Stimulation of F(1)-ATPase activity by sodium dodecyl sulfate

Torque generation in F1-ATPase devoid of the entire amino-terminal helix of the rotor that fills half of the stator orifice

F(1)-ATPase is an ATP-driven rotary molecular motor in which the central γ-subunit rotates inside a cylinder made of α(3)β(3) subunits. The amino and carboxyl termini of the γ rotor form a coiled coil of α-helices that penetrates the stator cylinder to serve as an axle. Crystal structures indicate that the axle is supported by the stator at two positions, at the orifice and by the hydrophobic sleeve surrounding the axle tip. The sleeve contacts are almost exclusively to the longer carboxyl-terminal helix, whereas nearly half the orifice contacts are to the amino-terminal helix. Here, we truncated the amino-terminal helix stepwise up to 50 residues, removing one half of the axle all the way up and far beyond the orifice. The half-sliced axle still rotated with an unloaded speed a quarter of the wild-type speed, with torque nearly half the wild-type torque. The truncations were made in a construct where the rotor tip was connected to a β-subunit via a short peptide linker. Linking alone did not change the rotational characteristics significantly. These and previous results show that nearly half the normal torque is generated if rotor-stator interactions either at the orifice or at the sleeve are preserved, suggesting that the make of the motor is quite robust.

Resolving stepping rotation in Thermus thermophilus H(+)-ATPase/synthase with an essentially drag-free probe

Vacuole-type ATPases (V_oV₁) and F_oF₁ ATP synthases couple ATP hydrolysis/synthesis in the soluble V₁ or F₁ portion with proton (or Na⁺) flow in the membrane-embedded V_o or F_o portion through rotation of one common shaft. Here we show at submillisecond resolutions the ATP-driven rotation of isolated V₁ and the whole V_oV₁ from Thermus thermophilus, by attaching a 40-nm gold bead for which viscous drag is almost negligible. V₁ made 120° steps, commensurate with the presence of three catalytic sites. Dwells between the steps involved at least two events other than ATP binding, one likely to be ATP hydrolysis. V_oV₁ exhibited 12 dwell positions per revolution, consistent with the 12-fold symmetry of the V_o rotor in T. thermophilus. Unlike F₁ that undergoes 80°–40° substepping, chemo-mechanical checkpoints in isolated V₁ are all at the ATP-waiting position, and V_o adds further bumps through stator–rotor interactions outside and remote from V₁.

Rotary ATPases F_oF₁ and V_oV₁ couple ATP hydrolysis with proton flow. Furuike et al. observe ATP-driven rotation in V₁ and V_oV₁, at submillisecond resolution, and find that rate-limiting reactions in V₁ all occur at the same angle, and stator–rotor interactions in V_o introduce additional checkpoints.