Preparation and reconstitution of F1F0 and F0 from Escherichia coli

Regulatory conformational changes of the ε subunit in single FRET-labeled FoF1-ATP synthase

Subunit ε is an intrinsic regulator of the bacterial F_oF₁-ATP synthase, the ubiquitous membrane-embedded enzyme that utilizes a proton motive force in most organisms to synthesize adenosine triphosphate (ATP). The C-terminal domain of ε can extend into the central cavity formed by the α and β subunits, as revealed by the recent X-ray structure of the F₁ portion of the Escherichia coli enzyme. This insertion blocks the rotation of the central γ subunit and, thereby, prevents wasteful ATP hydrolysis. Here we aim to develop an experimental system that can reveal conditions under which ε inhibits the holoenzyme F_oF₁-ATP synthase in vitro. Labeling the C-terminal domain of ε and the γ subunit specifically with two different fluorophores for single-molecule Förster resonance energy transfer (smFRET) allowed monitoring of the conformation of ε in the reconstituted enzyme in real time. New mutants were made for future three-color smFRET experiments to unravel the details of regulatory conformational changes in ε.

A functional His-tagged c subunit of the Escherichia coli F-type ATPase/Synthase

The c subunit of the Escherichia coli F0 has been tagged with a hexahistidine motif at its C-terminus. The tagged subunit is capable of forming functional F0 complexes that translocate protons in the absence of the F1 complex. In the presence of F1, the two sectors associate and display all biochemical activities of the wildtype enzyme: DCCD-inhibitable ATPase activity, ATP synthase activity, and ATP-dependent proton pumping. The enzyme can be solubilized and purified as an intact complex under native conditions on immobilized-metal affinity chromatography (IMAC) resin. The purified complex can be reincorporated into liposomes and demonstrates ATP-dependent proton pumping activity. Hexahistine tags placed at the N-terminus, in contrast, were all inactive. These experiments demonstrate the feasibility of tagging the c subunit for further studies of the F0 and suggest an important role for the N-terminus of the c subunit in either assembly or function of the protein.

Turnover number of Escherichia coli F0F1 ATP synthase for ATP synthesis in membrane vesicles

The rate of ATP synthesized by the ATP synthase (F0F1-ATPase) is limited by the rate of energy production via the respiratory chain, when measured in everted membrane vesicles of an Escherichia coli atp wild-type strain. After energization of the membranes with NADH, fractional inactivation of F0F1 by the covalent inhibitor N,N'-dicyclohexylcarbodiimide allowed the rate of ATP synthesis/mol remaining active ATP synthase complexes to increase; the active ATP synthase complexes were calculated using ATP hydrolysis rates as the defining parameter. In addition, variation of the assay temperature revealed an increase of the ATP synthesis rate up to a temperature of 37 degrees C, the optimal growth temperature of E. coli. In parallel, the amount of F0F1 complexes present in membrane vesicles was determined by immunoquantitation to be 3.3 +/- 0.3% of the membrane protein for cells grown in rich medium and 6.6 +/- 0.3% for cells grown in minimal medium with glycerol as sole carbon and energy source. Based on these data, a turnover number for ATP synthesis of 270 +/- 40 s(-1) could be determined in the presence of 5% active F0F1 complexes. Therefore, these studies demonstrate that the ATP synthase complex of E. coli has, with respect to maximum rates, the same capacity as the corresponding enzymes of eukaryotic organells.

ATP synthesis catalyzed by the ATP synthase of Escherichia coli reconstituted into liposomes

The H(+)-translocating F0F1-ATPase from Escherichia coli (EF0F1) was purified and reconstituted into preformed reverse-phase liposomes prepared from egg yolk phosphatidylcholine/phosphatidic acid. The EF0F1 liposomes were energized by an acid/base transition (pHout = 8.3; pHin = 5.0) and a superimposed K+/valinomycin diffusion potential ([K+]out = 100 mM; [K+]in = 0.6 mM) yielding a maximum rate (turnover number) of ATP synthesis of 27 +/- 8 mol ATP . mol EF0F1(-1) . s-1), i.e. 27 +/- 8 s-1. This reaction was inhibited by NH4Cl or by addition of the F0F1 inhibitor N,N'-dicyclohexylcarbodiimide. The rate of ATP synthesis measured as a function of the phosphate and ADP concentrations, can be described by Michaelis-Menten kinetics with a Km of 0.7 +/- 0.2 mM for phosphate ([ADP] = 200 microM) and a Km of 27 +/- 7 microM for ADP ([phosphate] = 5 mM), respectively.

Reconstitution of energy-linked activities of the solubilized F1F0 ATP synthase from Bacillus subtilis

The F1F0 ATP synthases from wild-type Bacillus subtilis and an uncoupler-resistant mutant have comparable subunit structures. In accord with an earlier hypothesis, ATP hydrolysis and ATP-Pi exchange by the two synthases were equally stimulated and inhibited by protonophores, respectively, when reconstituted alone in either wild-type or mutant lipids.

Inhibitory effect of modified bafilomycins and concanamycins on P- and V-type adenosinetriphosphatases

Various ATPases have been tested for their sensitivity to naturally occurring unusual macrolides and their chemically modified derivatives, which are structurally related to bafilomycin A1 (1), the first specific inhibitor of vacuolar ATPases. The structure-activity study showed that in general the concanamycins, 18-membered macrolides, are better and more specific inhibitors than the bafilomycins of this class of membrane-bound ATPases. The additional carbohydrate residue is not responsible for the improved activity. The importance of an intact hemiketal ring, which is part of an intramolecular hydrogen-bonding network, and the effects of the size of the macrolactone ring are discussed. The structurally related elaiophylin (13), a C2-symmetric macrodiolide antibiotic, proved to be inactive on vacuolar ATPases but still retained its inhibitory effect on P-type ATPases.

Characterization of the H(+)-pumping F1F0 ATPase of Vibrio alginolyticus

The F1F0 ATPase of Vibrio alginolyticus was cloned from a chromosomal lambda library. The unc operon, which contains the structural genes for the ATPase, was sequenced and shown to have a gene organization of uncIBEFHAGDC. The sequence of each subunit was compared with those of other eubacterial ATPases. The V. alginolyticus unc genes exhibited greater similarity to the Escherichia coli unc genes than to any of the other bacterial unc genes for which the sequence is available. The ATPase was expressed in an E. coli unc deletion strain, and the ATP hydrolytic activity was characterized. It has a pH optimum of 7.6 and is stimulated by the addition of Triton X-100 or any of a variety of salts. The recombinant F1F0 was purified 30.4-fold and reconstituted into proteoliposomes. This enzyme catalyzed the pumping of protons coupled to ATP hydrolysis as measured in fluorescence quenching experiments but would not pump Na+ ions under similar conditions.

Bafilomycins: a class of inhibitors of membrane ATPases from microorganisms, animal cells, and plant cells

Various membrane ATPases have been tested for their sensitivity to bafilomycin A1, a macrolide antibiotic. F1F0 ATPases from bacteria and mitochondria are not affected by this antibiotic. In contrast, E1E2 ATPases--e.g., the K+-dependent (Kdp) ATPase from Escherichia coli, the Na+,K+-ATPase from ox brain, and the Ca2+-ATPase from sarcoplasmic reticulum--are moderately sensitive to this inhibitor. Finally, membrane ATPases from Neurospora vacuoles, chromaffin granules, and plant vacuoles are extremely sensitive. From this we conclude that bafilomycin A1 is a valuable tool for distinguishing among the three different types of ATPases and represents the first relatively specific potent inhibitor of vacuolar ATPases.