1
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Walker V. The Intricacies of Renal Phosphate Reabsorption-An Overview. Int J Mol Sci 2024; 25:4684. [PMID: 38731904 PMCID: PMC11083860 DOI: 10.3390/ijms25094684] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/24/2024] [Revised: 04/17/2024] [Accepted: 04/19/2024] [Indexed: 05/13/2024] Open
Abstract
To maintain an optimal body content of phosphorus throughout postnatal life, variable phosphate absorption from food must be finely matched with urinary excretion. This amazing feat is accomplished through synchronised phosphate transport by myriads of ciliated cells lining the renal proximal tubules. These respond in real time to changes in phosphate and composition of the renal filtrate and to hormonal instructions. How they do this has stimulated decades of research. New analytical techniques, coupled with incredible advances in computer technology, have opened new avenues for investigation at a sub-cellular level. There has been a surge of research into different aspects of the process. These have verified long-held beliefs and are also dramatically extending our vision of the intense, integrated, intracellular activity which mediates phosphate absorption. Already, some have indicated new approaches for pharmacological intervention to regulate phosphate in common conditions, including chronic renal failure and osteoporosis, as well as rare inherited biochemical disorders. It is a rapidly evolving field. The aim here is to provide an overview of our current knowledge, to show where it is leading, and where there are uncertainties. Hopefully, this will raise questions and stimulate new ideas for further research.
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Affiliation(s)
- Valerie Walker
- Department of Clinical Biochemistry, University Hospital Southampton NHS Foundation Trust, Southampton General Hospital, Southampton S016 6YD, UK
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2
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Jönsson ÅLM, Hilberg O, Simonsen U, Christensen JH, Bendstrup E. New insights in the genetic variant spectrum of SLC34A2 in pulmonary alveolar microlithiasis; a systematic review. Orphanet J Rare Dis 2023; 18:130. [PMID: 37259144 DOI: 10.1186/s13023-023-02712-7] [Citation(s) in RCA: 4] [Impact Index Per Article: 4.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/10/2023] [Accepted: 04/30/2023] [Indexed: 06/02/2023] Open
Abstract
Pulmonary alveolar microlithiasis (PAM) is a rare autosomal recessive lung disease caused by variants in the SLC34A2 gene encoding the sodium-dependent phosphate transport protein 2B, NaPi-2b. PAM is characterized by deposition of calcium phosphate crystals in the alveoli. Onset and clinical course vary considerably; some patients remain asymptomatic while others develop severe respiratory failure with a significant symptom burden and compromised survival. It is likely that PAM is under-reported due to lack of recognition, misdiagnosis, and mild clinical presentation. Most patients are genetically uncharacterized as the diagnostic confirmation of PAM has traditionally not included a genetic analysis. Genetic testing may in the future be the preferred tool for diagnostics instead of invasive methods. This systematic review aims to provide an overview of the growing knowledge of PAM genetics. Rare variants in SLC34A2 are found in almost all genetically tested patients. So far, 34 allelic variants have been identified in at least 68 patients. A majority of these are present in the homozygous state; however, a few are found in the compound heterozygous form. Most of the allelic variants involve only a single nucleotide. Half of the variants are either nonsense or frameshifts, resulting in premature termination of the protein or decay of the mRNA. There is currently no cure for PAM, and the only effective treatment is lung transplantation. Management is mainly symptomatic, but an improved understanding of the underlying pathophysiology will hopefully result in development of targeted treatment options. More standardized data on PAM patients, including a genetic diagnosis covering larger international populations, would support the design and implementation of clinical studies to the benefit of patients. Further genetic characterization and understanding of how the molecular changes influence disease phenotype will hopefully allow earlier diagnosis and treatment of the disease in the future.
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Affiliation(s)
- Åsa Lina M Jönsson
- Department of Clinical Genetics, Aarhus University Hospital, Aarhus, Denmark.
- Department of Biomedicine, Aarhus University, Aarhus, Denmark.
| | - Ole Hilberg
- Department of Regional Health Research, University of Southern Denmark, Odense, Denmark.
- Department of Medicine, Lillebaelt Hospital, Vejle, Denmark.
| | - Ulf Simonsen
- Department of Biomedicine, Aarhus University, Aarhus, Denmark
| | | | - Elisabeth Bendstrup
- Centre for Rare Lung Diseases, Department of Respiratory Diseases and Allergy, Aarhus University Hospital, Aarhus, Denmark
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3
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Lv P, Li Y, Wang R, Zhang Y, Wang W, Liu Y, Shang Y, Su D, Wang W, Yang C. The pH sensor and ion binding of NhaD Na
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/H
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antiporter from IT superfamily. Mol Microbiol 2022; 118:244-257. [DOI: 10.1111/mmi.14965] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/28/2022] [Revised: 07/13/2022] [Accepted: 07/14/2022] [Indexed: 11/28/2022]
Affiliation(s)
- Peiwen Lv
- State Key Laboratory of Microbial Technology Institute of Microbial Technology, Shandong University Qingdao P. R. China
| | - Yaru Li
- State Key Laboratory of Microbial Technology Institute of Microbial Technology, Shandong University Qingdao P. R. China
| | - Ruimin Wang
- State Key Laboratory of Microbial Technology Institute of Microbial Technology, Shandong University Qingdao P. R. China
| | - Ye Zhang
- State Key Laboratory of Microbial Technology Institute of Microbial Technology, Shandong University Qingdao P. R. China
| | - Wenkai Wang
- State Key Laboratory of Microbial Technology Institute of Microbial Technology, Shandong University Qingdao P. R. China
| | - Yuanxiang Liu
- State Key Laboratory of Microbial Technology Institute of Microbial Technology, Shandong University Qingdao P. R. China
| | - Yan Shang
- State Key Laboratory of Microbial Technology Institute of Microbial Technology, Shandong University Qingdao P. R. China
| | - Dandan Su
- State Key Laboratory of Microbial Technology Institute of Microbial Technology, Shandong University Qingdao P. R. China
| | - Wei Wang
- State Key Laboratory of Microbial Technology Institute of Microbial Technology, Shandong University Qingdao P. R. China
| | - Chunyu Yang
- State Key Laboratory of Microbial Technology Institute of Microbial Technology, Shandong University Qingdao P. R. China
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4
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Bulatova L, Savenkova D, Nurgalieva A, Reshetnikova D, Timonina A, Skripova V, Bogdanov M, Kiyamova R. Toward a Topology-Based Therapeutic Design of Membrane Proteins: Validation of NaPi2b Topology in Live Ovarian Cancer Cells. Front Mol Biosci 2022; 9:895911. [PMID: 35911971 PMCID: PMC9335355 DOI: 10.3389/fmolb.2022.895911] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/14/2022] [Accepted: 06/22/2022] [Indexed: 11/13/2022] Open
Abstract
NaPi2b is a sodium-dependent phosphate transporter that belongs to the SLC34 family of transporters which is mainly responsible for phosphate homeostasis in humans. Although NaPi2b is widely expressed in normal tissues, its overexpression has been demonstrated in ovarian, lung, and other cancers. A valuable set of antibodies, including L2 (20/3) and MX35, and its humanized versions react strongly with an antigen on the surface of ovarian and other carcinoma cells. Although the topology of NaPi2b was predicted in silico, no direct experimental data are available for the orientation of NaPi2b extracellular domains in cancer cells. The presented results of antibody mapping of untagged NaPi2b in live ovarian carcinoma cells OVCAR-4 provide a platform for current and future epitope-based cancer therapies and serological diagnostics.
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Affiliation(s)
- Leisan Bulatova
- Research Laboratory “Biomarker”, Institute of Fundamental Medicine and Biology, Kazan Federal University, Kazan, Russian Federation
| | - Daria Savenkova
- Research Laboratory “Biomarker”, Institute of Fundamental Medicine and Biology, Kazan Federal University, Kazan, Russian Federation
| | - Alsina Nurgalieva
- Research Laboratory “Biomarker”, Institute of Fundamental Medicine and Biology, Kazan Federal University, Kazan, Russian Federation
| | - Daria Reshetnikova
- Research Laboratory “Biomarker”, Institute of Fundamental Medicine and Biology, Kazan Federal University, Kazan, Russian Federation
| | - Arina Timonina
- Research Laboratory “Biomarker”, Institute of Fundamental Medicine and Biology, Kazan Federal University, Kazan, Russian Federation
| | - Vera Skripova
- Research Laboratory “Biomarker”, Institute of Fundamental Medicine and Biology, Kazan Federal University, Kazan, Russian Federation
| | - Mikhail Bogdanov
- Research Laboratory “Biomarker”, Institute of Fundamental Medicine and Biology, Kazan Federal University, Kazan, Russian Federation
- Department of Biochemistry and Molecular Biology, McGovern Medical School, the University of Texas Health Science Center, Houston, TX, United States
- *Correspondence: Ramziya Kiyamova, ; Mikhail Bogdanov,
| | - Ramziya Kiyamova
- Research Laboratory “Biomarker”, Institute of Fundamental Medicine and Biology, Kazan Federal University, Kazan, Russian Federation
- *Correspondence: Ramziya Kiyamova, ; Mikhail Bogdanov,
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5
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Staritzbichler R, Yaklich E, Sarti E, Ristic N, Hildebrand PW, Forrest LR. AlignMe: an update of the web server for alignment of membrane protein sequences. Nucleic Acids Res 2022; 50:W29-W35. [PMID: 35609986 PMCID: PMC9252776 DOI: 10.1093/nar/gkac391] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/03/2022] [Revised: 04/19/2022] [Accepted: 05/10/2022] [Indexed: 11/14/2022] Open
Abstract
The AlignMe web server is dedicated to accurately aligning sequences of membrane proteins, a particularly challenging task due to the strong evolutionary divergence and the low compositional complexity of hydrophobic membrane-spanning proteins. AlignMe can create pairwise alignments of either two primary amino acid sequences or two hydropathy profiles. The web server for AlignMe has been continuously available for >10 years, supporting 1000s of users per year. Recent improvements include anchoring, multiple submissions, and structure visualization. Anchoring is the ability to constrain a position in an alignment, which allows expert information about related residues in proteins to be incorporated into an alignment without manual modification. The original web interface to the server limited the user to one alignment per submission, hindering larger scale studies. Now, batches of alignments can be initiated with a single submission. Finally, to provide structural context for the relationship between proteins, sequence similarity can now be mapped onto one or more structures (or structural models) of the proteins being aligned, by links to MutationExplorer, a web-based visualization tool. Together with a refreshed user interface, these features further enhance an important resource in the membrane protein community. The AlignMe web server is freely available at https://www.bioinfo.mpg.de/AlignMe/.
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Affiliation(s)
- René Staritzbichler
- University of Leipzig, Institute of Medical Physics and Biophysics, Härtelstr. 16-18, 04107 Leipzig, Germany
| | - Emily Yaklich
- Computational Structural Biology Section, National Institutes of Neurological Disorders and Stroke, National Institutes of Health, Bethesda, MD 20892, USA
| | - Edoardo Sarti
- Algorithms, Biology, Structure Unit Inria Sophia Antipolis - Méditerranée, 06902 Valbonne, France
| | - Nikola Ristic
- University of Leipzig, Institute of Medical Physics and Biophysics, Härtelstr. 16-18, 04107 Leipzig, Germany
| | - Peter W Hildebrand
- University of Leipzig, Institute of Medical Physics and Biophysics, Härtelstr. 16-18, 04107 Leipzig, Germany.,Charité -Universitätsmedizin Berlin, corporate member of Freie Universität Berlin and Humboldt-Universität zu Berlin, Institute of Medical Physics and Biophysics, 10117 Berlin, Germany
| | - Lucy R Forrest
- Computational Structural Biology Section, National Institutes of Neurological Disorders and Stroke, National Institutes of Health, Bethesda, MD 20892, USA
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6
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Jönsson ÅLM, Hernando N, Knöpfel T, Mogensen S, Bendstrup E, Hilberg O, Christensen JH, Simonsen U, Wagner CA. Impaired phosphate transport in SLC34A2 variants in patients with pulmonary alveolar microlithiasis. Hum Genomics 2022; 16:13. [PMID: 35443721 PMCID: PMC9019944 DOI: 10.1186/s40246-022-00387-y] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/31/2021] [Accepted: 03/23/2022] [Indexed: 11/26/2022] Open
Abstract
BACKGROUND Variants in SLC34A2 encoding the sodium-dependent phosphate transport protein 2b (NaPi-IIb) cause the rare lung disease pulmonary alveolar microlithiasis (PAM). PAM is characterised by the deposition of calcium-phosphate concretions in the alveoli usually progressing over time. No effective treatment is available. So far, 30 allelic variants in patients have been reported but only a few have been functionally characterised. This study aimed to determine the impact of selected SLC34A2 variants on transporter expression and phosphate uptake in cellular studies. METHODS Two nonsense variants (c.910A > T and c.1456C > T), one frameshift (c.1328delT), and one in-frame deletion (c.1402_1404delACC) previously reported in patients with PAM were selected for investigation. Wild-type and mutant c-Myc-tagged human NaPi-IIb constructs were expressed in Xenopus laevis oocytes. The transport function was investigated with a 32Pi uptake assay. NaPi-IIb protein expression and localisation were determined with immunoblotting and immunohistochemistry, respectively. RESULTS Oocytes injected with the wild-type human NaPi-IIb construct had significant 32Pi transport compared to water-injected oocytes. In addition, the protein had a molecular weight as expected for the glycosylated form, and it was readily detectable in the oocyte membrane. Although the protein from the Thr468del construct was synthesised and expressed in the oocyte membrane, phosphate transport was similar to non-injected control oocytes. All other mutants were non-functional and not expressed in the membrane, consistent with the expected impact of the truncations caused by premature stop codons. CONCLUSIONS Of four analysed SLC34A2 variants, only the Thr468del showed similar protein expression as the wild-type cotransporter in the oocyte membrane. All mutant transporters were non-functional, supporting that dysfunction of NaPi-IIb underlies the pathology of PAM.
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Affiliation(s)
- Åsa Lina M. Jönsson
- Department of Biomedicine, Aarhus University, Aarhus, Denmark
- Department of Clinical Genetics, Aarhus University Hospital, Aarhus, Denmark
| | - Nati Hernando
- Institute of Physiology, University of Zurich, Zurich, Switzerland
- Swiss National Center of Competence in Research NCCR Kidney.CH, Zurich, Switzerland
| | - Thomas Knöpfel
- Institute of Physiology, University of Zurich, Zurich, Switzerland
- Swiss National Center of Competence in Research NCCR Kidney.CH, Zurich, Switzerland
| | - Susie Mogensen
- Department of Biomedicine, Aarhus University, Aarhus, Denmark
| | - Elisabeth Bendstrup
- Centre for Rare Lung Diseases, Department of Respiratory Diseases and Allergy, Aarhus University Hospital, Aarhus, Denmark
| | - Ole Hilberg
- Medical Department, Vejle Hospital, Vejle, Denmark
| | | | - Ulf Simonsen
- Department of Biomedicine, Aarhus University, Aarhus, Denmark
| | - Carsten A. Wagner
- Institute of Physiology, University of Zurich, Zurich, Switzerland
- Swiss National Center of Competence in Research NCCR Kidney.CH, Zurich, Switzerland
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7
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Sauer DB, Wang B, Sudar JC, Song J, Marden J, Rice WJ, Wang DN. The ups and downs of elevator-type di-/tricarboxylate membrane transporters. FEBS J 2022; 289:1515-1523. [PMID: 34403567 PMCID: PMC9832446 DOI: 10.1111/febs.16158] [Citation(s) in RCA: 8] [Impact Index Per Article: 4.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/03/2021] [Revised: 07/27/2021] [Accepted: 08/16/2021] [Indexed: 01/13/2023]
Abstract
The divalent anion sodium symporter (DASS) family contains both sodium-driven anion cotransporters and anion/anion exchangers. The family belongs to a broader ion transporter superfamily (ITS), which comprises 24 families of transporters, including those of AbgT antibiotic efflux transporters. The human proteins in the DASS family play major physiological roles and are drug targets. We recently determined multiple structures of the human sodium-dependent citrate transporter (NaCT) and the succinate/dicarboxylate transporter from Lactobacillus acidophilus (LaINDY). Structures of both proteins show high degrees of structural similarity to the previously determined VcINDY fold. Conservation between these DASS protein structures and those from the AbgT family indicates that the VcINDY fold represents the overall protein structure for the entire ITS. The new structures of NaCT and LaINDY are captured in the inward- or outward-facing conformations, respectively. The domain arrangements in these structures agree with a rigid body elevator-type transport mechanism for substrate translocation across the membrane. Two separate NaCT structures in complex with a substrate or an inhibitor allowed us to explain the inhibition mechanism and propose a detailed classification scheme for grouping disease-causing mutations in the human protein. Structural understanding of multiple kinetic states of DASS proteins is a first step toward the detailed characterization of their entire transport cycle.
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Affiliation(s)
- David B. Sauer
- Skirball Institute of Biomolecular Medicine, New York University School of Medicine, New York, NY 10016, USA
| | - Bing Wang
- Cryo-Electron Microscopy Core, New York University School of Medicine, New York, NY 10016, USA
| | - Joseph C. Sudar
- Skirball Institute of Biomolecular Medicine, New York University School of Medicine, New York, NY 10016, USA
| | - Jinmei Song
- Skirball Institute of Biomolecular Medicine, New York University School of Medicine, New York, NY 10016, USA
| | - Jennifer Marden
- Skirball Institute of Biomolecular Medicine, New York University School of Medicine, New York, NY 10016, USA
| | - William J. Rice
- Cryo-Electron Microscopy Core, New York University School of Medicine, New York, NY 10016, USA
| | - Da-Neng Wang
- Skirball Institute of Biomolecular Medicine, New York University School of Medicine, New York, NY 10016, USA
- Department of Cell Biology, New York University School of Medicine, New York, NY 10016, USA
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8
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Dai YS, Pei WL, Wang YY, Wang Z, Zhuo MQ. Topology, tissue distribution, and transcriptional level of SLC34s in response to Pi and pH in grass carp Ctenopharyngodon idella. FISH PHYSIOLOGY AND BIOCHEMISTRY 2021; 47:1383-1393. [PMID: 34282499 DOI: 10.1007/s10695-021-00981-2] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 04/06/2021] [Accepted: 06/24/2021] [Indexed: 06/13/2023]
Abstract
In the present study, two new SLC34 family members, named slc34a1b and slc34a2a, were isolated and characterized from grass carp Ctenopharyngodon idella. Topology, tissue distribution, and transcriptional response to phosphorus (Pi) and pH were compared among three members of SLC34 family (slc34a1b, slc34a2a, and slc34a2b) in grass carp. The length of validated cDNAs of grass carp slc34a1b and slc34a2a was 1494 bp and 1902 bp, and these two cDNAs encoded 497 and 633 amino acid residues, respectively. The domain analysis showed that three SLC34 members of grass carp contain architecture similar to that in mammals. Moreover, the mRNA of three slc34s was widely expressed in nine tissues (heart, brain, intestine, kidney, liver, muscle, gill, spleen, and skin), but at various levels. Our results revealed that 6 mM and 9 mM Pi incubation significantly reduced the mRNA expression of three slc34s in both CIK and L8824 cell lines from grass carp. The expression of slc34a1b was decreased in the CIK cells, but not in the L8824 cells after 3 mM Pi incubation. In CIK cells, 3 mM Pi incubation downregulated the expression of slc34a1b and slc34a2a, but not slc34a2b. In addition, the expression of three slc34s was significantly reduced at acidic pH in the CIK cells. Taken together, we characterized three SLC34 family members, revealed their specific distribution among different tissues, and elucidated their transcriptional responses to Pi and pH in two cell lines from grass carp. Our findings provide an insight into the physiological function of three SLC34s in fish.
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Affiliation(s)
- Yong-Shuang Dai
- School of Animal Science and Nutritional Engineering, Wuhan Polytechnic University, Wuhan, 430070, China
| | - Wen-Li Pei
- School of Animal Science and Nutritional Engineering, Wuhan Polytechnic University, Wuhan, 430070, China
| | - Yuan-Yuan Wang
- School of Animal Science and Nutritional Engineering, Wuhan Polytechnic University, Wuhan, 430070, China
| | - Zhe Wang
- School of Animal Science and Nutritional Engineering, Wuhan Polytechnic University, Wuhan, 430070, China
| | - Mei-Qin Zhuo
- School of Animal Science and Nutritional Engineering, Wuhan Polytechnic University, Wuhan, 430070, China.
- Laboratory of Molecular Nutrition for Aquatic Economic Animals, Fishery College, Huazhong Agricultural University, Wuhan, 430070, China.
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9
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Pastor-Arroyo EM, Rodriguez JMM, Pellegrini G, Bettoni C, Levi M, Hernando N, Wagner CA. Constitutive depletion of Slc34a2/NaPi-IIb in rats causes perinatal mortality. Sci Rep 2021; 11:7943. [PMID: 33846411 PMCID: PMC8042035 DOI: 10.1038/s41598-021-86874-z] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/10/2020] [Accepted: 03/15/2021] [Indexed: 11/23/2022] Open
Abstract
Absorption of dietary phosphate (Pi) across intestinal epithelia is a regulated process mediated by transcellular and paracellular pathways. Although hyperphosphatemia is a risk factor for the development of cardiovascular disease, the amount of ingested Pi in a typical Western diet is above physiological needs. While blocking intestinal absorption has been suggested as a therapeutic approach to prevent hyperphosphatemia, a complete picture regarding the identity and regulation of the mechanism(s) responsible for intestinal absorption of Pi is missing. The Na+/Pi cotransporter NaPi-IIb is a secondary active transporter encoded by the Slc34a2 gene. This transporter has a wide tissue distribution and within the intestinal tract is located at the apical membrane of epithelial cells. Based on mouse models deficient in NaPi-IIb, this cotransporter is assumed to mediate the bulk of active intestinal absorption of Pi. However, whether or not this is also applicable to humans is unknown, since human patients with inactivating mutations in SLC34A2 have not been reported to suffer from Pi depletion. Thus, mice may not be the most appropriate experimental model for the translation of intestinal Pi handling to humans. Here, we describe the generation of a rat model with Crispr/Cas-driven constitutive depletion of Slc34a2. Slc34a2 heterozygous rats were indistinguishable from wild type animals under standard dietary conditions as well as upon 3 days feeding on low Pi. However, unlike in humans, homozygosity resulted in perinatal lethality.
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Affiliation(s)
- Eva Maria Pastor-Arroyo
- Institute of Physiology, University of Zürich, Winterthurerstrasse 190, 8057, Zurich, Switzerland
| | - Josep M Monné Rodriguez
- Laboratory for Animal Model Pathology (LAMP), Institute of Veterinary Pathology, Vetsuisse Faculty, University of Zurich, Winterthurerstrasse 268, 8057, Zurich, Switzerland
| | - Giovanni Pellegrini
- Laboratory for Animal Model Pathology (LAMP), Institute of Veterinary Pathology, Vetsuisse Faculty, University of Zurich, Winterthurerstrasse 268, 8057, Zurich, Switzerland
| | - Carla Bettoni
- Institute of Physiology, University of Zürich, Winterthurerstrasse 190, 8057, Zurich, Switzerland
| | - Moshe Levi
- Department of Biochemistry and Molecular and Cellular Biology, Georgetown University, Washington, DC, USA
| | - Nati Hernando
- Institute of Physiology, University of Zürich, Winterthurerstrasse 190, 8057, Zurich, Switzerland.
| | - Carsten A Wagner
- Institute of Physiology, University of Zürich, Winterthurerstrasse 190, 8057, Zurich, Switzerland.
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10
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De Paolis E, Scaglione GL, De Bonis M, Minucci A, Capoluongo E. CYP24A1 and SLC34A1 genetic defects associated with idiopathic infantile hypercalcemia: from genotype to phenotype. Clin Chem Lab Med 2020; 57:1650-1667. [PMID: 31188746 DOI: 10.1515/cclm-2018-1208] [Citation(s) in RCA: 18] [Impact Index Per Article: 4.5] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/12/2018] [Accepted: 02/22/2019] [Indexed: 02/07/2023]
Abstract
Loss of function mutations in the CYP24A1 gene, involved in vitamin D catabolism and in calcium homeostasis, are known to be the genetic drivers of both idiopathic infantile hypercalcemia (IIH) and adult renal stone disease. Recently, also defects in the SLC34A1 gene, encoding for the renal sodium-phosphate transporter NaPi-IIa, were associated with the disease. IIH typically affects infants and pediatric patients with a syndrome characterized by severe hypercalcemia, hypercalciuria, suppressed parathyroid hormone level and nephrolithiasis. In SLC34A1 mutated carriers, hypophosphatemia is also a typical biochemical tract. IIH may also persist undiagnosed into adulthood, causing an increased risk of nephrocalcinosis and renal complication. To note, a clinical heterogeneity characterizes IIH manifestation, principally due to the controversial gene-dose effect and, to the strong influence of environmental factors. The present review is aimed to provide an overview of the current molecular findings on the IIH disorder, giving a comprehensive description of the association between genotype and biochemical and clinical phenotype of the affected patients. We also underline that patients may benefit from genetic testing into a targeted diagnostic and therapeutic workflow.
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Affiliation(s)
- Elisa De Paolis
- Laboratory of Molecular Diagnostics and Genomics, Teaching and Research Hospital "Fondazione Policlinico Agostino Gemelli" - IRCCS, Catholic University of the Sacred Heart, Rome, Italy
| | - Giovanni Luca Scaglione
- Laboratory of Molecular Oncology, "Fondazione Giovanni Paolo II", Catholic University of Sacred Heart, Campobasso, Italy
| | - Maria De Bonis
- Laboratory of Molecular Diagnostics and Genomics, Teaching and Research Hospital "Fondazione Policlinico Agostino Gemelli" - IRCCS, Catholic University of the Sacred Heart, Rome, Italy
| | - Angelo Minucci
- Laboratory of Molecular Diagnostics and Genomics, Teaching and Research Hospital "Fondazione Policlinico Agostino Gemelli" - IRCCS, Catholic University of the Sacred Heart, Rome, Italy
| | - Ettore Capoluongo
- Laboratory of Molecular Diagnostics and Genomics, Teaching and Research Hospital "Fondazione Policlinico Agostino Gemelli" - IRCCS, Catholic University of the Sacred Heart, Rome, Italy
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11
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Tsai JY, Chu CH, Lin MG, Chou YH, Hong RY, Yen CY, Hsiao CD, Sun YJ. Structure of the sodium-dependent phosphate transporter reveals insights into human solute carrier SLC20. SCIENCE ADVANCES 2020; 6:eabb4024. [PMID: 32821837 PMCID: PMC7413737 DOI: 10.1126/sciadv.abb4024] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 02/21/2020] [Accepted: 06/26/2020] [Indexed: 05/14/2023]
Abstract
Inorganic phosphate (Pi) is a fundamental and essential element for nucleotide biosynthesis, energy supply, and cellular signaling in living organisms. Human phosphate transporter (hPiT) dysfunction causes numerous diseases, but the molecular mechanism underlying transporters remains elusive. We report the structure of the sodium-dependent phosphate transporter from Thermotoga maritima (TmPiT) in complex with sodium and phosphate (TmPiT-Na/Pi) at 2.3-angstrom resolution. We reveal that one phosphate and two sodium ions (Pi-2Na) are located at the core of TmPiT and that the third sodium ion (Nafore) is located near the inner membrane boundary. We propose an elevator-like mechanism for sodium and phosphate transport by TmPiT, with the TmPiT-Na/Pi complex adopting an inward occluded conformation. We found that disease-related hPiT variants carry mutations in the corresponding sodium- and phosphate-binding residues identified in TmPiT. Our three-dimensional structure of TmPiT provides a framework for understanding PiT dysfunction and for future structure-based drug design.
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Affiliation(s)
- Jia-Yin Tsai
- Department of Life Science and Institute of Bioinformatics and Structural Biology, College of Life Science, National Tsing Hua University, Hsinchu 30013, Taiwan (R.O.C.)
| | - Chen-Hsi Chu
- Department of Life Science and Institute of Bioinformatics and Structural Biology, College of Life Science, National Tsing Hua University, Hsinchu 30013, Taiwan (R.O.C.)
| | - Min-Guan Lin
- Institute of Molecular Biology, Academia Sinica, Taipei 11529, Taiwan (R.O.C.)
| | - Ying-Hsuan Chou
- Department of Life Science and Institute of Bioinformatics and Structural Biology, College of Life Science, National Tsing Hua University, Hsinchu 30013, Taiwan (R.O.C.)
| | - Ruei-Yi Hong
- Department of Life Science and Institute of Bioinformatics and Structural Biology, College of Life Science, National Tsing Hua University, Hsinchu 30013, Taiwan (R.O.C.)
| | - Cheng-Yi Yen
- Department of Life Science and Institute of Bioinformatics and Structural Biology, College of Life Science, National Tsing Hua University, Hsinchu 30013, Taiwan (R.O.C.)
| | - Chwan-Deng Hsiao
- Institute of Molecular Biology, Academia Sinica, Taipei 11529, Taiwan (R.O.C.)
- Corresponding author. (C.-D.H.); (Y.-J.S.)
| | - Yuh-Ju Sun
- Department of Life Science and Institute of Bioinformatics and Structural Biology, College of Life Science, National Tsing Hua University, Hsinchu 30013, Taiwan (R.O.C.)
- Corresponding author. (C.-D.H.); (Y.-J.S.)
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12
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Abstract
Phosphate is an essential nutrient for life and is a critical component of bone formation, a major signaling molecule, and structural component of cell walls. Phosphate is also a component of high-energy compounds (i.e., AMP, ADP, and ATP) and essential for nucleic acid helical structure (i.e., RNA and DNA). Phosphate plays a central role in the process of mineralization, normal serum levels being associated with appropriate bone mineralization, while high and low serum levels are associated with soft tissue calcification. The serum concentration of phosphate and the total body content of phosphate are highly regulated, a process that is accomplished by the coordinated effort of two families of sodium-dependent transporter proteins. The three isoforms of the SLC34 family (SLC34A1-A3) show very restricted tissue expression and regulate intestinal absorption and renal excretion of phosphate. SLC34A2 also regulates the phosphate concentration in multiple lumen fluids including milk, saliva, pancreatic fluid, and surfactant. Both isoforms of the SLC20 family exhibit ubiquitous expression (with some variation as to which one or both are expressed), are regulated by ambient phosphate, and likely serve the phosphate needs of the individual cell. These proteins exhibit similarities to phosphate transporters in nonmammalian organisms. The proteins are nonredundant as mutations in each yield unique clinical presentations. Further research is essential to understand the function, regulation, and coordination of the various phosphate transporters, both the ones described in this review and the phosphate transporters involved in intracellular transport.
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Affiliation(s)
- Nati Hernando
- University of Zurich-Irchel, Institute of Physiology, Zurich, Switzerland; Department of Medicine, University of Louisville School of Medicine, Louisville, Kentucky; and Robley Rex VA Medical Center, Louisville, Kentucky
| | - Kenneth Gagnon
- University of Zurich-Irchel, Institute of Physiology, Zurich, Switzerland; Department of Medicine, University of Louisville School of Medicine, Louisville, Kentucky; and Robley Rex VA Medical Center, Louisville, Kentucky
| | - Eleanor Lederer
- University of Zurich-Irchel, Institute of Physiology, Zurich, Switzerland; Department of Medicine, University of Louisville School of Medicine, Louisville, Kentucky; and Robley Rex VA Medical Center, Louisville, Kentucky
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13
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Abstract
Over the past 25 years, successive cloning of SLC34A1, SLC34A2 and SLC34A3, which encode the sodium-dependent inorganic phosphate (Pi) cotransport proteins 2a-2c, has facilitated the identification of molecular mechanisms that underlie the regulation of renal and intestinal Pi transport. Pi and various hormones, including parathyroid hormone and phosphatonins, such as fibroblast growth factor 23, regulate the activity of these Pi transporters through transcriptional, translational and post-translational mechanisms involving interactions with PDZ domain-containing proteins, lipid microdomains and acute trafficking of the transporters via endocytosis and exocytosis. In humans and rodents, mutations in any of the three transporters lead to dysregulation of epithelial Pi transport with effects on serum Pi levels and can cause cardiovascular and musculoskeletal damage, illustrating the importance of these transporters in the maintenance of local and systemic Pi homeostasis. Functional and structural studies have provided insights into the mechanism by which these proteins transport Pi, whereas in vivo and ex vivo cell culture studies have identified several small molecules that can modify their transport function. These small molecules represent potential new drugs to help maintain Pi homeostasis in patients with chronic kidney disease - a condition that is associated with hyperphosphataemia and severe cardiovascular and skeletal consequences.
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14
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Scheerer U, Netzer F, Bauer AF, Herschbach C. Measurements of 18 O-P i uptake indicate fast metabolism of phosphate in tree roots. PLANT BIOLOGY (STUTTGART, GERMANY) 2019; 21:565-570. [PMID: 30311347 DOI: 10.1111/plb.12922] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 07/20/2018] [Accepted: 10/07/2018] [Indexed: 06/08/2023]
Abstract
Phosphorus (P) nutrition of beech ecosystems depends on soil processes, plant internal P cycling and P acquisition. P uptake of trees in the field is currently not validated due to the lack of an experimental approach applicable in natural forests. Application of radiolabelled tracers such as 33 P and 32 P is limited to special research sites and not allowed in natural environments. Moreover, only one stable isotope of P, namely 31 P, exists. One alternative tool to measure P acquisition in the field could be the use of 18 O-labelled 31 P-phosphate (31 P18 O4 3- ). Phosphate (Pi ) uptake rates calculated from the 18 O enrichment of dried root material after application of 31 Pi 18 O4 3- via nutrient solution was always lower compared to 33 P incorporation, did not show increasing rates of Pi uptake at P deficiency under controlled conditions, and did not reveal seasonal fluctuations in the field. Consequently, a clear correlation between 33 P-based and 18 O-based Pi uptake by roots could not be established. Comparison of Pi uptake rates achieved from 33 P-Pi and 18 O-Pi application led to the conclusion of high Pi metabolism in roots after Pi uptake. The replacement of 18 O by 16 O from water in 18 O-Pi during root influx, but most probably after Pi uptake into roots, due to metabolic activities, indicates high and fast turnover of Pi . Hence, the use of 18 O-Pi as an alternative tool to estimate Pi acquisition of trees in the field must consider the increase of 18 O abundance in root water that was disregarded in dried root material.
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Affiliation(s)
- U Scheerer
- Chair of Tree Physiology, Institute of Forest Sciences, Albert-Ludwigs-University Freiburg, Freiburg, Germany
| | - F Netzer
- Chair of Tree Physiology, Institute of Forest Sciences, Albert-Ludwigs-University Freiburg, Freiburg, Germany
- Chair of Ecosystem Physiology, Institute of Forest Sciences, Albert-Ludwigs-University Freiburg, Freiburg, Germany
| | - A F Bauer
- Chair of Tree Physiology, Institute of Forest Sciences, Albert-Ludwigs-University Freiburg, Freiburg, Germany
| | - C Herschbach
- Chair of Tree Physiology, Institute of Forest Sciences, Albert-Ludwigs-University Freiburg, Freiburg, Germany
- Chair of Ecosystem Physiology, Institute of Forest Sciences, Albert-Ludwigs-University Freiburg, Freiburg, Germany
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15
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Wagner CA, Rubio-Aliaga I, Hernando N. Renal phosphate handling and inherited disorders of phosphate reabsorption: an update. Pediatr Nephrol 2019; 34:549-559. [PMID: 29275531 DOI: 10.1007/s00467-017-3873-3] [Citation(s) in RCA: 47] [Impact Index Per Article: 9.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 09/01/2017] [Revised: 12/08/2017] [Accepted: 12/12/2017] [Indexed: 01/12/2023]
Abstract
Renal phosphate handling critically determines plasma phosphate and whole body phosphate levels. Filtered phosphate is mostly reabsorbed by Na+-dependent phosphate transporters located in the brush border membrane of the proximal tubule: NaPi-IIa (SLC34A1), NaPi-IIc (SLC34A3), and Pit-2 (SLC20A2). Here we review new evidence for the role and relevance of these transporters in inherited disorders of renal phosphate handling. The importance of NaPi-IIa and NaPi-IIc for renal phosphate reabsorption and mineral homeostasis has been highlighted by the identification of mutations in these transporters in a subset of patients with infantile idiopathic hypercalcemia and patients with hereditary hypophosphatemic rickets with hypercalciuria. Both diseases are characterized by disturbed calcium homeostasis secondary to elevated 1,25-(OH)2 vitamin D3 as a consequence of hypophosphatemia. In vitro analysis of mutated NaPi-IIa or NaPi-IIc transporters suggests defective trafficking underlying disease in most cases. Monoallelic pathogenic mutations in both SLC34A1 and SLC34A3 appear to be very frequent in the general population and have been associated with kidney stones. Consistent with these findings, results from genome-wide association studies indicate that variants in SLC34A1 are associated with a higher risk to develop kidney stones and chronic kidney disease, but underlying mechanisms have not been addressed to date.
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Affiliation(s)
- Carsten A Wagner
- Institute of Physiology, University of Zurich, Winterthurerstrasse 190, 8057, Zurich, Switzerland. .,National Center for Competence in Research (NCCR) Kidney.CH, Zurich, Switzerland.
| | - Isabel Rubio-Aliaga
- Institute of Physiology, University of Zurich, Winterthurerstrasse 190, 8057, Zurich, Switzerland.,National Center for Competence in Research (NCCR) Kidney.CH, Zurich, Switzerland
| | - Nati Hernando
- Institute of Physiology, University of Zurich, Winterthurerstrasse 190, 8057, Zurich, Switzerland.,National Center for Competence in Research (NCCR) Kidney.CH, Zurich, Switzerland
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16
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Abstract
Calcium kidney stones are common worldwide. Most are idiopathic and composed of calcium oxalate. Calcium phosphate is present in around 80% and may initiate stone formation. Stone production is multifactorial with a polygenic genetic contribution. Phosphaturia is found frequently among stone formers but until recently received scant attention. This review examines possible mechanisms for the phosphaturia and its relevance to stone formation from a wide angle. There is a striking lack of clinical data. Phosphaturia is associated, but not correlated, with hypercalciuria, increased 1,25 dihydroxy-vitamin D [1,25 (OH)2D], and sometimes evidence of disturbances in proximal renal tubular function. Phosphate reabsorption in the proximal renal tubules requires tightly regulated interaction of many proteins. Paracellular flow through intercellular tight junctions is the major route of phosphate absorption from the intestine and can be reduced therapeutically in hyperphosphatemic patients. In monogenic defects stones develop when phosphaturia is associated with hypercalciuria, generally explained by increased 1,25 (OH)2D production in response to hypophosphatemia. Calcification does not occur in disorders with increased FGF23 when phosphaturia occurs in isolation and 1,25 (OH)2D is suppressed. Candidate gene studies have identified mutations in the phosphate transporters, but in few individuals. One genome-wide study identified a polymorphism of the phosphate transporter gene SLC34A4 associated with stones. Others did not find mutations obviously linked to phosphate reabsorption. Future genetic studies should have a wide trawl and should focus initially on groups of patients with clearly defined phenotypes. The global data should be pooled.
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Affiliation(s)
- Valerie Walker
- Department of Clinical Biochemistry, University Hospital Southampton NHS Foundation Trust, Southampton, United Kingdom.
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17
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Guillén N, Caldas YA, Levi M, Sorribas V. Identification and expression analysis of type II and type III P i transporters in the opossum kidney cell line. Exp Physiol 2018; 104:149-161. [PMID: 30379374 DOI: 10.1113/ep087217] [Citation(s) in RCA: 6] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/01/2018] [Accepted: 10/30/2018] [Indexed: 12/25/2022]
Abstract
NEW FINDINGS What is the central question of this study? The opossum kidney (OK) cell line is the main in vitro model of proximal tubular Pi transport, but it is incomplete because only the NaPiIIa Pi transporter has been identified. What is the main finding and its importance? We have cloned and characterized the Pi transporters NaPiIIc, PiT1 and PiT2 from OK cells and have analysed the relevance of the four transporters to Pi transport. All four transporters are involved in the upregulated Pi transport of cells incubated using a low-Pi medium, and only PiT1 is not involved in basal transport. ABSTRACT The apical membrane of renal proximal tubular epithelial cells is the main controller of phosphate homeostasis, because it determines the rate of urinary Pi excretion. The opossum kidney (OK) cell line is a good model for studying this function, but only NaPiIIa (NaPi4) has been identified to date as a Pi transporter in this cell line. In this work, we have identified three additional Pi transporters that are present in OK cells: NaPiIIc, PiT1 and PiT2. All three sequences are similar to the corresponding orthologues, but PiT1 is missing the first transmembrane domain. Confluent cells exhibit characteristics of type II Pi transport, which increases with alkalinity and is inhibited by phosphonoformic acid (PFA), and they mainly express NaPiIIa and NaPiIIc, with a low abundance of PiT1 and PiT2. Proliferating cells show a higher expression of PiT1 and PiT2 and a low expression of NaPiIIa and NaPiIIc. Adaptation to a low Pi concentration for 24 h induces the expression of RNA from NaPiIIa and NaPiIIc, which is not prevented by actinomycin D. Small interfering RNA transfections revealed that PiT1 is not necessary for Pi transport, but it is necessary for adaptation to a low Pi , similar to NaPiIIa and PiT2. Our study reveals the complexity of the coordination between the four Pi transporters, the variability of RNA expression according to confluence and the heterogeneous correlation between Pi transport and RNA levels.
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Affiliation(s)
- Natalia Guillén
- Department of Toxicology, University of Zaragoza, Zaragoza, Spain
| | - Yupanqui A Caldas
- Department of Toxicology, University of Zaragoza, Zaragoza, Spain.,Division of Renal Diseases and Hypertension, Department of Medicine, University of Colorado Denver, Aurora, CO, USA
| | - Moshe Levi
- Division of Renal Diseases and Hypertension, Department of Medicine, University of Colorado Denver, Aurora, CO, USA.,Department of Biochemistry and Molecular and Cellular Biology, Georgetown University, Washington, DC, USA
| | - Víctor Sorribas
- Department of Toxicology, University of Zaragoza, Zaragoza, Spain
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18
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Forster IC. The molecular mechanism of SLC34 proteins: insights from two decades of transport assays and structure-function studies. Pflugers Arch 2018; 471:15-42. [PMID: 30244375 DOI: 10.1007/s00424-018-2207-z] [Citation(s) in RCA: 17] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/01/2018] [Revised: 09/06/2018] [Accepted: 09/11/2018] [Indexed: 01/08/2023]
Abstract
The expression cloning some 25 years ago of the first member of SLC34 solute carrier family, the renal sodium-coupled inorganic phosphate cotransporter (NaPi-IIa) from rat and human tissue, heralded a new era of research into renal phosphate handling by focussing on the carrier proteins that mediate phosphate transport. The cloning of NaPi-IIa was followed by that of the intestinal NaPi-IIb and renal NaPi-IIc isoforms. These three proteins constitute the main secondary-active Na+-driven pathways for apical entry of inorganic phosphate (Pi) across renal and intestinal epithelial, as well as other epithelial-like organs. The key role these proteins play in mammalian Pi homeostasis was revealed in the intervening decades by numerous in vitro and animal studies, including the development of knockout animals for each gene and the detection of naturally occurring mutations that can lead to Pi-handling dysfunction in humans. In addition to characterising their physiological regulation, research has also focused on understanding the underlying transport mechanism and identifying structure-function relationships. Over the past two decades, this research effort has used real-time electrophysiological and fluorometric assays together with novel computational biology strategies to develop a detailed, but still incomplete, understanding of the transport mechanism of SLC34 proteins at the molecular level. This review will focus on how our present understanding of their molecular mechanism has evolved in this period by highlighting the key experimental findings.
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Affiliation(s)
- Ian C Forster
- Ion Channels and Human Diseases Laboratory, Florey Institute of Neuroscience and Mental Health, 30 Royal Parade, Parkville, VIC, 3052, Australia.
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19
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Structural models of the NaPi-II sodium-phosphate cotransporters. Pflugers Arch 2018; 471:43-52. [PMID: 30175376 PMCID: PMC6325988 DOI: 10.1007/s00424-018-2197-x] [Citation(s) in RCA: 10] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/22/2018] [Revised: 08/09/2018] [Accepted: 08/15/2018] [Indexed: 01/25/2023]
Abstract
Progress towards understanding the molecular mechanisms of phosphate homeostasis through sodium-dependent transmembrane uptake has long been stymied by the absence of structural information about the NaPi-II sodium-phosphate transporters. For many other coupled transporters, even those unrelated to NaPi-II, internal repeated elements have been revealed as a key feature that is inherent to their function. Here, we review recent structure prediction studies for NaPi-II transporters. Attempts to identify structural templates for NaPi-II transporters have leveraged the structural repeat perspective to uncover an otherwise obscured relationship with the dicarboxylate-sodium symporters (DASS). This revelation allowed the prediction of three-dimensional structural models of human NaPi-IIa and flounder NaPi-IIb, whose folds were evaluated by comparison with available biochemical data outlining the transmembrane topology and solvent accessibility of various regions of the protein. Using these structural models, binding sites for sodium and phosphate were proposed. The predicted sites were tested and refined based on detailed electrophysiological and biochemical studies and were validated by comparison with subsequently reported structures of transporters belonging to the AbgT family. Comparison with the DASS transporter VcINDY suggested a conformational mechanism involving a large, two-domain structural change, known as an elevator-like mechanism. These structural models provide a foundation for further studies into substrate binding, conformational change, kinetics, and energetics of sodium-phosphate transport. We discuss future opportunities, as well as the challenges that remain.
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20
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Hernando N, Wagner CA. Mechanisms and Regulation of Intestinal Phosphate Absorption. Compr Physiol 2018; 8:1065-1090. [PMID: 29978897 DOI: 10.1002/cphy.c170024] [Citation(s) in RCA: 41] [Impact Index Per Article: 6.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/26/2022]
Abstract
States of hypo- and hyperphosphatemia have deleterious consequences including rickets/osteomalacia and renal/cardiovascular disease, respectively. Therefore, the maintenance of appropriate plasma levels of phosphate is an essential requirement for health. This control is executed by the collaborative action of intestine and kidney whose capacities to (re)absorb phosphate are regulated by a number of hormonal and metabolic factors, among them parathyroid hormone, fibroblast growth factor 23, 1,25(OH)2 vitamin D3 , and dietary phosphate. The molecular mechanisms responsible for the transepithelial transport of phosphate across enterocytes are only partially understood. Indeed, whereas renal reabsorption entirely relies on well-characterized active transport mechanisms of phosphate across the renal proximal epithelia, intestinal absorption proceeds via active and passive mechanisms, with the molecular identity of the passive component still unknown. The active absorption of phosphate depends mostly on the activity and expression of the sodium-dependent phosphate cotransporter NaPi-IIb (SLC34A2), which is highly regulated by many of the factors, mentioned earlier. Physiologically, the contribution of NaPi-IIb to the maintenance of phosphate balance appears to be mostly relevant during periods of low phosphate availability. Therefore, its role in individuals living in industrialized societies with high phosphate intake is probably less relevant. Importantly, small increases in plasma phosphate, even within normal range, associate with higher risk of cardiovascular disease. Therefore, therapeutic approaches to treat hyperphosphatemia, including dietary phosphate restriction and phosphate binders, aim at reducing intestinal absorption. Here we review the current state of research in the field. © 2017 American Physiological Society. Compr Physiol 8:1065-1090, 2018.
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Affiliation(s)
- Nati Hernando
- National Center for Competence in Research NCCR Kidney.CH, Institute of Physiology, University Zurich-Irchel, Zurich, Switzerland
| | - Carsten A Wagner
- National Center for Competence in Research NCCR Kidney.CH, Institute of Physiology, University Zurich-Irchel, Zurich, Switzerland
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21
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Fearn A, Allison B, Rice SJ, Edwards N, Halbritter J, Bourgeois S, Pastor‐Arroyo EM, Hildebrandt F, Tasic V, Wagner CA, Hernando N, Sayer JA, Werner A. Clinical, biochemical, and pathophysiological analysis of SLC34A1 mutations. Physiol Rep 2018; 6:e13715. [PMID: 29924459 PMCID: PMC6010730 DOI: 10.14814/phy2.13715] [Citation(s) in RCA: 29] [Impact Index Per Article: 4.8] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/06/2018] [Revised: 04/30/2018] [Accepted: 05/01/2018] [Indexed: 12/11/2022] Open
Abstract
Mutations in SLC34A1, encoding the proximal tubular sodium-phosphate transporter NaPi-IIa, may cause a range of clinical phenotypes including infantile hypercalcemia, a proximal renal Fanconi syndrome, which are typically autosomal recessive, and hypophosphatemic nephrolithiasis, which may be an autosomal dominant trait. Here, we report two patients with mixed clinical phenotypes, both with metabolic acidosis, hyperphosphaturia, and renal stones. Patient A had a single heterozygous pathogenic missense mutation (p.I456N) in SLC34A1, consistent with the autosomal dominant pattern of renal stone disease in this family. Patient B, with an autosomal recessive pattern of disease, was compound heterozygous for SLC34A1 variants; a missense variant (p.R512C) together with a relatively common in-frame deletion p.V91A97del7 (91del7). Xenopus oocyte and renal (HKC-8) cell line transfection studies of the variants revealed limited cell surface localization, consistent with trafficking defects. Co-expression of wild-type and I456N and 91del7 appeared to cause intracellular retention in HKC-8, whereas the R512C mutant had a less dominant effect. Expression in Xenopus oocytes failed to demonstrate a significant dominant negative effect for I456N and R512C; however, a negative impact of 91del7 on [32 P]phosphate transport was found. In conclusion, we have investigated pathogenic alleles of SLC34A1 which contribute to both autosomal dominant and autosomal recessive renal stone disease.
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Affiliation(s)
- Amy Fearn
- Institute for Cell and Molecular BiosciencesMedical SchoolNewcastle UniversityNewcastleUnited Kingdom
| | - Benjamin Allison
- Institute for Cell and Molecular BiosciencesMedical SchoolNewcastle UniversityNewcastleUnited Kingdom
| | - Sarah J. Rice
- Institute of Genetic MedicineNewcastle UniversityNewcastleUnited Kingdom
| | - Noel Edwards
- Institute of Genetic MedicineNewcastle UniversityNewcastleUnited Kingdom
| | - Jan Halbritter
- Division of NephrologyDepartment of Internal MedicineUniversity Clinic LeipzigLeipzigGermany
| | | | | | - Friedhelm Hildebrandt
- Department of MedicineBoston Children's HospitalHarvard Medical SchoolBostonMassachusetts
| | - Velibor Tasic
- Medical Faculty SkopjeUniversity Children's HospitalSkopjeMacedonia
| | | | - Nati Hernando
- Institute of PhysiologyUniversity of ZurichZurichSwitzerland
| | - John A. Sayer
- Institute of Genetic MedicineNewcastle UniversityNewcastleUnited Kingdom
- Renal ServicesNewcastle Upon Tyne NHS Foundation TrustNewcastleUnited Kingdom
| | - Andreas Werner
- Institute for Cell and Molecular BiosciencesMedical SchoolNewcastle UniversityNewcastleUnited Kingdom
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22
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Colas C, Schlessinger A, Pajor AM. Mapping Functionally Important Residues in the Na +/Dicarboxylate Cotransporter, NaDC1. Biochemistry 2017; 56:4432-4441. [PMID: 28731330 DOI: 10.1021/acs.biochem.7b00503] [Citation(s) in RCA: 9] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Abstract
Transporters from the SLC13 family couple the transport of two to four Na+ ions with a di- or tricarboxylate, such as succinate or citrate. We have previously modeled mammalian members of the SLC13 family, including the Na+/dicarboxylate cotransporter NaDC1 (SLC13A2), based on a structure of the bacterial homologue VcINDY in an inward-facing conformation with one sodium ion bound at the Na1 site. In the study presented here, we modeled the outward-facing conformation of rabbit and human NaDC1 (rbNaDC1 and hNaDC1, respectively) using an outward-facing model of VcINDY as a template and identified residues in or near the putative Na2 and Na3 cation binding sites. Guided by the structural models in both conformations, we performed site-directed mutagenesis in rbNaDC1 for residues proposed to be in the Na+ or substrate binding sites. Cysteine substitution of T474 in the predicted Na2 binding site results in an inactive protein. The M539C mutant has a low apparent affinity for both sodium and lithium cations, suggesting that M539 may form part of the putative Na3 binding site. The Y432C and T86C mutants have increased Km values for succinate, supporting their proposed location in the outward-facing substrate binding site. In addition, cysteine labeling by MTSEA-biotin shows that Y432C is accessible from the outside of the cell, and the accessibility changes in the presence or absence of Na+. The results of this study improve our understanding of substrate and ion recognition in the mammalian members of the SLC13 family and provide a framework for developing conformationally specific inhibitors against these transporters.
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Affiliation(s)
- Claire Colas
- Department of Pharmacological Sciences, Icahn School of Medicine at Mount Sinai , New York, New York 10029, United States
| | - Avner Schlessinger
- Department of Pharmacological Sciences, Icahn School of Medicine at Mount Sinai , New York, New York 10029, United States
| | - Ana M Pajor
- Skaggs School of Pharmacy and Pharmaceutical Sciences, University of California-San Diego , La Jolla, California 92130-0714, United States
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23
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Cation Interactions and Membrane Potential Induce Conformational Changes in NaPi-IIb. Biophys J 2017; 111:973-88. [PMID: 27602725 DOI: 10.1016/j.bpj.2016.07.025] [Citation(s) in RCA: 15] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/21/2016] [Revised: 06/16/2016] [Accepted: 07/14/2016] [Indexed: 12/25/2022] Open
Abstract
Voltage-dependence of Na(+)-coupled phosphate cotransporters of the SLC34 family arises from displacement of charges intrinsic to the protein and the binding/release of one Na(+) ion in response to changes in the transmembrane electric field. Candidate coordination residues for the cation at the Na1 site were previously predicted by structural modeling using the x-ray structure of dicarboxylate transporter VcINDY as template and confirmed by functional studies. Mutations at Na1 resulted in altered steady-state and presteady-state characteristics that should be mirrored in the conformational changes induced by membrane potential changes. To test this hypothesis by functional analysis, double mutants of the flounder SLC34A2 protein were constructed that contain one of the Na1-site perturbing mutations together with a substituted cysteine for fluorophore labeling, as expressed in Xenopus oocytes. The locations of the mutations were mapped onto a homology model of the flounder protein. The effects of the mutagenesis were characterized by steady-state, presteady-state, and fluorometric assays. Changes in fluorescence intensity (ΔF) in response to membrane potential steps were resolved at three previously identified positions. These fluorescence data corroborated the altered presteady-state kinetics upon perturbation of Na1, and furthermore indicated concomitant changes in the microenvironment of the respective fluorophores, as evidenced by changes in the voltage dependence and time course of ΔF. Moreover, iodide quenching experiments indicated that the aqueous nature of the fluorophore microenvironment depended on the membrane potential. These findings provide compelling evidence that membrane potential and cation interactions induce significant large-scale structural rearrangements of the protein.
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24
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Loss of function of NaPiIIa causes nephrocalcinosis and possibly kidney insufficiency. Pediatr Nephrol 2016; 31:2289-2297. [PMID: 27378183 DOI: 10.1007/s00467-016-3443-0] [Citation(s) in RCA: 28] [Impact Index Per Article: 3.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 03/31/2016] [Revised: 05/22/2016] [Accepted: 05/23/2016] [Indexed: 12/27/2022]
Abstract
BACKGROUND Inherited metabolic disorders associated with nephrocalcinosis are rare conditions. The aim of this study was to identify the genetic cause of an Israeli-Arab boy from a consanguineous family with severe nephrocalcinosis and kidney insufficiency. METHODS Clinical and biochemical data of the proband and family members were obtained from both previous and recent medical charts. Genomic DNA was isolated from peripheral blood cells. The coding sequence and splice sites of candidate genes (CYP24A1, CYP27B1, FGF23, KLOTHO, SLC34A3 and SLC34A1) were sequenced directly. Functional studies were performed in Xenopus laevis oocytes and in transfected opossum kidney (OK) cells. RESULTS Our patient was identified as having nephrocalcinosis in utero, and at the age of 16.5 years, he had kidney insufficiency but no bone disease. Genetic analysis revealed a novel homozygous missense mutation, Arg215Gln, in SLC34A1, which encodes the renal sodium phosphate cotransporter NaPiIIa. Functional studies of the Arg215Gln mutant revealed reduced transport activity in Xenopus laevis oocytes and increased intracellular cytoplasmic accumulation in OK cells. CONCLUSIONS Our findings show that dysfunction of the human NaPiIIa causes severe renal calcification that may eventually lead to reduced kidney function, rather than complications of phosphate loss.
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25
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Werner A, Patti M, Zinad HS, Fearn A, Laude A, Forster I. Molecular determinants of transport function in zebrafish Slc34a Na-phosphate transporters. Am J Physiol Regul Integr Comp Physiol 2016; 311:R1213-R1222. [PMID: 27784684 DOI: 10.1152/ajpregu.00020.2016] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/14/2016] [Revised: 10/14/2016] [Accepted: 10/14/2016] [Indexed: 11/22/2022]
Abstract
The epithelial Na+-coupled phosphate cotransporter family Slc34a (NaPi-II) is well conserved in vertebrates and plays an essential role in maintaining whole body levels of inorganic phosphate (Pi). A three-dimensional model of the transport protein has recently been proposed with defined substrate coordination sites. Zebrafish express two NaPi-II isoforms with high sequence identity but a 10-fold different apparent Km for Pi ([Formula: see text]). We took advantage of the two zebrafish isoforms to investigate the contribution of specific amino acids to Pi coordination and transport. Mutations were introduced to gradually transform the low-affinity isoform into a high-affinity transporter. The constructs were expressed in Xenopus laevis oocytes and functionally characterized. Becaue the cotransport of Pi and Na involves multiple steps that could all influence [Formula: see text], we performed a detailed functional analysis to characterize the impact of the mutations on particular steps of the transport cycle. We used varying concentrations of the substrates Pi and its slightly larger analog, arsenate, as well as the cosubstrate, Na+ Moreover, electrogenic kinetics were performed to assess intramolecular movements of the transporter. All of the mutations were found to affect multiple transport steps, which suggested that the altered amino acids induced subtle structural changes rather than coordinating Pi directly. The likely positions of the critical residues were mapped to the model of human Slc34a, and their localization in relation to the proposed substrate binding pockets concurs well with the observed functional data.
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Affiliation(s)
- Andreas Werner
- Institute for Cell and Molecular Biosciences, Medical School, University of Newcastle upon Tyne, Newcastle upon Tyne, United Kingdom;
| | - Monica Patti
- Institute of Physiology and Zurich Center for Integrative Human Physiology, University of Zurich, Zürich, Switzerland; and
| | - Hany S Zinad
- Institute for Cell and Molecular Biosciences, Medical School, University of Newcastle upon Tyne, Newcastle upon Tyne, United Kingdom
| | - Amy Fearn
- Institute for Cell and Molecular Biosciences, Medical School, University of Newcastle upon Tyne, Newcastle upon Tyne, United Kingdom
| | - Alex Laude
- Bio-Imaging Unit, Medical School, University of Newcastle upon Tyne, United Kingdom
| | - Ian Forster
- Institute of Physiology and Zurich Center for Integrative Human Physiology, University of Zurich, Zürich, Switzerland; and
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26
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Watching the Pulleys Turn while the Elevator Moves in a Secondary Transporter. Biophys J 2016; 111:895-7. [DOI: 10.1016/j.bpj.2016.07.026] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/14/2016] [Revised: 07/18/2016] [Accepted: 07/20/2016] [Indexed: 11/19/2022] Open
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27
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Vergara-Jaque A, Fenollar-Ferrer C, Mulligan C, Mindell JA, Forrest LR. Family resemblances: A common fold for some dimeric ion-coupled secondary transporters. ACTA ACUST UNITED AC 2016; 146:423-34. [PMID: 26503722 PMCID: PMC4621753 DOI: 10.1085/jgp.201511481] [Citation(s) in RCA: 18] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/17/2023]
Abstract
The structures of two bacterial antiporters that act as multidrug resistance efflux pumps, MtrF and YdaH, resemble each other and that of the sodium-coupled succinate symporter VcINDY. Membrane transporter proteins catalyze the passage of a broad range of solutes across cell membranes, allowing the uptake and efflux of crucial compounds. Because of the difficulty of expressing, purifying, and crystallizing integral membrane proteins, relatively few transporter structures have been elucidated to date. Although every membrane transporter has unique characteristics, structural and mechanistic similarities between evolutionarily diverse transporters have been identified. Here, we compare two recently reported structures of membrane proteins that act as antimicrobial efflux pumps, namely MtrF from Neisseria gonorrhoeae and YdaH from Alcanivorax borkumensis, both with each other and with the previously published structure of a sodium-dependent dicarboxylate transporter from Vibrio cholerae, VcINDY. MtrF and YdaH belong to the p-aminobenzoyl-glutamate transporter (AbgT) family and have been reported as having architectures distinct from those of all other families of transporters. However, our comparative analysis reveals a similar structural arrangement in all three proteins, with highly conserved secondary structure elements. Despite their differences in biological function, the overall “design principle” of MtrF and YdaH appears to be almost identical to that of VcINDY, with a dimeric quaternary structure, helical hairpins, and clear boundaries between the transport and scaffold domains. This observation demonstrates once more that the same secondary transporter architecture can be exploited for multiple distinct transport modes, including cotransport and antiport. Based on our comparisons, we detected conserved motifs in the substrate-binding region and predict specific residues likely to be involved in cation or substrate binding. These findings should prove useful for the future characterization of the transport mechanisms of these families of secondary active transporters.
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Affiliation(s)
- Ariela Vergara-Jaque
- Computational Structural Biology Unit and Membrane Transport Biophysics Section, National Institutes of Neurological Disorders and Stroke, National Institutes of Health, Bethesda, MD 20824
| | - Cristina Fenollar-Ferrer
- Computational Structural Biology Unit and Membrane Transport Biophysics Section, National Institutes of Neurological Disorders and Stroke, National Institutes of Health, Bethesda, MD 20824
| | - Christopher Mulligan
- Computational Structural Biology Unit and Membrane Transport Biophysics Section, National Institutes of Neurological Disorders and Stroke, National Institutes of Health, Bethesda, MD 20824
| | - Joseph A Mindell
- Computational Structural Biology Unit and Membrane Transport Biophysics Section, National Institutes of Neurological Disorders and Stroke, National Institutes of Health, Bethesda, MD 20824
| | - Lucy R Forrest
- Computational Structural Biology Unit and Membrane Transport Biophysics Section, National Institutes of Neurological Disorders and Stroke, National Institutes of Health, Bethesda, MD 20824
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28
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Identification of the first sodium binding site of the phosphate cotransporter NaPi-IIa (SLC34A1). Biophys J 2016; 108:2465-2480. [PMID: 25992725 DOI: 10.1016/j.bpj.2015.03.054] [Citation(s) in RCA: 20] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/23/2014] [Revised: 02/20/2015] [Accepted: 03/17/2015] [Indexed: 01/08/2023] Open
Abstract
Transporters of the SLC34 family (NaPi-IIa,b,c) catalyze uptake of inorganic phosphate (Pi) in renal and intestinal epithelia. The transport cycle requires three Na(+) ions and one divalent Pi to bind before a conformational change enables translocation, intracellular release of the substrates, and reorientation of the empty carrier. The electrogenic interaction of the first Na(+) ion with NaPi-IIa/b at a postulated Na1 site is accompanied by charge displacement, and Na1 occupancy subsequently facilitates binding of a second Na(+) ion at Na2. The voltage dependence of cotransport and presteady-state charge displacements (in the absence of a complete transport cycle) are directly related to the molecular architecture of the Na1 site. The fact that Li(+) ions substitute for Na(+) at Na1, but not at the other sites (Na2 and Na3), provides an additional tool for investigating Na1 site-specific events. We recently proposed a three-dimensional model of human SLC34a1 (NaPi-IIa) including the binding sites Na2, Na3, and Pi based on the crystal structure of the dicarboxylate transporter VcINDY. Here, we propose nine residues in transmembrane helices (TM2, TM3, and TM5) that potentially contribute to Na1. To verify their roles experimentally, we made single alanine substitutions in the human NaPi-IIa isoform and investigated the kinetic properties of the mutants by voltage clamp and (32)P uptake. Substitutions at five positions in TM2 and one in TM5 resulted in relatively small changes in the substrate apparent affinities, yet at several of these positions, we observed significant hyperpolarizing shifts in the voltage dependence. Importantly, the ability of Li(+) ions to substitute for Na(+) ions was increased compared with the wild-type. Based on these findings, we adjusted the regions containing Na1 and Na3, resulting in a refined NaPi-IIa model in which five positions (T200, Q206, D209, N227, and S447) contribute directly to cation coordination at Na1.
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29
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The bacterial dicarboxylate transporter VcINDY uses a two-domain elevator-type mechanism. Nat Struct Mol Biol 2016; 23:256-63. [PMID: 26828963 PMCID: PMC5215794 DOI: 10.1038/nsmb.3166] [Citation(s) in RCA: 62] [Impact Index Per Article: 7.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/28/2015] [Accepted: 12/30/2015] [Indexed: 11/11/2022]
Abstract
Secondary transporters use alternating access mechanisms to couple uphill substrate movement to downhill ion flux. Most known transporters utilize a “rocking bundle” motion, where the protein moves around an immobile substrate binding site. However, the glutamate transporter homolog, GltPh, translocates its substrate binding site vertically across the membrane, an “elevator” mechanism. Here, we used the “repeat swap” approach to computationally predict the outward-facing state of the Na+/succinate transporter VcINDY, from Vibrio cholerae. Our model predicts a substantial “elevator”-like movement of vcINDY’s substrate binding site, with a vertical translation of ~15 Å and a rotation of ~43°; multiple disulfide crosslinks which completely inhibit transport provide experimental confirmation and demonstrate that such movement is essential. In contrast, crosslinks across the VcINDY dimer interface preserve transport, revealing an absence of large scale coupling between protomers.
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30
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Schlingmann KP, Ruminska J, Kaufmann M, Dursun I, Patti M, Kranz B, Pronicka E, Ciara E, Akcay T, Bulus D, Cornelissen EAM, Gawlik A, Sikora P, Patzer L, Galiano M, Boyadzhiev V, Dumic M, Vivante A, Kleta R, Dekel B, Levtchenko E, Bindels RJ, Rust S, Forster IC, Hernando N, Jones G, Wagner CA, Konrad M. Autosomal-Recessive Mutations in SLC34A1 Encoding Sodium-Phosphate Cotransporter 2A Cause Idiopathic Infantile Hypercalcemia. J Am Soc Nephrol 2015; 27:604-14. [PMID: 26047794 DOI: 10.1681/asn.2014101025] [Citation(s) in RCA: 148] [Impact Index Per Article: 16.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/22/2014] [Accepted: 04/03/2015] [Indexed: 12/18/2022] Open
Abstract
Idiopathic infantile hypercalcemia (IIH) is characterized by severe hypercalcemia with failure to thrive, vomiting, dehydration, and nephrocalcinosis. Recently, mutations in the vitamin D catabolizing enzyme 25-hydroxyvitamin D3-24-hydroxylase (CYP24A1) were described that lead to increased sensitivity to vitamin D due to accumulation of the active metabolite 1,25-(OH)2D3. In a subgroup of patients who presented in early infancy with renal phosphate wasting and symptomatic hypercalcemia, mutations in CYP24A1 were excluded. Four patients from families with parental consanguinity were subjected to homozygosity mapping that identified a second IIH gene locus on chromosome 5q35 with a maximum logarithm of odds (LOD) score of 6.79. The sequence analysis of the most promising candidate gene, SLC34A1 encoding renal sodium-phosphate cotransporter 2A (NaPi-IIa), revealed autosomal-recessive mutations in the four index cases and in 12 patients with sporadic IIH. Functional studies of mutant NaPi-IIa in Xenopus oocytes and opossum kidney (OK) cells demonstrated disturbed trafficking to the plasma membrane and loss of phosphate transport activity. Analysis of calcium and phosphate metabolism in Slc34a1-knockout mice highlighted the effect of phosphate depletion and fibroblast growth factor-23 suppression on the development of the IIH phenotype. The human and mice data together demonstrate that primary renal phosphate wasting caused by defective NaPi-IIa function induces inappropriate production of 1,25-(OH)2D3 with subsequent symptomatic hypercalcemia. Clinical and laboratory findings persist despite cessation of vitamin D prophylaxis but rapidly respond to phosphate supplementation. Therefore, early differentiation between SLC34A1 (NaPi-IIa) and CYP24A1 (24-hydroxylase) defects appears critical for targeted therapy in patients with IIH.
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Affiliation(s)
- Karl P Schlingmann
- Department of General Pediatrics, University Children's Hospital, Münster, Germany
| | - Justyna Ruminska
- Institute of Physiology and Zurich Center for Integrative Human Physiology (ZIHP), University of Zurich, Zurich, Switzerland
| | - Martin Kaufmann
- Department of Biomedical and Molecular Sciences, Queen's University, Kingston, Ontario, Canada
| | - Ismail Dursun
- Department of General Pediatrics, University Children's Hospital, Münster, Germany; Department of Pediatrics, Kayseri University, Kayseri, Turkey
| | - Monica Patti
- Institute of Physiology and Zurich Center for Integrative Human Physiology (ZIHP), University of Zurich, Zurich, Switzerland
| | - Birgitta Kranz
- Department of General Pediatrics, University Children's Hospital, Münster, Germany
| | - Ewa Pronicka
- Department of Medical Genetics, The Children's Memorial Health Institute, Warsaw, Poland
| | - Elzbieta Ciara
- Department of Medical Genetics, The Children's Memorial Health Institute, Warsaw, Poland
| | - Teoman Akcay
- Department of Pediatrics, Division of Pediatric Endocrinology, Marmara University, Istanbul, Turkey
| | - Derya Bulus
- Department of Pediatric Endocrinology, Keçiören Research and Educational Hospital, Ankara, Turkey
| | | | - Aneta Gawlik
- Department of Pediatrics, Medical University of Silesia, Katowice, Poland
| | - Przemysław Sikora
- Department of Pediatric Nephrology, Medical University of Lublin, Lublin, Poland
| | - Ludwig Patzer
- Children's Hospital St. Elisabeth and St. Barbara, Halle/Saale, Germany
| | - Matthias Galiano
- Department of Pediatrics, Friedrich-Alexander-University, Erlangen, Germany
| | - Veselin Boyadzhiev
- Department of Pediatrics, University Hospital St. Marina, Varna Medical University, Varna, Bulgaria
| | - Miroslav Dumic
- Department of Pediatrics, University Hospital Center, Zagreb, Croatia
| | | | - Robert Kleta
- University College London, London, United Kingdom
| | | | - Elena Levtchenko
- Department of Pediatric Nephrology, University Hospitals Leuven, Leuven, Belgium
| | - René J Bindels
- Department of Physiology, Radboud University Medical Center, Nijmegen, The Netherlands; and
| | - Stephan Rust
- Department of General Pediatrics, University Children's Hospital, Münster, Germany
| | - Ian C Forster
- Institute of Physiology and Zurich Center for Integrative Human Physiology (ZIHP), University of Zurich, Zurich, Switzerland
| | - Nati Hernando
- Institute of Physiology and Zurich Center for Integrative Human Physiology (ZIHP), University of Zurich, Zurich, Switzerland
| | - Glenville Jones
- Department of Biomedical and Molecular Sciences, Queen's University, Kingston, Ontario, Canada; Department of Medicine, Queen's University, Kingston, Ontario, Canada
| | - Carsten A Wagner
- Institute of Physiology and Zurich Center for Integrative Human Physiology (ZIHP), University of Zurich, Zurich, Switzerland
| | - Martin Konrad
- Department of General Pediatrics, University Children's Hospital, Münster, Germany;
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31
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Abstract
PURPOSE OF REVIEW Phosphate homeostasis is tightly controlled by the coordinated activity of bone, kidney, intestine, and parathyroid gland. The renal phosphate transporters have emerged as key regulators of both total body phosphate homeostasis and serum phosphate concentration. This review focuses on the latest updates in phosphate transport and transporters with an emphasis on renal phosphate transporters. RECENT FINDINGS Structure function analysis of type II sodium phosphate cotransporters has revealed motifs with significant similarity to those seen in other sodium-coupled solute transporters, identifying key amino acid residues important for solute binding and transport. Previously unidentified regulators of these transporters have been found, although their physiologic significance and interaction with more traditional regulators have not been established. Type II and type III sodium phosphate cotransporters play critical roles in bone, choroid plexus, and vascular physiology and pathophysiology. SUMMARY Increasing knowledge of structure function relationships for sodium phosphate cotransporters, as well as greater appreciation for the complexity of their regulation and role in renal and nonrenal tissue, brings the promise of newer, more specific treatments for disorders of phosphate homeostasis. VIDEO ABSTRACT http://links.lww.com/CONH/A10.
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Affiliation(s)
- Eleanor Lederer
- aMedical Services, Robley Rex VA Medical Center bKidney Disease Program, University of Louisville School of Medicine, Louisville, Kentucky, USA
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32
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Correlating charge movements with local conformational changes of a Na(+)-coupled cotransporter. Biophys J 2014; 106:1618-29. [PMID: 24739161 DOI: 10.1016/j.bpj.2014.02.028] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/26/2013] [Revised: 02/13/2014] [Accepted: 02/28/2014] [Indexed: 11/23/2022] Open
Abstract
To gain insight into the steady-state and dynamic characteristics of structural rearrangements of an electrogenic secondary-active cotransporter during its transport cycle, two measures of conformational change (pre-steady-state current relaxations and intensity of fluorescence emitted from reporter fluorophores) were investigated as a function of membrane potential and external substrate. Cysteines were substituted at three believed-new sites in the type IIb Na(+)-coupled inorganic phosphate cotransporter (SLC34A2 flounder isoform) that were predicted to be involved in conformational changes. Labeling at one site resulted in substantial suppression of transport activity, whereas for the other sites, function remained comparable to the wild-type. For these mutants, the properties of the pre-steady-state charge relaxations were similar for each, whereas fluorescence intensity changes differed significantly. Fluorescence changes could be accounted for by simulations using a five-state model with a unique set of apparent fluorescence intensities assigned to each state according to the site of labeling. Fluorescence reported from one site was associated with inward and outward conformations, whereas for the other sites, including four previously indentified sites, emissions were associated principally with one or the other orientation of the transporter. The same membrane potential change induced complementary changes in fluorescence at some sites, which suggested that the microenvironments of the respective fluorophores experience concomitant changes in polarity. In response to step changes in voltage, the pre-steady-state current relaxation and the time course of change in fluorescence intensity were described by single exponentials. For one mutant the time constants matched well with and without external Na(+), providing direct evidence that this label reports conformational changes accompanying intrinsic charge movement and cation interactions.
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33
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Wagner CA, Rubio-Aliaga I, Biber J, Hernando N. Genetic diseases of renal phosphate handling. Nephrol Dial Transplant 2014; 29:iv45-iv54. [DOI: 10.1093/ndt/gfu217] [Citation(s) in RCA: 33] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 08/30/2023] Open
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34
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Stamm M, Staritzbichler R, Khafizov K, Forrest LR. AlignMe--a membrane protein sequence alignment web server. Nucleic Acids Res 2014; 42:W246-51. [PMID: 24753425 PMCID: PMC4086118 DOI: 10.1093/nar/gku291] [Citation(s) in RCA: 69] [Impact Index Per Article: 6.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/25/2022] Open
Abstract
We present a web server for pair-wise alignment of membrane protein sequences, using the program AlignMe. The server makes available two operational modes of AlignMe: (i) sequence to sequence alignment, taking two sequences in fasta format as input, combining information about each sequence from multiple sources and producing a pair-wise alignment (PW mode); and (ii) alignment of two multiple sequence alignments to create family-averaged hydropathy profile alignments (HP mode). For the PW sequence alignment mode, four different optimized parameter sets are provided, each suited to pairs of sequences with a specific similarity level. These settings utilize different types of inputs: (position-specific) substitution matrices, secondary structure predictions and transmembrane propensities from transmembrane predictions or hydrophobicity scales. In the second (HP) mode, each input multiple sequence alignment is converted into a hydrophobicity profile averaged over the provided set of sequence homologs; the two profiles are then aligned. The HP mode enables qualitative comparison of transmembrane topologies (and therefore potentially of 3D folds) of two membrane proteins, which can be useful if the proteins have low sequence similarity. In summary, the AlignMe web server provides user-friendly access to a set of tools for analysis and comparison of membrane protein sequences. Access is available at http://www.bioinfo.mpg.de/AlignMe
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Affiliation(s)
- Marcus Stamm
- Computational Structural Biology Group, Max Planck Institute of Biophysics, Frankfurt am Main 60438, Germany
| | - René Staritzbichler
- Computational Structural Biology Group, Max Planck Institute of Biophysics, Frankfurt am Main 60438, Germany
| | - Kamil Khafizov
- Computational Structural Biology Group, Max Planck Institute of Biophysics, Frankfurt am Main 60438, Germany
| | - Lucy R Forrest
- Computational Structural Biology Group, Max Planck Institute of Biophysics, Frankfurt am Main 60438, Germany
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