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At least 19 recordsLinked to original sources
PubMed1992

Interaction between maltose-binding protein and the membrane-associated maltose transporter complex in Escherichia coli.

Active transport of maltose in Escherichia coli requires the presence of both maltose-binding protein (MBP) in the periplasm and a complex of MalF, MalG, and MalK proteins (FGK2) located in the cytoplasmic membrane. Earlier, mutants in malF or malG were isolated that are able to grow on maltose in the complete absence of MBP. When the wild-type malE+ allele, coding for MBP, was introduced into these MBP-independent mutants, they frequently lost their ability to grow on maltose. Furthermore, starting from these Mal- strains, Mal+ secondary mutants that contained suppressor mutations in malE were isolated. In this study, we examined the interaction of wild-type and mutant MBPs with wild-type and mutant FGK2 complexes by using right-side-out membrane vesicles. The vesicles from a MBP-independent mutant (malG511) transported maltose in the absence of MBP, with Km and Vmax values similar to those found in intact cells. However, addition of wild-type MBP to these mutant vesicles produced unexpected responses. Although malE+ malG511 cells could not utilize maltose, wild-type MBP at low concentrations stimulated the maltose uptake by malG511 vesicles. At higher concentrations of the wild-type MBP and maltose, however, maltose transport into malG511 vesicles became severely inhibited. This behaviour of the vesicles was also reflected in the phenotype of malE+ malG511 cells, which were found to be capable of transporting maltose from a low external concentration (1 microM), but apparently not from millimolar concentrations present in maltose minimal medium. We found that the mutant FGK2 complex, containing MalG511, had a much higher apparent affinity towards the wild-type MBP than did the wild-type FGK2 complex.(ABSTRACT TRUNCATED AT 250 WORDS)

ATP-Binding Cassette Transporters↗
PubMed1979

[Use of maltose and a mixture of maltose, fructose and xylitol in parenteral feeding].

Maltose or maltose in combination with fructose and xylitol was administered intravenously to eight healthy male subjects. Constant maltose levels could not be attained in the blood at an infusion rate of 0.125 g maltose/kg body-weight and hour. Maximal concentrations of maltose were found at the end of the infusion period. 8.6 +/- 1.2% of the administered radioactivity was excreted into urine within 8 hours. Regarding the enzymatically determined maltose and glucose, the maltose balance was more favorable with the loss of only 3--3.5% carbohydrates into urine. The highest oxidation rate of the administered maltose was 1.5 g maltose/human volunteer and hour. During the experimental period of 8 hours 7.4 g maltose, corresponding to 37% of the applied dosis of the disaccharid, has been oxidized to and excreted as 14CO2. Xylitol and fructose did not effect utilisation and balance of maltose. Only the urinary excretion of glucose was higher when the combined solution was applied. At a limited infusion rate (0.125 g maltose/kg body-weight and hour) maltose or the combined solution maltose--xylitol--fructose may be recommended for parenteral nutrition.

Adult↗
PubMed1991

The malX malY operon of Escherichia coli encodes a novel enzyme II of the phosphotransferase system recognizing glucose and maltose and an enzyme abolishing the endogenous induction of the maltose system.

Mutants lacking MalK, a subunit of the binding protein-dependent maltose-maltodextrin transport system, constitutively express the maltose genes. A second site mutation in malI abolishes the constitutive expression. The malI gene (at 36 min on the linkage map) codes for a typical repressor protein that is homologous to the Escherichia coli LacI, GalR, or CytR repressor (J. Reidl, K. Römisch, M. Ehrmann, and W. Boos, J. Bacteriol. 171:4888-4899, 1989). We now report that MalI regulates an adjacent and divergently oriented operon containing malX and malY. MalX encodes a protein with a molecular weight of 56,654, and the deduced amino acid sequence of MalX exhibits 34.9% identity to the enzyme II of the phosphototransferase system for glucose (ptsG) and 32.1% identity to the enzyme II for N-acetylglucosamine (nagE). When constitutively expressed, malX can complement a ptsG ptsM double mutant for growth on glucose. Also, a delta malE malT(Con) strain that is unable to grow on maltose due to its maltose transport defect becomes Mal+ after introduction of malI::Tn10 and the plasmid carrying malX. MalX-mediated transport of glucose and maltose is likely to occur by facilitated diffusion. We conclude that malX encodes a phosphotransferase system enzyme II that can recognize glucose and maltose as substrates even though these sugars may not represent the natural substrates of the system. The second gene in the operon, malY, encodes a protein of 43,500 daltons. Its deduced amino acid sequence exhibits weak homology to aminotransferase sequences. The presence of plasmid-encoded MalX alone was sufficient for complementing growth on glucose in a ptsM ptsG glk mutant, and the plasmid-encoded MalY alone was sufficient to abolish the constitutivity of the mal genes in a malK mutant. The overexpression of malY in a strain that is wild type with respect to the maltose genes strongly interferes with growth on maltose. This is not the case in a malT(Con) strain that expresses the mal genes constitutively. We conclude that malY encodes an enzyme that degrades the inducer of the maltose system or prevents its synthesis.

Amino Acid Sequence↗
PubMed1985

Interspecific reconstitution of maltose transport and chemotaxis in Escherichia coli with maltose-binding protein from various enteric bacteria.

In Escherichia coli, the periplasmic maltose-binding protein (MBP), the product of the malE gene, is the primary recognition component of the transport system for maltose and maltodextrins. It is also the maltose chemoreceptor, in which capacity it interacts with the signal transducer Tar (taxis to aspartate and some repellents). In studies of the maltose system in other members of the family Enterobacteriaceae, we found that MBP is produced by Salmonella typhimurium, Klebsiella pneumoniae, Enterobacter aerogenes, and Serratia marcescens. MBP from all of these species cross-reacted with antibody against the E. coli protein and had a similar molecular weight (about 40,000). The Shigella flexneri and Proteus mirabilis strains we examined did not synthesize MBP. The isoelectric points of MBP from different species varied from the acid extreme of E. coli (4.8) to the basic extreme of E. aerogenes (8.9). All species with MBP transported maltose with high affinity, although the Vmax for K. pneumoniae was severalfold lower than that for the other species. Maltose chemotaxis was observed only in E. coli and E. aerogenes. In S. typhimurium LT2, Tar was completely inactive in maltose taxis, although it signaled normally in response to aspartate. MBP isolated from all five species could be used to reconstitute maltose transport and taxis in a delta malE strain of E. coli after permeabilization of the outer membrane with calcium.

ATP-Binding Cassette Transporters↗
PubMed1990

Substrate-induced activation of maltose phosphorylase: interaction with the anomeric hydroxyl group of alpha-maltose and alpha-D-glucose controls the enzyme's glucosyltransferase activity.

Maltose phosphorylase, long considered strictly specific for beta-D-glucopyranosyl phosphate (beta-D-glucose 1-P), was found to catalyze the reaction beta-D-glucosyl fluoride + alpha-D-glucose----alpha-maltose + HF, at a rapid rate, V = 11.2 +/- 1.2 mumol/(min.mg), and K = 13.1 +/- 4.4 mM with alpha-D-glucose saturating, at 0 degrees C. This reaction is analogous to the synthesis of maltose from beta-D-glucose 1-P + D-glucose (the reverse of maltose phosphorolysis). In acting upon beta-D-glucosyl fluoride, maltose phosphorylase was found to use alpha-D-glucose as a cosubstrate but not beta-D-glucose or other close analogs (e.g., alpha-D-glucosyl fluoride) lacking an axial 1-OH group. Similarly, the enzyme was shown to use alpha-maltose as a substrate but not beta-maltose or close analogs (e.g., alpha-maltosyl fluoride) lacking an axial 1-OH group. These results indicate that interaction of the axial 1-OH group of the disaccharide donor or sugar acceptor with a particular protein group near the reaction center is required for effective catalysis. This interaction appears to be the means that leads maltose phosphorylase to promote a narrowly defined set of glucosyl transfer reactions with little hydrolysis, in contrast to other glycosylases that catalyze both hydrolytic and nonhydrolytic reactions.

Binding Sites↗
PubMed1987

Silent and functional changes in the periplasmic maltose-binding protein of Escherichia coli K12. I. Transport of maltose.

The malE gene encodes the periplasmic maltose-binding protein (MBP). Nineteen mutations that still permit synthesis of stable MBP were generated by random insertion of a BamHI octanucleotide into malE and six additional mutations by in-vitro recombinations between mutant genes. The sequence changes were determined; in most cases the linker insertion is accompanied by a small deletion (30 base-pairs on average). The mutant MBP were studied for export, growth on maltose and maltodextrins, maltose transport and binding, and maltose-induced fluorescence changes. Sixteen mutant MBP (out of 21 studied in detail) were found in the periplasmic space: 12 of them retained a high affinity for maltose, and 10 activity for growth on maltose. The results show that several regions of MBP are dispensable for stability, substrate binding and export. Three regions (residues 207 to 220, 297 to 303 and 364 to 370) may be involved in interactions with the MalF or MalG proteins. A region near the C-terminal end is important for maltose binding. Two regions of the mature protein (residues 18 to 42 and 280 to 296) are required for export to, or solubility in, the periplasm.

ATP-Binding Cassette Transporters↗
PubMed1985

Dependence of maltose transport and chemotaxis on the amount of maltose-binding protein.

Maltose-binding protein (MBP) is essential for maltose transport and chemotaxis in Escherichia coli. To perform these functions it must interact with two sets of cytoplasmic membrane proteins, the MalFGK transport complex and the chemotactic signal transducer Tar. MBP is present at high concentrations, on the order of 1 mM, in the periplasm of maltose-induced or malTc constitutive cells. To determine how the amount of MBP affects transport and taxis, we utilized a series of malE signal-sequence mutations that interfere with export of MBP. The MBP content in shock fluid from cells carrying the various mutations ranged from 4 to 23% of the malE+ level. The apparent Km for maltose transport varied by less than a factor of 2 among malE+ and mutant strains. At a saturating maltose concentration 9% (approximately 90 microM) of the malE+ amount of MBP was required for half-maximal uptake rates. Transport exhibited a sigmoidal dependence on the amount of periplasmic MBP, indicating that MBP may be involved in a cooperative interaction at some stage of the transport process. The chemotactic response to a saturating maltose stimulus exhibited a first-order dependence on the amount of periplasmic MBP. Thus, interaction of a single substrate-bound MBP with Tar appears sufficient to initiate a chemotactic signal from the transducer. A half-maximal chemotactic response occurred at 25% of the malE+ MBP level, suggesting that in vivo the KD for binding of maltose-loaded MBP to Tar is quite high (approximately 250 microM).

ATP-Binding Cassette Transporters↗
PubMed1992

Maltose chemotaxis involves residues in the N-terminal and C-terminal domains on the same face of maltose-binding protein.

The periplasmic maltose-binding protein (MBP) of Escherichia coli is the recognition component of the maltose chemoreceptor and of the active transport system for maltose. It interacts with the Tar chemotactic signal transducer and the integral cytoplasmic-membrane components (the MalF and MalG proteins) of the maltose transport system. Maltose binds in a cleft between the globular N-terminal and C-terminal domains of MBP, which are connected by a moveable hinge. The two domains undergo a large motion relative to one another as the protein moves from the open, unbound state to the closed, ligand-bound state. We generated, by doped-primer mutagenesis, amino acid substitutions that specifically disrupt the chemotactic function of MBP. These substitutions cluster in two well-defined regions that are nearly contiguous on the surface of MBP in its closed conformation. One region is in the N-terminal domain and one is in the C-terminal domain. The distance between the two regions is expected to change substantially as the protein goes from the open to the closed form. These results support a model in which ligand binding brings two recognition sites on MBP into the proper spatial relationship to interact with complementary sites on Tar. Mutations in MBP that appear to cause defects in interaction with MalF and MalG are distributed differently from mutations that primarily affect maltose taxis. We conclude that the regions of MBP that contact Tar and those that contact MalF and MalG are adjacent on the face of the protein opposite the hinge connecting the two domains and that those regions are largely, although perhaps not entirely, distinct.

ATP-Binding Cassette Transporters↗
PubMed1988

Maltose chemoreceptor of Escherichia coli: interaction of maltose-binding protein and the tar signal transducer.

The maltose chemoreceptor in Escherichia coli consists of the periplasmic maltose-binding protein (MBP) and the Tar signal transducer, which is localized in the cytoplasmic membrane. We previously isolated strains containing malE mutations that cause specific defects in the chemotactic function of MBP. Four of these mutations have now been characterized by DNA sequence analysis. Two of them replace threonine at residue 53 of MBP with isoleucine (MBP-TI53), one replaces an aspartate at residue 55 with asparagine (MBP-DN55), and the fourth replaces threonine at residue 345 with isoleucine (MBP-TI345). The chemotactic defects of MBP-TI53 and MBP-DN55, but not of MBP-TI345, are suppressed by mutations in the tar gene. Of the tar mutations, the most effective suppressor (isolated independently three times) replaces Arg-73 of Tar with tryptophan. Two other tar mutations that disrupt the aspartate chemoreceptor function of Tar also suppress the maltose taxis defects associated with MBP-TI53 and MBP-DN55. One of these mutations introduces glutamine at residue 73 of Tar, the other replaces arginine at residue 69 of Tar with cysteine. These results suggest that regions of MBP that include residues 53 to 55 and residue 345 are important for the interaction with Tar. In turn, arginines at residues 69 and 73 of Tar must be involved in the recognition of maltose-bound MBP and/or in the production of the attractant signal generated by Tar in response to maltose-bound MBP.

ATP-Binding Cassette Transporters↗
PubMed1987

Silent and functional changes in the periplasmic maltose-binding protein of Escherichia coli K12. II. Chemotaxis towards maltose.

We examined the chemotactic behavior of ten Escherichia coli mutants able to synthesize a modified periplasmic maltose-binding protein (MBP) retaining high affinity for maltose. Eight were able to grow on maltose (Mal+), two were not (Mal-). In the capillary assay six out of eight of the Mal+ strains showed an optimal response at the same concentration of maltose as the wild-type strain; the amplitude of the response was strongly reduced in two Mal+ mutants and partially affected in one. The amplitude of the chemotactic response of the two Mal- strains was at least equal to that of the wild type, so that the chemotactic and transport functions of MBP were dissociated in these two cases. We define two regions of the protein (residues 297 to 303 and 364 to 369), that are important both for the chemotactic response and for transport, and one region (residues 207 to 220) that is essential for transport but dispensable for chemotaxis. Interestingly, some regions that were found to be inessential for transport are also dispensable for chemotaxis.

ATP-Binding Cassette Transporters↗
PubMed1975

The binding of maltose to 'virgin' maltose-binding protein is biphasic.

The biphasic binding properties of the galactose-binding and maltose-binding proteins of Escherichia coli may be important in the functioning of these proteins as recognition components of chemoreceptors. However, Richarme and Kepes [Eur. J. Binding curve of the galactose-binding protein may be the result of isotopic dilution, during equilibrium dialysis, by unlabeled ligand retained by the binding throughout purification. Here the binding of maltose to maltose-binding protein which has never previously been exposed to sugar ('virgin' binding protein) is shown to be biphasic. This implies that the unusual binding properties are attributable to the maltose-binding protein itself.

Bacterial Proteins↗
PubMed1988

Allele-specific malE mutations that restore interactions between maltose-binding protein and the inner-membrane components of the maltose transport system.

Active accumulation of maltose and maltodextrins by Escherichia coli depends on an outer-membrane protein. LamB, a periplasmic maltose-binding protein (MalE, MBP) and three inner-membrane proteins, MalF, MalG and MalK. MalF and MalG are integral transmembrane proteins, while MalK is associated with the inner aspect of the cytoplasmic membrane via an interaction with MalG. Previously we have shown that MBP is essential for movement of maltose across the inner membrane. We have taken advantage of malF and malG mutants in which MBP interacts improperly with the membrane proteins. We describe the properties of malE mutations in which a proper interaction between MBP and defective MalF and MalG proteins has been restored. We found that these malE suppressor mutations are able to restore transport activity in an allele-specific manner. That is, a given malE mutation restores transport activity to different extents in different malF and malG mutants. Since both malF and malG mutations could be suppressed by allele-specific malE suppressors, we propose that, in wild-type bacteria, MBP interacts with sites on both MalF and MalG during active transport. The locations of different malE suppressor mutations indicate specific regions on MBP that are important for interacting with MalF and MalG.

ATP-Binding Cassette Transporters↗
PubMed1986

Galactose- and maltose-stimulated lipoamide dehydrogenase activities related to the binding-protein-dependent transport of galactose and maltose in toluenized cells of Escherichia coli.

The binding protein-dependent transport of galactose and maltose occurs at a reduced but significant rate in Escherichia coli cells which have undergone a mild toluenization. Dihydrolipoate and 3-acetyl-NAD produce a severalfold stimulation of these transports in the toluenized cells. In parallel to the stimulation of galactose and maltose transport by dihydrolipoate and 3-acetyl-NAD, there is a stimulation by galactose and maltose of lipoamide dehydrogenase activities which seem to be related to the binding-protein-dependent transport of these sugars. The lipoamide dehydrogenase component of the pyruvate and 2-oxoglutarate dehydrogenase complexes (the lpd gene product) is not involved in this stimulation. These results are discussed in relation to our recent studies showing a possible involvement of lipoic acid and of the 2-oxoacid dehydrogenases in the binding-protein-dependent transports.

ATP-Binding Cassette Transporters↗
PubMed1989

Active transport of maltose in membrane vesicles obtained from Escherichia coli cells producing tethered maltose-binding protein.

Attempts to reconstitute periplasmic binding protein-dependent transport activity in membrane vesicles have often resulted in systems with poor and rather inconsistent activity, possibly because of the need to add a large excess of purified binding protein to the vesicles. We circumvented this difficulty by using a mutant which produces a precursor maltose-binding protein that is translocated across the cytoplasmic membrane but is not cleaved by the signal peptidase (J. D. Fikes and P. J. Bassford, Jr., J. Bacteriol. 169:2352-2359, 1987). The protein remains tethered to the cytoplasmic membrane, presumably through the hydrophobic signal sequence, and we show here that the spheroplasts and membrane vesicles prepared from this mutant catalyze active maltose transport without the addition of purified maltose-binding protein. In vesicles, the transport requires electron donors, such as ascorbate and phenazine methosulfate or D-lactate. However, inhibition by dicyclohexylcarbodiimide and stimulation of transport by the inculsion of ADP or ATP in the intravesicular space suggest that ATP (or compounds derived from it) is involved in the energization of the transport. The transport activity of intact cells can be recovered without much inactivation in the vesicles, and their high activity and ease of preparation will be useful in studies of the mechanism of the binding protein-dependent transport process.

ATP-Binding Cassette Transporters↗