F-ATP-ase of Escherichia coli membranes: The ubiquitous MgADP-inhibited state and the inhibited state induced by the ε–subunit's C-terminal domain are mutually exclusive

Regulation of ATP hydrolysis by the ε subunit, ζ subunit and Mg-ADP in the ATP synthase of Paracoccus denitrificans

“…This is irrespective of the presence of the ζ subunit, the deletion of which exerts a consistent activating effect independent of the LDAO or selenite concentrations. We note that, for selenite, our results differ from results reported previously for the E. coli and Bacillus PS3 enzymes [ [37] , [38] , [39] , [40] ]; recently, Milgrom and Duncan proposed distinct pathways for Mg-ADP and ε-CTD inhibition [ 41 ] in E. coli , consistent with the [A] 50 value for selenite activation remaining the same in both their wild-type and ε-CTD-lacking E. coli membranes (4.7 and 4.4 mM, respectively). It is possible that the roles of the ε-CTD are different in P. denitrificans and E. coli .…”

“…While removing the ζ subunit appears to stimulate hydrolysis independently of the mode of activation, the patterns of activation observed upon removal of the ε-CTD are more varied, suggesting a more complex interplay with Mg-ADP inhibition, which is not yet fully understood. Although recent evidence points to a destabilizing/competing role of the ε-CTD on Mg-ADP, at least for the E. coli and Bacillus PS3 enzyme [ [37] , [38] , [39] , [40] , [41] ], our data suggest that the opposite could be true in P. denitrificans . In P. denitrificans , the ε-CTD may stabilize Mg-ADP inhibition, as removing the ε-CTD increases the enzyme's sensitivity to oxyanion activation ( Fig.…”

“…Early studies suggested that the ε-CTD acts against the ∆p-induced release of Mg-ADP [ 32 ]. However, there is growing evidence to indicate an opposing role, where inhibition by Mg-ADP and ε-CTD are distinct from each other and compete [ [37] , [38] , [39] , [40] , [41] ]. This is supported by observations that addition of the inhibitor azide, which stabilizes the Mg-ADP inhibited state, favors the non-inhibitory hairpin ('down') conformation of the ε-CTD [ 38 , 42 ] and by the strong inhibition of ATP hydrolysis by Mg-ADP in F 1 of the B. subtilis ATP synthase lacking the ε subunit [ 40 ].…”

“…Activation by LDAO facilitates the release of entrapped ADP by an unknown mechanism [ 16 , 28 , 43 ], whereas oxyanions such as sulfite or selenite are proposed to occupy phosphate binding sites in F 1 and to induce conformational changes to release the Mg-ADP [ 44 , 45 ]. These latter two activation methods are also influenced by the ε-CTD, which again makes it difficult to define the mechanism of activation [ 41 , 46 , 47 ].…”

Subunit epsilon ofE. coliF1FoATP synthase attenuates enzyme activity by modulating central stalk flexibility

“…Because F 1 F o ATP synthase can operate in reverse, cells have evolved mechanisms to avoid wasteful hydrolysis of ATP that could occur under physiological conditions. Bacterial ATP synthases appear to utilize a range of different mechanisms for inhibition, with nucleotides, ions and conformational changes likely making contributions 7,8 , with functional studies showing these mechanisms to be mutually exclusive 9 . MgADP is known to inhibit ATPases 10,11 , and can cause the enzyme to fall into a low energy minimum in which MgADP is bound tightly to the catalytic sites.…”