Glutamate-binding protein and its relation to glutamate transport in Escherichia coli K-12

Reconstitution of maltose transport in Escherichia coli: conditions affecting import of maltose-binding protein into the periplasm of calcium-treated cells

The reconstitution of active transport by the Ca2+ -induced import of exogenous binding protein was studied in detail in whole cells of a malE deletion mutant lacking the periplasmic maltose-binding protein. A linear increase in reconstitution efficiency was observed by increasing the Ca2+ - concentration in the reconstitution mixture up to 400 mM. A sharp pH optimum around pH 7.5 was measured for reconstitution. Reconstitution efficiency was highest at 0 degree C and decreased sharply with increasing temperature. The time necessary for optimal reconstitution at 0 degree C and 250 mM Ca2+ was about 1 min. The competence for reconstitution was highest in exponentially growing cultures with cell densities up to 1 X 10(9)/ml and declined when the cells entered the stationary-growth phase. The apparent Km for maltose uptake was the same as that of wild-type cells (1 to 2 microM). Vmax at saturating maltose-binding protein concentration was 125 pmol per min per 7.5 X 10(7) cells (30% of the wild-type activity). The concentration of maltose-binding protein required for half-maximal reconstitution was about 1 mM. The reconstitution procedure appears to be generally applicable. Thus, galactose transport in Escherichia coli could also be reconstituted by its respective binding protein. Maltose transport in E. coli was restored by maltose-binding protein isolated from Salmonella typhimurium. Finally, in S. typhimurium, histidine transport was reconstituted by the addition of shock fluid containing histidine-binding protein to a hisJ deletion mutant lacking histidine-binding protein. The method is fast and general enough to be used as a screening procedure to distinguish between transport mutants in which only the binding protein is affected and those in which additional transport components are affected.

Reconstitution of maltose transport in malB mutants of Escherichia coli through calcium-induced disruptions of the outer membrane

The barrier function of the Escherichia coli outer membrane against low concentrations of maltose in strains missing the lambda receptor was partially overcome by treating the cells for 3 h with 25 mM Ca2+. Kinetic analysis of maltose-transport revealed a Ca2+-induced shift of the apparent Km of the system from about 100 microM in cells pretreated with Tris to about 15 microM in cells pretreated with Tris plus Ca2+. In contrast to maltose transport in untreated cells, that of Ca2+-treated lamB cells was inhibited by molecules with a high molecular weight, such as amylopectin (molecular weight, 20,000), and anti-maltose-binding protein antibodies. In addition, lysozyme was shown to attack Ca2+-treated cells in contrast to untreated cells. The Ca2+-induced permeability increase of the outer membrane allowed reconstitution of maltose transport in a mutant missing the maltose-binding protein with osmotic shock fluid containing the maltose-binding protein. Even though Ca2+-treatment allowed the entry of large molecules, the release of the periplasmic maltose-binding protein or alkaline phosphatase was negligible.

Restoration of phosphate transport by the phosphate-binding protein in spheroplasts of Escherichia coli

Reconstitution of phosphate transport in Escherichia coli was demonstrated. Conversion of E. coli K10 cells to spheroplasts decreased phosphate transport to about 2%. Addition of purified phosphate-binding protein at physiological levels to these spheroplasts caused a mean 14-fold increase in phosphate transport rate. Crude shock fluid fractions were also stimulatory but not if the shock fluid was obtained from mutants lacking phosphate-binding protein. The effect of the binding protein was abolished by its specific antibody. The phosphate was shown to have entered the cell, where it became esterified. Reconstitution was not possible with cold-shocked or osmotically shocked cells.

Regulation of glucose transport in Aspergillus nidulans

Pyruvate and acetate inhibited the uptake of glucose by Aspergillus nidulans; although there were significant variations in glucose uptake rate, the intracellular concentration of acetate was almost identical in biotin-supplemented, normal and deficient cells. The in vitro activity of glucose-binding protein was not affected by biotin, avidin, acetate or acetyl-CoA.

Phosphate uptake and involvement of binding protein in Tween-80 supplemented culture of Aspergillus fumigatus

Tween-80 supplementation in submerged culture of Aspergillus fumigatus resulted in an increase of phosphate uptake. The uptake system was characterized as saturable, energy-dependent and operating against the concentration gradient. Control and Tween 80 cultures showed similar Km values for phosphate uptake (50 micrometer). Cold osmotic shock treatment of the cultures was found to cause considerable reduction in the ability to take up phosphorus with concomitant release of the binding protein into the shock fluid. Binding protein preparation from Tween-80 supplemented cells showed more activity than that from control cells.

1. Membrane vesicles of Escherichia coli K-12 CS7, a strain gentically derepressed for glutamate permease, maintain low aspartate transport activity, like that of prep

1. Membrane vesicles of Escherichia coli K-12 CS7, a strain gentically derepressed for glutamate permease, maintain low aspartate transport activity, like that of preparations of the wild-type parent. Growth of the parent CS101 on aspartate as the source of carnon or nitrogen results in derepression of both asparatate and glytamate transport. Growth of strain CS7 on aspartate derepresses aspartate transport to the same extent as in strains CS101, but only slightly increases the derepressed level of glutamate transport activity. 2. The affinity of the membrane transport system for glutamate is enhanced by sodium, while that for asparate is not. 3. Although the affinities for glutamate (23 muM) and aspartate (12 muM) are similar, aspartate does not inhibit glutamate transport, while glutamate competitively inhibits aspartate transport. 4. Aspartate transport, but not glutamate transport, is competitively inhibited by C4 dicarboxylic acids, whereas 2-oxoglutarate competitively inhibits glutamate transport, but not aspartate transport. 5. Competitive inhibition of L-aspartate transport by L-glutamate and by the 5-methyl ester of L-glutamate is abolished in the presence of 2-oxoglutarate. However, 2-oxoglutarate does not affect the competitive inhibition of L-aspartate transport by D-aspartate and by DL-threo-3-hydroxyaspartate. The relationship between the two dicarboxylic amino acid transport systems and the spatial characteristics of the aspartate carrier are discussed in the light of these findings.

Glutamate transport in membrane vesicles of the wild-type strain and glutamate-utilizing mutants of Escherichia coli

A highly specific energy-dependent glutamate transport system was demonstrated in membrane vesicles of glutamate-utilizing Escherichia coli K-12 mutants. The glutamate transport activity of membranes from the parent strain, unable to grow on glutamate, was very low. With ascorbate-phenazine methosulfate as the electron donor, mutant preparations displayed 17 to 20 times higher activity than did the wild type. However, the affinity of the mutant carrier for L-glutamate remained the same as in the parent strain. Comparative inhibition analysis of glutamate transport in whole cells and membrane vesicles and of in vitro binding of glutamate to a specific periplasmic-binding protein suggests that under certain conditions the latter may be a component of the E. coli K-12 glutamate transport system.

Effect of growth conditions on glutamate transport in the wild-type strain and glutamate-utilizing mutants of Escherichia coli

The effects of growth conditions on the glutamate transport activity of intact cells and membrane vesicles and on the levels of glutamate-binding protein in wild-type Escherichia coli K-12 CS101 and in two glutamate-utilizing mutants, CS7 and CS2TC, were studied. Growth of CS101 on aspartate as the sole source of carbon or nitrogen resulted in a severalfold increase in glutamate transport activity of intact cells and membrane preparations to levels characteristic of the operator-constitutive mutant CS7. The high glutamate transport activity of mutant CS7 was not depressed further by growth on aspartate. Synthesis of glutamate-binding protein was not enhanced by aspartate in either strain. Mutant CS2TC produces a heat-labile repressor of glutamate permease synthesis and is therefore able to grow on glutamate at 42 C but not at 30 C. CS2TC cells grown in a glycerol-minimal medium at the restrictive temperature (30 C) exhibit low glutamate transport activity. Growth on aspartate at 30 C results in derepressed synthesis of glutamate permease. Cells grown on glycerol at 42 C have high glutamate transport activity. No further derepression is obtained upon growth on aspartate. Growth of CS101 and CS7 in "rich broth" greatly reduces the levels of glutamate-binding protein but does not appreciably affect glutamate transport by whole cells or membrane preparations. The identity of the carrier and the role of the binding protein in glutamate transport are discussed in the light of these findings.

Soluble and membrane-bound aspartate-binding activities in Salmonella typhimurium

The specificities of the soluble and membrane aspartate-binding activities were compared with each other and with the specificity of aspartate chemotaxis and were found to be distinct. The soluble aspartate-binding protein was purified to homogeneity and had a molecular weight of 30,000. The dissociation constant was 10(-6) M for aspartate, and the protein bound glutamate, cysteic acid, and 2-amino-3-phosphonopropionate. Aspartate transport was inhibited by cysteic acid.

Purification and properties of glutamate binding protein from the periplasmic space of Escherichia coli K-12

Glutamate binding protein released from the periplasmic space of Escherichia coli K-12 by lysozyme-EDTA treatment was purified to homogeneity and its physical and chemical properties were studied. It is a basic protein with a pI of 9.1. Its molecular weight, determined in an analytical ultracentrifuge, and by gel filtration on Sephadex G-100 and dodecylsulphate acrylamide is 29 700, 27 800 and 32 000, respectively. The KD value for glutamate was 6.7 - 10- minus 6 M. L-Aspartate, reduced glutathione, G-glutamate-gamma-benzylester and L-glutamate-gamma-ethylester competitively inhibited glutamate binding with K-i; values of 7.8 - 10- minus 5, 1.1 - 10- minus 5, 1.0 - 10- minus 5 and 1.0 - 10- minus 5 M, respectively. Spheroplasts retained 40% of glutamate transport as compared to intact cells. The glutamate binding activity of a glutamate-utilizing strain (CS7), was 1.6 times as high as that of the glutamate non-utilizing parent strain (CS101). Similarly, the glutamate binding activity of a temperature conditional glutamate-utilizing mutant (CS2-TC) was 1.9 times higher when grown at the permissive temperature (42 degrees C) than when grown at the restrictive temperature (30 degrees C).

Sodium-stimulated glutamate transport in osmotically shocked cells and membrane vesicles of Escherichia coli

Three phenotypically distinct strains of Escherichia coli B were studied: one in which the transport of glutamate was strongly stimulated by sodium, one in which the transport was relatively independent of sodium, and one which did not transport glutamate. Membrane vesicle preparations from the three strains followed the behavior of whole cells with respect to sodium-stimulated transport. Although glutamate-binding material could be released from cells by osmotic shock, its affinity for glutamate was not significantly influenced by sodium. Furthermore, the shocked cells retained sodium-stimulated transport. The accumulated results suggest that the sodium-activated glutamate transport system resides in the cytoplasmic membrane and that releasable binding protein(s) is not intimately involved in its function.

Sodium and potassium requirements for active transport of glutamate by Escherichia coli K-12

Active transport of glutamate by Escherichia coli K-12 requires both Na(+) and K(+) ions. Increasing the concentration of Na(+) in the medium results in a decrease in the K(m) of the uptake system for glutamate; the capacity is not affected. Glutamate uptake by untreated cells is not stimulated by K(+). K(+)-depleted cells show a greatly reduced capacity for glutamate uptake. Preincubation of such cells in the presence of K(+) fully restores their capacity for glutamate uptake when Na(+) ions are also present in the uptake medium. Addition of either K(+) or Na(+) alone restores glutamate uptake to only about 20% of its maximum capacity in the presence of both cations. Changes in K(+) concentration affect the capacity for glutamate uptake but have no effect on the K(m) of the glutamate transport system. Ouabain does not inhibit the (Na(+)-K(+))-stimulated glutamate uptake by intact cells or spheroplasts of E. coli K-12.

Glutamate transport in Escherichia coli K-12: nonidentity of carriers mediating entry and exit

The exit of glutamate from Escherichia coli K-12 cells preloaded with the radioactive amino acid and its relation to the reaction of entry were studied. Experiments with cells preloaded to different intracellular concentrations of radioactive glutamate confirmed our earlier conclusion that glutamate exit was a first-order reaction. l-Glutamate, competitive inhibitors of glutamate uptake (d-glutamate and l-glutamate-gamma-methyl ester), noncompetitive inhibitors of glutamate uptake (l-serine and l-alanine), and the energy poison NaN(3) all accelerated glutamate exit 2.8-fold. No additive effect was observed in the presence of NaN(3) together with l-glutamate. Preloading with cold l-glutamate did not increase the rate of uptake of radioactive glutamate. It is concluded that the acceleration of glutamate exit in the presence of l-glutamate in the medium is not due to exchange diffusion and that l-glutamate and azide affect exit indirectly by preventing recapture. Sucrose, 25%, slowed down glutamate exit by a factor of about 4.7 and increased the steady-state level of glutamate accumulation to about the same extent. Increasing the intracellular K(+) concentration enhanced glutamate uptake but did not affect the half-time of exit. It is concluded that separate carriers are most probably involved in mediating the entry and exit reactions.