Direct observation of stepping rotation of V-ATPase reveals rigid component in coupling between Vo and V1 motors

ATP synthesis of Enterococcus hirae V-ATPase driven by sodium motive force

V-ATPases generally function as ion pumps driven by ATP hydrolysis in the cell, but their capability of ATP synthesis remains largely unexplored. Here we show ATP synthesis of Na+-transporting Enterococcus hirae V-ATPase (EhVoV1) driven by the electrochemical potential gradient of Na+ across the membrane (sodium motive force, smf). We reconstituted EhVoV1 into liposome and performed a luciferin/luciferase-based assay to analyze ATP synthesis quantitatively. Our result demonstrates that EhVoV1 synthesizes ATP with a rate of 4.7 s-1 under high smf (269.3 mV). The Michaelis constants for ADP (21 μM) and inorganic phosphate (2.1 mM) in ATP synthesis reaction were comparable to those for ATP synthases, suggesting similar substrate affinities among rotary ATPases regardless of their physiological functions. Both components of smf, Na+ concentration gradient across the membrane (ΔpNa) and membrane potential (Δψ), contributed to ATP synthesis, with ΔpNa showing a slightly larger impact. At the equilibrium points where smf and Gibbs free energy of ATP synthesis are balanced, EhVoV1 showed reversible reactions between ATP synthesis and hydrolysis. The obtained Na+/ATP ratio (3.2 ± 0.4) closely matched the value expected from the structural symmetry ratio between EhVo and EhV1 (10/3 = 3.3), indicating tight coupling between ATP synthesis/hydrolysis and Na+ transport. These results reveal the inherent functional reversibility of EhVoV1. We propose that the physiological function of EhVoV1in vivo is determined by relatively small smf against large Gibbs free energy of ATP synthesis, in addition to the absence of inhibitory mechanisms of ATP hydrolysis which are known for ATP synthases.

Na+-V-ATPase inhibitor curbs VRE growth and unveils Na+ pathway structure

Vancomycin-resistant Enterococcus faecium (VRE) is a major cause of nosocomial infections, particularly endocarditis and sepsis. With the diminishing effectiveness of antibiotics against VRE, new antimicrobial agents are urgently needed. Our previous research demonstrated the crucial role of Na+-transporting V-ATPase in Enterococcus hirae for growth under alkaline conditions. In this study, we identified a compound, V-161, from 70,600 compounds, which markedly inhibits E. hirae V-ATPase activity. V-161 not only inhibits VRE growth in alkaline conditions but also significantly suppresses VRE colonization in the mouse small intestine. Furthermore, we unveiled the high-resolution structure of the membrane VO part due to V-161 binding. V-161 binds to the interface of the c-ring and a-subunit, constituting the Na+ transport pathway in the membrane, thereby halting its rotation. This structural insight presents potential avenues for developing therapeutic agents for VRE treatment and elucidates the Na+ transport pathway and mechanism.

Visualizing Single V-ATPase Rotation Using Janus Nanoparticles

Understanding the function of rotary molecular motors, such as rotary ATPases, relies on our ability to visualize single-molecule rotation. Traditional imaging methods often involve tagging those motors with nanoparticles (NPs) and inferring their rotation from the translational motion of NPs. Here, we report an approach using "two-faced" Janus NPs to directly image the rotation of a single V-ATPase from Enterococcus hirae, an ATP-driven rotary ion pump. By employing a 500 nm silica/gold Janus NP, we exploit its asymmetric optical contrast, a silica core with a gold cap on one hemisphere, to achieve precise imaging of the unidirectional counterclockwise rotation of single V-ATPase motors immobilized on surfaces. Despite the added viscous load from the relatively large Janus NP probe, our approach provides accurate torque measurements of a single V-ATPase. This study underscores the advantages of Janus NPs over conventional probes, establishing them as powerful tools for the single-molecule analysis of rotary molecular motors.

Visualizing Single V-ATPase Rotation Using Janus Nanoparticles

Understanding the function of rotary molecular motors, such as the rotary ATPases, relies on our ability to visualize the single-molecule rotation. Traditional imaging methods often involve tagging those motors with nanoparticles (NPs) and inferring their rotation from translational motion of NPs. Here, we report an approach using "two-faced" Janus NPs to directly image the rotation of single V-ATPase from Enterococcus hirae, an ATP-driven rotary ion pump. By employing a 500-nm silica/gold Janus NP, we exploit its asymmetric optical contrast - silica core with a gold cap on one hemisphere - to achieve precise imaging of the unidirectional counter-clockwise rotation of single V-ATPase motors immobilized on surfaces. Despite the added viscous load from the relatively large Janus NP probe, our approach provides accurate torque measurements of single V-ATPase. This study underscores the advantages of Janus NPs over conventional probes, establishing them as powerful tools for single-molecule analysis of rotary molecular motors.

Six states of Enterococcus hirae V-type ATPase reveals non-uniform rotor rotation during turnover

The vacuolar-type ATPase from Enterococcus hirae (EhV-ATPase) is a thus-far unique adaptation of V-ATPases, as it performs Na⁺ transport and demonstrates an off-axis rotor assembly. Recent single molecule studies of the isolated V₁ domain have indicated that there are subpauses within the three major states of the pseudo three-fold symmetric rotary enzyme. However, there was no structural evidence for these. Herein we activate the EhV-ATPase complex with ATP and identified multiple structures consisting of a total of six states of this complex by using cryo-electron microscopy. The orientations of the rotor complex during turnover, especially in the intermediates, are not as perfectly uniform as expected. The densities in the nucleotide binding pockets in the V₁ domain indicate the different catalytic conditions for the six conformations. The off-axis rotor and its' interactions with the stator a-subunit during rotation suggests that this non-uniform rotor rotation is performed through the entire complex.