Myosin and Other Energy-Transducing ATPases: Structural Dynamics Studied by Electron Paramagnetic Resonance.

The objective of this article was to document the energy-transducing and regulatory interactions in supramolecular complexes such as motor, pump, and clock ATPases. The dynamics and structural features were characterized by motion and distance measurements using spin-labeling electron paramagnetic resonance (EPR) spectroscopy. In particular, we focused on myosin ATPase with actin-troponin-tropomyosin, neural kinesin ATPase with microtubule, P-type ion-motive ATPase, and cyanobacterial clock ATPase. Finally, we have described the relationships or common principles among the molecular mechanisms of various energy-transducing systems and how the large-scale thermal structural transition of flexible elements from one state to the other precedes the subsequent irreversible chemical reactions.

Molecular characterization and differential expression suggested diverse functions of P-type II Ca2+ATPases in Triticum aestivum L.

BACKGROUND: Plant P-type II Ca2+ATPases are formed by two distinct groups of proteins (ACAs and ECAs) that perform pumping of Ca2+ outside the cytoplasm during homeostasis, and play vital functions during development and stress management. In the present study, we have performed identification and characterisation of P-type II Ca 2+ ATPase gene family in an important crop plant Triticum aestivum. RESULTS: Herein, a total of 33 TaACA and 9 TaECA proteins were identified from the various chromosomes and sub-genomes of Triticum aestivum. Phylogenetic analysis revealed clustering of the homoeologous TaACA and TaECA proteins into 11 and 3 distinct groups that exhibited high sequence homology and comparable structural organization as well. Both TaACA and TaECA group proteins consisted of eight to ten transmembrane regions, and their respective domains and motifs. Prediction of sub-cellular localization was found variable for most of the proteins; moreover, it was consistent with the evolutionarily related proteins from rice and Arabidopsis in certain cases. The occurrence of assorted sets of cis-regulatory elements indicated their diverse functions. The differential expression of various TaACA and TaECA genes during developmental stages suggested their roles in growth and development. The modulated expression during heat, drought, salt and biotic stresses along with the occurrence of various stress specific cis-regulatory elements suggested their association with stress response. Interaction of these genes with numerous development and stress related genes indicated their decisive role in various biological processes and signaling. CONCLUSION: T. aestivum genome consisted of a maximum of 42 P-type II Ca 2+ ATPase genes, derived from each A, B and D sub-genome. These genes may play diverse functions during plant growth and development. They may also be involved in signalling during abiotic and biotic stresses. The present study provides a comprehensive insight into the role of P-type II Ca 2+ ATPase genes in T. aestivum. However, the specific function of each gene needs to be established, which could be utilized in future crop improvement programs.

Hemiplegic migraine type 2 caused by a novel variant within the P-type ATPase motif in ATP1A2 concomitant with a CACNA1A variant.

BACKGROUND: Familial hemiplegic migraine (FHM) is an inherited autosomal dominant disorder characterized by migraine with reversible hemiplegia. FHM1 is caused by variants in CACNA1A, encoding a P/Q type neuronal voltage-gated calcium channel α subunit, which is also associated with episodic ataxia type 2 (EA2). FHM2 is associated with ATP1A2, which codes for an Na+/K+-ATPase isoform 2 subunit. CASE PRESENTATION: We identified an FHM2 family, the mother and her daughter, with a novel variant in ATP1A2, p.Gly377Asp, located in a well-conserved P-type ATPase motif. Additionally, the mother harbored deletion in the CACNA1A, associated with EA2, but her daughter did not. The mother presented migraine with typical aura without motor deficit, whereas her daughter had migraine accompanied by recurrent motor deficit and altered consciousness. The additional CACNA1A deletion in the mother might serve as a modifier. CONCLUSION: Our report emphasizes the importance of genetic analysis to diagnose neurological ion channel/transporter diseases.

Structural Basis of Substrate-Independent Phosphorylation in a P4-ATPase Lipid Flippase.

P4-ATPases define a eukaryotic subfamily of the P-type ATPases, and are responsible for the transverse flip of specific lipids from the extracellular or luminal leaflet to the cytosolic leaflet of cell membranes. The enzymatic cycle of P-type ATPases is divided into autophosphorylation and dephosphorylation half-reactions. Unlike most other P-type ATPases, P4-ATPases transport their substrate during dephosphorylation only, i.e. the phosphorylation half-reaction is not associated with transport. To study the structural basis of the distinct mechanisms of P4-ATPases, we have determined cryo-EM structures of Drs2p-Cdc50p from Saccharomyces cerevisiae covering multiple intermediates of the cycle. We identify several structural motifs specific to Drs2p and P4-ATPases in general that decrease movements and flexibility of domains as compared to other P-type ATPases such as Na+/K+-ATPase or Ca2+-ATPase. These motifs include the linkers that connect the transmembrane region to the actuator (A) domain, which is responsible for dephosphorylation. Additionally, mutation of Tyr380, which interacts with conserved Asp340 of the distinct DGET dephosphorylation loop of P4-ATPases, highlights a functional role of these P4-ATPase specific motifs in the A-domain. Finally, the transmembrane (TM) domain, responsible for transport, also undergoes less extensive conformational changes, which is ensured both by a longer segment connecting TM helix 4 with the phosphorylation site, and possible stabilization by the auxiliary subunit Cdc50p. Collectively these adaptions in P4-ATPases are responsible for phosphorylation becoming transport-independent.

Structure and ion-release mechanism of PIB-4-type ATPases.

Transition metals, such as zinc, are essential micronutrients in all organisms, but also highly toxic in excessive amounts. Heavy-metal transporting P-type (PIB) ATPases are crucial for homeostasis, conferring cellular detoxification and redistribution through transport of these ions across cellular membranes. No structural information is available for the PIB-4-ATPases, the subclass with the broadest cargo scope, and hence even their topology remains elusive. Here, we present structures and complementary functional analyses of an archetypal PIB-4-ATPase, sCoaT from Sulfitobacter sp. NAS14-1. The data disclose the architecture, devoid of classical so-called heavy-metal-binding domains (HMBDs), and provide fundamentally new insights into the mechanism and diversity of heavy-metal transporters. We reveal several novel P-type ATPase features, including a dual role in heavy-metal release and as an internal counter ion of an invariant histidine. We also establish that the turnover of PIB-ATPases is potassium independent, contrasting to many other P-type ATPases. Combined with new inhibitory compounds, our results open up for efforts in for example drug discovery, since PIB-4-ATPases function as virulence factors in many pathogens.

Heavy metals such as zinc and cobalt are toxic at high levels, yet most organisms need tiny amounts for their cells to work properly. As a result, proteins studded through the cell membrane act as gatekeepers to finetune import and export. These proteins are central to health and disease; their defect can lead to fatal illnesses in humans, and they also help bacteria infect other organisms. Despite their importance, little is known about some of these metal-export proteins. This is particularly the case for P_IB-4-ATPases, a subclass found in plants and bacteria and which includes, for example, a metal transporter required for bacteria to cause tuberculosis. Intricate knowledge of the three-dimensional structure of these proteins would help to understand how they select metals, shuttle the compounds in and out of cells, and are controlled by other cellular processes. To reveal this three-dimensional organisation, Grønberg et al. used X-ray diffraction, where high-energy radiation is passed through crystals of protein to reveal the positions of atoms. They focused on a type of PIB-4-ATPases found in bacteria as an example. The work showed that the protein does not contain the metal-binding regions seen in other classes of metal exporters; however, it sports unique features that are crucial for metal transport such as an adapted pathway for the transport of zinc and cobalt across the membrane. In addition, Grønberg et al. tested thousands of compounds to see if they could block the activity of the protein, identifying two that could kill bacteria. This better understanding of how PIB-4-ATPases work could help to engineer plants capable of removing heavy metals from contaminated soils, as well as uncover new compounds to be used as antibiotics.

The endoplasmic reticulum P5A-ATPase is a transmembrane helix dislocase.

Organelle identity depends on protein composition. How mistargeted proteins are selectively recognized and removed from organelles is incompletely understood. Here, we found that the orphan P5A-adenosine triphosphatase (ATPase) transporter ATP13A1 (Spf1 in yeast) directly interacted with the transmembrane segment (TM) of mitochondrial tail-anchored proteins. P5A-ATPase activity mediated the extraction of mistargeted proteins from the endoplasmic reticulum (ER). Cryo-electron microscopy structures of Saccharomyces cerevisiae Spf1 revealed a large, membrane-accessible substrate-binding pocket that alternately faced the ER lumen and cytosol and an endogenous substrate resembling an α-helical TM. Our results indicate that the P5A-ATPase could dislocate misinserted hydrophobic helices flanked by short basic segments from the ER. TM dislocation by the P5A-ATPase establishes an additional class of P-type ATPase substrates and may correct mistakes in protein targeting or topogenesis.

The N- or C-terminal cytoplasmic regions of P4-ATPases determine their cellular localization.

Mammalian P4-ATPases specifically localize to the plasma membrane and the membranes of intracellular compartments. P4-ATPases contain 10 transmembrane domains, and their N- and C-terminal (NT and CT) regions face the cytoplasm. Among the ATP10 and ATP11 proteins of P4-ATPases, ATP10A, ATP10D, ATP11A, and ATP11C localize to the plasma membrane, while ATP10B and ATP11B localize to late endosomes and early/recycling endosomes, respectively. We previously showed that the NT region of ATP9B is critical for its localization to the Golgi apparatus, while the CT regions of ATP11C isoforms are critical for Ca2+-dependent endocytosis or polarized localization at the plasma membrane. Here, we conducted a comprehensive analysis of chimeric proteins and found that the NT region of ATP10 proteins and the CT region of ATP11 proteins are responsible for their specific subcellular localization. Importantly, the ATP10B NT and the ATP11B CT regions were found to harbor a trafficking and/or targeting signal that allows these P4-ATPases to localize to late endosomes and early/recycling endosomes, respectively. Moreover, dileucine residues in the NT region of ATP10B were required for its trafficking to endosomal compartments. These results suggest that the NT and CT sequences of P4-ATPases play a key role in their intracellular trafficking.

Serine phosphorylation regulates the P-type potassium pump KdpFABC.

KdpFABC is an ATP-dependent K+ pump that ensures bacterial survival in K+-deficient environments. Whereas transcriptional activation of kdpFABC expression is well studied, a mechanism for down-regulation when K+ levels are restored has not been described. Here, we show that KdpFABC is inhibited when cells return to a K+-rich environment. The mechanism of inhibition involves phosphorylation of Ser162 on KdpB, which can be reversed in vitro by treatment with serine phosphatase. Mutating Ser162 to Alanine produces constitutive activity, whereas the phosphomimetic Ser162Asp mutation inactivates the pump. Analyses of the transport cycle show that serine phosphorylation abolishes the K+-dependence of ATP hydrolysis and blocks the catalytic cycle after formation of the aspartyl phosphate intermediate (E1~P). This regulatory mechanism is unique amongst P-type pumps and this study furthers our understanding of how bacteria control potassium homeostasis to maintain cell volume and osmotic potential.

Coordinated Roles of the Putative Ceramide-Conjugation Protein, Cwh43, and a Mn2+-Transporting, P-Type ATPase, Pmr1, in Fission Yeast.

Genetically controlled mechanisms of cell division and quiescence are vital for responding to changes in the nutritional environment and for cell survival. Previously, we have characterized temperature-sensitive (ts) mutants of the cwh43 gene in fission yeast, Schizosaccharomyces pombe, which is required for both cell proliferation and nitrogen starvation-induced G0 quiescence. Cwh43 encodes an evolutionarily conserved transmembrane protein that localizes in endoplasmic reticulum (ER). Defects in this protein fail to divide in low glucose and lose mitotic competence under nitrogen starvation, and also affect lipid metabolism. Here, we identified mutations of the pmr1 gene, which encodes an evolutionarily conserved Ca2+/Mn2+-transporting P-type ATPase, as potent extragenic suppressors of ts mutants of the cwh43 gene. Intriguingly, these pmr1 mutations specifically suppressed the ts phenotype of cwh43 mutants, among five P-type Ca2+- and/or Mn2+-ATPases reported in this organism. Cwh43 and Pmr1 co-localized in the ER. In cwh43 mutant cells, addition of excessive manganese to culture media enhanced the severe defect in cell morphology, and caused abnormal accumulation of a cell wall component, 1, 3-ß-glucan. In contrast, these abnormal phenotypes were abolished by deletion of the pmr1+ gene, as well as by removal of Mn2+ from the culture medium. Furthermore, nutrition-related phenotypes of cwh43 mutant cells were rescued in the absence of Pmr1. Our findings indicate that the cellular processes regulated by Cwh43 are appropriately balanced with Pmr1-mediated Mn2+ transport into the ER.

Tetrahydrocarbazoles are a novel class of potent P-type ATPase inhibitors with antifungal activity.

We have identified a series of tetrahydrocarbazoles as novel P-type ATPase inhibitors. Using a set of rationally designed analogues, we have analyzed their structure-activity relationship using functional assays, crystallographic data and computational modeling. We found that tetrahydrocarbazoles inhibit adenosine triphosphate (ATP) hydrolysis of the fungal H+-ATPase, depolarize the fungal plasma membrane and exhibit broad-spectrum antifungal activity. Comparative inhibition studies indicate that many tetrahydrocarbazoles also inhibit the mammalian Ca2+-ATPase (SERCA) and Na+,K+-ATPase with an even higher potency than Pma1. We have located the binding site for this compound class by crystallographic structure determination of a SERCA-tetrahydrocarbazole complex to 3.0 Å resolution, finding that the compound binds to a region above the ion inlet channel of the ATPase. A homology model of the Candida albicans H+-ATPase based on this crystal structure, indicates that the compounds could bind to the same pocket and identifies pocket extensions that could be exploited for selectivity enhancement. The results of this study will aid further optimization towards selective H+-ATPase inhibitors as a new class of antifungal agents.

Comprehensive comparison of two protein family of P-ATPases (13A1 and 13A3) in insects.

The P-type ATPases (P-ATPases) are present in all living cells where they mediate ion transport across membranes on the expense of ATP hydrolysis. Different ions which are transported by these pumps are protons like calcium, sodium, potassium, and heavy metals such as manganese, iron, copper, and zinc. Maintenance of the proper gradients for essential ions across cellular membranes makes P-ATPases crucial for cell survival. In this study, characterization of two families of P-ATPases including P-ATPase 13A1 and P-ATPase 13A3 protein was compared in two different insect species from different orders. According to the conserved motifs found with MEME, nine motifs were shared by insects of 13A1 family but eight in 13A3 family. Seven different insect species from 13A1 and five samples from 13A3 family were selected as the representative samples for functional and structural analyses. The structural and functional analyses were performed with ProtParam, SOPMA, SignalP 4.1, TMHMM 2.0, ProtScale and ProDom tools in the ExPASy database. The tertiary structure of Bombus terrestris as a sample of each family of insects were predicted by the Phyre2 and TM-score servers and their similarities were verified by SuperPose server. The tertiary structures were predicted via the "c3b9bA" model (PDB Accession Code: 3B9B) in P-ATPase 13A1 family and "c2zxeA" model (PDB Accession Code: 2ZXE) in P-ATPase 13A3 family. A phylogenetic tree was constructed with MEGA 6.06 software using the Neighbor-joining method. According to the results, there was a high identity of P-ATPase families so that they should be derived from a common ancestor however they belonged to separate groups. In protein-protein interaction analysis by STRING 10.0, six common enriched pathways of KEGG were identified in B. terrestris in both families. The obtained data provide a background for bioinformatic studies of the function and evolution of other insects and organisms.