The stimulating role of subunit F in ATPase activity inside the A1-complex of the Methanosarcina mazei Gö1 A1AO ATP synthase

Vacuolar ATPase subunit F is critical for larval survival in Henosepilachna vigintioctopunctata

Vacuolar ATPase (vATPase) is an important proton pump in insect tissues including gut and Malpighian tubule. Subunit F, one of the 16 subunits of the vATPase holoenzyme, is not well characterized. Here, we found that two HvvATPaseF isoforms were highly expressed in the hindgut and Malpighian tubules (MT) in the 28-spotted lady-beetle Henosepilachna vigintioctopunctata, an agricultural pest that feeds on Solanaceae and Cucurbitaceae. Knockdown of both HvvATPaseF variants by RNA interference (RNAi) delayed larval growth and negatively affected ecdysis and adult emergence. In the midgut, RNAi treatment resulted in the disappearance of peritrophic membrane, the reduction in the size and the impaired integrity of the gut, which was associated with sparse principle cells and an increase in TUNEL- and EdU-positive cells. Whereas the MT were opaque and the tubule lumens were full of urine in dsegfp-fed larvae, the tubules were clear and the tubule lumens were empty in the dsvATPaseF-fed larvae. HvvATPaseF knockdown was also associated with a decrease in the abundance of the fat body and the levels of glucose, trehalose, triglyceride, total soluble amino acids and proteins, and an increase in glycogen. Consistent with the known effects of sugars on chitin formation, both the expression level of a chitin biosynthesis gene and the thickness of the head capsule cuticle were reduced in the HvvATPaseF-depleted beetles. Our results demonstrated that subunit F plays an essential role in H. vigintioctopunctata development.

Bacterial F-type ATP synthases follow a well-choreographed assembly pathway

F-type ATP synthases are multiprotein complexes composed of two separate coupled motors (F₁ and F_O) generating adenosine triphosphate (ATP) as the universal major energy source in a variety of relevant biological processes in mitochondria, bacteria and chloroplasts. While the structure of many ATPases is solved today, the precise assembly pathway of F₁F_O-ATP synthases is still largely unclear. Here, we probe the assembly of the F₁ complex from Acetobacterium woodii. Using laser induced liquid bead ion desorption (LILBID) mass spectrometry, we study the self-assembly of purified F₁ subunits in different environments under non-denaturing conditions. We report assembly requirements and identify important assembly intermediates in vitro and in cellula. Our data provide evidence that nucleotide binding is crucial for in vitro F₁ assembly, whereas ATP hydrolysis appears to be less critical. We correlate our results with activity measurements and propose a model for the assembly pathway of a functional F₁ complex.

ATPases are the macromolecular machines for cellular energy production. Here the authors investigate factors that govern the assembly of the F₁ complex from a bacterial F-type ATPase and relate differences in activity of complexes assembled in cells and in vitro to structural changes.

Rotary Ion-Translocating ATPases/ATP Synthases: Diversity, Similarities, and Differences

Ion-translocating ATPases and ATP synthases (F-, V-, A-type ATPases, and several P-type ATPases and ABC-transporters) catalyze ATP hydrolysis or ATP synthesis coupled with the ion transport across the membrane. F-, V-, and A-ATPases are protein nanomachines that combine transmembrane transport of protons or sodium ions with ATP synthesis/hydrolysis by means of a rotary mechanism. These enzymes are composed of two multisubunit subcomplexes that rotate relative to each other during catalysis. Rotary ATPases phosphorylate/dephosphorylate nucleotides directly, without the generation of phosphorylated protein intermediates. F-type ATPases are found in chloroplasts, mitochondria, most eubacteria, and in few archaea. V-type ATPases are eukaryotic enzymes present in a variety of cellular membranes, including the plasma membrane, vacuoles, late endosomes, and trans-Golgi cisternae. A-type ATPases are found in archaea and some eubacteria. F- and A-ATPases have two main functions: ATP synthesis powered by the proton motive force (pmf) or, in some prokaryotes, sodium-motive force (smf) and generation of the pmf or smf at the expense of ATP hydrolysis. In prokaryotes, both functions may be vitally important, depending on the environment and the presence of other enzymes capable of pmf or smf generation. In eukaryotes, the primary and the most crucial function of F-ATPases is ATP synthesis. Eukaryotic V-ATPases function exclusively as ATP-dependent proton pumps that generate pmf necessary for the transmembrane transport of ions and metabolites and are vitally important for pH regulation. This review describes the diversity of rotary ion-translocating ATPases from different organisms and compares the structural, functional, and regulatory features of these enzymes.

Structural Asymmetry and Kinetic Limping of Single Rotary F-ATP Synthases

F-ATP synthases use proton flow through the FO domain to synthesize ATP in the F₁ domain. In Escherichia coli, the enzyme consists of rotor subunits γεc10 and stator subunits (αβ)₃δab₂. Subunits c10 or (αβ)₃ alone are rotationally symmetric. However, symmetry is broken by the b₂ homodimer, which together with subunit δa, forms a single eccentric stalk connecting the membrane embedded FO domain with the soluble F₁ domain, and the central rotating and curved stalk composed of subunit γε. Although each of the three catalytic binding sites in (αβ)₃ catalyzes the same set of partial reactions in the time average, they might not be fully equivalent at any moment, because the structural symmetry is broken by contact with b₂δ in F₁ and with b₂a in FO. We monitored the enzyme's rotary progression during ATP hydrolysis by three single-molecule techniques: fluorescence video-microscopy with attached actin filaments, Förster resonance energy transfer between pairs of fluorescence probes, and a polarization assay using gold nanorods. We found that one dwell in the three-stepped rotary progression lasting longer than the other two by a factor of up to 1.6. This effect of the structural asymmetry is small due to the internal elastic coupling.

Structure and function of Mycobacterium-specific components of F-ATP synthase subunits α and ε

The Mycobacterium tuberculosis (Mtb) F₁F_O-ATP synthase (α₃:β₃:γ:δ:ε:a:b:b':c₉) is an essential enzyme that supplies energy for both the aerobic growing and the hypoxic dormant stage of the mycobacterial life cycle. Employing the heterologous F-ATP synthase model system α^chi₃:β₃:γ we showed previously, that transfer of the C-terminal domain (CTD) of Mtb subunit α (Mtα_514-549) to a standard F-ATP synthase α subunit suppresses ATPase activity. Here we determined the 3D reconstruction from electron micrographs of the α^chi₃:β₃:γ complex reconstituted with the Mtb subunit ε (Mtε), which has been shown to crosstalk with the CTD of Mtα. Together with the first solution shape of Mtb subunit α (Mtα), derived from solution X-ray scattering, the structural data visualize the extended C-terminal stretch of the mycobacterial subunit α. In addition, Mtε mutants MtεR62L, MtεE87A, Mtε_6-121, and Mtε_1-120, reconstituted with α^chi₃:β₃:γ provided insight into their role in coupling and in trapping inhibiting MgADP. NMR solution studies of MtεE87A gave insights into how this residue contributes to stability and crosstalk between the N-terminal domain (NTD) and the CTD of Mtε. Analyses of the N-terminal mutant Mtε_6-121 highlight the differences of the NTD of mycobacterial subunit ε to the well described Geobacillus stearothermophilus or Escherichia coli counterparts. These data are discussed in context of a crosstalk between the very N-terminal amino acids of Mtε and the loop region of one c subunit of the c-ring turbine for coupling of proton-translocation and ATP synthesis activity.

Crystallographic and enzymatic insights into the mechanisms of Mg-ADP inhibition in the A1 complex of the A1AO ATP synthase

F-ATP synthases are described to have mechanisms which regulate the unnecessary depletion of ATP pool during an energy limited state of the cell. Mg-ADP inhibition is one of the regulatory features where Mg-ADP gets entrapped in the catalytic site, preventing the binding of ATP and further inhibiting ATP hydrolysis. Knowledge about the existence and regulation of the related archaeal-type A₁A_O ATP synthases (A₃B₃CDE₂FG₂ac) is limited. We demonstrate MgADP inhibition of the enzymatically active A₃B₃D- and A₃B₃DF complexes of Methanosarcina mazei Gö1 A-ATP synthase and reveal the importance of the amino acids P235 and S238 inside the P-loop (GPFGSGKTV) of the catalytic A subunit. Substituting these two residues by the respective P-loop residues alanine and cysteine (GAFGCGKTV) of the related eukaryotic V-ATPase increases significantly the ATPase activity of the enzyme variant and abolishes MgADP inhibition. The atomic structure of the P235A, S238C double mutant of subunit A of the Pyrococcus horikoshii OT3 A-ATP synthase provides details of how these critical residues affect nucleotide-binding and ATP hydrolysis in this molecular engine. The qualitative data are confirmed by quantitative results derived from fluorescence correlation spectroscopy experiments.

Conformational dynamics of the rotary subunit F in the A3 B3 DF complex of Methanosarcina mazei Gö1 A-ATP synthase monitored by single-molecule FRET

In archaea the A₁ A_O ATP synthase uses a transmembrane electrochemical potential to generate ATP, while the soluble A₁ domain (subunits A₃ B₃ DF) alone can hydrolyse ATP. The three nucleotide-binding AB pairs form a barrel-like structure with a central orifice that hosts the rotating central stalk subunits DF. ATP binding, hydrolysis and product release cause a conformational change inside the A:B-interface, which enforces the rotation of subunits DF. Recently, we reported that subunit F is a stimulator of ATPase activity. Here, we investigated the nucleotide-dependent conformational changes of subunit F relative to subunit D during ATP hydrolysis in the A₃ B₃ DF complex of the Methanosarcina mazei Gö1 A-ATP synthase using single-molecule Förster resonance energy transfer. We found two conformations for subunit F during ATP hydrolysis.

Power Stroke Angular Velocity Profiles of Archaeal A-ATP Synthase Versus Thermophilic and Mesophilic F-ATP Synthase Molecular Motors

The angular velocities of ATPase-dependent power strokes as a function of the rotational position for the A-type molecular motor A₃B₃DF, from the Methanosarcina mazei Gö1 A-ATP synthase, and the thermophilic motor α₃β₃γ, from Geobacillus stearothermophilus (formerly known as Bacillus PS3) F-ATP synthase, are resolved at 5 μs resolution for the first time. Unexpectedly, the angular velocity profile of the A-type was closely similar in the angular positions of accelerations and decelerations to the profiles of the evolutionarily distant F-type motors of thermophilic and mesophilic origins, and they differ only in the magnitude of their velocities. M. mazei A₃B₃DF power strokes occurred in 120° steps at saturating ATP concentrations like the F-type motors. However, because ATP-binding dwells did not interrupt the 120° steps at limiting ATP, ATP binding to A₃B₃DF must occur during the catalytic dwell. Elevated concentrations of ADP did not increase dwells occurring 40° after the catalytic dwell. In F-type motors, elevated ADP induces dwells 40° after the catalytic dwell and slows the overall velocity. The similarities in these power stroke profiles are consistent with a common rotational mechanism for A-type and F-type rotary motors, in which the angular velocity is limited by the rotary position at which ATP binding occurs and by the drag imposed on the axle as it rotates within the ring of stator subunits.