synthesize mainly proline-rich proteins, (3) translations with [3H]proline and [35S]methionine give identical labeling patterns from cell-free translations are all precipitated by antibodies to proline-rich proteins. At least six different proline-rich proteins are translated with poly(A+) mRNA from glands of treated animals. Each of these proteins is likely a translation product of a separate, specific mRNA. The dramatic changes in protein synthesis of rat parotid glands in response to isoproterenol treatment suggest to us that the parotid gland of the isoproterenol-treated rat is an excellent model system to study the overall responsiveness of gene expression to catecholamines.

Animals↗
PubMed1991

Reassessment of the random coil conformation: vibrational CD study of proline oligopeptides and related polypeptides.

The "random coil" conformational problem is examined by comparison of vibrational CD (VCD) spectra of various polypeptide model systems with that of proline oligomers [(Pro)n] and poly(L-proline). VCD, ir and uv CD spectra of blocked L-proline oligopeptides [(Pro)n, n = 2-12] in different solvents are reported and compared to the spectra of poly(L-proline) II, poly(L-glutamic acid), and unblocked proline oligomers. Based on the chain-length dependence of the VCD and electronic CD (ECD) spectra of proline oligomers, it is established that VCD spectra are dominated by short-range interactions. The VCD of random coil model polypeptides is shown to be identical in shape but smaller in magnitude than poly(L-proline) II and of similar magnitude to that of (Pro)n (n = 3, 4). Based on the spectral evidence, it is concluded that the "random coil" conformation has a large fraction of helical regions, conformationally similar to the left-handed, 3(1) polyproline II helix, as was previously suggested by Krimm and co-workers. This conclusion is further supported by studies of effects of salt (CaCl2, LiBr, LiClO4), temperature (5-75 degrees C), and pH on the VCD spectra of L-proline oligomers, poly(L-proline) II, and poly(L-glutamic acid). These show that, after each of these perturbations, a significant local ordering remains in the oligomers and polymers studied, and that charged polypeptides such as poly(L-glutamic acid) are more flexible than are polyproline or even L-proline oligomers.

Circular Dichroism↗
PubMed1981

The role of proline in osmoregulation in Salmonella typhimurium and Escherichia coli.

Previously we demonstrated that high intracellular proline levels conferred enhanced osmotolerance on Salmonella typhimurium. Stimulation of growth rate under conditions of osmotic inhibition could be brought about either by the addition of proline to the culture media or by mutations which result in proline over-production. Here, we report that there is a novel proline transport system in S. typhimurium which is activated in media of elevated osmolarity. this conclusion is based on the observation that putP- proP- double mutants, which lack both of the known proline permeases are resistant in minimal medium to the toxic proline analogues 3,4-dehydro-D, L-proline and L-azetidine-2-carboxylate. However, they regain sensitivity to the analogues in media of elevated osmolarity. Selecting resistance to 3,4-dehydro-D, L-proline in media of elevated osmolarity, we obtained mutants of putP- proP- strains which lack the osmotically activated proline permease. In these strains, exogenous proline could no longer alleviate osmotic inhibition.

Biological Transport↗