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Zhekova HR, Jiang J, Wang W, Tsirulnikov K, Kayık G, Khan HM, Azimov R, Abuladze N, Kao L, Newman D, Noskov SY, Tieleman DP, Hong Zhou Z, Pushkin A, Kurtz I. CryoEM structures of anion exchanger 1 capture multiple states of inward- and outward-facing conformations. Commun Biol 2022; 5:1372. [PMID: 36517642 PMCID: PMC9751308 DOI: 10.1038/s42003-022-04306-8] [Citation(s) in RCA: 10] [Impact Index Per Article: 5.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/17/2022] [Accepted: 11/28/2022] [Indexed: 12/15/2022] Open
Abstract
Anion exchanger 1 (AE1, band 3) is a major membrane protein of red blood cells and plays a key role in acid-base homeostasis, urine acidification, red blood cell shape regulation, and removal of carbon dioxide during respiration. Though structures of the transmembrane domain (TMD) of three SLC4 transporters, including AE1, have been resolved previously in their outward-facing (OF) state, no mammalian SLC4 structure has been reported in the inward-facing (IF) conformation. Here we present the cryoEM structures of full-length bovine AE1 with its TMD captured in both IF and OF conformations. Remarkably, both IF-IF homodimers and IF-OF heterodimers were detected. The IF structures feature downward movement in the core domain with significant unexpected elongation of TM11. Molecular modeling and structure guided mutagenesis confirmed the functional significance of residues involved in TM11 elongation. Our data provide direct evidence for an elevator-like mechanism of ion transport by an SLC4 family member.
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Affiliation(s)
- Hristina R Zhekova
- Centre for Molecular Simulation, Department of Biological Sciences, University of Calgary, Calgary, Canada
| | - Jiansen Jiang
- Department of Medicine, Division of Nephrology, David Geffen School of Medicine, University of California, Los Angeles, CA, USA
- Department of Microbiology, Immunology and Molecular Genetics, University of California, Los Angeles (UCLA), Los Angeles, CA, USA
- California NanoSystems Institute, UCLA, Los Angeles, CA, USA
| | - Weiguang Wang
- Department of Medicine, Division of Nephrology, David Geffen School of Medicine, University of California, Los Angeles, CA, USA
- Department of Microbiology, Immunology and Molecular Genetics, University of California, Los Angeles (UCLA), Los Angeles, CA, USA
- California NanoSystems Institute, UCLA, Los Angeles, CA, USA
| | - Kirill Tsirulnikov
- Department of Medicine, Division of Nephrology, David Geffen School of Medicine, University of California, Los Angeles, CA, USA
| | - Gülru Kayık
- Centre for Molecular Simulation, Department of Biological Sciences, University of Calgary, Calgary, Canada
| | - Hanif Muhammad Khan
- Centre for Molecular Simulation, Department of Biological Sciences, University of Calgary, Calgary, Canada
| | - Rustam Azimov
- Department of Medicine, Division of Nephrology, David Geffen School of Medicine, University of California, Los Angeles, CA, USA
| | - Natalia Abuladze
- Department of Medicine, Division of Nephrology, David Geffen School of Medicine, University of California, Los Angeles, CA, USA
| | - Liyo Kao
- Department of Medicine, Division of Nephrology, David Geffen School of Medicine, University of California, Los Angeles, CA, USA
| | - Debbie Newman
- Department of Medicine, Division of Nephrology, David Geffen School of Medicine, University of California, Los Angeles, CA, USA
| | - Sergei Yu Noskov
- Centre for Molecular Simulation, Department of Biological Sciences, University of Calgary, Calgary, Canada
| | - D Peter Tieleman
- Centre for Molecular Simulation, Department of Biological Sciences, University of Calgary, Calgary, Canada
| | - Z Hong Zhou
- Department of Microbiology, Immunology and Molecular Genetics, University of California, Los Angeles (UCLA), Los Angeles, CA, USA
- California NanoSystems Institute, UCLA, Los Angeles, CA, USA
| | - Alexander Pushkin
- Department of Medicine, Division of Nephrology, David Geffen School of Medicine, University of California, Los Angeles, CA, USA
| | - Ira Kurtz
- Department of Medicine, Division of Nephrology, David Geffen School of Medicine, University of California, Los Angeles, CA, USA.
- Brain Research Institute, University of California, Los Angeles, CA, USA.
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2
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Jiang J, Magilnick N, Tsirulnikov K, Abuladze N, Atanasov I, Ge P, Narla M, Pushkin A, Zhou ZH, Kurtz I. Single particle electron microscopy analysis of the bovine anion exchanger 1 reveals a flexible linker connecting the cytoplasmic and membrane domains. PLoS One 2013; 8:e55408. [PMID: 23393575 PMCID: PMC3564912 DOI: 10.1371/journal.pone.0055408] [Citation(s) in RCA: 20] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/19/2012] [Accepted: 12/21/2012] [Indexed: 11/18/2022] Open
Abstract
Anion exchanger 1 (AE1) is the major erythrocyte membrane protein that mediates chloride/bicarbonate exchange across the erythrocyte membrane facilitating CO₂ transport by the blood, and anchors the plasma membrane to the spectrin-based cytoskeleton. This multi-protein cytoskeletal complex plays an important role in erythrocyte elasticity and membrane stability. An in-frame AE1 deletion of nine amino acids in the cytoplasmic domain in a proximity to the membrane domain results in a marked increase in membrane rigidity and ovalocytic red cells in the disease Southeast Asian Ovalocytosis (SAO). We hypothesized that AE1 has a flexible region connecting the cytoplasmic and membrane domains, which is partially deleted in SAO, thus causing the loss of erythrocyte elasticity. To explore this hypothesis, we developed a new non-denaturing method of AE1 purification from bovine erythrocyte membranes. A three-dimensional (3D) structure of bovine AE1 at 2.4 nm resolution was obtained by negative staining electron microscopy, orthogonal tilt reconstruction and single particle analysis. The cytoplasmic and membrane domains are connected by two parallel linkers. Image classification demonstrated substantial flexibility in the linker region. We propose a mechanism whereby flexibility of the linker region plays a critical role in regulating red cell elasticity.
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Affiliation(s)
- Jiansen Jiang
- Department of Microbiology, Immunology and Molecular Genetics, and California NanoSystems Institute, University of California Los Angeles, Los Angeles, California, United States of America
- Structural Computational Biology and Molecular Biophysics Program, Baylor College of Medicine, Houston, Texas, United States of America
| | - Nathaniel Magilnick
- Department of Medicine, D. Geffen School of Medicine at University of California Los Angeles, Los Angeles, California, United States of America
| | - Kirill Tsirulnikov
- Department of Medicine, D. Geffen School of Medicine at University of California Los Angeles, Los Angeles, California, United States of America
| | - Natalia Abuladze
- Department of Medicine, D. Geffen School of Medicine at University of California Los Angeles, Los Angeles, California, United States of America
| | - Ivo Atanasov
- Department of Microbiology, Immunology and Molecular Genetics, and California NanoSystems Institute, University of California Los Angeles, Los Angeles, California, United States of America
| | - Peng Ge
- Department of Microbiology, Immunology and Molecular Genetics, and California NanoSystems Institute, University of California Los Angeles, Los Angeles, California, United States of America
| | - Mohandas Narla
- New York Blood Centre, New York, New York, United States of America
| | - Alexander Pushkin
- Department of Medicine, D. Geffen School of Medicine at University of California Los Angeles, Los Angeles, California, United States of America
- * E-mail: (IK); (ZHZ); (AP)
| | - Z. Hong Zhou
- Department of Microbiology, Immunology and Molecular Genetics, and California NanoSystems Institute, University of California Los Angeles, Los Angeles, California, United States of America
- Structural Computational Biology and Molecular Biophysics Program, Baylor College of Medicine, Houston, Texas, United States of America
- * E-mail: (IK); (ZHZ); (AP)
| | - Ira Kurtz
- Department of Medicine, D. Geffen School of Medicine at University of California Los Angeles, Los Angeles, California, United States of America
- Brain Research Institute, University of California Los Angeles, Los Angeles, California, United States of America
- * E-mail: (IK); (ZHZ); (AP)
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3
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Abstract
SLC4A gene family proteins include bicarbonate transporters that move HCO(3)(-) across the plasma membrane and regulate intracellular pH and transepithelial movement of acid-base equivalents. These transporters are Cl/HCO(3) exchangers, electrogenic Na/HCO(3) cotransporters, electroneutral Na/HCO(3) cotransporters, and Na(+)-driven Cl/HCO(3) exchanger. Studies of the bicarbonate transporters in vitro and in vivo have demonstrated their physiological importance for acid-base homeostasis at the cellular and systemic levels. Recent advances in structure/function analysis have also provided valuable information on domains or motifs critical for regulation, ion translocation, and protein topology. This chapter focuses on the molecular mechanisms of ion transport along with associated structural aspects from mutagenesis of particular residues and from chimeric constructs. Structure/function studies have helped to understand the mechanism by which ion substrates are moved via the transporters. This chapter also describes some insights into the structure of SLC4A1 (AE1) and SLC4A4 (NBCe1) transporters. Finally, as some SLC4A transporters exist in concert with other proteins in the cells, the structural features associated with protein-protein interactions are briefly discussed.
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Affiliation(s)
- Inyeong Choi
- Department of Physiology, Emory University, Atlanta, Georgia, USA.
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4
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Kim LY, Johnson MC, Schmidt‐Krey I. Cryo‐EM in the Study of Membrane Transport Proteins. Compr Physiol 2012; 2:283-93. [DOI: 10.1002/cphy.c110028] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/10/2022]
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Kao L, Sassani P, Azimov R, Pushkin A, Abuladze N, Peti-Peterdi J, Liu W, Newman D, Kurtz I. Oligomeric structure and minimal functional unit of the electrogenic sodium bicarbonate cotransporter NBCe1-A. J Biol Chem 2008; 283:26782-94. [PMID: 18658147 DOI: 10.1074/jbc.m804006200] [Citation(s) in RCA: 52] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/20/2023] Open
Abstract
The electrogenic sodium bicarbonate cotransporter NBCe1-A mediates the basolateral absorption of sodium and bicarbonate in the proximal tubule. In this study the oligomeric state and minimal functional unit of NBCe1-A were investigated. Wild-type (wt) NBCe1-A isolated from mouse kidney or heterologously expressed in HEK293 cells was predominantly in a dimeric state as was shown using fluorescence energy transfer, pulldown, immunoprecipitation, cross-linking experiments, and nondenaturing perfluorooctanoate-PAGE. NBCe1-A monomers were found to be covalently linked by S-S bonds. When each of the 15 native cysteine residues were individually removed on a wt-NBCe1-A backbone, dimerization of the cotransporter was not affected. In experiments involving multiple native cysteine residue removal, both Cys(630) and Cys(642) in extracellular loop 3 were shown to mediate S-S bond formation between NBCe1-A monomers. When native NBCe1-A cysteine residues were individually reintroduced into a cysteineless NBCe1-A mutant backbone, the finding that a Cys(992) construct that lacked S-S bonds functioned normally indicated that stable covalent linkage of NBCe1-A monomers was not a necessary requirement for functional activity of the cotransporter. Studies using concatameric constructs of wt-NBCe1-A, whose activity is resistant to methanesulfonate reagents, and an NBCe1-A(T442C) mutant, whose activity is completely inhibited by methanesulfonate reagents, confirmed that NBCe1-A monomers are functional. Our results demonstrate that wt-NBCe1-A is predominantly a homodimer, dependent on S-S bond formation that is composed of functionally active monomers.
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Affiliation(s)
- Liyo Kao
- Division of Nephrology, David Geffen School Medicine, UCLA, Los Angeles, California 90095-1689, USA
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6
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Pushkin A, Kurtz I. SLC4 base (HCO3 -, CO3 2-) transporters: classification, function, structure, genetic diseases, and knockout models. Am J Physiol Renal Physiol 2006; 290:F580-99. [PMID: 16461757 DOI: 10.1152/ajprenal.00252.2005] [Citation(s) in RCA: 116] [Impact Index Per Article: 6.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022] Open
Abstract
In prokaryotic and eukaryotic organisms, biochemical and physiological processes are sensitive to changes in H(+) activity. For these processes to function optimally, a variety of proteins have evolved that transport H(+)/base equivalents across cell and organelle membranes, thereby maintaining the pH of various intracellular and extracellular compartments within specific limits. The SLC4 family of base (HCO(3)(-), CO(3)(2(-))) transport proteins plays an essential role in mediating Na(+)- and/or Cl(-)-dependent base transport in various tissues and cell types in mammals. In addition to pH regulation, specific members of this family also contribute to vectorial transepithelial base transport in several organ systems including the kidney, pancreas, and eye. The importance of these transporters in mammalian cell biology is highlighted by the phenotypic abnormalities resulting from spontaneous SLC4 mutations in humans and targeted deletions in murine knockout models. This review focuses on recent advances in our understanding of the molecular organization and functional properties of SLC4 transporters and their role in disease.
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Affiliation(s)
- Alexander Pushkin
- Division of Nephrology, David Geffen School of Medicine at UCLA, University of California-Los Angeles, 10833 Le Conte Avenue, Rm. 7-155 Factor Bldg., Los Angeles, CA 90095, USA
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7
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Abuladze N, Azimov R, Newman D, Sassani P, Liu W, Tatishchev S, Pushkin A, Kurtz I. Critical amino acid residues involved in the electrogenic sodium-bicarbonate cotransporter kNBC1-mediated transport. J Physiol 2005; 565:717-30. [PMID: 15817634 PMCID: PMC1464572 DOI: 10.1113/jphysiol.2005.084988] [Citation(s) in RCA: 31] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/08/2022] Open
Abstract
We have previously reported a topological model of the electrogenic Na(+)-HCO(3)(-) cotransporter (NBC1) in which the cotransporter spans the plasma membrane 10 times with N- and C-termini localized intracellularly. An analysis of conserved amino acid residues among members of the SLC4 superfamily in both the transmembrane segments (TMs) and intracellular/extracellular loops (ILs/ELs) provided the basis for the mutagenesis approach taken in the present study to determine amino acids involved in NBC1-mediated ion transport. Using large-scale mutagenesis, acidic and basic amino acids putatively involved in ion transport mediated by the predominant variant of NBC1 expressed in the kidney (kNBC1) were mutated to neutral and/or oppositely charged amino acids. All mutant kNBC1 cotransporters were expressed in HEK-293T cells and the Na(+)-dependent base flux of the mutants was determined using intracellular pH measurements with 2',7'-bis-(carboxyethyl)-5(6)-carboxyfluorescein (BCECF). Critical glutamate, aspartate, lysine, arginine and histidine residues in ILs/ELs and TMs were detected that were essential for kNBC1-mediated Na(+)-dependent base transport. In addition, critical phenylalanine, serine, tyrosine, threonine and alanine residues in TMs and ILs/ELs were detected. Furthermore, several amino acid residues in ILs/ELs and TMs were shown to be essential for membrane targeting. The data demonstrate asymmetry of distribution of kNBC1 charged amino acids involved in ion recognition in putative outward-facing and inward-facing conformations. A model summarizing key amino acid residues involved in kNBC1-mediated ion transport is presented.
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Affiliation(s)
- Natalia Abuladze
- Division of Nephrology, David Geffen School of Medicine at UCLA, 10833 Le Conte Avenue, Room 7-155 Factor Building, Los Angeles, CA 90095, USA
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8
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Dahl NK, Jiang L, Chernova MN, Stuart-Tilley AK, Shmukler BE, Alper SL. Deficient HCO3- transport in an AE1 mutant with normal Cl- transport can be rescued by carbonic anhydrase II presented on an adjacent AE1 protomer. J Biol Chem 2003; 278:44949-58. [PMID: 12933803 DOI: 10.1074/jbc.m308660200] [Citation(s) in RCA: 41] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
Cl-/HCO3- exchange activity mediated by the AE1 anion exchanger is reduced by carbonic anhydrase II (CA2) inhibition or by prevention of CA2 binding to the AE1 C-terminal cytoplasmic tail. This type of AE1 inhibition is thought to represent reduced metabolic channeling of HCO3- to the intracellular HCO3- binding site of AE1. To test the hypothesis that CA2 binding might itself allosterically activate AE1 in Xenopus oocytes, we compared Cl-/Cl- and Cl-/HCO3- exchange activities of AE1 polypeptides with truncation and missense mutations in the C-terminal tail. The distal renal tubular acidosis-associated AE1 901X mutant exhibited both Cl-/Cl- and Cl-/HCO3- exchange activities. In contrast, AE1 896X, 891X, and AE1 missense mutants in the CA2 binding site were inactive as Cl-/HCO3- exchangers despite exhibiting normal Cl-/Cl- exchange activities. Co-expression of CA2 enhanced wild-type AE1-mediated Cl-/HCO3- exchange, but not Cl-/Cl- exchange. CA2 co-expression could not rescue Cl-/HCO3- exchange activity in AE1 mutants selectively impaired in Cl-/HCO3- exchange. However, co-expression of transport-incompetent AE1 mutants with intact CA2 binding sites completely rescued Cl-/HCO3- exchange by an AE1 missense mutant devoid of CA2 binding, with activity further enhanced by CA2 co-expression. The same transport-incompetent AE1 mutants failed to rescue Cl-/HCO3- exchange by the AE1 truncation mutant 896X, despite preservation of the latter's core CA2 binding site. These data increase the minimal extent of a functionally defined CA2 binding site in AE1. The inter-protomeric rescue of HCO3- transport within the AE1 dimer shows functional proximity of the C-terminal cytoplasmic tail of one protomer to the anion translocation pathway in the adjacent protomer within the AE1 heterodimer. The data strongly support the hypothesis that an intact transbilayer anion translocation pathway is completely contained within an AE1 monomer.
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Affiliation(s)
- Neera K Dahl
- Molecular Medicine and Renal Units, Beth Israel Deaconess Medical Center, Department of Medicine, Harvard Medical School, Boston, Massachusetts 02215, USA
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9
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Abstract
Na(+)/H(+) antiporters are membrane proteins that play a major role in pH and Na(+) homeostasis of cells throughout the biological kingdom, from bacteria to humans and higher plants. The emerging genomic sequence projects already have started to reveal that the Na(+)/H(+) antiporters cluster in several families. Structure and function studies of a purified antiporter protein have as yet been conducted mainly with NhaA, the key Na(+)/H(+) antiporter of Escherichia coli. This antiporter has been overexpressed, purified and reconstituted in a functional form in proteoliposomes. It has recently been crystallized in both 3D as well as 2D crystals. The NhaA 2D crystals were analyzed by cryoelectron microscopy and a density map at 4 A resolution was obtained and a 3D map was reconstructed. NhaA is shown to exist in the 2D crystals as a dimer of monomers each composed of 12 transmembrane segments with an asymmetric helix packing. This is the first insight into the structure of a polytopic membrane protein. Many Na(+)/H(+) antiporters are characterized by very dramatic sensitivity to pH, a property that corroborates their role in pH homeostasis. The molecular mechanism underlying this pH sensitivity has been studied in NhaA. Amino acid residues involved in the pH response have been identified. Conformational changes transducing the pH change into a change in activity were found in loop VIII-IX and at the N-terminus by probing trypsin digestion or binding of a specific monoclonal antibody respectively. Regulation by pH of the eukaryotic Na(+)/H(+) antiporters involves an intricate signal transduction pathway (recently reviewed by Yun et al., Am. J. Physiol. 269 (1995) G1-G11). The transcription of NhaA has been shown to be regulated by a novel Na(+)-specific regulatory network. It is envisaged that interdisciplinary approaches combining structure, molecular and cell biology as well as genomics should be applied in the future to the study of this important group of transporters.
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Affiliation(s)
- E Padan
- Department of Microbial and Molecular Ecology, Institute of Life Sciences, Hebrew University of Jerusalem, Israel.
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10
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Rigaud J, Chami M, Lambert O, Levy D, Ranck J. Use of detergents in two-dimensional crystallization of membrane proteins. BIOCHIMICA ET BIOPHYSICA ACTA 2000; 1508:112-28. [PMID: 11090821 DOI: 10.1016/s0005-2736(00)00307-2] [Citation(s) in RCA: 74] [Impact Index Per Article: 3.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
Abstract
Structure determination at high resolution is actually a difficult challenge for membrane proteins and the number of membrane proteins that have been crystallized is still small and far behind that of soluble proteins. Because of their amphiphilic character, membrane proteins need to be isolated, purified and crystallized in detergent solutions. This makes it difficult to grow the well-ordered three-dimensional crystals that are required for high resolution structure analysis by X-ray crystallography. In this difficult context, growing crystals confined to two dimensions (2D crystals) and their structural analysis by electron crystallography has opened a new way to solve the structure of membrane proteins. However, 2D crystallization is one of the major bottlenecks in the structural studies of membrane proteins. Advances in our understanding of the interaction between proteins, lipids and detergents as well as development and improvement of new strategies will facilitate the success rate of 2D crystallization. This review deals with the various available strategies for obtaining 2D crystals from detergent-solubilized intrinsic membrane proteins. It gives an overview of the methods that have been applied and gives details and suggestions of the physical processes leading to the formation of the ordered arrays which may be of help for getting more proteins crystallized in a form suitable for high resolution structural analysis by electron crystallography.
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Affiliation(s)
- J Rigaud
- Institut Curie, Section de Recherche, UMR-CNRS 168 and LRC-CEA 8, 11 rue Pierre et Marie Curie, 75231, Paris, France.
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11
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Yin CC, Aldema-Ramos ML, Borges-Walmsley MI, Taylor RW, Walmsley AR, Levy SB, Bullough PA. The quarternary molecular architecture of TetA, a secondary tetracycline transporter from Escherichia coli. Mol Microbiol 2000; 38:482-92. [PMID: 11069672 DOI: 10.1046/j.1365-2958.2000.02149.x] [Citation(s) in RCA: 46] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022]
Abstract
TetA, a tetracycline cation/proton antiporter, was expressed in Escherichia coli with a C-terminal tag of six histidines, solubilized in dodecyl maltoside and purified in a single step using Ni2+ affinity chromatography. Two-dimensional crystals were obtained after reconstitution of purified protein with lipids. Electron microscopy of negatively stained crystals revealed a trigonal symmetry, from which we infer that this secondary transporter has a trimeric structure. An overall molecular envelope can be described by a triangle of side approximately 100 A enclosing a central stain-filled depression. These dimensions are consistent with those obtained from projection views of single, isolated TetA particles that also display a trimeric architecture, confirming that the threefold symmetry is not simply a consequence of crystal-packing interactions. These data represent the first direct view of the quarternary arrangement of any antibiotic efflux pump. They are fully consistent with biochemical data on TetA, which indicate that it functions as a multimer and that the monomer consists of two domains, one of which plays the major part in oligomerization interactions.
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Affiliation(s)
- C C Yin
- Krebs Institute for Biomolecular Research, Department of Molecular Biology and Biotechnology, University of Sheffield, Firth Court, Western Bank, Sheffield S10 2TN, UK
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12
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Zolotarev AS, Shmukler BE, Alper SL. AE2 anion exchanger polypeptide is a homooligomer in pig gastric membranes: a chemical cross-linking study. Biochemistry 1999; 38:8521-31. [PMID: 10387099 DOI: 10.1021/bi990337h] [Citation(s) in RCA: 17] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Abstract
Although considerable information is available on the oligomeric states of the AE1 (band 3) anion exchanger, little is known about the physiological state of the polypeptides encoded by the nonerythroid AE genes, AE2 and AE3. We have previously characterized the proteolytic susceptibility of native pig gastric AE2. In the course of studies in which pig gastric membranes were treated with the AE2 transport antagonist, DIDS, we noted evidence for cross-linking of AE2 proteolytic fragments to higher-order oligomeric forms. We have characterized the ability of DIDS and of selected N-hydroxysuccinimide cross-linking agents to increase the proportion of SDS-resistant oligomers of pig gastric AE2 and its proteolytic fragments. Cross-linking exhibited time and concentration dependence. N-Terminal protein sequencing proved that DIDS treatment created AE2 homodimers. Putative homotetramers were also observed. Protomers were cross-linked via residues within the C-terminal 40 kDa of AE2. Prior proteolytic cleavage of AE2 in membranes resulted in decreased yield of subsequently cross-linked products. AE2 cross-linking could not be detected in membranes pretreated by hypotonic wash and freeze-thaw. The results are interpreted in light of the deduced amino acid sequence of the transmembrane domain of pig AE2.
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Affiliation(s)
- A S Zolotarev
- Molecular Medicine Unit, Beth Israel Deaconess Medical Center, Department of Medicine, Harvard Medical School, Boston, Massachusetts 02215, USA
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13
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Taylor AM, Boulter J, Harding SE, Cölfen H, Watts A. Hydrodynamic properties of human erythrocyte band 3 solubilized in reduced Triton X-100. Biophys J 1999; 76:2043-55. [PMID: 10096900 PMCID: PMC1300178 DOI: 10.1016/s0006-3495(99)77361-3] [Citation(s) in RCA: 19] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/21/2022] Open
Abstract
The oligomeric state and function of band 3, purified by sulfhydryl affinity chromatography in reduced Triton X-100, was investigated. Size exclusion high-performance liquid chromatography showed that a homogeneous population of band 3 dimers could be purified from whole erythrocyte membranes. The elution profile of band 3 purified from membranes that had been stripped of its cytoskeleton before solubilization was a broad single peak describing a heterogeneous population of oligomers with a mean Stokes radius of 100 A. Sedimentation velocity ultracentrifugation analysis confirmed particle heterogeneity and further showed monomer/dimer/tetramer equilibrium self-association. Whether the conversion of dimer to the form described by a Stokes radius of 100 A was initiated by removal of cytoskeletal components, alkali-induced changes in band 3 conformation, or alkali-induced loss of copurifying ligands remains unclear. After incubation at 20 degrees C for 24 h, both preparations of band 3 converted to a common form characterized by a mean Stokes radius of 114 A. This form of the protein, examined by equilibrium sedimentation ultracentrifugation, is able to self-associate reversibly, and the self-association can be described by a dimer/tetramer/hexamer model, although the presence of higher oligomers cannot be discounted. The ability of the different forms of the protein to bind stilbene disulfonates revealed that the dimer had the highest inhibitor binding affinity, and the form characterized by a mean Stokes radius of 114 A to have the lowest.
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Affiliation(s)
- A M Taylor
- Department of Biochemistry, Oxford University, Oxford, OX1 3QU, England
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14
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Askin D, Bloomberg GB, Chambers EJ, Tanner MJ. NMR solution structure of a cytoplasmic surface loop of the human red cell anion transporter, band 3. Biochemistry 1998; 37:11670-8. [PMID: 9709005 DOI: 10.1021/bi973158d] [Citation(s) in RCA: 13] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/08/2023]
Abstract
The membrane domain of the human red cell anion transport protein, band 3, is too large to be studied by solution nuclear magnetic resonance spectroscopy (NMR), and its amphiphilic nature requires the use of detergents for solubilization. An alternative approach is to divide the protein into smaller (trans-membrane or surface loop) domains for NMR study. We report the structure of a 46-residue synthetic peptide that corresponds to the cytoplasmic surface loop connecting the putative 12th and 13th trans-membrane spans (residues 796-841) in the 14 span model of band 3. This peptide was shown by circular dichroism (CD) to be 38% helical in 30% trifluoroacetic acid. Two regions of helix (one close to the N-terminus of the peptide and one close to the C-terminus of the peptide) were identified by NMR. Long-range nuclear Overhauser effect (NOE) cross-peaks showed the two helices to be in near proximity. The helices were separated by a proline-rich loop that exhibited local order but was mobile with respect to the rest of the peptide. We discuss how the NMR structure of this loop fits the current models of band 3 structure and topology and the results of recent mutagenesis experiments. A cyclic version of this peptide was synthesized and studied by CD, but NMR studies were not possible due to the low solubility of this peptide.
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Affiliation(s)
- D Askin
- Department of Biochemistry, School of Medical Sciences, Bristol University, UK
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15
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Hasler L, Heymann JB, Engel A, Kistler J, Walz T. 2D crystallization of membrane proteins: rationales and examples. J Struct Biol 1998; 121:162-71. [PMID: 9615435 DOI: 10.1006/jsbi.1998.3960] [Citation(s) in RCA: 81] [Impact Index Per Article: 3.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Abstract
The difficulty in crystallizing channel proteins in three dimensions limits the use of X-ray crystallography in solving their structures. In contrast, the amphiphilic character of integral membrane proteins promotes their integration into artificial lipid bilayers. Protein-protein interactions may lead to ordering of the proteins within the lipid bilayer into two-dimensional crystals that are amenable to structural studies by electron crystallography and atomic force microscopy. While reconstitution of membrane proteins with lipids is readily achieved, the mechanisms for crystal formation during or after reconstitution are not well understood. The nature of the detergent and lipid as well as pH and counter-ions is known to influence the crystal type and quality. Protein-protein interactions may also promote crystal stacking and aggregation of the sheet-like crystals, posing problems in data collection. Although highly promising, the number of well-studied examples is still too small to draw conclusions that would be applicable to any membrane protein of interest. Here we discuss parameters influencing the outcome of two-dimensional crystallization trials using prominent examples of channel protein crystals and highlight areas where further improvements to crystallization protocols can be made.
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Affiliation(s)
- L Hasler
- Maurice E. Müller Institute for Microscopy, Biozentrum, University of Basel, Switzerland
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16
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Abstract
This review discusses recent advances in our understanding of the structure, function and molecular genetics of the membrane domain of red cell anion exchanger, band 3 (AE1), and its role in red cell and kidney disease. A new model for the topology of band 3 has been proposed, which suggests the membrane domain has 12 membrane spans, rather than the 14 membrane spans of earlier models. The major difference between the models is in the topology of the region on the C-terminal side of membrane spans 1-7. Two dimensional crystals of the deglycosylated membrane domain of band 3 have yielded two and three dimensional projection maps of the membrane domain dimer at low resolution. The human band 3 gene has been completely sequenced and this has facilitated the study of natural band 3 mutations and their involvement in disease. About 20% of hereditary spherocytosis cases arise from heterozygosity for band 3 mutations, and result in the absence or decrease of the mutant protein in the red cell membrane. Several other natural band 3 mutations are known that appear to be clinically benign, but alter red cell phenotype or are associated with altered red cell blood group antigens. These include the mutant band 3 present in Southeast Asian ovalocytosis, a condition which provides protection against cerebral malaria in children. Familial distal renal tubular acidosis, a condition associated with kidney stones, has been shown to result from a novel group of band 3 mutations. The total absence of band 3 has been described in animals-occurring naturally in cattle and after targeted disruption in mice. Some of these severely anaemic animals survive, so band 3 is not strictly essential for life. Although the band 3-negative red cells were very unstable, they contained a normally-assembled red cell skeleton, suggesting that the bilayer of the normal red cell membrane is stabilized by band 3 interactions with membrane lipids, rather than by interactions with the spectrin skeleton.
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Affiliation(s)
- M J Tanner
- Department of Biochemistry, School of Medical Sciences, University of Bristol, UK
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17
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Vince JW, Sarabia VE, Reithmeier RA. Self-association of Band 3, the human erythrocyte anion exchanger, in detergent solution. BIOCHIMICA ET BIOPHYSICA ACTA 1997; 1326:295-306. [PMID: 9218560 DOI: 10.1016/s0005-2736(97)00033-3] [Citation(s) in RCA: 23] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 02/04/2023]
Abstract
Dimeric Band 3 purified in n-dodecyl octaethyleneglycol (C12E8) underwent an irreversible, temperature-dependent association, resulting in a complex with a Stokes radius slightly larger than a native tetramer, before forming a higher molecular weight aggregate. Self-association occurred with a half-time of about 1 h at 37 degrees C but did not occur at 0 degrees C after several days. No change in the secondary structure of Band 3, as observed by circular dichroism, occurred during the association process. However, self-association of Band 3 was accompanied by loss of the stilbene disulfonate inhibitor binding site. No association or loss of inhibitor binding occurred with the dimeric membrane domain under similar incubation conditions. The membrane domain dimer was also stable over a wide range of pH (5.5-9.5) and buffer conditions, while Band 3 aggregated below pH 6.5. Inhibitors of anion transport, which stabilize the membrane domain, slowed the association. Band 3, depleted of phospholipids by extensive washing of resin-bound protein with detergent or, incubated with excess detergent, was more prone to aggregation. The membrane domain also showed some aggregation when depleted of lipids. Preparations could be stabilized by adding dimyristoylphosphatidylcholine (DMPC) prior to the 37 degrees C incubation. The effect of inhibitors and DMPC was additive, with a combination of 1 mM 4,4'-dinitrostilbene-2,2'-disulfonate (DNDS) and 1:1 (wt/wt) DMPC:Band 3 stabilizing 90% of the protein to a 24-h incubation at 37 degrees C. The results suggest that self-association of Band 3 dimers is promoted by the cytoplasmic domain but results in alterations to the membrane domain involving the loss of essential phospholipids. Addition of phospholipid or inhibitors to Band 3 results in a stable preparation of the intact protein that may be suitable for crystallization studies.
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Affiliation(s)
- J W Vince
- MRC Group in Membrane Biology, Department of Medicine, University of Toronto, Canada
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18
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Dolder M, Engel A, Zulauf M. The micelle to vesicle transition of lipids and detergents in the presence of a membrane protein: towards a rationale for 2D crystallization. FEBS Lett 1996; 382:203-8. [PMID: 8612753 DOI: 10.1016/0014-5793(96)00180-9] [Citation(s) in RCA: 60] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/31/2023]
Abstract
The assembly of two-dimensional membrane protein crystals in the presence of lipids was analyzed with quasielastic light scattering and electron microscopy. Mixtures of detergent-solubilized lipids and/or proteins were submitted to slow or rapid dilution while measuring the hydrodynamic radii of the aggregates. Lipids alone exhibited lambda-shaped dilution curves with intermediate rod-shaped particles that converted into small vesicles. Depending on the protein-protein and protein-lipid interactions, detergent-solubilized protein-lipid mixtures showed a sharp transition from micelles to large densely packed proteoliposomes. Electron microscopy revealed that formation of crystals occurred shortly after this phase transition.
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Affiliation(s)
- M Dolder
- Institute of Cell Biology, ETH, Zürich, Switzerland
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19
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Chapter 13 Structure of the erythrocyte band 3 anion exchanger. ACTA ACUST UNITED AC 1996. [DOI: 10.1016/s1383-8121(96)80054-6] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register]
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20
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Haltia T, Freire E. Forces and factors that contribute to the structural stability of membrane proteins. BIOCHIMICA ET BIOPHYSICA ACTA 1995; 1241:295-322. [PMID: 7640299 DOI: 10.1016/0304-4157(94)00161-6] [Citation(s) in RCA: 84] [Impact Index Per Article: 2.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 01/26/2023]
Abstract
While a considerable amount of literature deals with the structural energetics of water-soluble proteins, relatively little is known about the forces that determine the stability of membrane proteins. Similarly, only a few membrane protein structures are known at atomic resolution, although new structures have recently been described. In this article, we review the current knowledge about the structural features of membrane proteins. We then proceed to summarize the existing literature regarding the thermal stability of bacteriorhodopsin, cytochrome-c oxidase, the band 3 protein, Photosystem II and porins. We conclude that a fundamental difference between soluble and membrane proteins is the high thermal stability of intrabilayer secondary structure elements in membrane proteins. This property manifests itself as incomplete unfolding, and is reflected in the observed low enthalpies of denaturation of most membrane proteins. By contrast, the extramembranous parts of membrane proteins may behave much like soluble proteins. A brief general account of thermodynamics factors that contribute to the stability of water soluble and membrane proteins is presented.
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Affiliation(s)
- T Haltia
- Department of Biology, Johns Hopkins University, Baltimore, MD 21218, USA
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21
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Watts A, Ulrich AS, Middleton DA. Membrane protein structure: the contribution and potential of novel solid state NMR approaches. Mol Membr Biol 1995; 12:233-46. [PMID: 8520624 DOI: 10.3109/09687689509072423] [Citation(s) in RCA: 40] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/31/2023]
Abstract
Alternative methods for describing molecular detail for large integral membrane proteins are required in the absence of routine crystallographic approaches. Novel solid state NMR methods, devised for the study of large molecular assemblies, are now finding applications in biological systems, including integral membrane proteins. Wild-type and genetically engineered proteins can be investigated and detailed information about side chains, prosthetic groups, ligands (e.g. drugs) and binding sites can be deduced. The molecular structure and dynamics of selected parts of the proteins are accessible by a range of different solid state NMR approaches. Inter- and intra-atomic distances can be determined rather accurately (within ångströms) and the orientation of molecular bonds (within 2 degrees) can be measured in ideal cases. Here, a brief description of the methods is given and then some specific examples described with an indication of the future potential for the approaches in studying membrane proteins. It is anticipated that this emerging NMR methodology will be more widely used in the future, not only for resolving local structure, but also for more expansive descriptions of membrane protein structure at atomic resolution.
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Affiliation(s)
- A Watts
- Department of Biochemistry, University of Oxford, UK
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22
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Kiyatkin AB, Natarajan P, Munshi S, Minor W, Johnson JE, Low PS. Crystallization and preliminary X-ray analysis of the cytoplasmic domain of human erythrocyte band 3. Proteins 1995; 22:293-7. [PMID: 7479704 DOI: 10.1002/prot.340220312] [Citation(s) in RCA: 9] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/25/2023]
Abstract
A cytoplasmic domain of the human erythrocyte membrane protein band 3 (M(r) = 42,500), residues 1-379, expressed in and purified from E. coli, has been crystallized by the method of vapor diffusion in sitting drops with subsequent streak-seeding at room temperature. Initial crystals were grown from solutions containing 65-68% saturated ammonium sulfate at pH 4.9 and 2 mg/ml protein. Subsequent streak-seeding into solutions of 50-53% ammonium sulfate at pH 4.9 and 7 mg/ml protein produced single crystals suitable for X-ray analysis, which contained pure protein as revealed by gel electrophoresis. The crystals belong to the monoclinic space group C2 with cell dimensions of a = 178.8 A, b = 90.5 A, c = 122.1 A, and beta = 131.3 degrees and diffract at least to 2.7 A resolution (at 100 K). A self-rotation function shows the presence of approximate 222 local symmetry.
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Affiliation(s)
- A B Kiyatkin
- Department of Chemistry, Purdue University, West Lafayette, Indiana 47907-1393, USA
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23
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Haltia T, Freire E. Forces and factors that contribute to the structural stability of membrane proteins. BIOCHIMICA ET BIOPHYSICA ACTA 1995; 1228:1-27. [PMID: 7857960 DOI: 10.1016/0005-2728(94)00161-w] [Citation(s) in RCA: 129] [Impact Index Per Article: 4.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 01/27/2023]
Abstract
While a considerable amount of literature deals with the structural energetics of water-soluble proteins, relatively little is known about the forces that determine the stability of membrane proteins. Similarly, only a few membrane protein structures are known at atomic resolution, although new structures have recently been described. In this article, we review the current knowledge about the structural features of membrane proteins. We then proceed to summarize the existing literature regarding the thermal stability of bacteriorhodopsin, cytochrome-c oxidase, the band 3 protein, Photosystem II and porins. We conclude that a fundamental difference between soluble and membrane proteins is the high thermal stability of intrabilayer secondary structure elements in membrane proteins. This property manifests itself as incomplete unfolding, and is reflected in the observed low enthalpies of denaturation of most membrane proteins. By contrast, the extramembranous parts of membrane proteins may behave much like soluble proteins. A brief general account of thermodynamics factors that contribute to the stability of water soluble and membrane proteins is presented.
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Affiliation(s)
- T Haltia
- Department of Biology, Johns Hopkins University, Baltimore, MD 21218
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24
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Abstract
In the past year, novel mammalian exchanger and co-transporter isoforms have been characterized. Specialized subdomains within these oligomeric transporters have been shown to be involved in biosynthesis, targeting, transport and regulation. Progress on the structural front has been limited due to the lack of high-resolution structures, but transport mutants responsible for disease states continue to be identified.
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25
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Abstract
The electroneutral exchange of chloride and bicarbonate across the human erythrocyte membrane is facilitated by Band 3, a 911 amino acid glycoprotein. The 43 kDa amino-terminal cytosolic domain binds the cytoskeleton, haemoglobin and glycolytic enzymes. The 52 kDa carboxyl-terminal membrane domain mediates anion transport. The protein is a functional dimer, in which the two subunits probably interact with one another by an allosteric mechanism. It is proposed that the link between the mobile cytoplasmic and the membrane-spanning domains of the protein is flexible, based on recent biochemical, biophysical and structural data. This explains the long-standing puzzle that attachment to the cytoskeletal spectrin and actin does not appear to restrict the rotational movement of the Band 3 protein in the erythrocyte membrane. In the Band 3 isoform from the Southeast Asian Ovalocytes (SAO) this link is altered, resulting a tighter attachment of the cytoskeleton to the plasma membrane and a more rigid red blood cell.
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Affiliation(s)
- D N Wang
- European Molecular Biology Laboratory, Heidelberg, Germany
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26
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Ortwein R, Oslender-Kohnen A, Deuticke B. Band 3, the anion exchanger of the erythrocyte membrane, is also a flippase. BIOCHIMICA ET BIOPHYSICA ACTA 1994; 1191:317-23. [PMID: 8172917 DOI: 10.1016/0005-2736(94)90182-1] [Citation(s) in RCA: 17] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 01/29/2023]
Abstract
The transbilayer reorientation (flip-flop) of the long-chain amphiphilic anion DENSA (5-(N-decyl)aminonaphthalene-2-sulfonic acid) in the erythrocyte membrane was studied by fluorescence spectroscopy. DENSA intercalates into the membrane at a high membrane/water partition coefficient (3.2.10(5)) and rapidly reorients from the outer to the inner layer in a first order process (k = 0.11 min-1, 37 degrees C, pH 7.4) leading to a steady-state distribution inner:outer layer of about 30:70. The activation energy of the fully reversible and symmetric flip process is about 110 kJ/mol. DIDS and various other established covalent and non-covalent inhibitors of anion transport via the erythrocyte anion exchanger, band 3 (AE 1), suppress the flip to a minimum of about 30-35% of the control. The flip is also inhibited by Cl- with a half maximal inhibitory concentration equal to that required for the inhibition of the exchange flux of ordinary anions via band 3. These findings indicate the involvement of a band 3 mediated (DIDS-sensitive) component of the flip and a DIDS-insensitive one, possibly involving, at least to some extent, simple transbilayer 'diffusion'. This latter component is stimulated by diamide, an SH oxidant known to increase the permeability of the membrane lipid domain of the erythrocyte. Alcohols (butanol, hexanol) accelerate both flip components. Papain treatment, known to inhibit 'ordinary' anion exchange, accelerates both flip and flop. The results suggest that band 3 protein, besides being a conventional transporter of anions, can act as a flippase translocating anionic, membrane-intercalated amphiphiles approaching the transporter from the lipid domain. The flippase mode of operation of band 3 must, however, differ in its mechanism from the conventional exchange mode.
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Affiliation(s)
- R Ortwein
- Institut für Physiologie, Medizinische Fakultät, Rheinisch-Westfälisch Technische Hochschule, Aachen, Germany
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27
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GARGARO AR, BLOOMBERG GB, DEMPSEY CE, MURRAY M, TANNER MJA. The solution structures of the first and second transmembrane-spanning segments of band 3. ACTA ACUST UNITED AC 1994. [DOI: 10.1111/j.1432-1033.1994.tb18757.x] [Citation(s) in RCA: 25] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
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28
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Robin Harris J, Horne RW. Negative staining: A brief assessment of current technical benefits, limitations and future possibilities. Micron 1994. [DOI: 10.1016/0968-4328(94)90051-5] [Citation(s) in RCA: 28] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/27/2022]
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29
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