Further studies on the binding of maltose to the maltose-binding protein of Escherichia coli.
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Bacterial Proteins↗
Biomedical subjects
G L Hazelbauer
Publications and source records attributed to G L Hazelbauer.
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↗
Maltose chemoreceptor of Escherichia coli.
Strains carrying mutations in the maltose system of Escherichia coli were assayed for maltose taxis, maltose uptake at 1 and 10 muM maltose, and maltose-binding activity released by osmotic shock. An earlier conclusion that the metabolism of maltose is not necessary for chemoreception is extended to include the functioning of maltodextrin phosphorylase, the product of malP, and the genetic control of the maltose receptor by the product of malT is confirmed. Mutants in malF and malK are defective in maltose transport at low concentrations as well as high concentrations, as previously shown, but are essentially normal in maltose taxis. The product of malE has been previously shown to be the maltose-binding protein and was implicated in maltose transport. Most malE mutants are defective in maltose taxis, and all those tested are defective in maltose transport at low concentrations. Thus, as previously suggested, the maltose-binding protein probably serves as the recognition component of the maltose receptor, as well as a component of the transport system. tsome malE mutants release maltose-binding activity and are tactic toward maltose, although defective in maltose transport, implying that the binding protein has separate sites for interaction with the chemotaxis and transport systems. Some mutations in lamB, whose product is the receptor for the bacteriophage lamba, cause defects in maltose taxis, indicating some involvement of that product in maltose reception.
Aspartic Acid↗
Role of the receptor for bacteriophage lambda in the functioning of the maltose chemoreceptor of Escherichia coli.
Chemotaxis towards maltose is specifically defective in many strains of Escherichia coli carrying mutations affecting lamB, the gene coding for the outer membrane receptor for bacteriophage lambda. However, with one exception, the most extreme effect of lamB mutants on the maltose response as determined in the capillary assay is a shift to higher sugar concentrations and a reduction in the number of bacteria accumulated to about 25% of the wild-type level. The severity of the taxis defect is strongly correlated with reduced ability of the cells to take up the maltose present at 1 and 10 muM. Evidence presented here and in the accompanying paper indicates that the lambda receptor is involved in the transport of maltose at these concentrations. The effects of lamB mutations on maltose taxis can be explained by postulating that the high-affinity maltose transport system in which the lambda receptor participates transfers maltose from the surrounding medium across the outer membrane and into the periplasmic space. If the maltose chemoreceptor detects sugar present in the periplasmic space, and not molecules external to the outer membrane, then defective transport of low concentrations of maltose into the periplasm would result in the observed apparent reduction in the sensitivity of the maltose receptor. Thus, the lambda receptor protein would participate in maltose chemorecepton only indirectly through its role in maltose transport.
Binding Sites↗
Reconstitution of a chemically excitable membrane.
Membrane fragments rich in cholinergic (nicotinic) receptor sites, purified from homogenates of Torpedo marmorata electric organ, are dissolved in high concentrations of Na cholate and Tris buffer in the presence of Na ethylenediaminetetraacetate, without loss of the ability to bind Naja nigricollis [(3)H]alpha-toxin. After extensive dialysis to remove cholate, the solution is supplemented with crude lipids extracted from native membrane fragments and MgCl(2)-CaCl(2) added dropwise to the mixture as a concentrated solution. The reconstituted membranes obtained retain (22)Na(+). Release of Na from these microsacs increases in the presence of carbamylcholine and the alpha-toxin from N. nigricollis blocks this effect.
Animals↗
Chemotaxis toward sugars in Escherichia coli.
Using a quantitative assay for measuring chemotaxis, we tested a variety of sugars and sugar derivatives for their ability to attract Escherichia coli bacteria. The most effective attractants, i.e., those that have thresholds near 10(-5) M or below, are N-acetyl-d-glucosamine, 6-deoxy-d-glucose, d-fructose, d-fucose, 1-d-glycerol-beta-d-galactoside, galactitol, d-galactose, d-glucosamine, d-glucose, alpha-d-glucose-1-phosphate, lactose, maltose, d-mannitol, d-mannose, methyl-beta-d-galactoside, methyl-beta-d-glucoside, d-ribose, d-sorbitol, and trehalose. Lactose, and probably d-glucose-1-phosphate, are attractive only after conversion to the free monosaccharide, while the other attractants do not require breakdown for taxis. Nine different chemoreceptors are involved in detecting these various attractants. They are called the N-acetyl-glucosamine, fructose, galactose, glucose, maltose, mannitol, ribose, sorbitol, and trehalose chemoreceptors; the specificity of each was studied. The chemoreceptors, with the exception of the one for d-glucose, are inducible. The galactose-binding protein serves as the recognition component of the galactose chemoreceptor. E. coli also has osmotically shockable binding activities for maltose and d-ribose, and these appear to serve as the recognition components for the corresponding chemoreceptors.
Amino Sugars↗
Role of the galactose binding protein in chemotaxis of Escherichia coli toward galactose.
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Bacterial Proteins↗
Escherichia coli mutants defective in chemotaxis toward specific chemicals.
Mutants of Escherichia coli K12 have been found which fail to carry out chemotaxis toward certain chemicals only. One mutant exhibits greatly reduced chemotaxis toward L-serine but has no detectable defect either in uptake or in oxidative metabolism of that compound. Another mutant is not attracted to D-galactose and certain related sugars. There is a correlation between the galactose chemotaxis defect and a defect in galactose uptake, perhaps indicating a common component for chemotaxis and uptake systems. The results are discussed in terms of a model for chemotaxis in which attractants are detected by specific "chemoreceptors."
Chemotaxis↗
Studies of the structural organization of a bacterial chemoreceptor by electron microscopy.
We used analysis by electron microscopy to obtain structural information about a transmembrane receptor that mediates chemotaxis in Escherichia coli. Two-dimensional arrays of regularly packed particles of the receptor Trg were obtained by reconstitution of purified, detergent-solubilized protein into lipid bilayers. Preliminary image processing of negatively stained arrays revealed an almost square 8.8 x 8.8-nm unit cell and resolved the particles into four peaks of density around a central depression. In certain conditions, reconstituted, Trg-containing bilayers associated into membrane stacks. The regular spacing of the stacks provided a value of 15 nm for the dimension of the receptor normal to the membrane. Using these dimensions, the estimated occupied volume of the structure would be sufficient to contain four monomers of Trg. This tetramer form may be a dimer of two antiparallel or parallel homodimers. Our analysis indicates that a receptor monomer is approximately 4.4 nm at the widest point and 15 nm long. Given the dimensions of the periplasmic domain of the closely related receptor Tars, determined by X-ray crystallography, and a minimum bilayer thickness of 3 nm, the cytoplasmic domain would be approximately 5.0 by 4.4 nm. Higher resolution analysis should reveal additional information about receptor structure.
Bacterial Proteins↗