A structural model of the vacuolar ATPase from transmission electron microscopy

Environmental Proteomics Elucidates Phototrophic Biofilm Responses to Ornamental Lighting on Stone-built Heritage

Recent studies are showing that some lights suitable for illuminating the urban fabric (i.e. that do not include the red, green and blue sets of primary colours) may halt biological colonisation on monuments, mainly that caused by phototrophic subaerial biofilms (SABs), which may exacerbate the biodeterioration of substrates. However, the light-triggered mechanisms that cause changes in the growth of the phototrophs remain unknown. Environmental proteomics could be used to provide information about the changes in the SAB metabolism under stress inflicted by nocturnal lighting. Here, laboratory-produced SABs, composed of Chlorophyta, Streptophyta and Cyanobacteriota, were subjected to three types of lighting used for monuments: cool white, warm white and amber + green (potentially with a biostatic effect). A control without light (i.e. darkness) was also included for comparison. The nocturnal lighting impaired the capacity of the SABs to decompose superoxide radicals and thus protect themselves from oxidative stress. Cool white and warm white light both strongly affected the proteomes of the SABs and reduced the total peptide content, with the extent of the reduction depending on the genera of the organisms involved. Analysis of the photo-damaging effect of amber + green light on the biofilm metabolism revealed a negative impact on photosystems I and II and production of photosystem antenna protein-like, as well as a triggering effect on protein metabolism (synthesis, folding and degradation). This research provides, for the first-time, a description of the proteomic changes induced by lighting on SABs colonising illuminated monuments in urban areas.

Guanidine-Derived Polymeric Nanoinhibitors Target the Lysosomal V-ATPase and Activate AMPK Pathway to Ameliorate Liver Lipid Accumulation

Current research efforts in polymer and nanotechnology applications are primarily focused on cargo delivery to enhance the therapeutic index, with limited attention being paid to self-molecularly targeted nanoparticles, which may also exhibit significant therapeutic potential. Long-term and anomalous lipid accumulation in the liver is a highly relevant factor contributing to liver diseases. However, the development of the reliable medications and their pharmacological mechanisms remain insufficient. Herein, a polyguanide nanoinhibitors (PGNI) depot is constructed by copolymerizing biguanide derivatives in different proportions onto prepolymers. The nanoinhibitors for their ability to ameliorate lipid accumulation in vitro and in vivo is screened, and subsequently demonstrated that covalently polymeric guanidine chains exhibit superior efficacy in ameliorating hepatic lipid accumulation via heterogeneous mechanisms compared to small-molecule guanidine. It is found that PGNIs stabilize guanidine metabolism in the liver, preferably for biosafety. More importantly, PGNI is ingested and localized in hepatocyte lysosomes and is locked to interact with vesicular adenosine triphosphatase (V-ATPase) on lysosomes, leading to the inhibition of V-ATPase and lysosomal acidification, thereby activating the AMPK pathway, reducing fatty acid synthesis, and enhancing lipolysis and fatty acid oxidation. These results imply that polymer-formed nanoparticles can serve as targeted inhibitors, offering a novel approach for therapeutic applications.

Development of an agroinfiltration-based transient hairpin RNA expression system in pak choi leaves (Brassica rapa ssp. chinensis) for RNA interference against Liriomyza sativae

The vegetable leafminer (Liriomyza sativae) is a devastating invasive pest of many vegetable crops and horticultural plants worldwide, causing serious economic loss. Conventional control strategy against this pest mainly relies on the synthetic chemical pesticides, but widespread use of insecticides easily causes insecticide resistance development and is harmful to beneficial organisms and environment. In this context, a more environmentally friendly pest management strategy based on RNA interference (RNAi) has emerged as a powerful tool to control of insect pests. Here we report a successful oral RNAi in L. sativae after feeding on pak choi (Brassica rapa ssp. chinensis) that transiently express hairpin RNAs targeting vital genes in this pest. First, potentially lethal genes are identified by searching an L. sativae transcriptome for orthologs of the widely used V-ATPase A and actin genes, then expression levels are assessed during different life stages and in different adult tissues. Interestingly, the highest expression levels for V-ATPase A are observed in the adult heads (males and females) and for actin in the abdomens of adult females. We also assessed expression patterns of the target hairpin RNAs in pak choi leaves and found that they reach peak levels 72 h post agroinfiltration. RNAi-mediated knockdown of each target was then assessed by letting adult L. sativae feed on agroinfiltrated pak choi leaves. Relative transcript levels of each target gene exhibit significant reductions over the feeding time, and adversely affect survival of adult L. sativae at 24 h post infestation in genetically unmodified pak choi plants. These results demonstrate that the agroinfiltration-mediated RNAi system has potential for advancing innovative environmentally safe pest management strategies for the control of leaf-mining species.

Aerobic exercise attenuates autophagy-lysosomal flux deficits by ADRB2/β2-adrenergic receptor-mediated V-ATPase assembly factor VMA21 signaling in APP-PSEN1/PS1 mice

Growing evidence suggests that macroautophagy/autophagy-lysosomal pathway deficits contribute to the accumulation of amyloid-β (Aβ) in Alzheimer disease (AD). Aerobic exercise (AE) has long been investigated as an approach to delay and treat AD, although the exact role and mechanism are not well known. Here, we revealed that AE could reverse autophagy-lysosomal deficits via activation of ADRB2/β2-adrenergic receptor, leading to significant attenuation of amyloid-β pathology in APP-PSEN1/PS1 mice. Molecular mechanism research found that AE could reverse autophagy deficits by upregulating the AMP-activated protein kinase (AMPK)-MTOR (mechanistic target of rapamycin kinase) signaling pathway. Moreover, AE could reverse V-ATPase function by upregulating VMA21 levels. Inhibition of ADRB2 by propranolol (antagonist, 30 μM) blocked AE-attenuated Aβ pathology and cognitive deficits by inhibiting autophagy-lysosomal flux. AE may mitigate AD via many pathways, while ADRB2-VMA21-V-ATPase could improve cognition by enhancing the clearance of Aβ through the autophagy-lysosomal pathway, which also revealed a novel theoretical basis for AE attenuating pathological progression and cognitive deficits in AD.

Integrated transcriptomics and metabolomics reveal protective effects on heart of hibernating Daurian ground squirrels

Hibernating mammals are natural models of resistance to ischemia, hypoxia-reperfusion injury, and hypothermia. Daurian ground squirrels (spermophilus dauricus) can adapt to endure multiple torpor-arousal cycles without sustaining cardiac damage. However, the molecular regulatory mechanisms that underlie this adaptive response are not yet fully understood. This study investigates morphological, functional, genetic, and metabolic changes that occur in the heart of ground squirrels in three groups: summer active (SA), late torpor (LT), and interbout arousal (IBA). Morphological and functional changes in the heart were measured using hematoxylin-eosin (HE) staining, Masson staining, echocardiography, and enzyme-linked immunosorbent assay (ELISA). Results showed significant changes in cardiac function in the LT group as compared with SA or IBA groups, but no irreversible damage occurred. To understand the molecular mechanisms underlying these phenotypic changes, transcriptomic and metabolomic analyses were conducted to assess differential changes in gene expression and metabolite levels in the three groups of ground squirrels, with a focus on GO and KEGG pathway analysis. Transcriptomic analysis showed that differentially expressed genes were involved in the remodeling of cytoskeletal proteins, reduction in protein synthesis, and downregulation of the ubiquitin-proteasome pathway during hibernation (including LT and IBA groups), as compared with the SA group. Metabolomic analysis revealed increased free amino acids, activation of the glutathione antioxidant system, altered cardiac fatty acid metabolic preferences, and enhanced pentose phosphate pathway activity during hibernation as compared with the SA group. Combining the transcriptomic and metabolomic data, active mitochondrial oxidative phosphorylation and creatine-phosphocreatine energy shuttle systems were observed, as well as inhibition of ferroptosis signaling pathways during hibernation as compared with the SA group. In conclusion, these results provide new insights into cardio-protection in hibernators from the perspective of gene and metabolite changes and deepen our understanding of adaptive cardio-protection mechanisms in mammalian hibernators.

Tender love and disassembly: How a TLDc domain protein breaks the V-ATPase

Vacuolar ATPases (V-ATPases, V1 Vo -ATPases) are rotary motor proton pumps that acidify intracellular compartments, and, when localized to the plasma membrane, the extracellular space. V-ATPase is regulated by a unique process referred to as reversible disassembly, wherein V1 -ATPase disengages from Vo proton channel in response to diverse environmental signals. Whereas the disassembly step of this process is ATP dependent, the (re)assembly step is not, but requires the action of a heterotrimeric chaperone referred to as the RAVE complex. Recently, an alternative pathway of holoenzyme disassembly was discovered that involves binding of Oxidation Resistance 1 (Oxr1p), a poorly characterized protein implicated in oxidative stress response. Unlike conventional reversible disassembly, which depends on enzyme activity, Oxr1p induced dissociation can occur in absence of ATP. Yeast Oxr1p belongs to the family of TLDc domain containing proteins that are conserved from yeast to mammals, and have been implicated in V-ATPase function in a variety of tissues. This brief perspective summarizes what we know about the molecular mechanisms governing both reversible (ATP dependent) and Oxr1p driven (ATP independent) V-ATPase dissociation into autoinhibited V1 and Vo subcomplexes.

Transcriptome Analysis of Immune Responses and Metabolic Regulations of Chinese Soft-Shelled Turtle (Pelodiscus sinensis) against Edwardsiella tarda Infection

The Chinese soft-shelled turtle (Pelodiscus sinensis) is an important aquatic species in southern China that is threatened by many serious diseases. Edwardsiella tarda is one of the highly pathogenic bacteria that cause the white abdominal shell disease. Yet, little is known about the immune and metabolic responses of the Chinese soft-shelled turtle against E. tarda infection. In the paper, gene expression profiles in the turtle liver were obtained to study the immune responses and metabolic regulations induced by E. tarda infection using RNA sequencing. A total of 3908 differentially expressed unigenes between the experimental group and the control group were obtained by transcriptome analysis, among them, were the significantly upregulated unigenes and downregulated unigenes 2065 and 1922, respectively. Further annotation and analysis revealed that the DEGs were mainly enriched in complement and coagulation cascades, phagosome, and steroid hormone biosynthesis pathways, indicating that they were mainly associated with defense mechanisms in the turtle liver against E. tarda four days post infection. For the first time, we reported on the gene profile of anti-E. tarda response in the soft-shelled turtle, and our research might provide valuable data to support further study on anti-E. tarda defense mechanisms in turtles

Host Cyanobacteria Killing by Novel Lytic Cyanophage YongM: A Protein Profiling Analysis

Cyanobacteria are autotrophic prokaryotes that can proliferate robustly in eutrophic waters through photosynthesis. This can lead to outbreaks of lake “water blooms”, which result in water quality reduction and environmental pollution that seriously affect fisheries and aquaculture. The use of cyanophages to control the growth of cyanobacteria is an important strategy to tackle annual cyanobacterial blooms. YongM is a novel lytic cyanophage with a broad host spectrum and high efficiency in killing its host, cyanobacteria FACHB-596. However, changes in cyanophage protein profile during infestation and killing of the host remains unknown. To characterize the proteins and its regulation networks involved in the killing of host cyanobacteria by YongM and evaluate whether this strain YongM could be used as a chassis for further engineering to be a powerful tool in dealing with cyanobacterial blooms, we herein applied 4D label-free high-throughput quantitative proteomics to analyze differentially expressed proteins (DEPs) involved in cyanobacteria host response infected 1 and 8 h with YongM cyanophage. Metabolic pathways, such as photosynthesis, photosynthesis-antennal protein, oxidative phosphorylation, ribosome, carbon fixation, and glycolysis/glycol-isomerization were significantly altered in the infested host, whereas DEPs were associated with the metabolic processes of photosynthesis, precursor metabolites, energy production, and organic nitrogen compounds. Among these DEPs, key proteins involved in YongM-host interaction may be photosystem I P700 chlorophyll-a apolipoprotein, carbon dioxide concentration mechanism protein, cytochrome B, and some YongM infection lysis-related enzymes. Our results provide comprehensive information of protein profiles during the invasion and killing of host cyanobacteria by its cyanophage, which may shed light on future design and manipulation of artificial cyanophages against water blooms.

Cryo-EM and MD infer water-mediated proton transport and autoinhibition mechanisms of Vo complex

Rotary vacuolar adenosine triphosphatases (V-ATPases) drive transmembrane proton transport through a V_o proton channel subcomplex. Despite recent high-resolution structures of several rotary ATPases, the dynamic mechanism of proton pumping remains elusive. Here, we determined a 2.7-Å cryo-electron microscopy (cryo-EM) structure of yeast V_o proton channel in nanodisc that reveals the location of ordered water molecules along the proton path, details of specific protein-lipid interactions, and the architecture of the membrane scaffold protein. Moreover, we uncover a state of V_o that shows the c-ring rotated by ~14°. Molecular dynamics simulations demonstrate that the two rotary states are in thermal equilibrium and depict how the protonation state of essential glutamic acid residues couples water-mediated proton transfer with c-ring rotation. Our cryo-EM models and simulations also rationalize a mechanism for inhibition of passive proton transport as observed for free V_o that is generated as a result of V-ATPase regulation by reversible disassembly in vivo.

Screening and function discussion of a hereditary renal tubular acidosis family pathogenic gene

Hereditary distal renal tubular acidosis (dRTA) is a rare disease of H⁺ excretion defect of α-intercalated cells in renal collecting duct, caused by decreased V-ATPase function due to mutations in the ATP6V1B1 or ATP6V0A4 genes. In the present study, a genetic family with 5 members of the complete dRTA phenotype were found with distal tubule H⁺ secretion disorder, hypokalemia, osteoporosis, and kidney stones. A variant NM_020632.2:c.1631C > T (p.Ser544Leu) in exon 16 on an ATP6V0A4 gene associated with dRTA was detected by next generation sequencing target region capture technique and verified by Sanger sequencing, which suggested that except for one of the patients who did not receive the test, the other four patients all carried the p.S544L heterozygote. In transfected HEK293T cells, cells carrying p.S544L-mut showed early weaker ATPase activity and a slower Phi recovery rate after rapid acidification. By immunofluorescence localization, it was observed that the expression level of p.S544L-mut on the cell membrane increased and the distribution was uneven. Co-immunoprecipitation showed the a4 subunit of ATP6V0A4/p.S544L-mut could not bind to the B1 subunit, which might affect the correct assembly of V-ATPase. The present study of dRTA family suggests that the p.S544L variant may be inherited in a dominant manner.

Transcriptome profiling reveals key roles of phagosome and NOD-like receptor pathway in spotting diseased Strongylocentrotus intermedius

Spotting disease is a common disease in the process of aquaculture and restocking of the sea urchin Strongylocentrotus intermedius and leads to mass mortality. To characterize the molecular processes and candidate genes related to spotting disease in S. intermedius, we conducted next-generation sequencing to assess the key genes/pathways in spotting diseased sea urchin (DUG) compared to healthy ones (HUG). A total of 321.1 million clean reads were obtained and assembled into 93,877 Unigenes with an N50 of 1185 bp, in which 86.48% of them matched to the genome sequence of the sea urchin S. purpuratus and 27,456 Unigenes mapped to Nr database. Salmon expression analysis revealed 1557 significantly differently expressed genes (DEGs) between DUG and HUG. These DEGs were enriched into 151 KEGG pathways including a core set of immune correlated pathways notably in phagosome and NOD-like receptor signaling. DUG displayed an obvious downregulation in these immune pathways. The expression patterns of six DEGs were confirmed by RT-qPCR, and the expressions were consistent with the results of RNA-seq. Furthermore, 15,990 SSRs were identified and a total of 235,249 and 295,567 candidate SNPs were identified from DUG and HUG, respectively. All these results provided basic information for our understanding of spotting disease outbreak in sea urchin.

Altered Proteins in the Hippocampus of Patients with Mesial Temporal Lobe Epilepsy

Mesial temporal lobe epilepsy (MTLE) is usually associated with drug-resistant seizures and cognitive deficits. Efforts have been made to improve the understanding of the pathophysiology of MTLE for new therapies. In this study, we used proteomics to determine the differential expression of proteins in the hippocampus of patients with MTLE compared to control samples. By using the two-dimensional electrophoresis method (2-DE), the proteins were separated into spots and analyzed by LC-MS/MS. Spots that had different densitometric values for patients and controls were selected for the study. The following proteins were found to be up-regulated in patients: isoform 1 of serum albumin (ALB), proton ATPase catalytic subunit A (ATP6V1A), heat shock protein 70 (HSP70), dihydropyrimidinase-related protein 2 (DPYSL2), isoform 1 of myelin basic protein (MBP), and dihydrolipoamide S-acethyltransferase (DLAT). The protein isoform 3 of the spectrin alpha chain (SPTAN1) was down-regulated while glutathione S-transferase P (GSTP1) and protein DJ-1 (PARK7) were found only in the hippocampus of patients with MTLE. Interactome analysis of the nine proteins of interest revealed interactions with 20 other proteins, most of them involved with metabolic processes (37%), presenting catalytic activity (37%) and working as hydrolyses (25%), among others. Our results provide evidence supporting a direct link between synaptic plasticity, metabolic disturbance, oxidative stress with mitochondrial damage, the disruption of the blood–brain barrier and changes in CNS structural proteins with cell death and epileptogenesis in MTLE. Besides this, the presence of markers of cell survival indicated a compensatory mechanism. The over-expression of GSTP1 in MTLE could be related to drug-resistance.

The Peripheral Stalk of Rotary ATPases

Rotary ATPases are a family of enzymes that are thought of as molecular nanomotors and are classified in three types: F, A, and V-type ATPases. Two members (F and A-type) can synthesize and hydrolyze ATP, depending on the energetic needs of the cell, while the V-type enzyme exhibits only a hydrolytic activity. The overall architecture of all these enzymes is conserved and three main sectors are distinguished: a catalytic core, a rotor and a stator or peripheral stalk. The peripheral stalks of the A and V-types are highly conserved in both structure and function, however, the F-type peripheral stalks have divergent structures. Furthermore, the peripheral stalk has other roles beyond its stator function, as evidenced by several biochemical and recent structural studies. This review describes the information regarding the organization of the peripheral stalk components of F, A, and V-ATPases, highlighting the key differences between the studied enzymes, as well as the different processes in which the structure is involved.

The curious case of vacuolar ATPase: regulation of signaling pathways

The Vacuolar ATPase (V-ATPase) is a proton pump responsible for controlling the intracellular and extracellular pH of cells. The structure of V-ATPase has been highly conserved among all eukaryotic cells and is involved in diverse functions across species. V-ATPase is best known for its acidification of endosomes and lysosomes and is also important for luminal acidification of specialized cells. Several reports have suggested the involvement of V-ATPase in maintaining an alkaline intracellular and acidic extracellular pH thereby aiding in proliferation and metastasis of cancer cells respectively. Increased expression of V-ATPase and relocation to the plasma membrane aids in cancer modulates key tumorigenic cell processes like autophagy, Warburg effect, immunomoduation, drug resistance and most importantly cancer cell signaling. In this review, we discuss the direct role of V-ATPase in acidification and indirect regulation of signaling pathways, particularly Notch Signaling.

Breaking up and making up: The secret life of the vacuolar H+ -ATPase

The vacuolar ATPase (V-ATPase; V₁ V_o -ATPase) is a large multisubunit proton pump found in the endomembrane system of all eukaryotic cells where it acidifies the lumen of subcellular organelles including lysosomes, endosomes, the Golgi apparatus, and clathrin-coated vesicles. V-ATPase function is essential for pH and ion homeostasis, protein trafficking, endocytosis, mechanistic target of rapamycin (mTOR), and Notch signaling, as well as hormone secretion and neurotransmitter release. V-ATPase can also be found in the plasma membrane of polarized animal cells where its proton pumping function is involved in bone remodeling, urine acidification, and sperm maturation. Aberrant (hypo or hyper) activity has been associated with numerous human diseases and the V-ATPase has therefore been recognized as a potential drug target. Recent progress with moderate to high-resolution structure determination by cryo electron microscopy and X-ray crystallography together with sophisticated single-molecule and biochemical experiments have provided a detailed picture of the structure and unique mode of regulation of the V-ATPase. This review summarizes the recent advances, focusing on the structural and biophysical aspects of the field.

Affinity Purification and Structural Features of the Yeast Vacuolar ATPase Vo Membrane Sector

The membrane sector (Vo) of the proton pumping vacuolar ATPase (V-ATPase, V1Vo-ATPase) from Saccharomyces cerevisiae was purified to homogeneity, and its structure was characterized by EM of single molecules and two-dimensional crystals. Projection images of negatively stained Vo two-dimensional crystals showed a ring-like structure with a large asymmetric mass at the periphery of the ring. A cryo-EM reconstruction of Vo from single-particle images showed subunits a and d in close contact on the cytoplasmic side of the proton channel. A comparison of three-dimensional reconstructions of free Vo and Vo as part of holo V1Vo revealed that the cytoplasmic N-terminal domain of subunit a (aNT) must undergo a large conformational change upon enzyme disassembly or (re)assembly from Vo, V1, and subunit C. Isothermal titration calorimetry using recombinant subunit d and aNT revealed that the two proteins bind each other with a Kd of ~5 μm. Treatment of the purified Vo sector with 1-palmitoyl-2-hydroxy-sn-glycero-3-[phospho-rac-(1-glycerol)] resulted in selective release of subunit d, allowing purification of a VoΔd complex. Passive proton translocation assays revealed that both Vo and VoΔd are impermeable to protons. We speculate that the structural change in subunit a upon release of V1 from Vo during reversible enzyme dissociation plays a role in blocking passive proton translocation across free Vo and that the interaction between aNT and d seen in free Vo functions to stabilize the Vo sector for efficient reassembly of V1Vo.

Protein-protein interactions within the ensemble, eukaryotic V-ATPase, and its concerted interactions with cellular machineries

The V1VO-ATPase (V-ATPase) is the important proton-pump in eukaryotic cells, responsible for pH-homeostasis, pH-sensing and amino acid sensing, and therefore essential for cell growths and metabolism. ATP-cleavage in the catalytic A3B3-hexamer of V1 has to be communicated via several so-called central and peripheral stalk units to the proton-pumping VO-part, which is membrane-embedded. A unique feature of V1VO-ATPase regulation is its reversible disassembly of the V1 and VO domain. Actin provides a network to hold the V1 in proximity to the VO, enabling effective V1VO-assembly to occur. Besides binding to actin, the 14-subunit V-ATPase interacts with multi-subunit machineries to form cellular sensors, which regulate the pH in cellular compartments or amino acid signaling in lysosomes. Here we describe a variety of subunit-subunit interactions within the V-ATPase enzyme during catalysis and its protein-protein assembling with key cellular machineries, essential for cellular function.

HAI-178 antibody-conjugated fluorescent magnetic nanoparticles for targeted imaging and simultaneous therapy of gastric cancer

The successful development of safe and highly effective nanoprobes for targeted imaging and simultaneous therapy of in vivo gastric cancer is a great challenge. Herein we reported for the first time that anti-α-subunit of ATP synthase antibody, HAI-178 monoclonal antibody-conjugated fluorescent magnetic nanoparticles, was successfully used for targeted imaging and simultaneous therapy of in vivo gastric cancer. A total of 172 specimens of gastric cancer tissues were collected, and the expression of α-subunit of ATP synthase in gastric cancer tissues was investigated by immunohistochemistry method. Fluorescent magnetic nanoparticles were prepared and conjugated with HAI-178 monoclonal antibody, and the resultant HAI-178 antibody-conjugated fluorescent magnetic nanoparticles (HAI-178-FMNPs) were co-incubated with gastric cancer MGC803 cells and gastric mucous GES-1 cells. Gastric cancer-bearing nude mice models were established, were injected with prepared HAI-178-FMNPs via tail vein, and were imaged by magnetic resonance imaging and small animal fluorescent imaging system. The results showed that the α-subunit of ATP synthase exhibited high expression in 94.7% of the gastric cancer tissues. The prepared HAI-178-FMNPs could target actively MGC803 cells, realized fluorescent imaging and magnetic resonance imaging of in vivo gastric cancer, and actively inhibited growth of gastric cancer cells. In conclusion, HAI-178 antibody-conjugated fluorescent magnetic nanoparticles have a great potential in applications such as targeted imaging and simultaneous therapy of in vivo early gastric cancer cells in the near future.

Eukaryotic V-ATPase: novel structural findings and functional insights

The eukaryotic V-type adenosine triphosphatase (V-ATPase) is a multi-subunit membrane protein complex that is evolutionarily related to F-type adenosine triphosphate (ATP) synthases and A-ATP synthases. These ATPases/ATP synthases are functionally conserved and operate as rotary proton-pumping nano-motors, invented by Nature billions of years ago. In the first part of this review we will focus on recent structural findings of eukaryotic V-ATPases and discuss the role of different subunits in the function of the V-ATPase holocomplex. Despite structural and functional similarities between rotary ATPases, the eukaryotic V-ATPases are the most complex enzymes that have acquired some unconventional cellular functions during evolution. In particular, the novel roles of V-ATPases in the regulation of cellular receptors and their trafficking via endocytotic and exocytotic pathways were recently uncovered. In the second part of this review we will discuss these unique roles of V-ATPases in modulation of function of cellular receptors, involved in the development and progression of diseases such as cancer and diabetes as well as neurodegenerative and kidney disorders. Moreover, it was recently revealed that the V-ATPase itself functions as an evolutionarily conserved pH sensor and receptor for cytohesin-2/Arf-family GTP-binding proteins. Thus, in the third part of the review we will evaluate the structural basis for and functional insights into this novel concept, followed by the analysis of the potentially essential role of V-ATPase in the regulation of this signaling pathway in health and disease. Finally, future prospects for structural and functional studies of the eukaryotic V-ATPase will be discussed.

An update in the structure, function, and regulation of V-ATPases: the role of the C subunit

Vacuolar ATPases (V-ATPases) are present in specialized proton secretory cells in which they pump protons across the membranes of various intracellular organelles and across the plasma membrane. The proton transport mechanism is electrogenic and establishes an acidic pH and a positive transmembrane potential in these intracellular and extracellular compartments. V-ATPases have been found to be practically identical in terms of the composition of their subunits in all eukaryotic cells. They have two distinct structures: a peripheral catalytic sector (V1) and a hydrophobic membrane sector (V0) responsible for driving protons. V-ATPase activity is regulated by three different mechanisms, which control pump density, association/dissociation of the V1 and V0 domains, and secretory activity. The C subunit is a 40-kDa protein located in the V1 domain of V-ATPase. The protein is encoded by the ATP6V1C gene and is located at position 22 of the long arm of chromosome 8 (8q22.3). The C subunit has very important functions in terms of controlling the regulation of the reversible dissociation of V-ATPases.

Vma8p-GFP fusions can be functionally incorporated into V-ATPase, suggesting structural flexibility at the top of V1

The vacuolar ATPase (V-ATPase) complex of yeast (Saccharomyces cerevisiae) is comprised of two sectors, V(1) (catalytic) and V(O) (proton transfer). The hexameric (A(3)B(3)) cylinder of V(1) has a central cavity that must accommodate at least part of the rotary stalk of V-ATPase, a key component of which is subunit D (Vma8p). Recent electron microscopy (EM) data for the prokaryote V-ATPase complex (Thermus thermophilus) suggest that subunit D penetrates deeply into the central cavity. The functional counterpart of subunit D in mitochondrial F(1)F(O)-ATP synthase, subunit γ, occupies almost the entire length of the central cavity. To test whether the structure of yeast Vma8p mirrors that of subunit γ, we probed the location of the C-terminus of Vma8p by attachment of a large protein adduct, green fluorescent protein (GFP). We found that truncated Vma8p proteins lacking up to 40 C-terminal residues fused to GFP can be incorporated into functional V-ATPase complexes, and are able to support cell growth under alkaline conditions. We conclude that large protein adducts can be accommodated at the top of the central cavity of V(1) without compromising V-ATPase function, arguing for structural flexibility of the V(1) sector.

Isolation and ultrastructural characterization of squid synaptic vesicles

Synaptic vesicles contain a variety of proteins and lipids that mediate fusion with the pre-synaptic membrane. Although the structures of many synaptic vesicle proteins are known, an overall picture of how they are organized at the vesicle surface is lacking. In this paper, we describe a better method for the isolation of squid synaptic vesicles and characterize the results. For highly pure and intact synaptic vesicles from squid optic lobe, glycerol density gradient centrifugation was the key step. Different electron microscopic methods show that vesicle membrane surfaces are largely covered with structures corresponding to surface proteins. Each vesicle contains several stalked globular structures that extend from the vesicle surface and are consistent with the V-ATPase. BLAST search of a library of squid expressed sequence tags identifies 10 V-ATPase subunits, which are expressed in the squid stellate ganglia. Negative-stain tomography demonstrates directly that vesicles flatten during the drying step of negative staining, and furthermore shows details of individual vesicles and other proteins at the vesicle surface.

Structural bases of physiological functions and roles of the vacuolar H(+)-ATPase

Vacuolar-type H(+)-ATPases (V-ATPases) is a large multi-protein complex containing at least 14 different subunits, in which subunits A, B, C, D, E, F, G, and H compose the peripheral 500-kDa V(1) responsible for ATP hydrolysis, and subunits a, c, c', c″, and d assembly the 250-kDa membrane-integral V(0) harboring the rotary mechanism to transport protons across the membrane. The assembly of V-ATPases requires the presence of all V(1) and V(0) subunits, in which the V(1) must be completely assembled prior to association with the V(0), accordingly the V(0) failing to assemble cannot provide a membrane anchor for the V(1), thereby prohibiting membrane association of the V-ATPase subunits. The V-ATPase mediates acidification of intracellular compartments and regulates diverse critical physiological processes of cell for functions of its numerous functional subunits. The core catalytic mechanism of the V-ATPase is a rotational catalytic mechanism. The V-ATPase holoenzyme activity is regulated by the reversible assembly/disassembly of the V(1) and V(0), the targeting and recycling of V-ATPase-containing vesicles to and from the plasma membrane, the coupling ratio between ATP hydrolysis and proton pumping, ATP, Ca(2+), and its inhibitors and activators.

The NMR solution structure of subunit G (G(61)(-)(101)) of the eukaryotic V1VO ATPase from Saccharomyces cerevisiae

Subunit G is an essential stalk subunit of the eukaryotic proton pump V(1)V(O) ATPase. Previously the structure of the N-terminal region, G(1)(-)(59), of the 13kDa subunit G was solved at higher resolution. Here solution NMR was performed to determine the structure of the recombinant C-terminal region (G(61)(-)(101)) of subunit G of the Saccharomyces cerevisiae V(1)V(O) ATPase. The protein forms an extended alpha-helix between residues 64 and 100, whereby the first five- and the last residues of G(61)(-)(101) are flexible. The surface charge distribution of G(61)(-)(101) reveals an amphiphilic character at the C-terminus due to positive and negative charge distribution at one side and a hydrophobic surface on the opposite side of the structure. The hydrophobic surface pattern is mainly formed by alanine residues. The alanine residues 72, 74 and 81 were exchanged by a single cysteine in the entire subunit G. Cysteines at positions 72 and 81 showed disulfide formation. In contrast, no crosslink could be formed for the mutant Ala74Cys. Together with the recently determined NMR solution structure of G(1)(-)(59), the presented solution structure of G(61)(-)(101) enabled us to present a first structural model of the entire subunit G of the S. cerevisiae V(1)V(O) ATPase.

Analysis of pupal head proteome and its alteration in diapausing pupae of Helicoverpa armigera

The proteomic approach has proven to be an useful tool for understanding insect diapause processes. Using 2D gel electrophoresis and matrix assisted laser/desorption ionization (MALDI) time of flight (TOF), we identified 24 proteins in the head of Helicoverpa armigera pupae with diverse functional characteristics, including cytoskeleton proteins, heat-shock proteins, insect development regulation factors, ATPases, proteins regulating signal pathway and enzymes involved in metabolism, etc. A proteomic comparison between nondiapausing and diapausing pupae revealed three proteins that were present only in nondiapausing pupae, and six proteins represented >or=2.0-fold or <or=0.5-fold changes. The differentially expressed proteins, including heat-shock protein 90, chitin deacetylase, alpha-tubulin and transitional endoplasmic reticulum ATPase, etc. were reported for the first time in H. armigera. Identification of these proteins will enable us to further characterize the regulated functions of diapause in this important species.

Proteomic analysis of novel Cry1Ac binding proteins in Helicoverpa armigera (Hübner)

Aminopeptidase N (APN) and cadherin-like proteins have been previously identified as Cry1Ac-binding proteins in Helicoverpa armigera (Hübner). In this study, a proteomic approach was used to identify novel Cry1Ac-binding proteins in H. armigera. Brush border membrane vesicles (BBMV) of H. armigera were extracted and separated by two-dimensional gel electrophoresis (2-DE). Cry1Ac-binding proteins were detected using antisera against Cry1Ac. Peptide mass fingerprinting (PMF) was used to identify Cry1Ac-binding proteins. In total, four proteins were identified as candidate Cry1Ac-binding proteins in H. armigera: vacuolar ATP synthase (V-ATPase) subunit B, actin, heat shock cognate protein (HSCP), and a novel protein.

The little we know on the structure and machinery of V-ATPase

The life of every eukaryotic cell depends on the function of vacuolar H+-ATPase (V-ATPase). Today we know that V-ATPase is vital for many more physiological and biochemical processes than it was expected three decades ago when the enzyme was discovered. These range from a crucial role in the function of internal organelles such as vacuoles, lysosomes, synaptic vesicles, endosomes, secretory granules and the Golgi apparatus to the plasma membrane of several organisms and specific tissues, and specialized cells. The overall structure and mechanism of action of the V-ATPase is supposed to be similar to that of the well-characterized F-type ATP synthase (F-ATPase). Both consist of a soluble catalytic domain (V1 or F1) that is coupled to a membrane-spanning domain (Vo or Fo) by one or more `stalk' components. Owing to the complexity and challenging properties of V-ATPase its study is lagging behind that of its relative F-ATPase. Time will tell whether V-ATPase shares an identical mechanism of action with F-ATPase or its mode of operation is unique.

The tether connecting cytosolic (N terminus) and membrane (C terminus) domains of yeast V-ATPase subunit a (Vph1) is required for assembly of V0 subunit d

V-ATPases are molecular motors that reversibly disassemble in vivo. Anchored in the membrane is subunit a. Subunit a has a movable N terminus that switches positions during disassembly and reassembly. Deletions were made at residues securing the N terminus of subunit a (yeast isoform Vph1) to its membrane-bound C-terminal domain in order to understand the role of this conserved region for V-ATPase function. Shrinking of the tether made cells pH-sensitive (vma phenotype) because assembly of V(0) subunit d was harmed. Subunit d did not co-immunoprecipitate with subunit a and the c-ring. Cells contained pools of V(1) and V(0)(-d) that failed to form V(1)V(0), and very low levels of V-ATPase subunits were found at the membrane. Although subunit d expression was stable and at wild-type levels, growth defects were rescued by exogenous VMA6 (subunit d). Stable V(1)V(0) assembled after yeast cells were co-transformed with VMA6 and mutant VPH1. Tether-less V(1)V(0) was delivered to the vacuole and active. It retained 63-71% of the wild-type activity and was responsive to glucose. Tether-less V(1)V(0) disassembled and reassembled after brief glucose depletion and readdition. The N terminus retained binding to V(1) subunits and the C terminus to phosphofructokinase. Thus, no major structural change was generated at the N and C termini of subunit a. We concluded that early steps of V(0) assembly and trafficking were likely impaired by shorter tethers and rescued by VMA6.

Assembly of subunit d (Vma6p) and G (Vma10p) and the NMR solution structure of subunit G (G(1-59)) of the Saccharomyces cerevisiae V(1)V(O) ATPase

Understanding the structural traits of subunit G is essential, as it is needed for V(1)V(O) assembly and function. Here solution NMR of the recombinant N- (G(1-59)) and C-terminal segment (G(61-114)) of subunit G, has been performed in the absence and presence of subunit d of the yeast V-ATPase. The data show that G does bind to subunit d via its N-terminal part, G(1-59) only. The residues of G(1-59) involved in d binding are Gly7 to Lys34. The structure of G(1-59) has been solved, revealing an alpha-helix between residues 10 and 56, whereby the first nine- and the last three residues of G(1-59) are flexible. The surface charge distribution of G(1-59) reveals an amphiphilic character at the N-terminus due to positive and negative charge distribution at one side and a hydrophobic surface on the opposite side of the structure. The C-terminus exhibits a strip of negative residues. The data imply that G(1-59)-d assembly is accomplished by hydrophobic interactions and salt-bridges of the polar residues. Based on the recently determined NMR structure of segment E(18-38) of subunit E of yeast V-ATPase and the presently solved structure of G(1-59), both proteins have been docked and binding epitopes have been analyzed.

Structure of the yeast vacuolar ATPase

The subunit architecture of the yeast vacuolar ATPase (V-ATPase) was analyzed by single particle transmission electron microscopy and electrospray ionization (ESI) tandem mass spectrometry. A three-dimensional model of the intact V-ATPase was calculated from two-dimensional projections of the complex at a resolution of 25 angstroms. Images of yeast V-ATPase decorated with monoclonal antibodies against subunits A, E, and G position subunit A within the pseudo-hexagonal arrangement in the V1, the N terminus of subunit G in the V1-V0 interface, and the C terminus of subunit E at the top of the V1 domain. ESI tandem mass spectrometry of yeast V1-ATPase showed that subunits E and G are most easily lost in collision-induced dissociation, consistent with a peripheral location of the subunits. An atomic model of the yeast V-ATPase was generated by fitting of the available x-ray crystal structures into the electron microscopy-derived electron density map. The resulting atomic model of the yeast vacuolar ATPase serves as a framework to help understand the role the peripheral stalk subunits are playing in the regulation of the ATP hydrolysis driven proton pumping activity of the vacuolar ATPase.

New insights into structure-function relationships between archeal ATP synthase (A1A0) and vacuolar type ATPase (V1V0)

Adenosine triphosphate, ATP, is the energy currency of living cells. While ATP synthases of archae and ATP synthases of pro- and eukaryotic organisms operate as energy producers by synthesizing ATP, the eukaryotic V-ATPase hydrolyzes ATP and thus functions as energy transducer. These enzymes share features like the hydrophilic catalytic- and the membrane-embedded ion-translocating sector, allowing them to operate as nano-motors and to transform the transmembrane electrochemical ion gradient into ATP or vice versa. Since archaea are rooted close to the origin of life, the A-ATP synthase is probably more similar in its composition and function to the "original" enzyme, invented by Nature billion years ago. On the contrary, the V-ATPases have acquired specific structural, functional and regulatory features during evolution. This review will summarize the current knowledge on the structure, mechanism and regulation of A-ATP synthases and V-ATPases. The importance of V-ATPase in pathophysiology of diseases will be discussed.

V H+-ATPase along the yeast secretory pathway: energization of the ER and Golgi membranes

H+ transport driven by V H+-ATPase was found in membrane fractions enriched with ER/PM and Golgi/Golgi-like membranes of Saccharomyces cerevisiae efficiently purified in sucrose density gradient from the vacuolar membranes according to the determination of the respective markers including vacuolar Ca2+-ATPase, Pmc1::HA. Purification of ER from PM by a removal of PM modified with concanavalin A reduced H+ transport activity of P H+-ATPase by more than 75% while that of V H+-ATPase remained unchanged. ER H+ ATPase exhibits higher resistance to bafilomycin (I50=38.4 nM) than Golgi and vacuole pumps (I50=0.18 nM). The ratio between a coupling efficiency of the pumps in ER, membranes heavier than ER, vacuoles and Golgi is 1.0, 2.1, 8.5 and 14 with the highest coupling in the Golgi. The comparative analysis of the initial velocities of H+ transport mediated by V H+-ATPases in the ER, Golgi and vacuole membrane vesicles, and immunoreactivity of the catalytic subunit A and regulatory subunit B further supported the conclusion that V H+-ATPase is the intrinsic enzyme of the yeast ER and Golgi and likely presented by distinct forms and/or selectively regulated.

The d subunit plays a central role in human vacuolar H(+)-ATPases

The multi-subunit vacuolar-type H(+)-ATPase consists of a V(1) domain (A-H subunits) catalyzing ATP hydrolysis and a V(0) domain (a, c, c', c", d, e) responsible for H(+) translocation. The mammalian V(0) d subunit is one of the least-well characterized, and its function and position within the pump are still unclear. It has two different forms encoded by separate genes, d1 being ubiquitous while d2 is predominantly expressed at the cell surface in kidney and osteoclast. To determine whether it forms part of the pump's central stalk as suggested by bacterial A-ATPase studies, or is peripheral as hypothesized from a yeast model, we investigated both human d subunit isoforms. In silico structural modelling demonstrated that human d1 and d2 are structural orthologues of bacterial subunit C, despite poor sequence identity. Expression studies of d1 and d2 showed that each can pull down the central stalk's D and F subunits from human kidney membrane, and in vitro studies using D and F further showed that the interactions between these proteins and the d subunit is direct. These data indicate that the d subunit in man is centrally located within the pump and is thus important in its rotary mechanism.

Morphological and cytochemical characterization of spores and gills of Lepista sordida (Fungi: Basidiomycota)

Some ultrastructural and cytochemical aspects of Lepista sordida are described. Basidiospores with verruculose and irregular ornamentations were observed through scanning electron microscopy. Confocal microscopy indicated that most of them exhibited a single large lipid body, no acidic vesicles and nucleus localized in the cell periphery.

Three-dimensional reconstruction of bovine brain V-ATPase by cryo-electron microscopy and single particle analysis

Bovine V-ATPase from brain clathrin-coated vesicles was investigated by cryo-electron microscopy and single particle analysis. Our studies revealed great flexibility of the central linker region connecting V1 and V0. As a consequence, the two sub-complexes were processed separately and the resulting volumes were merged computationally. We present the first three-dimensional (3D) map of a V-ATPase obtained from cryo-electron micrographs. The overall resolution was estimated 34A by Fourier shell correlation (0.5 cutoff). Our 3D reconstruction shows a large peripheral stalk and a smaller, isolated peripheral density, suggesting a second, less well-resolved peripheral connection. The 3D map reveals new features of the large peripheral stator and of the collar-like density attached to the membrane domain. Our analyses of the membrane domain indicate the presence of six proteolipid subunits. In addition, we could localize the V0 subunit a flanking the large peripheral stalk.

Molecular anatomy of a trafficking organelle

Membrane traffic in eukaryotic cells involves transport of vesicles that bud from a donor compartment and fuse with an acceptor compartment. Common principles of budding and fusion have emerged, and many of the proteins involved in these events are now known. However, a detailed picture of an entire trafficking organelle is not yet available. Using synaptic vesicles as a model, we have now determined the protein and lipid composition; measured vesicle size, density, and mass; calculated the average protein and lipid mass per vesicle; and determined the copy number of more than a dozen major constituents. A model has been constructed that integrates all quantitative data and includes structural models of abundant proteins. Synaptic vesicles are dominated by proteins, possess a surprising diversity of trafficking proteins, and, with the exception of the V-ATPase that is present in only one to two copies, contain numerous copies of proteins essential for membrane traffic and neurotransmitter uptake.

The emerging structure of vacuolar ATPases

Bioenergetics and physiology of primary pumps have been revitalized by new insights into the mechanism of energizing biomembranes. Structural information is becoming available, and the three-dimensional structure of F-ATPase is being resolved. The growing understanding of the fundamental mechanism of energy coupling may revolutionize our view of biological processes. The F- and V-ATPases (vacuolar-type ATPase) exhibit a common mechanical design in which nucleotide-binding on the catalytic sector, through a cycle of conformation changes, drives the transmembrane passage of protons by turning a membrane-embedded rotor. This motor can run in forward or reverse directions, hydrolyzing ATP as it pumps protons uphill or creating ATP as protons flow downhill. In contrast to F-ATPases, whose primary function in eukaryotic cells is to form ATP at the expense of the proton-motive force (pmf), V-ATPases function exclusively as an ATP-dependent proton pump. The pmf generated by V-ATPases in organelles and membranes of eukaryotic cells is utilized as a driving force for numerous secondary transport processes. V- and F-ATPases have similar structure and mechanism of action, and several of their subunits evolved from common ancestors. Electron microscopy studies of V-ATPase revealed its general structure at low resolution. Recently, several structures of V-ATPase subunits, solved by X-ray crystallography with atomic resolution, were published. This, together with electron microscopy low-resolution maps of the whole complex, and biochemistry cross-linking experiments, allows construction of a structural model for a part of the complex that may be used as a working hypothesis for future research.

Identification of a Domain in the Vo Subunit d That Is Critical for Coupling of the Yeast Vacuolar Proton-translocating ATPase

Vacuolar proton-translocating ATPase pumps consist of two domains, V(1) and V(o). Subunit d is a component of V(o) located in a central stalk that rotates during catalysis. By generating mutations, we showed that subunit d couples ATP hydrolysis and proton transport. The mutation F94A strongly uncoupled the enzyme, preventing proton transport but not ATPase activity. C-terminal mutations changed coupling as well; ATPase activity was decreased by 59-72%, whereas proton transport was not measurable (E328A) or was moderately reduced (E317A and C329A). Except for W325A, which had low levels of V(1)V(o), mutations allowed wild-type assembly regardless of the fact that subunits E and d were reduced at the membrane. N- and C-terminal deletions of various lengths were inhibitory and gradually destabilized subunit d, limiting V(1)V(o) formation. Both N and C terminus were required for V(o) assembly. The N-terminal truncation 2-19Delta prevented V(1)V(o) formation, although subunit d was available. The C terminus was required for retention of subunits E and d at the membrane. In addition, the C terminus of its bacterial homolog (subunit C from T. thermophilus) stabilized the yeast subunit d mutant 310-345Delta and allowed assembly of the rotor structure with subunits A and B. Structural features conserved between bacterial and eukaryotic subunit d and the significance of domain 3 for vacuolar proton-translocating ATPase function are discussed.

Transport ATPases: structure, motors, mechanism and medicine: a brief overview

Today we know there are four different types of ATPases that operate within biological membranes with the purpose of moving many different types of ions or molecules across these membranes. Some of these ions or molecules are transported into cells, some out of cells, and some in or out of organelles within cells. These ATPases span the biological world from bacteria to eukaryotic cells and have become most simply and commonly known as "transport ATPases." The price that each cell type pays for transport work is counted in molecules of hydrolyzed ATP, a metabolic currency that is itself regenerated by a transport ATPase working in reverse, i.e., the ATP synthase. Four major classes of transport ATPases, the P, V, F, and ABC types are now known. In addition to being involved in many different types of biological/physiological processes, mutations in these proteins also account for a large number of diseases. The purpose of this introductory article to a mini-review series on transport ATPases is to provide the reader with a very brief and focused look at this important area of research that has an interesting history and bears significance to cell physiology, biochemistry, immunology, nanotechnology, and medicine, including drug discovery. The latter involves potential applications to a whole host of diseases ranging from cancer to those that affect bones (osteoporosis), ears (hearing), eyes (macromolecular degeneration), the heart (hypercholesterolemia/cardiac arrest,), immune system (immune deficiency disease), kidney (nephrotoxicity), lungs (cystic fibrosis), pancreas (diabetes and cystic fibrosis), skin (Darier disease), and stomach (ulcers).

Structural and functional features of yeast V-ATPase subunit C

V-ATPase is a multi-subunit membrane protein complex, it translocates protons across biological membranes, generating electrical and pH gradients which are used for varieties of cellular processes. V-ATPase is composed of two distinct sub-complexes: a membrane bound V0 sub-complex, composed of 6 different subunits, which is responsible for proton transport and a soluble cytosolic facing V1 sub-complex, composed of 8 different subunits which hydrolyse ATP. The two sub-complexes are held together via a flexible stator. One of the main features of eukaryotic V-ATPase is its ability to reversibly dissociate to its sub-complexes in response to changing cellular conditions, which arrest both proton translocation and ATP hydrolysis, suggesting a regulation function. Subunit C (vma5p in yeast) was shown by several biochemical, genetic and recent structural data to function as a flexible stator holding the two sectors of the complex together and regulating the reversible association/dissociation of the complex, partly via association with F-actin filaments. Structural features of subunit C that allow smooth energy conversion and interaction with actin and nucleotides are discussed.

The V-type H+ ATPase: molecular structure and function, physiological roles and regulation

It was nearly 30 years before the V-type H+ ATPase was admitted to the small circle of bona fide transport ATPases alongside F-type and P-type ATPases. The V-type H+ ATPase is an ATP-driven enzyme that transforms the energy of ATP hydrolysis to electrochemical potential differences of protons across diverse biological membranes via the primary active transport of H+. In turn, the transmembrane electrochemical potential of H+ is used to drive a variety of (i) secondary active transport systems via H+-dependent symporters and antiporters and (ii) channel-mediated transport systems. For example, expression of Cl- channels or transporters next to the V-type H+ ATPase in vacuoles of plants and fungi and in lysosomes of animals brings about the acidification of the endosomal compartment, and the expression of the H+/neurotransmitter antiporter next to the V-type H+ ATPase concentrates neurotransmitters in synaptic vesicles. First found in association with endosomal membranes, the V-type H+ ATPase is now also found in increasing examples of plasma membranes where the proton pump energizes transport across cell membranes and entire epithelia. The molecular details reveal up to 14 protein subunits arranged in (i) a cytoplasmic V1 complex, which mediates the hydrolysis of ATP, and (ii) a membrane-embedded V0 complex, which translocates H+ across the membrane. Clever experiments have revealed the V-type H+ ATPase as a molecular motor akin to F-type ATPases. The hydrolysis of ATP turns a rotor consisting largely of one copy of subunits D and F of the V1 complex and a ring of six or more copies of subunit c of the V0 complex. The rotation of the ring is thought to deliver H+ from the cytoplasmic to the endosomal or extracellular side of the membrane, probably via channels formed by subunit a. The reversible dissociation of V1 and V0 complexes is one mechanism of physiological regulation that appears to be widely conserved from yeast to animal cells. Other mechanisms, such as subunit-subunit interactions or interactions of the V-type H+ ATPase with other proteins that serve physiological regulation, remain to be explored. Some diseases can now be attributed to genetic alterations of specific subunits of the V-type H+ ATPase.

Localization of subunit C (Vma5p) in the yeast vacuolar ATPase by immuno electron microscopy

Vacuolar ATPases (V1V0 -ATPases) function in proton translocation across lipid membranes of subcellular compartments. We have used antibody labeling and electron microscopy to define the position of subunit C in the vacuolar ATPase from yeast. The data show that subunit C is binding at the interface of the ATPase and proton channel, opposite from another stalk density previously identified as subunit H [Wilkens S., Inoue T., and Forgac M. (2004) Three-dimensional structure of the vacuolar ATPase - Localization of subunit H by difference imaging and chemical cross-linking. J. Biol. Chem. 279, 41942-41949]. A picture of the vacuolar ATPase stalk domain is emerging in which subunits C and H are positioned to play a role in reversible enzyme dissociation and activity silencing.

Rotary molecular motors

The F-, V-, and A-adenosine triphosphatases (ATPases) represent a family of evolutionarily related ion pumps found in every living cell. They either function to synthesize adenosine triphosphate (ATP) at the expense of an ion gradient or they act as primary ion pumps establishing transmembrane ion motive force at the expense of ATP hydrolysis. The A-, F-, and V-ATPases are rotary motor enzymes. Synthesis or hydrolysis of ATP taking place in the three catalytic sites of the membrane extrinsic domain is coupled to ion translocation across the single ion channel in the membrane-bound domain via rotation of a central part of the complex with respect to a static portion of the enzyme. This chapter reviews recent progress in the structure determination of several members of the family of F-, A-, and V-ATPases and our current understanding of the rotary mechanism of energy coupling.