Molecular properties of the ATP synthetase from Escherichia coli

Chemical modification of the F0 part of the ATP synthase (F1F0) from Escherichia coli. Effects on proton conduction and F1 binding

The purified F0 part of the ATP synthase complex from Escherichia coli was incorporated into liposomes and chemically modified by various reagents. The modified F0-liposomes were assayed for H+ uptake and, after reconstitution with F1, for total and dicyclohexylcarbodiimide-sensitive ATPase activity. The water-soluble carbodiimide, 1-ethyl-3-(-3-dimethylaminopropyl)carbodiimide methiodide, (1.2 mM), inhibited H+ uptake to a great extent. Binding of F1 was almost unaffected, but the hydrolysis of ATP was uncoupled from H+ transport. This is reflected by the inhibition of dicyclohexylcarbodiimide-sensitive ATPase activity. Woodward's reagent K, N-ethyl-5-phenylisoxazolium-3'-sulfonate, inhibited both H+ uptake and total ATPase activity. Modification of arginine residues by phenylglyoxal (20 mM) was followed by inhibition of the F1 binding activity by 80% of the control. H+ translocation was reduced to 70%. Diethylpyrocarbonate (3 mM) exhibited a strong inhibiting effect on H+ uptake but not on F1 binding. Modification of tyrosine (by tetranitromethane) as well as lysine residues (by succinic anhydride) did not affect F0 functions. From the data presented we conclude that carboxyl-groups, different from the dicyclohexylcarbodiimide-binding site, are involved in H+ translocation through F0 and, in part, in the functional binding of F1. Furthermore, for the latter function, also arginine residues seem to be important. The role of histidine residues remains unclear at present.

Neutron small angle scattering of matched proteoliposomes with incorporated F0F1 ATPase complex from Rhodospirillum rubrum FR1. An approach to the structure of membrane proteins in their natural environment

Purified F0F1 ATPase from Rhodospirillum rubrum FR1 has been incorporated into lipid vesicles from the partially deuterated phospholipid dimyristoylglycerophosphocholine (DMPC-D54). These proteoliposomes were able to carry out energy transducing reactions. The incorporation of the membrane protein was controlled by freeze fracture electron microscopy. A method for structural research of the membrane protein in its natural environment has been developed by means of neutron small angle scattering. Using the contrast variation technique, the lipid part of the proteoliposomes was matched by adding an appropriate amount of D2O to the solvent. Thus the neutron scattering profile of F0F1 ATPase incorporated into vesicles was separated from the neutron scattering of the liposome. F0F1 ATPase incorporated in a lipid bilayer, as well as the free enzyme, yields a radius of gyration of Rg = 6.0 +/- 0.1 nm which leads to an overall diameter of 15.5 nm. This result suggests that the monomeric form of F0F1 ATPase is incorporated in DMPC-D54 membranes at 20 degrees C.

ATP synthetase (F1F0) of Escherichia coli K-12. High-yield preparation of functional F0 by hydrophobic affinity chromatography

1. The purified ATP synthetase complex (F1F0) from Escherichia coli was adsorbed to immobilized poly-(L-lysine)-deoxycholic acid. About 0.7 mg F1F0 were bound per ml of settled gel. The hydrophilic F1 part was dissociated from the complex by treatment with 7 M urea. F0 was eluted in high yield either with deoxycholate (6 mM) or taurodeoxycholate (10 mM). About 14% of the total protein bound to the column was eluted as F0, which corresponds to 64% of the total F0 in the F1F0 complex. 2. The purified F0 preparation obtained was composed of three different kinds of subunits with apparent molecular weights of 24000 (a), 19000 (b) and 8300 (c), respectively as determined by sodium dodecyl sulfate gel electrophoresis. 3. After incorporation into liposomes and the generation of a potassium diffusion potential by valinomycin, the F0 preparation mediated H+ translocation. This H+ uptake is inhibited by either dicyclohexylcarbodiimide or purified F1 ATPase. 4. Incubation of F0-containing liposomes with F1 led to the reconstitution of an ATP-driven quenching of acridine-dye fluorescence. The quenching was abolished by uncoupler and prevented by dicyclohexylcarbodiimide.

Size and shape of the alpha subunit of the (Ca,Mg)-dependent adenosinetriphosphate from Escherichia coli in solution in the presence and absence of ATP

The alpha subunit of the (Ca, Mg)-dependent ATPase from Escherichia coli was studied in solution by means of X-ray scattering experiments at variable contrast and in the presence of ATP. The experiments were carried out on an absolute scale in the range of (45.0 nm-1) less than h less than (1.5 nm-1) at pH 8.0. The experiments show that this system and the complex of the alpha subunit with ATP can be considered to be ideal and monodisperse so that the following parameters for the alpha subunit and its complex with ATP were determined: the radius of gyration, the volume, the degree of hydration, the maximum particle diameter, and the molecular weight. The molecular weight of the alpha subunit was determined as 58 500 +/- 3000 by means of light scattering measurements, and 57 700 +/- 25 000 by the small-angle X-ray scattering experiments. The radius of gyration of the alpha subunit at pH 8.0 was determined to 2.64 +/- 0.02 nm, the maximum chord in solution to 10.0 +/- 0.5 nm, the volume to 102.4 +/- 2.5 nm3, and the degree of hydration to 0.34 +/- 0.02 mg X g-1. Binding of ATP to the alpha subunit causes structural changes. These changes are reflected in the radius of gyration, Rg = 2.45 +/- 0.015 nm, in the volume, 117.6 +/- 1.5 nm3, and in the maximum chord length in solution, 7.8 +/- 0.5 nm. These changes imply a decrease of the axial ratio from 2.4 to 1.4, i.e. ATP-binding induced an increase in isometry of the alpha subunit.