The TF1-ATPase and ATPase activities of assembled alpha 3 beta 3 gamma, alpha 3 beta 3 gamma delta, and alpha 3 beta 3 gamma epsilon complexes are stimulated by low and inhibited by high concentrations of rhodamine 6G whereas the dye only inhibits the alpha 3 beta 3, and alpha 3 beta 3 delta complexes

Activation of Bacterial F-ATPase by LDAO: Deciphering the Molecular Mechanism

Proton FOF1 ATP synthase catalyzes the formation of ATP from ADP and inorganic phosphate coupled with transmembrane proton transfer using the energy of the protonmotive force (pmf). As pmf decreases, the direction of the reaction is reversed and the enzyme generates pmf, transferring protons across the membrane using the energy of ATP hydrolysis. ATPase activity of the enzyme can be suppressed by ADP in a non-competitive manner (ADP-inhibition), and in a number of bacteria, it can be inhibited by conformational changes in the regulatory C-terminal domain of the ε subunit. Lauryldimethylamine oxide (LDAO), a zwitterionic detergent, is known to attenuate both of these inhibitory mechanisms, significantly increasing the ATPase activity of the enzyme. For this reason, LDAO is sometimes used for semi-quantitative estimation of the enzyme's susceptibility to these regulatory mechanisms. However, the binding site of LDAO in ATP synthase remains unknown. The mechanism by which the detergent counteracts ADP-inhibition and the inhibition involving the ε subunit is also unclear. We performed molecular docking and predicted that LDAO binding might occur at the catalytic site of ATP synthase, whether empty or containing nucleotides. Molecular dynamics simulations showed that LDAO could affect the mobility of the loop in the β subunit (residues β404-415 in Escherichia coli ATP synthase) near the catalytic site. Mutagenesis of residue β409 in the E. coli enzyme and the corresponding β419 residue in the Bacillus subtilis ATP synthase revealed that the type of side chain of this residue indeed affects LDAO-dependent stimulation of ATPase activity. We also found that LDAO activates the enzyme more strongly in the presence of 100 mM sulfate compared to sulfate-free medium. This phenomenon is likely due to the enhancement of ADP-inhibition of the enzyme by sulfate.

Two-stimuli manipulation of a biological motor

F1-ATPase is an enzyme acting as a rotary nano-motor. During catalysis subunits of this enzyme complex rotate relative to other parts of the enzyme. Here we demonstrate that the combination of two input stimuli causes stop of motor rotation. Application of either individual stimulus did not significantly influence motor motion. These findings may contribute to the development of logic gates using single biological motor molecules.

The alpha/beta interfaces of alpha(1)beta(1), alpha(3)beta(3), and F1: domain motions and elastic energy stored during gamma rotation

ATP synthase (F(o)F(1)) consists of F(1) (ATP-driven motor) and F(o) (H(+)-driven motor). F(1) is a complex of alpha(3)beta(3)gammadeltaepsilon subunits, and gamma is the rotating cam in alpha(3)beta(3). Thermophilic F(1) (TF(1)) is exceptional in that it can be crystallized as a beta monomer and an alpha(3)beta(3) oligomer, and it is sufficiently stable to allow alphabeta refolding and reassembly of hybrid complexes containing 1, 2, and 3 modified alpha or beta. The nucleotide-dependent open-close conversion of conformation is an inherent property of an isolated beta and energy and signals are transferred through alpha/beta interfaces. The catalytic and noncatalytic interfaces of both mitochondrial F(1) (MF(1)) and TF(1) were analyzed by an atom search within the limits of 0.40 nm across the alphabeta interfaces. Seven (plus thermophilic loop in TF(1)) contact areas are located at both the catalytic and noncatalytic interfaces on the open beta form. The number of contact areas on closed beta increased to 11 and 9, respectively, in the catalytic and noncatalytic interfaces. The interfaces in the barrel domain are immobile. The torsional elastic strain applied through the mobile areas is concentrated in hinge residues and the P-loop in beta. The notion of elastic energy in F(o)F(1) has been revised. X-ray crystallography of F(1) is a static snap shot of one state and the elastic hypotheses are still inconsistent with the structure, dyamics, and kinetics of F(o)F(1). The domain motion and elastic energy in F(o)F(1) will be elucidated by time-resolved crystallography.

The regulator of the F1 motor: inhibition of rotation of cyanobacterial F1-ATPase by the epsilon subunit

The chloroplast-type F(1) ATPase is the key enzyme of energy conversion in chloroplasts, and is regulated by the endogenous inhibitor epsilon, tightly bound ADP, the membrane potential and the redox state of the gamma subunit. In order to understand the molecular mechanism of epsilon inhibition, we constructed an expression system for the alpha(3)beta(3)gamma subcomplex in thermophilic cyanobacteria allowing thorough investigation of epsilon inhibition. epsilon Inhibition was found to be ATP-independent, and different to that observed for bacterial F(1)-ATPase. The role of the additional region on the gamma subunit of chloroplast-type F(1)-ATPase in epsilon inhibition was also determined. By single molecule rotation analysis, we succeeded in assigning the pausing angular position of gamma in epsilon inhibition, which was found to be identical to that observed for ATP hydrolysis, product release and ADP inhibition, but distinctly different from the waiting position for ATP binding. These results suggest that the epsilon subunit of chloroplast-type ATP synthase plays an important regulator for the rotary motor enzyme, thus preventing wasteful ATP hydrolysis.