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Zhang W, Ding D, Lu Y, Chen H, Jiang P, Zuo P, Wang G, Luo J, Yin Y, Luo J, Yin Y. Structural and functional insights into the lipid regulation of human anion exchanger 2. Nat Commun 2024; 15:759. [PMID: 38272905 PMCID: PMC10810954 DOI: 10.1038/s41467-024-44966-0] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/06/2023] [Accepted: 01/11/2024] [Indexed: 01/27/2024] Open
Abstract
Anion exchanger 2 (AE2) is an electroneutral Na+-independent Cl-/HCO3- exchanger belongs to the SLC4 transporter family. The widely expressed AE2 participates in a variety of physiological processes, including transepithelial acid-base secretion and osteoclastogenesis. Both the transmembrane domains (TMDs) and the N-terminal cytoplasmic domain (NTD) are involved in regulation of AE2 activity. However, the regulatory mechanism remains unclear. Here, we report a 3.2 Å cryo-EM structure of the AE2 TMDs in complex with PIP2 and a 3.3 Å full-length mutant AE2 structure in the resting state without PIP2. We demonstrate that PIP2 at the TMD dimer interface is involved in the substrate exchange process. Mutation in the PIP2 binding site leads to the displacement of TM7 and further stabilizes the interaction between the TMD and the NTD. Reduced substrate transport activity and conformation similar to AE2 in acidic pH indicating the central contribution of PIP2 to the function of AE2.
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Affiliation(s)
- Weiqi Zhang
- Institute of Systems Biomedicine, Department of Pathology, Beijing Key Laboratory of Tumor Systems Biology, Peking-Tsinghua Center for Life Sciences, School of Basic Medical Sciences, Peking University Health Science Center, Beijing, 100191, China
| | - Dian Ding
- Institute of Systems Biomedicine, Department of Pathology, Beijing Key Laboratory of Tumor Systems Biology, Peking-Tsinghua Center for Life Sciences, School of Basic Medical Sciences, Peking University Health Science Center, Beijing, 100191, China
| | - Yishuo Lu
- Institute of Systems Biomedicine, Department of Pathology, Beijing Key Laboratory of Tumor Systems Biology, Peking-Tsinghua Center for Life Sciences, School of Basic Medical Sciences, Peking University Health Science Center, Beijing, 100191, China
| | - Hongyi Chen
- Institute of Systems Biomedicine, Department of Pathology, Beijing Key Laboratory of Tumor Systems Biology, Peking-Tsinghua Center for Life Sciences, School of Basic Medical Sciences, Peking University Health Science Center, Beijing, 100191, China
| | - Peijun Jiang
- Institute of Systems Biomedicine, Department of Pathology, Beijing Key Laboratory of Tumor Systems Biology, Peking-Tsinghua Center for Life Sciences, School of Basic Medical Sciences, Peking University Health Science Center, Beijing, 100191, China
| | - Peng Zuo
- Institute of Systems Biomedicine, Department of Pathology, Beijing Key Laboratory of Tumor Systems Biology, Peking-Tsinghua Center for Life Sciences, School of Basic Medical Sciences, Peking University Health Science Center, Beijing, 100191, China
| | - Guangxi Wang
- Institute of Systems Biomedicine, Department of Pathology, Beijing Key Laboratory of Tumor Systems Biology, Peking-Tsinghua Center for Life Sciences, School of Basic Medical Sciences, Peking University Health Science Center, Beijing, 100191, China
| | - Juan Luo
- Institute of Precision Medicine, Peking University Shenzhen Hospital, Shenzhen, 518036, China
| | - Yue Yin
- Department of Pharmacology, School of Basic Medical Sciences, Peking University Health Science Center, Beijing, China
| | - Jianyuan Luo
- Department of Medical Genetics, School of Basic Medical Sciences, Peking University Health Science Center, Beijing, China
| | - Yuxin Yin
- Institute of Systems Biomedicine, Department of Pathology, Beijing Key Laboratory of Tumor Systems Biology, Peking-Tsinghua Center for Life Sciences, School of Basic Medical Sciences, Peking University Health Science Center, Beijing, 100191, China.
- Institute of Precision Medicine, Peking University Shenzhen Hospital, Shenzhen, 518036, China.
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2
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Identification of multiple substrate binding sites in SLC4 transporters in the outward-facing conformation: Insights into the transport mechanism. J Biol Chem 2021; 296:100724. [PMID: 33932403 PMCID: PMC8191340 DOI: 10.1016/j.jbc.2021.100724] [Citation(s) in RCA: 15] [Impact Index Per Article: 5.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/20/2020] [Revised: 04/21/2021] [Accepted: 04/27/2021] [Indexed: 01/17/2023] Open
Abstract
Solute carrier family 4 (SLC4) transporters mediate the transmembrane transport of HCO3-, CO32-, and Cl- necessary for pH regulation, transepithelial H+/base transport, and ion homeostasis. Substrate transport with varying stoichiometry and specificity is achieved through an exchange mechanism and/or through coupling of the uptake of anionic substrates to typically co-transported Na+. Recently solved outward-facing structures of two SLC4 members (human anion exchanger 1 [hAE1] and human electrogenic sodium bicarbonate cotransporter 1 [hNBCe1]) with different transport modes (Cl-/HCO3- exchange versus Na+-CO32- symport) revealed highly conserved three-dimensional organization of their transmembrane domains. However, the exact location of the ion binding sites and their protein-ion coordination motifs are still unclear. In the present work, we combined site identification by ligand competitive saturation mapping and extensive molecular dynamics sampling with functional mutagenesis studies which led to the identification of two substrate binding sites (entry and central) in the outward-facing states of hAE1 and hNBCe1. Mutation of residues in the identified binding sites led to impaired transport in both proteins. We also showed that R730 in hAE1 is crucial for anion binding in both entry and central sites, whereas in hNBCe1, a Na+ acts as an anchor for CO32- binding to the central site. Additionally, protonation of the central acidic residues (E681 in hAE1 and D754 in hNBCe1) alters the ion dynamics in the permeation cavity and may contribute to the transport mode differences in SLC4 proteins. These results provide a basis for understanding the functional differences between hAE1 and hNBCe1 and may facilitate potential drug development for diseases such as proximal and distal renal tubular acidosis.
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3
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Contessoto VG, de Oliveira VM, de Carvalho SJ, Oliveira LC, Leite VBP. NTL9 Folding at Constant pH: The Importance of Electrostatic Interaction and pH Dependence. J Chem Theory Comput 2016; 12:3270-7. [PMID: 27327651 DOI: 10.1021/acs.jctc.6b00399] [Citation(s) in RCA: 21] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Abstract
The folding process of the N-terminal domain of ribosomal protein L9 (NTL9) was investigated at constant-pH computer simulations. Evaluation of the role of electrostatic interaction during folding was carried out by including a Debye-Hückel potential into a Cα structure-based model (SBM). In this study, the charges of the ionizable residues and the electrostatic potential are susceptible to the solution conditions, such as pH and ionic strength, as well as to the presence of charged groups. Simulations were performed under different pHs, and the results were validated by comparing them with experimental values of pKa and with denaturation experiment data. Also, the free energy profiles, Φ-values, and folding routes were calculated for each condition. It was shown how charges vary along the folding under different pH, which is subject to different scenarios. This study reveals how simplified models can capture essential physical features, reproducing experimental results, and presenting the role of electrostatic interactions before, during, and after the transition state.
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Affiliation(s)
- Vinícius G Contessoto
- Departamento de Física, Instituto de Biociências, Letras e Ciências Exatas, Universidade Estadual Paulista (UNESP) , São José do Rio Preto, São Paulo 15054-000, Brazil
| | - Vinícius M de Oliveira
- Departamento de Física, Instituto de Biociências, Letras e Ciências Exatas, Universidade Estadual Paulista (UNESP) , São José do Rio Preto, São Paulo 15054-000, Brazil
| | - Sidney J de Carvalho
- Departamento de Física, Instituto de Biociências, Letras e Ciências Exatas, Universidade Estadual Paulista (UNESP) , São José do Rio Preto, São Paulo 15054-000, Brazil
| | - Leandro C Oliveira
- Departamento de Física, Instituto de Biociências, Letras e Ciências Exatas, Universidade Estadual Paulista (UNESP) , São José do Rio Preto, São Paulo 15054-000, Brazil
| | - Vitor B P Leite
- Departamento de Física, Instituto de Biociências, Letras e Ciências Exatas, Universidade Estadual Paulista (UNESP) , São José do Rio Preto, São Paulo 15054-000, Brazil
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Liu Y, Yang J, Chen LM. Structure and Function of SLC4 Family [Formula: see text] Transporters. Front Physiol 2015; 6:355. [PMID: 26648873 PMCID: PMC4664831 DOI: 10.3389/fphys.2015.00355] [Citation(s) in RCA: 42] [Impact Index Per Article: 4.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/18/2015] [Accepted: 11/10/2015] [Indexed: 12/12/2022] Open
Abstract
The solute carrier SLC4 family consists of 10 members, nine of which are [Formula: see text] transporters, including three Na(+)-independent Cl(-)/[Formula: see text] exchangers AE1, AE2, and AE3, five Na(+)-coupled [Formula: see text] transporters NBCe1, NBCe2, NBCn1, NBCn2, and NDCBE, as well as "AE4" whose Na(+)-dependence remains controversial. The SLC4 [Formula: see text] transporters play critical roles in pH regulation and transepithelial movement of electrolytes with a broad range of demonstrated physiological relevances. Dysfunctions of these transporters are associated with a series of human diseases. During the past decades, tremendous amount of effort has been undertaken to investigate the topological organization of the SLC4 transporters in the plasma membrane. Based upon the proposed topology models, mutational and functional studies have identified important structural elements likely involved in the ion translocation by the SLC4 transporters. In the present article, we review the advances during the past decades in understanding the structure and function of the SLC4 transporters.
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Affiliation(s)
- Ying Liu
- Key Laboratory of Molecular Biophysics of Ministry of Education, Department of Biophysics and Molecular Physiology, School of Life Science and Technology, Huazhong University of Science and TechnologyWuhan, China
| | - Jichun Yang
- Department of Physiology and Pathophysiology, School of Basic Medical Sciences, Peking University Health Science CenterBeijing, China
| | - Li-Ming Chen
- Key Laboratory of Molecular Biophysics of Ministry of Education, Department of Biophysics and Molecular Physiology, School of Life Science and Technology, Huazhong University of Science and TechnologyWuhan, China
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5
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Molecular cloning and functional characterization of zebrafish Slc4a3/Ae3 anion exchanger. Pflugers Arch 2014; 466:1605-18. [PMID: 24668450 DOI: 10.1007/s00424-014-1494-2] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/19/2014] [Revised: 02/24/2014] [Accepted: 03/04/2014] [Indexed: 12/15/2022]
Abstract
The zebrafish genome encodes two slc4a1 genes, one expressed in erythroid tissues and the other in the HR (H(+)-ATPase-rich) type of embryonic skin ionocytes, and two slc4a2 genes, one in proximal pronephric duct and the other in several extrarenal tissues of the embryo. We now report cDNA cloning and functional characterization of zebrafish slc4a3/ae3 gene products. The single ae3 gene on chromosome 9 generates at least two low-abundance ae3 transcripts differing only in their 5'-untranslated regions and encoding a single definitive Ae3 polypeptide of 1170 amino acids. The 7 kb upstream of the apparent initiator Met in ae3 exon 3 comprises multiple diverse, mobile repeat elements which disrupt and appear to truncate the Ae3 N-terminal amino acid sequence that would otherwise align with brain Ae3 of other species. Embryonic ae3 mRNA expression was detected by whole mount in situ hybridization only in fin buds at 24-72 hpf, but was detectable by RT-PCR across a range of embryonic and adult tissues. Epitope-tagged Ae3 polypeptide was expressed at or near the surface of Xenopus oocytes, and mediated low rates of DIDS-sensitive (36)Cl(-)/Cl(-) exchange in influx and efflux assays. As previously reported for Ae2 polypeptides, (36)Cl(-) transport by Ae3 was inhibited by both extracellular and intracellular acidic pH, and stimulated by alkaline pH. However, zebrafish Ae3 differed from Ae2 polypeptides in its insensitivity to NH4Cl and to hypertonicity. We conclude that multiple repeat elements have disrupted the 5'-end of the zebrafish ae3 gene, associated with N-terminal truncation of the protein and reduced anion transport activity.
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6
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Bonar P, Schneider HP, Becker HM, Deitmer JW, Casey JR. Three-dimensional model for the human Cl-/HCO3- exchanger, AE1, by homology to the E. coli ClC protein. J Mol Biol 2013; 425:2591-608. [PMID: 23583773 DOI: 10.1016/j.jmb.2013.04.005] [Citation(s) in RCA: 17] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/21/2013] [Revised: 03/20/2013] [Accepted: 04/03/2013] [Indexed: 01/19/2023]
Abstract
AE1 mediates electroneutral 1:1 exchange of bicarbonate for chloride across the plasma membrane of erythrocytes and type A cells of the renal collecting duct. No high-resolution structure is available for the AE1 membrane domain, which alone is required for its transport activity. A recent electron microscopy structure of the AE1 membrane domain was proposed to have a similar protein fold to ClC chloride channels. We developed a three-dimensional homology model of the AE1 membrane domain, using the Escherichia coli ClC channel structure as a template. This model agrees well with a long list of biochemically established spatial constraints for AE1. To investigate the AE1 transport mechanism, we created point mutations in regions corresponding to E. coli ClC transport mechanism residues. When expressed in HEK293 cells, several mutants had Cl(-)/HCO3(-) exchange rates significantly different from that of wild-type AE1. When further assessed in Xenopus laevis oocytes, there were significant changes in the transport activity of several AE1 point mutants as assessed by changes in pH. None of the mutants, however, added an electrogenic component to AE1 transport activity. This indicates that the AE1 point mutants altered the transport activity of AE1, without changing its electrogenicity and stoichiometry. The homology model successfully identified residues in AE1 that are critical to AE1 transport activity. Thus, we conclude that AE1 has a similar protein fold to ClC chloride channels.
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Affiliation(s)
- Pamela Bonar
- Membrane Protein Disease Research Group, Department of Biochemistry, University of Alberta, Edmonton, Canada T6G 2H7
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7
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SLC4A2-mediated Cl-/HCO3- exchange activity is essential for calpain-dependent regulation of the actin cytoskeleton in osteoclasts. Proc Natl Acad Sci U S A 2013; 110:2163-8. [PMID: 23341620 DOI: 10.1073/pnas.1206392110] [Citation(s) in RCA: 27] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022] Open
Abstract
Bone remodeling requires osteoclasts to generate and maintain an acidified resorption compartment between the apical membrane and the bone surface to solubilize hydroxyapatite crystals within the bone matrix. This acidification process requires (i) apical proton secretion by a vacuolar H(+)-ATPase, (ii) actin cytoskeleton reorganization into a podosome belt that forms a gasket to restrict lacunar acid leakage, and (iii) basolateral chloride uptake and bicarbonate extrusion by an anion exchanger to provide Cl(-) permissive for apical acid secretion while preventing cytoplasmic alkalinization. Here we show that osteoclast-targeted deletion in mice of solute carrier family 4 anion exchanger member 2 (Slc4a2) results in osteopetrosis. We further demonstrate a previously unrecognized consequence of SLC4A2 loss of function in the osteoclast: dysregulation of calpain-dependent podosome disassembly, leading to abnormal actin belt formation, cell spreading, and migration. Rescue of SLC4A2-deficient osteoclasts with functionally defined mutants of SLC4A2 indicates regulation of actin cytoskeletal reorganization by anion-exchange activity and intracellular pH, independent of SLC4A2's long N-terminal cytoplasmic domain. These data suggest that maintenance of intracellular pH in osteoclasts through anion exchange regulates the actin superstructures required for bone resorption.
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8
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Reimold FR, Stewart AK, Stolpe K, Heneghan JF, Shmukler BE, Alper SL. Substitution of transmembrane domain Cys residues alters pH(o)-sensitive anion transport by AE2/SLC4A2 anion exchanger. Pflugers Arch 2012; 465:839-51. [PMID: 23271450 DOI: 10.1007/s00424-012-1196-6] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/06/2012] [Revised: 11/19/2012] [Accepted: 11/30/2012] [Indexed: 10/27/2022]
Abstract
AE2/SLC4A2 is the most widely expressed of the Na(+)-independent SLC4 Cl(-)/HCO3 (-) exchangers and is essential for postnatal survival, but its structure remains unknown. We have generated and expressed a mouse AE2 construct devoid of transmembrane domain cysteine (Cys) residues, mAE2Cys-less, to enhance the utility of Cys-substitution mutagenesis for structural and structure-function studies of mAE2. mAE2Cys-less expressed in Xenopus oocytes exhibited partial reduction of stilbene disulfonate-sensitive anion exchange activity. This activity was independent of the mAE2 N-terminal cytosolic domain and was accompanied by near-normal surface expression, without change in K 1/2 for extracellular Cl(-). mAE2Cys-less exhibited wildtype activation of anion exchange by hypertonicity and by NH4Cl, and wildtype inhibition of anion exchange by acidic intracellular pH (pHi) in the absence of NH4 (+). However, inhibition of anion exchange by extracellular pH (pHo) exhibited an alkaline shifted pHo(50) value of at least 0.6-0.7 pH units. Although SO4 (2-) transport by mAE2Cys-less resembled wildtype mAE2 in its stimulation by acidic pHo, the absence of transmembrane domain Cys residues abrogated activation of oxalate transport by acidic pHo. The contrasting enhancement of SO4 (2-) transport by alkaline pHo in the mAE1 anion translocation pathway mutant E699Q (Am J Physiol Cell Physiol 295: C302) was phenocopied by the corresponding mutant E1007Q in both AE2 and AE2Cys-less. However, the absence of transmembrane domain Cys residues exacerbated the reduced basal anion transport function exhibited by this and other missense substitutions at AE2 residue E1007. AE2Cys-less will be a valuable experimental tool for structure-function studies of the SLC4 gene family, but its utility for studies of AE2 regulation by extracellular pH must be evaluated in the context of its alkaline-shifted pHo sensitivity, resembling that of AE2 gastric parietal cell variant AE2c1.
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Affiliation(s)
- Fabian R Reimold
- Renal Division and Molecular and Vascular Medicine Division, Beth Israel Deaconess Medical Center, 99 Brookline Avenue, RN-380F, Boston, MA 02215, USA
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Stewart AK, Kedar PS, Shmukler BE, Vandorpe DH, Hsu A, Glader B, Rivera A, Brugnara C, Alper SL. Functional characterization and modified rescue of novel AE1 mutation R730C associated with overhydrated cation leak stomatocytosis. Am J Physiol Cell Physiol 2011; 300:C1034-46. [PMID: 21209359 PMCID: PMC3093938 DOI: 10.1152/ajpcell.00447.2010] [Citation(s) in RCA: 29] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/03/2010] [Accepted: 12/23/2010] [Indexed: 01/20/2023]
Abstract
We report the novel, heterozygous AE1 mutation R730C associated with dominant, overhydrated, cation leak stomatocytosis and well-compensated anemia. Parallel elevations of red blood cell cation leak and ouabain-sensitive Na(+) efflux (pump activity) were apparently unaccompanied by increased erythroid cation channel-like activity, and defined ouabain-insensitive Na(+) efflux pathways of nystatin-treated cells were reduced. Epitope-tagged AE1 R730C at the Xenopus laevis oocyte surface exhibited severely reduced Cl(-) transport insensitive to rescue by glycophorin A (GPA) coexpression or by methanethiosulfonate (MTS) treatment. AE1 mutant R730K preserved Cl(-) transport activity, but R730 substitution with I, E, or H inactivated Cl(-) transport. AE1 R730C expression substantially increased endogenous oocyte Na(+)-K(+)-ATPase-mediated (86)Rb(+) influx, but ouabain-insensitive flux was minimally increased and GPA-insensitive. The reduced AE1 R730C-mediated sulfate influx did not exhibit the wild-type pattern of stimulation by acidic extracellular pH (pH(o)) and, unexpectedly, was partially rescued by exposure to sodium 2-sulfonatoethyl methanethiosulfonate (MTSES) but not to 2-aminoethyl methanethiosulfonate hydrobromide (MTSEA) or 2-(trimethylammonium)ethyl methanethiosulfonate bromide (MTSET). AE1 R730E correspondingly exhibited acid pH(o)-stimulated sulfate uptake at rates exceeding those of wild-type AE1 and AE1 R730K, whereas mutants R730I and R730H were inactive and pH(o) insensitive. MTSES-treated oocytes expressing AE1 R730C and untreated oocytes expressing AE1 R730E also exhibited unprecedented stimulation of Cl(-) influx by acid pH(o). Thus recombinant cation-leak stomatocytosis mutant AE1 R730C exhibits severely reduced anion transport unaccompanied by increased Rb(+) and Li(+) influxes. Selective rescue of acid pH(o)-stimulated sulfate uptake and conferral of acid pH(o)-stimulated Cl(-) influx, by AE1 R730E and MTSES-treated R730C, define residue R730 as critical to selectivity and regulation of anion transport by AE1.
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Affiliation(s)
- Andrew K Stewart
- Division of Nephrology, Beth Israel Deaconess Medical Center, 330 Brookline Ave., Boston, MA 02215, USA
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Chen LM, Liu Y, Boron WF. Role of an extracellular loop in determining the stoichiometry of Na+-HCO₃⁻ cotransporters. J Physiol 2011; 589:877-90. [PMID: 21224233 DOI: 10.1113/jphysiol.2010.198713] [Citation(s) in RCA: 27] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/19/2022] Open
Abstract
The Na+–HCO₃⁻ cotransporters (NBCs) of the solute carrier 4 family (SLC4) are critical for regulating pH in cells as well as in fluids such as blood and cerebrospinal fluid. Moreover, mutations and gene disruptions in NBC are linked to a wide range of pathologies. NBCe1 (SLC4A4) is electrogenic because it has an apparent Na+:HCO₃⁻ stoichiometry of 1:2 or 1:3, whereas NBCn1 (SLC4A7) is electroneutral because it has an apparent stoichiometry of 1:1. Because stoichiometry influences the effect of transport on membrane potential and vice versa, a central question is what structural features underlie electrogenicity versus electroneutrality. A previous study on rat NBCe1/n1 chimeras demonstrated that the structural elements determining the electrogenicity of NBCe1-A are located within the transmembrane domain, excluding the large third extracellular loop. In the present study we generated a series of chimeras of human NBCe1-A and human NBCn1-A. We found that replacing merely the predicted fourth extracellular loop (EL4) – containing 32 amino acid residues that include 7 prolines – of human NBCe1-A with EL4 of NBCn1-A creates an electroneutral NBC. The opposite switch converts an electroneutral construct to one with electrogenic properties. The introduction of an N-glycosylation site into EL4 confirms that at least a part of it is exposed to the extracellular fluid. We hypothesize that putative EL4 either contributes to the substrate-binding vestibule or indirectly influences substrate binding by interacting with one or more transmembrane segments, thereby controlling the nature of transport.
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Affiliation(s)
- Li-Ming Chen
- Department of Biological Science, Key Laboratory of Molecular Biophysics of Ministry of Education, Huazhong University of Science and Technology School of Life Science and Technology, 1037 Luoyu Road, Wuhan, Hubei Province 430074, P.R. China.
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11
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Piermarini PM, Grogan LF, Lau K, Wang L, Beyenbach KW. A SLC4-like anion exchanger from renal tubules of the mosquito (Aedes aegypti): evidence for a novel role of stellate cells in diuretic fluid secretion. Am J Physiol Regul Integr Comp Physiol 2009; 298:R642-60. [PMID: 20042685 DOI: 10.1152/ajpregu.00729.2009] [Citation(s) in RCA: 39] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Abstract
Transepithelial fluid secretion across the renal (Malpighian) tubule epithelium of the mosquito (Aedes aegypti) is energized by the vacuolar-type (V-type) H(+)-ATPase and not the Na(+)-K(+)-ATPase. Located at the apical membrane of principal cells, the V-type H(+)-ATPase translocates protons from the cytoplasm to the tubule lumen. Secreted protons are likely to derive from metabolic H(2)CO(3), which raises questions about the handling of HCO(3)(-) by principal cells. Accordingly, we tested the hypothesis that a Cl/HCO(3) anion exchanger (AE) related to the solute-linked carrier 4 (SLC4) superfamily mediates the extrusion of HCO(3)(-) across the basal membrane of principal cells. We began by cloning from Aedes Malpighian tubules a full-length cDNA encoding an SLC4-like AE, termed AeAE. When expressed heterologously in Xenopus oocytes, AeAE is both N- and O-glycosylated and mediates Na(+)-independent intracellular pH changes that are sensitive to extracellular Cl(-) concentration and to DIDS. In Aedes Malpighian tubules, AeAE is expressed as two distinct forms: one is O-glycosylated, and the other is N-glycosylated. Significantly, AeAE immunoreactivity localizes to the basal regions of stellate cells but not principal cells. Concentrations of DIDS that inhibit AeAE activity in Xenopus oocytes have no effects on the unstimulated rates of fluid secretion mediated by Malpighian tubules as measured by the Ramsay assay. However, in Malpighian tubules stimulated with kinin or calcitonin-like diuretic peptides, DIDS reduces the diuretic rates of fluid secretion to basal levels. In conclusion, Aedes Malpighian tubules express AeAE in the basal region of stellate cells, where this transporter may participate in producing diuretic rates of transepithelial fluid secretion.
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Affiliation(s)
- Peter M Piermarini
- Department of Biomedical Sciences, Cornell University, Ithaca, NY 14853, USA.
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Hulikova A, Zatovicova M, Svastova E, Ditte P, Brasseur R, Kettmann R, Supuran CT, Kopacek J, Pastorek J, Pastorekova S. Intact intracellular tail is critical for proper functioning of the tumor-associated, hypoxia-regulated carbonic anhydrase IX. FEBS Lett 2009; 583:3563-8. [DOI: 10.1016/j.febslet.2009.10.060] [Citation(s) in RCA: 28] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/10/2009] [Revised: 10/14/2009] [Accepted: 10/20/2009] [Indexed: 11/25/2022]
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Adijanto J, Banzon T, Jalickee S, Wang NS, Miller SS. CO2-induced ion and fluid transport in human retinal pigment epithelium. ACTA ACUST UNITED AC 2009; 133:603-22. [PMID: 19468075 PMCID: PMC2713148 DOI: 10.1085/jgp.200810169] [Citation(s) in RCA: 76] [Impact Index Per Article: 5.1] [Reference Citation Analysis] [Abstract] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/12/2023]
Abstract
In the intact eye, the transition from light to dark alters pH, [Ca2+], and [K] in the subretinal space (SRS) separating the photoreceptor outer segments and the apical membrane of the retinal pigment epithelium (RPE). In addition to these changes, oxygen consumption in the retina increases with a concomitant release of CO2 and H2O into the SRS. The RPE maintains SRS pH and volume homeostasis by transporting these metabolic byproducts to the choroidal blood supply. In vitro, we mimicked the transition from light to dark by increasing apical bath CO2 from 5 to 13%; this maneuver decreased cell pH from 7.37 ± 0.05 to 7.14 ± 0.06 (n = 13). Our analysis of native and cultured fetal human RPE shows that the apical membrane is significantly more permeable (≈10-fold; n = 7) to CO2 than the basolateral membrane, perhaps due to its larger exposed surface area. The limited CO2 diffusion at the basolateral membrane promotes carbonic anhydrase–mediated HCO3 transport by a basolateral membrane Na/nHCO3 cotransporter. The activity of this transporter was increased by elevating apical bath CO2 and was reduced by dorzolamide. Increasing apical bath CO2 also increased intracellular Na from 15.7 ± 3.3 to 24.0 ± 5.3 mM (n = 6; P < 0.05) by increasing apical membrane Na uptake. The CO2-induced acidification also inhibited the basolateral membrane Cl/HCO3 exchanger and increased net steady-state fluid absorption from 2.8 ± 1.6 to 6.7 ± 2.3 µl × cm−2 × hr−1 (n = 5; P < 0.05). The present experiments show how the RPE can accommodate the increased retinal production of CO2 and H2O in the dark, thus preventing acidosis in the SRS. This homeostatic process would preserve the close anatomical relationship between photoreceptor outer segments and RPE in the dark and light, thus protecting the health of the photoreceptors.
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Affiliation(s)
- Jeffrey Adijanto
- Department of Chemical and Biomolecular Engineering, University of Maryland, College Park, MD 20742, USA
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Xu WQ, Song LJ, Liu Q, Zhao L, Zheng L, Yan ZW, Fu GH. Expression of anion exchanger 1 is associated with tumor progress in human gastric cancer. J Cancer Res Clin Oncol 2009; 135:1323-30. [PMID: 19330352 DOI: 10.1007/s00432-009-0573-9] [Citation(s) in RCA: 23] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/08/2008] [Accepted: 03/09/2009] [Indexed: 12/28/2022]
Abstract
PURPOSE Anion exchanger 1 (AE1) is a transmembrane glycoprotein which is abundantly expressed in erythrocyte plasma membrane and mediates the electroneutral exchange of Cl(-) and HCO(3) (-). We previously reported that the AE1 protein was unexpectedly expressed in the gastric and colonic cancer and take part in the carcinogenesis of the cancer cells. The aim of the present study is to determine the potential clinical implications of AE1 expression in gastric carcinoma. METHODS Immunohistochemistry assay was used to determine the expression of AE1 protein. The expression of AE1 in normal and malignant tissues from 286 patients with early and advanced gastric carcinoma was examined. The correlations of AE1 expression with clinicopathological parameters, including age, tumor size, location and subtypes, expression frequency, survival period and lymph metastasis were assessed by Chi-squared test and t test analysis. RESULTS AE1 immunoreactivity was negative in normal gastric tissue. Positive immunostaining of AE1 was detected in gastric carcinoma regardless of the location. AE1 was most frequently expressed in the gastric antrum carcinoma compared with gastric body cancer (P = 0.034). Expression of AE1 was significantly associated with bigger tumor size, deeper invasion, shorter survival period, and non-lymph metastasis. In para-cancer tissues of intestinal-type gastric cancer, the expression frequency of AE1 was higher than that in diffuse-type (P = 0.011). CONCLUSION The results showed a strong association of AE1 expression with the onset and progression of the gastric cancer and that may be helpful for improving the tumor classification and the treatment of cancer.
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Affiliation(s)
- Wei-Qing Xu
- Department of Pathology, Institutes of Medical Sciences, Key Laboratory of Cell Differentiation and Apoptosis of Chinese Ministry of Education, Shanghai Jiao Tong University School of Medicine, Shanghai 200025, People's Republic of China
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Stewart AK, Kurschat CE, Vaughan-Jones RD, Alper SL. Putative re-entrant loop 1 of AE2 transmembrane domain has a major role in acute regulation of anion exchange by pH. J Biol Chem 2008; 284:6126-39. [PMID: 19103596 DOI: 10.1074/jbc.m802051200] [Citation(s) in RCA: 29] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/09/2023] Open
Abstract
Normal pH sensitivity of the SLC4A2/AE2 anion exchanger requires transmembrane domain (TMD) amino acid (aa) residues not conserved in the homologous but relatively pH-insensitive SLC4A1/AE1 polypeptide. We tested the hypothesis that the nonconserved aa cluster 1075DKPK1078 within the first putative re-entrant loop (RL1) of AE2 TMD contributes to pH sensor function by studying anion exchange function of AE2 mutants in which these and other RL1 aa were systematically substituted with corresponding RL1 aa from AE1. Regulation of Cl-/Cl- and Cl-/HCO(-)3 exchange by intracellular pH (pHi) or extracellular pH (pHo) was measured as 4,4'-di-isothiocyanatostilbene-2,2' disulfonic acid-sensitive 36Cl- efflux from Xenopus oocytes. AE2 RL1 mutants 1075AAAQ1078 and 1075AAAQN1079 showed reduced pHi sensitivity and pHo sensitivity was acid-shifted by approximately 1 pH unit. Individual mutants D1075A and P1077A exhibited moderately altered pH sensitivity, whereas a range of substitutions at conserved AE2 Ile-1079 substantially altered sensitivity to pHo and/or pHi. Substitution of the complete AE1 RL1 with AE2 RL1 failed to confer AE2-like pH sensitivity onto AE1. Replacement, however, of AE1 RL1 763SGPGAAAQ770 with AE2 1071VAPGDKPK1078 restored pHi sensitivity to the chimera AE2(1-920)/AE1(613-929) without affecting its low sensitivity to pHo. The results show that acute regulation of AE2 by pH requires RL1 of the TMD. We propose that critical segments of RL1 constitute part of an AE2 pH sensor that, together with residues within the N-terminal half of the TMD, constrain the AE2 polypeptide in a conformation required for regulation of anion exchange by pHi.
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Affiliation(s)
- Andrew K Stewart
- Department of Medicine, Harvard Medical School, and Molecular and Vascular Medicine Unit, Beth Israel Deaconess Medical Center, Boston, Massachusetts 02215, USA
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Chernova MN, Stewart AK, Barry PN, Jennings ML, Alper SL. Mouse Ae1 E699Q mediates SO42-i/anion-o exchange with [SO42-]i-dependent reversal of wild-type pHo sensitivity. Am J Physiol Cell Physiol 2008; 295:C302-12. [PMID: 18480299 DOI: 10.1152/ajpcell.00109.2008] [Citation(s) in RCA: 11] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Abstract
The SLC4A1/AE1 gene encodes the electroneutral Cl(-)/HCO(3)(-) exchanger of erythrocytes and renal type A intercalated cells. AE1 mutations cause familial spherocytic and stomatocytic anemias, ovalocytosis, and distal renal tubular acidosis. The mutant mouse Ae1 polypeptide E699Q expressed in Xenopus oocytes cannot mediate Cl(-)/HCO(3)(-) exchange or (36)Cl(-) efflux but exhibits enhanced dual sulfate efflux mechanisms: electroneutral exchange of intracellular sulfate for extracellular sulfate (SO(4)(2-)(i)/SO(4)(2-)(o) exchange), and electrogenic exchange of intracellular sulfate for extracellular chloride (SO(4)(2-)(i)/Cl(-)(o) exchange). Whereas wild-type AE1 mediates 1:1 H(+)/SO(4)(2-) cotransport in exchange for either Cl(-) or for the H(+)/SO(4)(2-) ion pair, mutant Ae1 E699Q transports sulfate without cotransport of protons, similar to human erythrocyte AE1 in which the corresponding E681 carboxylate has been chemically converted to the alcohol (hAE1 E681OH). We now show that in contrast to the normal cis-stimulation by protons of wild-type AE1-mediated SO(4)(2-) transport, both SO(4)(2-)(i)/Cl(-)(o) exchange and SO(4)(2-)(i)/SO(4)(2-)(o) exchange mediated by mutant Ae1 E699Q are inhibited by acidic pH(o) and activated by alkaline pH(o). hAE1 E681OH displays a similarly altered pH(o) dependence of SO(4)(2-)(i)/Cl(-)(o) exchange. Elevated [SO(4)(2-)](i) increases the K(1/2) of Ae1 E699Q for both extracellular Cl(-) and SO(4)(2-), while reducing inhibition of both exchange mechanisms by acid pH(o). The E699Q mutation also leads to increased potency of self-inhibition by extracellular SO(4)(2-). Study of the Ae1 E699Q mutation has revealed the existence of a novel pH-regulatory site of the Ae1 polypeptide and should continue to provide valuable paths toward understanding substrate selectivity and self-inhibition in SLC4 anion transporters.
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Affiliation(s)
- Marina N Chernova
- Molecular and Vascular Medicine Unit, Beth Israel Deaconess Med. Ctr., 330 Brookline Ave., Boston, MA 02215, USA
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Shmukler BE, Clark JS, Hsu A, Vandorpe DH, Stewart AK, Kurschat CE, Choe SK, Zhou Y, Amigo J, Paw BH, Alper SL. Zebrafish ae2.2 encodes a second slc4a2 anion exchanger. Am J Physiol Regul Integr Comp Physiol 2007; 294:R1081-91. [PMID: 18046018 DOI: 10.1152/ajpregu.00690.2007] [Citation(s) in RCA: 9] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Abstract
The genome of zebrafish (Danio rerio) encodes two unlinked genes equally closely related to the SLC4A2/AE2 anion exchanger genes of mammals. One of these is the recently reported zebrafish ae2 gene (Shmukler BE, Kurschat CE, Ackermann GE, Jiang L, Zhou Y, Barut B, Stuart-Tilley AK, Zhao J, Zon LI, Drummond IA, Vandorpe DH, Paw BH, Alper SL. Am J Physiol Renal Physiol Renal Physiol 289: F835-F849, 2005), now called ae2.1. We now report the structural and functional characterization of Ae2.2, the product of the second zebrafish Ae2 gene, ae2.2. The ae2.2 gene of zebrafish linkage group 24 encodes a polypeptide of 1,232 aa in length, sharing 70% amino acid identity with zebrafish Ae2.1 and 67% identity with mouse AE2a. Zebrafish Ae2.2 expressed in Xenopus oocytes encodes a 135-kDa polypeptide that mediates bidirectional, DIDS-sensitive Cl(-)/Cl(-) exchange and Cl(-)/HCO3(-) exchange. Ae2.2-mediated Cl(-)/Cl(-) exchange is cation independent, voltage insensitive, and electroneutral. Acute regulation of anion exchange mediated by Ae2.2 includes activation by NH4+ and independent inhibition by acidic intracellular pH and by acidic extracellular pH. In situ hybridization reveals low-level expression of Ae2.2 mRNA in zebrafish embryo, most notably in posterior tectum, eye, pharynx, epidermal cells, and axial vascular structures, without notable expression in the Ae2.1-expressing pronephric duct. Knockdown of Ae2.2 mRNA, of Ae2.1 mRNA, or of both with nontoxic or minimally toxic levels of N-morpholino oligomers produced no grossly detectable morphological phenotype, and preserved normal structure of the head and the pronephric duct at 24 h postfertilization.
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Affiliation(s)
- Boris E Shmukler
- Molecular and Vascular Medicine and Renal Units, Beth Israel Deaconess Medical Center E/RW763, 330 Brookline Ave., Boston, MA 02215, USA
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Stewart AK, Kurschat CE, Vaughan-Jones RD, Shmukler BE, Alper SL. Acute regulation of mouse AE2 anion exchanger requires isoform-specific amino acid residues from most of the transmembrane domain. J Physiol 2007; 584:59-73. [PMID: 17690150 PMCID: PMC2277056 DOI: 10.1113/jphysiol.2007.136119] [Citation(s) in RCA: 16] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/25/2022] Open
Abstract
The widely expressed anion exchanger polypeptide AE2/SLC4A2 is acutely inhibited by acidic intracellular (pH(i)), by acidic extracellular pH (pH(o)), and by the calmodulin inhibitor, calmidazolium, whereas it is acutely activated by NH(4)(+). The homologous erythroid/kidney AE1/SLC4A1 polypeptide is insensitive to these regulators. Each of these AE2 regulatory responses requires the presence of AE2's C-terminal transmembrane domain (TMD). We have now measured (36)Cl(-) efflux from Xenopus oocytes expressing bi- or tripartite AE2-AE1 chimeras to define TMD subregions in which AE2-specific sequences contribute to acute regulation. The chimeric AE polypeptides were all functional at pH(o) 7.4, with the sole exception of AE2((1-920))/AE1((613-811))/AE2((1120-1237)). Reciprocal exchanges of the large third extracellular loops were without effect. AE2 regulation by pH(i), pH(o) and NH(4)(+) was retained after substitution of C-terminal AE2 amino acids 1120-1237 (including the putative second re-entrant loop, two TM spans and the cytoplasmic tail) with the corresponding AE1 sequence. In contrast, the presence of this AE2 C-terminal sequence was both necessary and sufficient for inhibition by calmidazolium. All other tested TMD substitutions abolished AE2 pH(i) sensitivity, abolished or severely attenuated sensitivity to pH(o) and removed sensitivity to NH(4)(+). Loss of AE2 pH(i) sensitivity was not rescued by co-expression of a complementary AE2 sequence within separate full-length chimeras or AE2 subdomains. Thus, normal regulation of AE2 by pH and other ligands requires AE2-specific sequence from most regions of the AE2 TMD, with the exceptions of the third extracellular loop and a short C-terminal sequence. We conclude that the individual TMD amino acid residues previously identified as influencing acute regulation of AE2 exert that influence within a regulatory structure requiring essential contributions from multiple regions of the AE2 TMD.
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Affiliation(s)
- A K Stewart
- Department of Medicine, Harvard Medical School, Beth Israel Deaconess Medical Center, Boston, MA 02215, USA
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