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About 60-85% of total phosphorus (P) in cereal crops is finally allocated to seeds, where it is required for seed development, germination and early growth. However, little is known about the molecular mechanisms underlying P allocation to seeds. Here, we found that two members (OsPHO1;1 and OsPHO1;2) of the PHO1 gene family are involved in the distribution of P to seeds in rice. Both OsPHO1;1 and OsPHO1;2 were localized to the plasma membrane and showed influx transport activities for inorganic phosphate. At the reproductive stage, both OsPHO1;1 and OsPHO1;2 showed higher expression in node I, the uppermost node connecting to the panicle. OsPHO1;1 was mainly localized at the phloem region of diffuse vascular bundles (DVBs) of node I, while OsPHO1;2 was expressed in the xylem parenchyma cells of the enlarged vascular bundles (EVBs). In addition, they were also expressed in the ovular vascular trace, the outer layer of the inner integument (OsPHO1;1) and in the nucellar epidermis (OsPHO1;2) of caryopses. Knockout of OsPHO1;2, as well as OsPHO1;1 to a lesser extent, decreased the distribution of P to the seed, resulting in decreased seed size and delayed germination. Taken together, OsPHO1;2 expressed in node I is responsible for the unloading of P from the xylem of EVBs, while OsPHO1;1 is involved in reloading P into the phloem of DVBs for subsequent allocation of P to seeds. Furthermore, OsPHO1;1 and OsPHO1;2 expression in the caryopsis is important for delivering P from the maternal tissues to the filial tissues for seed development.

DOI： 10.1093/pcp/pcaa074

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Multidrug resistance (MDR) poses a major challenge to medicine. A principle cause of MDR is through active efflux by MDR transporters situated in the bacterial membrane. Here we present the crystal structure of the major facilitator superfamily (MFS) drug/H+ antiporter MdfA from Escherichia coli in an outward open conformation. Comparison with the inward facing (drug binding) state shows that, in addition to the expected change in relative orientations of the N- and C-terminal lobes of the antiporter, the conformation of TM5 is kinked and twisted. In vitro reconstitution experiments demonstrate the importance of selected residues for transport and molecular dynamics simulations are used to gain insights into antiporter switching. With the availability of structures of alternative conformational states, we anticipate that MdfA will serve as a model system for understanding drug efflux in MFS MDR antiporters.

DOI： 10.1038/s41467-018-06306-x

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Structural analysis of purified active membrane proteins can be performed by mass spectrometry (MS). However, no large-scale expression systems for active eukaryotic membrane proteins are available. Moreover, because membrane proteins cannot easily be digested by trypsin and ionized, they are difficult to analyze by MS. We developed a method for mass spectral analysis of eukaryotic membrane proteins combined with an overexpression system in Escherichia coli. Vesicular glutamate transporter 2 (VGLUT2/SLC17A6) with a soluble α-helical protein and histidine tag on the N- and C-terminus, respectively, was overexpressed in E. coli, solubilized with detergent, and purified by Ni-NTA affinity chromatography. Proteoliposomes containing VGLUT2 retained glutamate transport activity. For MS analysis, the detergent was removed from purified VGLUT2 by trichloroacetic acid precipitation, and VGLUT2 was then subjected to reductive alkylation and tryptic digestion. The resulting peptides were detected with 88% coverage by matrix-assisted laser desorption ionization time-of-flight (MALDI-TOF) MS with or without liquid chromatography. Vesicular excitatory amino acid transporter and vesicular acetylcholine transporter were also detected with similar coverage by the same method. Thus this methodology could be used to analyze purified eukaryotic active transporters. Structural analysis with chemical modifiers by MS could have applications in functional binding analysis for drug discovery.

DOI： 10.1021/acs.jproteome.7b00777

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Neutrophils migrate to sites infected by pathogenic microorganisms. This migration is regulated by neutrophil-secreted ATP, which stimulates neutrophils in an autocrine manner through purinergic receptors on the plasma membrane. Although previous studies have shown that ATP is released through channels at the plasma membrane of the neutrophil, it remains unknown whether it is also released through alternate secretory systems involving vesicular mechanisms. In this study, we investigated the possible involvement of vesicular nucleotide transporter (VNUT), a key molecule for vesicular storage and nucleotide release, in ATP secretion from neutrophils. RT-PCR and Western blotting analysis indicated that VNUT is expressed in mouse neutrophils. Immunohistochemical analysis indicated that VNUT mainly colocalized with matrix metalloproteinase-9 (MMP-9), a marker of tertiary granules, which are secretory organelles. In mouse neutrophils, ATP release was inhibited by clodronate, which is a potent VNUT inhibitor. Furthermore, neutrophils from VNUT/ mice did not release ATP and exhibited significantly reduced migration in vitro and in vivo. These findings suggest that tertiary granule-localized VNUT is responsible for vesicular ATP release and subsequent neutrophil migration. Thus, these findings suggest an additional mechanism through which ATP is released by neutrophils.

DOI： 10.1074/jbc.M117.810168

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Authorship：Lead author,　Last author,　Corresponding author   Language：Japanese  

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：NATURE PUBLISHING GROUP  

Mulitidrug and toxic compound extrusion (MATE) family transporters export xenobiotics to maintain cellular homeostasis. The human MATE transporters mediate the excretion of xenobiotics and cationic clinical drugs, whereas some plant MATE transporters are responsible for aluminum tolerance and secondary metabolite transport. Here we report the crystal structure of the eukaryotic MATE transporter from Arabidopsis thaliana, at 2.6 angstrom resolution. The structure reveals that its carboxy-terminal lobe (C-lobe) contains an extensive hydrogen-bonding network with well-conserved acidic residues, and their importance is demonstrated by the structure-based mutational analysis. The structural and functional analyses suggest that the transport mechanism involves the structural change of transmembrane helix 7, induced by the formation of a hydrogen-bonding network upon the protonation of the conserved acidic residue in the C-lobe. Our findings provide insights into the transport mechanism of eukaryotic MATE transporters, which is important for the improvement of the pharmacokinetics of the clinical drugs.

DOI： 10.1038/s41467-017-01541-0

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Despite the high incidence of neuropathic and inflammatory pain worldwide, effective drugs with few side effects are currently unavailable for the treatment of chronic pain. Recently, researchers have proposed that inhibitors of purinergic chemical transmission, which plays a key role in the pathological pain response, may allow for targeted treatment of pathological neuropathic and inflammatory pain. However, such therapeutic analgesic agents have yet to be developed. In the present study, we demonstrated that clodronate, a first-generation bisphosphonate with comparatively fewer side effects than traditional treatments, significantly attenuates neuropathic and inflammatory pain unrelated to bone abnormalities via inhibition of vesicular nucleotide transporter (VNUT), a key molecule for the initiation of purinergic chemical transmission. In vitro analyses indicated that clodronate inhibits VNUT at a half-maximal inhibitory concentration of 15.6 nM without affecting other vesicular neurotransmitter transporters, acting as an allosteric modulator through competition with Cl-. A low concentration of clodronate impaired vesicular ATP release from neurons, microglia, and immune cells. In vivo analyses revealed that clodronate is more effective than other therapeutic agents in attenuating neuropathic and inflammatory pain, as well as the accompanying inflammation, in wild-type but not VNUT-/- mice, without affecting basal nociception. These findings indicate that clodronate may represent a unique treatment strategy for chronic neuropathic and inflammatory pain via inhibition of vesicular ATP release.

DOI： 10.1073/pnas.1704847114

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：WILEY-V C H VERLAG GMBH  

Purpose: Mutation of the klotho gene in mice elicits a syndrome resembling accelerated human aging. However, there is limited evidence for the role of Klotho in the kidney. We conducted a comparative proteome analysis of wild-type (WT) and klotho-knockout (kl(-/-)) mouse kidneys to identify proteins involved in Klotho deficiency.Experimental design: MALDI imaging MS (MALDI-IMS) of frozen kidney sections from 7-wk-old male WT and kl(-/-) mice was used to determine genotype-specific differences in the MS distribution. Proteins uniquely distributed in kl-/-kidneys were identified by subsequent analysis of adjacent trypsinized sections by MALDI-IMS in combination with LC-MS/MS. Immunohistochemistry and western blotting were adopted in qualitative and quantitation analysis.Results: Ninety-seven and 69 proteins identified by LC-MS/MS were matched to the MALDI-IMS spectra in WT and kl(-/-) mouse kidneys, respectively. Among protein types matched, nucleic acid binding proteins were most abundant, followed by enzymes. We identified secretogranin-1 (SCG1), which was predominately distributed in the glomeruli and renal tubules of kl(-/-) mouse kidneys. Immunohistochemistry for SCG1 mirrored images of MALDI-IMS.Conclusions: SCG1 may be a candidate protein involved in Klotho deficiency. Although further research is needed to investigate the role of SCG1 in the kidney, we show the usefulness of MALDI-IMS combined with LC-MS/MS.

DOI： 10.1002/prca.201600095

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：AMER SOC BIOCHEMISTRY MOLECULAR BIOLOGY INC  

Mast cells are secretory cells that play an important role in host defense by discharging various intragranular contents, such as histamine and serotonin, upon stimulation of Fc receptors. The granules also contain spermine and spermidine, which can act as modulators of mast cell function, although the mechanism underlying vesicular storage remains unknown. Vesicular polyamine transporter (VPAT), the fourth member of the SLC18 transporter family, is an active transporter responsible for vesicular storage of spermine and spermidine in neurons. In the present study, we investigated whether VPAT functions in mast cells. RT-PCR and Western blotting indicated VPAT expression in murine bone marrow-derived mast cells (BMMCs). Immunohistochemical analysis indicated that VPAT is colocalized with VAMP3 but not with histamine, serotonin, cathepsin D, VAMP2, or VAMP7. Membrane vesicles from BMMCs accumulated spermidine upon the addition of ATP in a reserpine- and bafilomycin A(1)-sensitive manner. BMMCs secreted spermine and spermidine upon the addition of either antigen or A23187 in the presence of Ca2+, and the antigen-mediated release, which was shown to be temperature-dependent and sensitive to bafilomycin A(1) and tetanus toxin, was significantly suppressed by VPAT gene RNA interference. Under these conditions, expression of vesicular monoamine transporter 2 was unaffected, but antigen-dependent histamine release was significantly suppressed, which was recovered by the addition of 1 mm spermine. These results strongly suggest that VPAT is expressed and is responsible for vesicular storage of spermine and spermidine in novel secretory granules that differ from histamine- and serotonin-containing granules and is involved in vesicular release of these polyamines from mast cells.

DOI： 10.1074/jbc.M116.756197

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Phosphorus is an important nutrient for crop productivity. More than 60% of the total phosphorus in cereal crops is finally allocated into the grains and is therefore removed at harvest. This removal accounts for 85% of the phosphorus fertilizers applied to the field each year(1,2). However, because humans and non-ruminants such as poultry, swine and fish cannot digest phytate, the major form of phosphorus in the grains, the excreted phosphorus causes eutrophication of waterways. A reduction in phosphorus accumulation in the grain would contribute to sustainable and environmentally friendly agriculture. Here we describe a rice transporter, SULTR-like phosphorus distribution transporter (SPDT), that controls the allocation of phosphorus to the grain. SPDT is expressed in the xylem region of both enlarged-and diffuse-vascular bundles of the nodes, and encodes a plasma-membrane-localized transporter for phosphorus. Knockout of this gene in rice (Oryza sativa) altered the distribution of phosphorus, with decreased phosphorus in the grains but increased levels in the leaves. Total phosphorus and phytate in the brown de-husked rice were 20-30% lower in the knockout lines, whereas yield, seed germination and seedling vigour were not affected. These results indicate that SPDT functions in the rice node as a switch to allocate phosphorus preferentially to the grains. This finding provides a potential strategy to reduce the removal of phosphorus from the field and lower the risk of eutrophication of waterways.

DOI： 10.1038/nature20610

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The bladder urothelium is more than just a barrier. When the bladder is distended, the urothelium functions as a sensor to initiate the voiding reflex, during which it releases ATP via multiple mechanisms. However, the mechanisms underlying this ATP release in response to the various stretch stimuli caused by bladder filling remain largely unknown. Therefore, the aim of this study was to elucidate these mechanisms. By comparing vesicular nucleotide transporter (VNUT)-deficient and wildtype male mice, we showed that ATP has a crucial role in urine storage through exocytosis via a VNUT-dependent mechanism. VNUT was abundantly expressed in the bladder urothelium, and when the urothelium was weakly stimulated (i.e. in the early filling stages), it released ATP by exocytosis. VNUT-deficient mice showed reduced bladder compliance from the early storage phase and displayed frequent urination in inappropriate places without a change in voiding function. We conclude that urothelial, VNUT-dependent ATP exocytosis is involved in urine storage mechanisms that promote the relaxation of the bladder during the early stages of filling.

DOI： 10.1038/srep29761

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Language：English   Publishing type：Part of collection (book)   Publisher：ANNUAL REVIEWS  

Vesicular neurotransmitter transporters are responsible for the accumulation of neurotransmitters in secretory vesicles and play essential roles in chemical transmission. The SLC17 family contributes to sequestration of anionic neurotransmitters such as glutamate, aspartate, and nucleotides. Identification and subsequent cellular and molecular biological studies of SLC17 transporters unveiled the principles underlying the actions of these transporters. Recent progress in reconstitution methods in combination with postgenomic approaches has advanced studies on neurotransmitter transporters. This review summarizes the molecular properties of SLC17-type transporters and recent findings regarding the novel SLC18 transporter.

DOI： 10.1146/annurev-pharmtox-010814-124816

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Manganese is an essential metal for plant growth. A number of transporters involved in the uptake of manganese from soils, and its translocation to the shoot, have been identified in Arabidopsis and rice. However, the transporter responsible for the radial transport of manganese out of root exodermis and endodermis cells and into the root stele remains unknown. Here, we show that metal tolerance protein 9 (MTP9), a member of the cation diffusion facilitator family, is a critical player in this process in rice (Oryza sativa). We find that MTP9 is mainly expressed in roots, and that the resulting protein is localized to the plasma membrane of exo- and endodermis cells, at the proximal side of these cell layers (opposite the manganese uptake transporter Nramp5, which is found at the distal side). We demonstrate that MTP9 has manganese transport activity by expression in proteoliposomes and yeast, and show that knockout of MTP9 in rice reduces manganese uptake and its translocation to shoots. We conclude that at least in rice MTP9 is required for manganese translocation to the root stele, and thereby manganese uptake.

DOI： 10.1038/NPLANTS.2015.170

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Membrane potential (Delta psi)-driven and Cl--dependent organic anion transport is a primary function of the solute carrier family 17 (SLC17) transporter family. Although the transport substrates and physiological relevance of the major members are well understood, SLC17A2 protein known to be Na+-phosphate cotransporter 3 (NPT3) is far less well characterized. In the present study, we investigated the transport properties and expression patterns of mouse SLC17A2 protein (mNPT3). Proteoliposomes containing the purified mNPT3 protein took up radiolabeled p-aminohippuric acid (PAH) in a Delta psi- and Cl--dependent manner. The mNPT3-mediated PAH uptake was inhibited by 4,4'-diisothiocyanostilbene- 2,2'-disulfonic acid (DIDs) and Evans blue, common inhibitors of SLC17 family members. The PAH uptake was also inhibited by various anionic compounds, such as hydrophilic nonsteroidal anti-inflammatory drugs (NSAIDs) and urate. Consistent with these observations, the proteoliposome took up radiolabeled urate in a Delta psi- and Cl--dependent manner. Immunohistochemistry with specific antibodies against mNPT3 combined with RT-PCR revealed that mNPT3 is present in various tissues, including the hepatic bile duct, luminal membranes of the renal urinary tubules, maternal side of syncytiotrophoblast in the placenta, apical membrane of follicle cells in the thyroid, bronchiole epithelial cells in the lungs, and astrocytes around blood vessels in the cerebrum. These results suggested that mNPT3 is a polyspecific organic anion transporter that is involved in circulation of urate throughout the body.

DOI： 10.1152/ajpcell.00048.2015

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Extrusion of chloroquine (CQ) from digestive vacuoles through the Plasmodium falciparum CQ resistance transporter (PfCRT) is essential to establish CQ resistance of the malaria parasite. However, the physiological relevance of PfCRT and how CQ-resistant PfCRT gains the ability to transport CQ remain unknown. We prepared proteoliposomes containing purified CQ-sensitive and CQ-resistant PfCRTs and measured their transport activities. All PfCRTs tested actively took up tetraethylammonium, verapamil, CQ, basic amino acids, polypeptides, and polyamines at the expense of an electrochemical proton gradient. CQ-resistant PfCRT exhibited decreased affinity for CQ, resulting in increased CQ uptake. Furthermore, CQ competitively inhibited amino acid transport. Thus, PfCRT is a H+-coupled polyspecific nutrient and drug exporter.

DOI： 10.1073/pnas.1417102112

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Authorship：Lead author,　Corresponding author   Language：English   Publishing type：Research paper (scientific journal)   Publisher：NATURE PUBLISHING GROUP  

Ascorbate is an antioxidant and coenzyme for various metabolic reactions in vivo. In plant chloroplasts, high ascorbate levels are required to overcome photoinhibition caused by strong light. However, ascorbate is synthesized in the mitochondria and the molecular mechanisms underlying ascorbate transport into chloroplasts are unknown. Here we show that AtPHT4;4, a member of the phosphate transporter 4 family of Arabidopsis thaliana, functions as an ascorbate transporter. In vitro analysis shows that proteoliposomes containing the purified AtPHT4; 4 protein exhibit membrane potential- and Cl- dependent ascorbate uptake. The AtPHT4; 4 protein is abundantly expressed in the chloroplast envelope membrane. Knockout of AtPHT4; 4 results in decreased levels of the reduced form of ascorbate in the leaves and the heat dissipation process of excessive energy during photosynthesis is compromised. Taken together, these observations indicate that the AtPHT4; 4 protein is an ascorbate transporter at the chloroplast envelope membrane, which may be required for tolerance to strong light stress.

DOI： 10.1038/ncomms6928

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Authorship：Lead author,　Corresponding author   Language：Japanese  

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Authorship：Lead author   Language：English   Publishing type：Research paper (scientific journal)   Publisher：NATURE PUBLISHING GROUP  

Neuroendocrine cells store ATP in secretory granules and release it along with hormones that may trigger a variety of cellular responses in a process called purinergic chemical transmission. Although the vesicular nucleotide transporter (VNUT) has been shown to be involved in vesicular storage and release of ATP, its physiological relevance in vivo is far less well understood. In Vnut knockout (Vnut(-/-)) mice, we found that the loss of functional VNUT in adrenal chromaffin granules and insulin granules in the islets of Langerhans led to several significant effects. Vesicular ATP accumulation and depolarization-dependent ATP release were absent in the chromaffin granules of Vnut(-/-) mice. Glucose-responsive ATP release was also absent in pancreatic beta-cells in Vnut(-/-) mice, while glucose-responsive insulin secretion was enhanced to a greater extent than that in wild-type tissue. Vnut(-/-) mice exhibited improved glucose tolerance and low blood glucose upon fasting due to increased insulin sensitivity. These results demonstrated an essential role of VNUT in vesicular storage and release of ATP in neuroendocrine cells in vivo and suggest that vesicular ATP and/or its degradation products act as feedback regulators in catecholamine and insulin secretion, thereby regulating blood glucose homeostasis.

DOI： 10.1038/srep06689

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Spermine and spermidine act as neuromodulators upon binding to the extracellular site(s) of various ionotropic receptors, such as N-methyl-D-aspartate receptors. To gain access to the receptors, polyamines synthesized in neurons and astrocytes are stored in secretory vesicles and released upon depolarization. Although vesicular storage is mediated in an ATP-dependent, reserpine-sensitive fashion, the transporter responsible for this process remains unknown. SLC18B1 is the fourth member of the SLC18 transporter family, which includes vesicular monoamine transporters and vesicular acetylcholine transporter. Proteoliposomes containing purified human SLC18B1 protein actively transport spermine and spermidine by exchange of H+. SLC18B1 protein is predominantly expressed in the hippocampus and is associated with vesicles in astrocytes. SLC18B1 gene knockdown decreased both SLC18B1 protein and spermine/spermidine contents in astrocytes. These results indicated that SLC18B1 encodes a vesicular polyamine transporter (VPAT).

DOI： 10.1038/srep06836

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：American Physiological Society  

Nucleotides are stored in the dense granules of platelets. The release of nucleotides triggers one of the first steps in a series of cascades responsible for blood coagulation. However, the mechanism of how the nucleotides are accumulated in the granules is still far less understood. The transporter protein responsible for storage of nucleotides in the neuroendocrine cells has been identified and characterized. We hypothesized that the vesicular nucleotide transporter (VNUT) is also involved in the vesicular storage of nucleotides in platelets. In this article, we present three lines of evidence that VNUT is responsible for the vesicular storage of nucleotides in platelets and that vesicular ATP transport is crucial for platelet function, detection and characterization of VNUT activity in platelets isolated from healthy humans and MEG-01 cells, RNA interference experiments on MEG-01 cells, and studies on nucleotide transport and release with a selective inhibitor.

DOI： 10.14814/phy2.12034

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Vesicular nucleotide transporter (VNUT) is responsible for vesicular ATP storage in ATP-secreting cells. In the present study, we examined the effects on VNUT-mediated transport of ATP release inhibitors such as ATP-binding cassette (ABC) proteins, hemichannels, maxi anion channels and P2X7 receptor. The ATP transport activity of proteoliposomes containing purified human VNUT was blocked by glibenclamide, carbenoxolone, 18 á-glycyrrhetinic acid, flufenamic acid, arachidonic acid and A438079 without the formation of Äø (positive inside) as a driving force being affected. Thus, inhibitors of ATP release may inhibit VNUT and subsequent ATP release, since the previous works proved that inhibitors of ATP release blocked VNUT-mediated ATP release at the cell level. © 2013 The Pharmaceutical Society of Japan.

DOI： 10.1248/bpb.b13-00544

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SLC17A1 protein (NPT1) was the first identified member of the SLC17 phosphate transporter family, and is known to mediate Na+/inorganic phosphate (Pi) co-transport when expressed in Xenopus oocytes. Although this protein was suggested to be a renal polyspecific anion exporter, its transport properties were not well characterized. The clean biochemical approach revealed that proteoliposomes comprising purified NPT1 as the only protein source transport various organic anions such as urate, p-aminohippuric acid (PAH), and acetylsalicylic acid (aspirin) in a membrane potential (δ̄)-driven and Cl- -dependent manner. Human NPT1 carrying an SNP mutation, Thr269Ile, known to increase the risk of gout, exhibited 32% lower urate transport activity compared to the wild type protein, leading to the conclusion that NPT1 is the long searched for transporter responsible for renal urate excretion. In the present article, we summarized the history of identification of the urate exporter and its possible involvement in the dynamism of urate under physiological and pathological conditions. © 2013 Bentham Science Publishers.

DOI： 10.2174/18744672113069990035

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Togawa N, Miyaji T, Izawa S, Omote H, Moriyama Y. A Na+ phosphate cotransporter homologue (SLC17A4 protein) is an intestinal organic anion exporter. Am J Physiol Cell Physiol 302: C1652-C1660, 2012. First published March 28, 2012; doi:10.1152/ajpcell.00015.2012.-The SLC17 anion transporter family comprises nine members that transport various organic anions in membrane potential (Delta psi)- and Cl- dependent manners. Although the transport substrates and physiological relevance of the majority of the members have already been determined, little is known about SLC17A4 proteins known to be Na+-phosphate cotransporter homologue (NPT homologue). In the present study, we investigated the expression and transport properties of human SLC17A4 protein. Using specific antibodies, we found that a human NPT homologue is specifically expressed and present in the intestinal brush border membrane. Proteoliposomes containing the purified protein took up radiolabeled p-aminohippuric acid (PAH) in a Cl--dependent manner at the expense of an electrochemical gradient of protons, especially Delta psi, across the membrane. The Delta psi- and Cl--dependent PAH uptake was inhibited by diisothiocyanostilbene-2,2'-disulfonic acid and Evans blue, common inhibitors of SLC17 family members. cis-Inhibition studies revealed that various anionic compounds, such as hydrophilic nonsteroidal anti-inflammatory drugs, pravastatin, and urate inhibited the PAH uptake. Proteoliposomes took up radiolabeled urate, with the uptake having properties similar to those of PAH uptake. These results strongly suggested that the human NPT homologue acts as a polyspecific organic anion exporter in the intestines. Since SLC17A1 protein (NPT1) and SLC17A3 protein (NPT4) are responsible for renal urate extrusion, our results reveal the possible involvement of a NPT homologue in urate extrusion from the intestinal duct.

DOI： 10.1152/ajpcell.00015.2012

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Background: The vesicular nucleotide transporter (VNUT) transports nucleotides in the presence of Mg2+.
Results: VNUT transports divalent cations in a membrane potential-and nucleotide-dependent manner.
Conclusion: VNUT transports divalent cations as a nucleotide complex.
Significance: VNUT functions as a divalent cation importer in secretory vesicles.

DOI： 10.1074/jbc.M111.277269

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Authorship：Lead author,　Corresponding author   Language：English   Publishing type：Research paper (scientific journal)   Publisher：WILEY-BLACKWELL  

Sialin, the protein coded by SLC17A5, is responsible for membrane potential (Delta psi)-driven aspartate and glutamate transport into synaptic vesicles in addition to H(+)/sialic acid cotransport in lysosomes. Rodent sialin mutants harboring the mutations associated with Salla disease in humans did not transport aspartate and glutamate whereas H(+)/sialic acid cotransport activity was about one-third of the wild-type protein. In this study, we investigate the effects of various mutations on the transport activities of human sialin. Proteoliposomes containing purified heterologously expressed human sialin exhibited both Delta psi-driven aspartate and glutamate transport activity and H(+)/sialic acid co-transport activity. Aspartate and glutamate transport was not detected in the R39C and K136E mutant forms of SLC17A5 protein associated with Salla disease, whereas H(+)/sialic acid co-transport activity corresponded to 30-50% of the recombinant wild-type protein. In contrast, SLC17A5 protein harboring the mutations associated with infantile sialic acid storage disease, H183R and Delta 268SSLRN272 still showed normal levels of Delta psi-driven aspartate and glutamate transport even though H(+)/sialic acid co-transport activity was absent. Human sialin carrying the G328E mutation that causes both phenotypes, and P334R and G378V mutations that cause infantile sialic acid storage disease showed no transport activity. These results support the idea that people suffering from Salla disease have been defective in aspartergic and glutamatergic neurotransmissions.

DOI： 10.1111/j.1471-4159.2011.07388.x

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Authorship：Lead author   Language：Japanese   Publisher：The Biophysical Society of Japan General Incorporated Association  

DOI： 10.2142/biophys.51.228

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：PERGAMON-ELSEVIER SCIENCE LTD  

Human multidrug and toxic compound extrusion 2 (hMATE2) is a kidney-specific isoform of hMATE1, an exporter of toxic organic cations (OCs) of exogenous and endogenous origins at the final excretion step in the kidneys and liver (Otsuka et al., 2005), and contains a splicing variant, MATE2K, that has an exon of hMATE2 deleted (Masuda et al., 2006). In the present study, we characterized the degree of expression and the transport properties of hMATE2. Quantitative PCR analysis with probes specific for hMATE2 indicated the presence of hMATE2 mRNA in the kidneys, which corresponded to 39% of total mRNA encoding both hMATE2 and hMATE2K. hMATE2-specific antibodies immunostained the renal urinary tubules. Upon expression in HEK293 cells, hMATE2 was localized in intracellular vesicular structures, and thus transport activity of tetraethylammonium (TEA), a typical substrate for MATE transporters, by the cells was not detected. The hMATE2 protein was purified and reconstituted into liposomes. An artificially imposed pH gradient (Delta pH) across the proteoliposomal membrane drove the uptake of TEA. Dissipation of Delta pH by ammonium sulfate effectively inhibited the TEA uptake, while that of the membrane potential by valinomycin had little effect. The profiles of cis-inhibition of TEA transport by hMATE2 and hMATE2K are similar to each other. Thus, both hMATE2 and hMATE2K equally operate in the human kidneys to extrude OCs into the urine. (C) 2011 Elsevier Ltd. All rights reserved.

DOI： 10.1016/j.biocel.2011.03.005

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Glutamate plays essential roles in chemical transmission as a major excitatory neurotransmitter. The accumulation of glutamate in Secretory vesicles is mediated by vesicular glutamate transporters (VGLUTs) that together with the driving electrochemical gradient of proteins influence the subsequent quantum release Of glutamate and the function of higher order neurons. The vesicular content of glutamate is Well correlated with membrane potential (Delta psi) which suggests that Delta psi determines the vesicular glutamate concentration The transport of glutamate into secretory vesicles is highly dependent on Cl(-). This anion stimulates glutamate transport but is inhibitory at higher concentrations. Accumulating evidence indicates that Cl(-) regulates glutamate transport through control of VGLUT activity and the H(+) electrochemical gradient. Recently, a comprehensive study demonstrated that Cl(-) regulation of VGLUT is competitively inhibited by metabolic intermediates such as ketone bodies. It also showed that ketone bodies are effective in controlling epilepsy. These results suggest a correlation between metabolic state and higher order brain function. We propose a novel function for Cl(-) as a fundamental regulator for signal transmission.

DOI： 10.1021/bi200567k

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Authorship：Lead author   Language：Japanese  

J-GLOBAL

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Authorship：Lead author   Language：English   Publishing type：Research paper (scientific journal)   Publisher：PHARMACEUTICAL SOC JAPAN  

Aspartate, an excitatory amino acid, is known to be stored in synaptic vesicles and exocytosed from some neurons to perform aspartergic neurotransmission. Through in vitro reconstitution, we found that sialin, a lysosomal sialic acid exporter, is responsible for the vesicular storage of aspartate in hippocampal neurons and pinealocytes. Mutations found in Salla disease cause decreased aspartate transport activity without affecting sialic acid transport. Thus, sialin is a multifunctional transporter. It is possible that people with Salla disease lose the ability of aspartergic neurotransmission, and this could explain why Salla disease involves severe neurological defects.

DOI： 10.1248/bpb.33.1783

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PubMed

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：CELL PRESS  

Fasting has been used to control epilepsy since antiquity, but the mechanism of coupling between metabolic state and excitatory neurotransmission remains unknown. Previous work has shown that the vesicular glutamate transporters (VGLUTs) required for exocytotic release of glutamate undergo an unusual form of regulation by Cl(-). Using functional reconstitution of the purified VGLUTs into proteoliposomes, we now show that Cl(-) acts as an allosteric activator, and the ketone bodies that increase with fasting inhibit glutamate release by competing with at the site of allosteric regulation. Consistent with these observations, acetoacetate reduced quantal size at hippocampal synapses and suppresses glutamate release and seizures evoked with 4-aminopyridine in the brain. The results indicate an unsuspected link between metabolic state and excitatory neurotransmission through anion-dependent regulation of VGLUT activity.

DOI： 10.1016/j.neuron.2010.09.002

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：AMER SOC BIOCHEMISTRY MOLECULAR BIOLOGY INC  

SLC17A1 protein (NPT1) is the first identified member of the SLC17 phosphate transporter family and mediates the transmembrane cotransport of Na+/P-i in oocytes. Although this protein is believed to be a renal polyspecific anion exporter, its transport properties are not well characterized. Here, we show that proteoliposomes containing purified SLC17A1 transport various organic anions such as p-aminohippuric acid and acetylsalicylic acid (aspirin) in an inside positive membrane potential (Delta psi)-dependent manner. We found that NPT1 also transported urate. The uptake characteristics were similar to that of SLC17 members in its Cl- dependence and inhibitor sensitivity. When arginine 138, an essential amino acid residue for members of the SLC17 family such as the vesicular glutamate transporter, was specifically mutated to alanine, the resulting mutant protein was inactive in Delta psi-dependent anion transport. Heterologously expressed and purified human NPT1 carrying the single nucleotide polymorphism mutation that is associated with increased risk of gout in humans exhibited 32% lower urate transport activity compared with the wild type protein. These results strongly suggested that NPT1 is a Cl--dependent polyspecific anion exporter involved in urate excretion under physiological conditions.

DOI： 10.1074/jbc.M110.122721

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：NATL ACAD SCIENCES  

Abscisic acid (ABA) is one of the most important phytohormones involved in abiotic stress responses, seed maturation, germination, and senescence. ABA is predominantly produced in vascular tissues and exerts hormonal responses in various cells, including guard cells. Although ABA responses require extrusion of ABA from ABA-producing cells in an intercellular ABA signaling pathway, the transport mechanisms of ABA through the plasma membrane remain unknown. Here we isolated an ATP-binding cassette (ABC) transporter gene, AtABCG25, from Arabidopsis by genetically screening for ABA sensitivity. AtABCG25 was expressed mainly in vascular tissues. The fluorescent protein-fused AtABCG25 was localized at the plasma membrane in plant cells. In membrane vesicles derived from AtABCG25-expressing insect cells, AtABCG25 exhibited ATP-dependent ABA transport. The AtABCG25-overexpressing plants showed higher leaf temperatures, implying an influence on stomatal regulation. These results strongly suggest that AtABCG25 is an exporter of ABA and is involved in the intercellular ABA signaling pathway. The presence of the ABA transport mechanism sheds light on the active control of multicellular ABA responses to environmental stresses among plant cells.

DOI： 10.1073/pnas.0912516107

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Authorship：Lead author   Language：English   Publishing type：Research paper (scientific journal)   Publisher：NATL ACAD SCIENCES  

Aspartate is an excitatory amino acid that is costored with glutamate in synaptic vesicles of hippocampal neurons and synaptic-like microvesicles (SLMVs) of pinealocytes and is exocytosed and stimulates neighboring cells by binding to specific cell receptors. Although evidence increasingly supports the occurrence of aspartergic neurotransmission, this process is still debated because the mechanism for the vesicular storage of aspartate is unknown. Here, we show that sialin, a lysosomal H+/sialic acid cotransporter, is present in hippocampal synaptic vesicles and pineal SLMVs. RNA interference of sialin expression decreased exocytosis of aspartate and glutamate in pinealocytes. Proteoliposomes containing purified sialin actively accumulated aspartate and glutamate to a similar extent when inside positive membrane potential is imposed as the driving force. Sialin carrying a mutation found in people suffering from Salla disease (R39C) was completely devoid of aspartate and glutamate transport activity, although it retained appreciable H+/sialic acid cotransport activity. These results strongly suggest that sialin possesses dual physiological functions and acts as a vesicular aspartate/glutamate transporter. It is possible that people with Salla disease lose aspartergic (and also the associated glutamatergic) neurotransmission, and this could provide an explanation for why Salla disease causes severe neurological defects.

DOI： 10.1073/pnas.0804015105

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：NATL ACAD SCIENCES  

ATP is a major chemical transmitter in purinergic signal transmission. Before secretion, ATIP is stored in secretory vesicles found in purinergic cells. Although the presence of active transport mechanisms for ATP has been postulated for a long time, the proteins responsible for its vesicular accumulation remains unknown. The transporter encoded by the human and mouse SLC17A9 gene, a novel member of an anion transporter family, was predominantly expressed in the brain and adrenal gland. The mouse and bovine counterparts were associated with adrenal chromaffin granules. Proteoliposomes containing purified transporter actively took up ATP, ADP, and GTP by using membrane potential as the driving force. The uptake properties of the reconstituted transporter were similar to that of the ATP uptake by synaptic vesicles and chromaffin granules. Suppression of endogenous SLC17A9 expression in PC12 cells decreased exocytosis of ATP. These findings strongly suggest that SLC17A9 protein is a vesicular nucleotide transporter and should lead to the elucidation of the molecular mechanism of ATP secretion in purinergic signal transmission.

DOI： 10.1073/pnas.0800141105

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：BLACKWELL PUBLISHING  

Vesicular glutamate transporter (VGLUT) is responsible for the vesicular storage of (L)-glutamate, and plays an essential role in glutamate-mediated intercellular signal transmission in the CNS and in some neuroendocrine cells. Intestinal L cells are the glucose-responsive neuroendocrine cells responsible for the secretion of glucagon-like peptide 1 (GLP-1). We have shown that intestinal L cells express VGLUT2, a VGLUT isoform, which suggests that L cells secrete (L)-glutamate. In the present study, we investigated this possibility using GLUTag mouse clonal L cells. RT-PCR and northern blot analyses revealed expression of the VGLUT1 and VGLUT2 genes, but not of the VGLUT3 gene. Western blot analysis revealed immunological counterparts for VGLUT2, whereas an immunological counterpart of VGLUT1 was not detected. Indirect immunofluorescence microscopy revealed a punctate distribution of VGLUT2 immunoreactivity throughout the cells, which co-localized with GLP-1. Double-labeling immunoelectronmicroscopy confirmed the association of VGLUT2 with GLP-1-containing secretory granules. The membrane fraction exhibited ATP-dependent (L)-glutamate uptake, which was sensitive to bafilomycin A1 (a vacuolar proton ATPase inhibitor) and Evans blue (a VGLUT inhibitor) but insensitive to (D,L)-aspartate. Upon depolarization with KCl, GLUTag cells secreted appreciable amounts of (L)-glutamate and GLP-1. (D)-Glucose and methyl-alpha-(D)-glucopyranoside, stimulators of exocytosis of GLP-1, also triggered the secretion of (L)-glutamate. The (L)-glutamate secretion was partially dependent on Ca2+ and sensitive to bafilomycin A1. These results demonstrated that GLUTag cells stored (L)-glutamate in secretory granules and secreted it with GLP-1 by exocytosis. As GLUTag cells and intestinal L cells express kainate receptors and plasma membrane glutamate transporters, these results support the concept of (L)-glutamate-mediated intercellular signaling in the vicinity of intestinal L cells.

DOI： 10.1111/j.1471-4159.2005.03575.x

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J-GLOBAL

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Language：Japanese  

J-GLOBAL

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Language：Japanese   Publisher：(公社)日本薬学会  

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Language：Japanese  

J-GLOBAL

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Language：English   Publishing type：Research paper, summary (international conference)   Publisher：SPRINGER  

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Language：English   Publishing type：Research paper, summary (international conference)   Publisher：SPRINGER  

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Language：English   Publishing type：Research paper, summary (international conference)   Publisher：SPRINGER  

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Language：English   Publishing type：Research paper, summary (international conference)   Publisher：SPRINGER  

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Language：Japanese   Publisher：(一社)日本内分泌学会  

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Language：English   Publishing type：Research paper, summary (international conference)   Publisher：ELSEVIER IRELAND LTD  

DOI： 10.1016/j.neures.2010.07.994

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Language：English   Publishing type：Research paper, summary (international conference)   Publisher：ELSEVIER IRELAND LTD  

DOI： 10.1016/j.neures.2009.09.280

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Language：English   Publishing type：Research paper, summary (international conference)   Publisher：PHARMACEUTICAL SOC JAPAN  

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Language：Japanese   Presentation type：Symposium, workshop panel (nominated)  

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Language：Japanese   Presentation type：Symposium, workshop panel (public)  

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Language：Japanese   Presentation type：Oral presentation (invited, special)  

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Language：Japanese   Presentation type：Symposium, workshop panel (nominated)  

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Language：Japanese   Presentation type：Symposium, workshop panel (nominated)  

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Language：Japanese   Presentation type：Symposium, workshop panel (public)  

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Language：Japanese   Presentation type：Public lecture, seminar, tutorial, course, or other speech  

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Language：Japanese   Presentation type：Symposium, workshop panel (nominated)  

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Language：English   Presentation type：Symposium, workshop panel (nominated)  

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Language：Japanese   Presentation type：Oral presentation (invited, special)  

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Language：English   Presentation type：Oral presentation (invited, special)  

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Language：Japanese   Presentation type：Symposium, workshop panel (nominated)  

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Language：English   Presentation type：Symposium, workshop panel (public)  

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Language：Japanese   Presentation type：Symposium, workshop panel (nominated)  

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Language：Japanese   Presentation type：Oral presentation (invited, special)  

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Language：Japanese   Presentation type：Symposium, workshop panel (nominated)  

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Language：Japanese   Presentation type：Symposium, workshop panel (public)  

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Language：Japanese   Presentation type：Symposium, workshop panel (nominated)  

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Applicant：国立大学法人 岡山大学

Application no：特願2013-155640  Date applied：2013.7.26

Announcement no：特開2015-023831  Date announced：2015.2.5

J-GLOBAL

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Applicant：国立大学法人 岡山大学

Application no：JP2008059079  Date applied：2008.5.16

Announcement no：WO2008-143192  Date announced：2008.11.27

J-GLOBAL

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Applicant：国立大学法人 岡山大学

Application no：特願2008-552574  Date applied：2008.5.16

Patent/Registration no：特許第5317056号  Date issued：2013.7.19

J-GLOBAL

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