Coupling factor ATPase complex of Rhodospirillum rubrum. Purification and characterization of an oligomycin and N,N'-dicyclohexylcarbodiimide-sensitive (Ca+ + Mg2+)-ATPase

ATP synthase and the actions of inhibitors utilized to study its roles in human health, disease, and other scientific areas

ATP synthase, a double-motor enzyme, plays various roles in the cell, participating not only in ATP synthesis but in ATP hydrolysis-dependent processes and in the regulation of a proton gradient across some membrane-dependent systems. Recent studies of ATP synthase as a potential molecular target for the treatment of some human diseases have displayed promising results, and this enzyme is now emerging as an attractive molecular target for the development of new therapies for a variety of diseases. Significantly, ATP synthase, because of its complex structure, is inhibited by a number of different inhibitors and provides diverse possibilities in the development of new ATP synthase-directed agents. In this review, we classify over 250 natural and synthetic inhibitors of ATP synthase reported to date and present their inhibitory sites and their known or proposed modes of action. The rich source of ATP synthase inhibitors and their known or purported sites of action presented in this review should provide valuable insights into their applications as potential scaffolds for new therapeutics for human and animal diseases as well as for the discovery of new pesticides and herbicides to help protect the world's food supply. Finally, as ATP synthase is now known to consist of two unique nanomotors involved in making ATP from ADP and P(i), the information provided in this review may greatly assist those investigators entering the emerging field of nanotechnology.

Mutations in the beta-subunit Thr(159) and Glu(184) of the Rhodospirillum rubrum F(0)F(1) ATP synthase reveal differences in ligands for the coupled Mg(2+)- and decoupled Ca(2+)-dependent F(0)F(1) activities

In the crystal structure of the mitochondrial F(1)-ATPase, the beta-Thr(163) residue was identified as a ligand to Mg(2+) and the beta-Glu(188) as directly involved in catalysis. We replaced the equivalent beta-Thr(159) of the chromatophore F(0)F(1) ATP synthase of Rhodospirillum rubrum with Ser, Ala, or Val and the Glu(184) with Gln or Lys. The mutant beta subunits were isolated and tested for their capacity to assemble into a beta-less chromatophore F(0)F(1) and restore its lost activities. All of them were found to bind into the beta-less enzyme with the same efficiency as the wild type beta subunit, but only the beta-Thr(159) --> Ser mutant restored the activity of the assembled enzyme. These results indicate that both Thr(159) and Glu(184) are not required for assembly and that Glu(184) is indeed essential for all the membrane-bound chromatophore F(0)F(1) activities. A detailed comparison between the wild type and the beta-Thr(159) --> Ser mutant revealed a rather surprising difference. Although this mutant restored the wild type levels and all specific properties of this F(0)F(1) proton-coupled ATP synthesis as well as Mg- and Mn-dependent ATP hydrolysis, it did not restore at all the proton-decoupled CaATPase activity. This clear difference between the ligands for Mg(2+) and Mn(2+), where threonine can be replaced by serine, and Ca(2+), where only threonine is active, suggests that the beta-subunit catalytic site has different conformational states when occupied by Ca(2+) as compared with Mg(2+). These different states might result in different interactions between the beta and gamma subunits, which are involved in linking F(1) catalysis with F(0) proton-translocation and can thus explain the complete absence of Ca-dependent proton-coupled F(0)F(1) catalytic activity.

Tight nucleotide binding sites and ATPase activities of the Rhodospirillum rubrum RrF1-ATPase as compared to spinach chloroplast CF1-ATPase

Solubilized Rhodospirillum rubrum RrF1-ATPase, depleted of loosely bound nucleotides, retains 2.6 mol of tightly bound ATP and ADP/mol of enzyme. Incubation of the depleted RrF1 with Mg(2+)-ATP or Mg(2+)-AMP-PNP, followed by passage through two successive Sephadex centrifuge columns, results in retention of a maximal number of 4 mol of tightly bound nucleotides/mol of RrF1. They include 1.5 mol of nonexchangeable ATP, whereas all tightly bound ADP is fully exchangeable. A similar retention of only four out of the six nucleotide binding sites present on CF1 has been observed after its passage through one or two centrifuge columns. These results indicate that the photosynthetic, unlike the respiratory, F1-ATPases have faster koff constants for two of the Mg-dependent nucleotide binding sites. This could be the reason for the tenfold lower Mg2+ than Ca(2+)-ATPase activity observed with native RrF1, as with epsilon-depleted, activated CF1. An almost complete conversion of both RrF1 and CF1 from Ca(2+)- to Mg(2+)-dependent ATPases is obtained upon addition of octylglucoside, at concentrations below its CMC, to the ATPase assay medium. Thus, octylglucoside seems to affect directly the RrF1 and CF1 divalent cation binding site(s), in addition to its proposed role in relieving their inhibition by free Mg2+ ions. The RrF1-ATPase activity is 30-fold more sensitive than CF1 to efrapeptin, and completely resistant to either inhibition or stimulation by the CF1 effector, tentoxin. Octylglucoside decreases the inhibition by efrapeptin and tentoxin, but exposes on CF1 a low-affinity, stimulatory site for tentoxin.

Activation of Mg-ATP hydrolysis in isolated Rhodospirillum rubrum H+-ATPase

The effects of lauryl dimethylamine oxide on the Rhodospirillum rubrum H+-ATPase have been studied. This detergent activates Mg2+-dependent ATP hydrolysis in the isolated R. rubrum F0-F1 34-fold, whereas the Ca2+-ATPase activity is only slightly modified. ATPase activation by lauryl dimethylamine oxide enhances the effect on ATP hydrolysis exerted by free Mg2+ ions. Concentrations of free Mg2+ in the range of 0.025 mM favor activation while higher concentrations inhibit ATPase activity by approximately 70%. Steady-state kinetic analysis shows that lauryl dimethylamine oxide induces a complex kinetic behavior for Mg-ATP in the chromatophores, similar to the untreated F0-F1 complex. The initial rate value for Mg-ATP unisite catalysis was found to be 6.3 times higher (3.5 X 10(-3) mol Pi per mol R. rubrum F0-F1 per second) in the presence than in the absence of detergent, where the initial rate was 5.5 X 10(-4) mol Pi per mol R. rubrum F0-F1 per second. These experiments show that lauryl dimethylamine oxide shifts the cation requirement for ATP-hydrolysis of the isolated R. rubrum H+-ATPase from Ca2+ to Mg2+ and that it activates both multisite and unisite catalysis. Results are discussed in relation to the possibility of a regulatory role by Mg2+ ions on ATP hydrolysis expressed through subunit interactions.

Antibodies to the F1-ATPase of Rhodospirillum rubrum and its purified native beta-subunit: inhibition of ATP-linked activities in R. rubrum and in lettuce

1. Antibodies prepared against the Rhodospirillum rubrum F1-ATPase (RrF1) and its purified, native-beta-subunit, exhibited cross-reactivity with the following soluble preparations of R. rubrum ATPase: RrF0 . F1, RrF1 and the beta-subunit. Anti-RrF1, but not anti-beta antibodies, also formed precipitin lines with soluble beta-less Rrf1, indicating that antigenic determinants of both the beta-subunit and the other four RrF1-subunits are expressed in the whole RrF1 molecule. Both antibodies agglutinated the R. rubrum chromatophores, suggesting that the beta-subunit is located on the external part of RrF1. 2. Both antibodies inhibited ATP synthesis and hydrolysis activities of R. rubrum chromatophores, as well as all the soluble ATPase reactions. Similar concentrations of each antibody were required for 50% inhibition of all these reactions, but anti-RrF1 was always somewhat more effective than anti-beta. These data indicate that the beta-subunit is involved in the catalytic site of the RrF1-enzyme. 3. The antibodies prepared against R. rubrum F1-ATPase and its beta-subunit could bind the soluble chloroplast F1-ATPase (CF1) and inhibited ATP-linked reactions carried out by chloroplasts and by soluble CF1. In these reactions, unlike in the R. rubrum ones, anti-beta was a more potent inhibitor than the anti-RrF1 antibody. The cross-reaction obtained between the antibodies raised against R. rubrum F1 and its beta-subunit and the chloroplast CF1 indicates the presence of similar antigenic determinants in the photosynthetic prokaryotic and eukaryotic F1-ATPases, which have been conserved during evolution.