1
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Hiraizumi M, Akashi T, Murasaki K, Kishida H, Kumanomidou T, Torimoto N, Nureki O, Miyaguchi I. Transport and inhibition mechanism of the human SGLT2-MAP17 glucose transporter. Nat Struct Mol Biol 2024; 31:159-169. [PMID: 38057552 PMCID: PMC10803289 DOI: 10.1038/s41594-023-01134-0] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/10/2023] [Accepted: 09/22/2023] [Indexed: 12/08/2023]
Abstract
Sodium-glucose cotransporter 2 (SGLT2) is imporant in glucose reabsorption. SGLT2 inhibitors suppress renal glucose reabsorption, therefore reducing blood glucose levels in patients with type 2 diabetes. We and others have developed several SGLT2 inhibitors starting from phlorizin, a natural product. Using cryo-electron microscopy, we present the structures of human (h)SGLT2-MAP17 complexed with five natural or synthetic inhibitors. The four synthetic inhibitors (including canagliflozin) bind the transporter in the outward conformations, while phlorizin binds it in the inward conformation. The phlorizin-hSGLT2 interaction exhibits biphasic kinetics, suggesting that phlorizin alternately binds to the extracellular and intracellular sides. The Na+-bound outward-facing and unbound inward-open structures of hSGLT2-MAP17 suggest that the MAP17-associated bundle domain functions as a scaffold, with the hash domain rotating around the Na+-binding site. Thus, Na+ binding stabilizes the outward-facing conformation, and its release promotes state transition to inward-open conformation, exhibiting a role of Na+ in symport mechanism. These results provide structural evidence for the Na+-coupled alternating-access mechanism proposed for the transporter family.
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Affiliation(s)
- Masahiro Hiraizumi
- Discovery Technology Laboratories Sohyaku Innovative Research Division, Mitsubishi Tanabe Pharma, Yokohama, Japan.
- Department of Chemistry and Biotechnology, Graduate School of Engineering, The University of Tokyo, Tokyo, Japan.
| | - Tomoya Akashi
- DMPK Research Laboratories Sohyaku Innovative Research Division, Mitsubishi Tanabe Pharma, Yokohama, Japan
| | - Kouta Murasaki
- Discovery Technology Laboratories Sohyaku Innovative Research Division, Mitsubishi Tanabe Pharma, Yokohama, Japan
| | - Hiroyuki Kishida
- Discovery Technology Laboratories Sohyaku Innovative Research Division, Mitsubishi Tanabe Pharma, Yokohama, Japan
| | - Taichi Kumanomidou
- Discovery Technology Laboratories Sohyaku Innovative Research Division, Mitsubishi Tanabe Pharma, Yokohama, Japan
| | - Nao Torimoto
- Discovery Technology Laboratories Sohyaku Innovative Research Division, Mitsubishi Tanabe Pharma, Yokohama, Japan
| | - Osamu Nureki
- Department of Biological Sciences, Graduate School of Science, The University of Tokyo, Tokyo, Japan.
| | - Ikuko Miyaguchi
- Discovery Technology Laboratories Sohyaku Innovative Research Division, Mitsubishi Tanabe Pharma, Yokohama, Japan.
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2
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Diederich J, Mounkoro P, Tirado HA, Chevalier N, Van Schaftingen E, Veiga-da-Cunha M. SGLT5 is the renal transporter for 1,5-anhydroglucitol, a major player in two rare forms of neutropenia. Cell Mol Life Sci 2023; 80:259. [PMID: 37594549 PMCID: PMC10439028 DOI: 10.1007/s00018-023-04884-8] [Citation(s) in RCA: 5] [Impact Index Per Article: 5.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/16/2023] [Revised: 06/20/2023] [Accepted: 07/17/2023] [Indexed: 08/19/2023]
Abstract
Neutropenia and neutrophil dysfunction in glycogen storage disease type 1b (GSD1b) and severe congenital neutropenia type 4 (SCN4), associated with deficiencies of the glucose-6-phosphate transporter (G6PT/SLC37A4) and the phosphatase G6PC3, respectively, are the result of the accumulation of 1,5-anhydroglucitol-6-phosphate in neutrophils. This is an inhibitor of hexokinase made from 1,5-anhydroglucitol (1,5-AG), an abundant polyol in blood. 1,5-AG is presumed to be reabsorbed in the kidney by a sodium-dependent-transporter of uncertain identity, possibly SGLT4/SLC5A9 or SGLT5/SLC5A10. Lowering blood 1,5-AG with an SGLT2-inhibitor greatly improved neutrophil counts and function in G6PC3-deficient and GSD1b patients. Yet, this effect is most likely mediated indirectly, through the inhibition of the renal 1,5-AG transporter by glucose, when its concentration rises in the renal tubule following inhibition of SGLT2. To identify the 1,5-AG transporter, both human and mouse SGLT4 and SGLT5 were expressed in HEK293T cells and transport measurements were performed with radiolabelled compounds. We found that SGLT5 is a better carrier for 1,5-AG than for mannose, while the opposite is true for human SGLT4. Heterozygous variants in SGLT5, associated with a low level of blood 1,5-AG in humans cause a 50-100% reduction in 1,5-AG transport activity tested in model cell lines, indicating that SGLT5 is the predominant kidney 1,5-AG transporter. These and other findings led to the conclusion that (1) SGLT5 is the main renal transporter of 1,5-AG; (2) frequent heterozygous mutations (allelic frequency > 1%) in SGLT5 lower blood 1,5-AG, favourably influencing neutropenia in G6PC3 or G6PT deficiency; (3) the effect of SGLT2-inhibitors on blood 1,5-AG level is largely indirect; (4) specific SGLT5-inhibitors would be more efficient to treat these neutropenias than SGLT2-inhibitors.
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Affiliation(s)
- Jennifer Diederich
- Metabolic Research Group, de Duve Institute and UCLouvain, de Duve Institute, 75, Av. Hippocrate, 1200, Brussels, Belgium
| | - Pierre Mounkoro
- Metabolic Research Group, de Duve Institute and UCLouvain, de Duve Institute, 75, Av. Hippocrate, 1200, Brussels, Belgium
| | - Hernan A Tirado
- Metabolic Research Group, de Duve Institute and UCLouvain, de Duve Institute, 75, Av. Hippocrate, 1200, Brussels, Belgium
| | - Nathalie Chevalier
- Metabolic Research Group, de Duve Institute and UCLouvain, de Duve Institute, 75, Av. Hippocrate, 1200, Brussels, Belgium
| | - Emile Van Schaftingen
- Metabolic Research Group, de Duve Institute and UCLouvain, de Duve Institute, 75, Av. Hippocrate, 1200, Brussels, Belgium
| | - Maria Veiga-da-Cunha
- Metabolic Research Group, de Duve Institute and UCLouvain, de Duve Institute, 75, Av. Hippocrate, 1200, Brussels, Belgium.
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3
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Bazzone A, Zerlotti R, Barthmes M, Fertig N. Functional characterization of SGLT1 using SSM-based electrophysiology: Kinetics of sugar binding and translocation. Front Physiol 2023; 14:1058583. [PMID: 36824475 PMCID: PMC9941201 DOI: 10.3389/fphys.2023.1058583] [Citation(s) in RCA: 4] [Impact Index Per Article: 4.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/30/2022] [Accepted: 01/17/2023] [Indexed: 02/10/2023] Open
Abstract
Beside the ongoing efforts to determine structural information, detailed functional studies on transporters are essential to entirely understand the underlying transport mechanisms. We recently found that solid supported membrane-based electrophysiology (SSME) enables the measurement of both sugar binding and transport in the Na+/sugar cotransporter SGLT1 (Bazzone et al, 2022a). Here, we continued with a detailed kinetic characterization of SGLT1 using SSME, determining KM and KD app for different sugars, kobs values for sugar-induced conformational transitions and the effects of Na+, Li+, H+ and Cl- on sugar binding and transport. We found that the sugar-induced pre-steady-state (PSS) charge translocation varies with the bound ion (Na+, Li+, H+ or Cl-), but not with the sugar species, indicating that the conformational state upon sugar binding depends on the ion. Rate constants for the sugar-induced conformational transitions upon binding to the Na+-bound carrier range from 208 s-1 for D-glucose to 95 s-1 for 3-OMG. In the absence of Na+, rate constants are decreased, but all sugars bind to the empty carrier. From the steady-state transport current, we found a sequence for sugar specificity (Vmax/KM): D-glucose > MDG > D-galactose > 3-OMG > D-xylose. While KM differs 160-fold across tested substrates and plays a major role in substrate specificity, Vmax only varies by a factor of 1.9. Interestingly, D-glucose has the lowest Vmax across all tested substrates, indicating a rate limiting step in the sugar translocation pathway following the fast sugar-induced electrogenic conformational transition. SGLT1 specificity for D-glucose is achieved by optimizing two ratios: the sugar affinity of the empty carrier for D-glucose is similarly low as for all tested sugars (KD,K app = 210 mM). Affinity for D-glucose increases 14-fold (KD,Na app = 15 mM) in the presence of sodium as a result of cooperativity. Apparent affinity for D-glucose during transport increases 8-fold (KM = 1.9 mM) compared to KD,Na app due to optimized kinetics. In contrast, KM and KD app values for 3-OMG and D-xylose are of similar magnitude. Based on our findings we propose an 11-state kinetic model, introducing a random binding order and intermediate states corresponding to the electrogenic transitions detected via SSME upon substrate binding.
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Affiliation(s)
- Andre Bazzone
- Nanion Technologies GmbH, Munich, Germany,*Correspondence: Andre Bazzone,
| | - Rocco Zerlotti
- Nanion Technologies GmbH, Munich, Germany,Department of Structural Biology, Faculty of Biology and Pre-Clinics, Institute of Biochemistry, Genetics and Microbiology, University of Regensburg, Regensburg, Germany
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4
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del Alamo D, DeSousa L, Nair RM, Rahman S, Meiler J, Mchaourab HS. Integrated AlphaFold2 and DEER investigation of the conformational dynamics of a pH-dependent APC antiporter. Proc Natl Acad Sci U S A 2022; 119:e2206129119. [PMID: 35969794 PMCID: PMC9407458 DOI: 10.1073/pnas.2206129119] [Citation(s) in RCA: 14] [Impact Index Per Article: 7.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/07/2022] [Accepted: 07/08/2022] [Indexed: 11/18/2022] Open
Abstract
The Amino Acid-Polyamine-Organocation (APC) transporter GadC contributes to the survival of pathogenic bacteria under extreme acid stress by exchanging extracellular glutamate for intracellular γ-aminobutyric acid (GABA). Its structure, determined in an inward-facing conformation at alkaline pH, consists of the canonical LeuT-fold with a conserved five-helix inverted repeat, thereby resembling functionally divergent transporters such as the serotonin transporter SERT and the glucose-sodium symporter SGLT1. However, despite this structural similarity, it is unclear if the conformational dynamics of antiporters such as GadC follow the blueprint of these or other LeuT-fold transporters. Here, we used double electron-electron resonance (DEER) spectroscopy to monitor the conformational dynamics of GadC in lipid bilayers in response to acidification and substrate binding. To guide experimental design and facilitate the interpretation of the DEER data, we generated an ensemble of structural models in multiple conformations using a recently introduced modification of AlphaFold2 . Our experimental results reveal acid-induced conformational changes that dislodge the Cterminus from the permeation pathway coupled with rearrangement of helices that enables isomerization between inward- and outward-facing states. The substrate glutamate, but not GABA, modulates the dynamics of an extracellular thin gate without shifting the equilibrium between inward- and outward-facing conformations. In addition to introducing an integrated methodology for probing transporter conformational dynamics, the congruence of the DEER data with patterns of structural rearrangements deduced from ensembles of AlphaFold2 models illuminates the conformational cycle of GadC underpinning transport and exposes yet another example of the divergence between the dynamics of different families in the LeuT-fold.
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Affiliation(s)
- Diego del Alamo
- Department of Molecular Physiology and Biophysics, Vanderbilt University, Nashville, TN 37212
- Department of Chemistry, Vanderbilt University, Nashville, TN 37212
| | - Lillian DeSousa
- Department of Molecular Physiology and Biophysics, Vanderbilt University, Nashville, TN 37212
| | - Rahul M. Nair
- Department of Molecular Physiology and Biophysics, Vanderbilt University, Nashville, TN 37212
| | - Suhaila Rahman
- Department of Molecular Physiology and Biophysics, Vanderbilt University, Nashville, TN 37212
| | - Jens Meiler
- Department of Chemistry, Vanderbilt University, Nashville, TN 37212
- Institute for Drug Discovery, Leipzig University, Leipzig, Germany 04109
| | - Hassane S. Mchaourab
- Department of Molecular Physiology and Biophysics, Vanderbilt University, Nashville, TN 37212
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5
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Del Alamo D, Meiler J, Mchaourab HS. Principles of Alternating Access in LeuT-fold Transporters: Commonalities and Divergences. J Mol Biol 2022; 434:167746. [PMID: 35843285 DOI: 10.1016/j.jmb.2022.167746] [Citation(s) in RCA: 8] [Impact Index Per Article: 4.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/02/2022] [Revised: 07/08/2022] [Accepted: 07/09/2022] [Indexed: 11/15/2022]
Abstract
Found in all domains of life, transporters belonging to the LeuT-fold class mediate the import and exchange of hydrophilic and charged compounds such as amino acids, metals, and sugar molecules. Nearly two decades of investigations on the eponymous bacterial transporter LeuT have yielded a library of high-resolution snapshots of its conformational cycle linked by solution-state experimental data obtained from multiple techniques. In parallel, its topology has been observed in symporters and antiporters characterized by a spectrum of substrate specificities and coupled to gradients of distinct ions. Here we review and compare mechanistic models of transport for LeuT, its well-studied homologs, as well as functionally distant members of the fold, emphasizing the commonalities and divergences in alternating access and the corresponding energy landscapes. Our integrated summary illustrates how fold conservation, a hallmark of the LeuT fold, coincides with divergent choreographies of alternating access that nevertheless capitalize on recurrent structural motifs. In addition, it highlights the knowledge gap that hinders the leveraging of the current body of research into detailed mechanisms of transport for this important class of membrane proteins.
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Affiliation(s)
- Diego Del Alamo
- Department of Molecular Physiology and Biophysics, Vanderbilt University, Nashville, TN, USA; Department of Chemistry, Vanderbilt University, Nashville, TN, USA. https://twitter.com/DdelAlamo
| | - Jens Meiler
- Department of Chemistry, Vanderbilt University, Nashville, TN, USA; Institute for Drug Discovery, Leipzig University, Leipzig, DE, USA. https://twitter.com/MeilerLab
| | - Hassane S Mchaourab
- Department of Molecular Physiology and Biophysics, Vanderbilt University, Nashville, TN, USA.
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6
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Wright EM. SGLT2 Inhibitors: Physiology and Pharmacology. KIDNEY360 2021; 2:2027-2037. [PMID: 35419546 PMCID: PMC8986039 DOI: 10.34067/kid.0002772021] [Citation(s) in RCA: 44] [Impact Index Per Article: 14.7] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 04/23/2021] [Accepted: 09/17/2021] [Indexed: 02/07/2023]
Abstract
SGLTs are sodium glucose transporters found on the luminal membrane of the proximal tubule, where they reabsorb some 180 g (1 mol) of glucose from the glomerular filtrate each day. The natural glucoside phlorizin completely blocks glucose reabsorption. Oral SGLT2 inhibitors are rapidly absorbed into the blood stream, where theyremain in the circulation for hours. On glomerular filtration, they bind specifically to SGLT2 in the luminal membrane of the early proximal tubule to reduce glucose reabsorption by 50%-60%. Because of glucose excretion, these drugs lower plasma glucose and glycosylated hemoglobin levels in patients with type 2 diabetes mellitus. The drugs also protect against heart and renal failure. The aim of this review is to summarize what is known about the physiology of renal SGLTs and the pharmacology of SGLT drugs.
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Affiliation(s)
- Ernest M Wright
- Department of Physiology, David Geffen School of Medicine at UCLA, Los Angeles, California
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7
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Han L, Qu Q, Aydin D, Panova O, Robertson MJ, Xu Y, Dror RO, Skiniotis G, Feng L. Structure and mechanism of the SGLT family of glucose transporters. Nature 2021; 601:274-279. [PMID: 34880492 DOI: 10.1038/s41586-021-04211-w] [Citation(s) in RCA: 45] [Impact Index Per Article: 15.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/16/2019] [Accepted: 11/04/2021] [Indexed: 12/24/2022]
Abstract
Glucose is a primary energy source in living cells. The discovery in 1960s that a sodium gradient powers the active uptake of glucose in the intestine1 heralded the concept of a secondary active transporter that can catalyse the movement of a substrate against an electrochemical gradient by harnessing energy from another coupled substrate. Subsequently, coupled Na+/glucose transport was found to be mediated by sodium-glucose cotransporters2,3 (SGLTs). SGLTs are responsible for active glucose and galactose absorption in the intestine and for glucose reabsorption in the kidney4, and are targeted by multiple drugs to treat diabetes5. Several members within the SGLT family transport key metabolites other than glucose2. Here we report cryo-electron microscopy structures of the prototypic human SGLT1 and a related monocarboxylate transporter SMCT1 from the same family. The structures, together with molecular dynamics simulations and functional studies, define the architecture of SGLTs, uncover the mechanism of substrate binding and selectivity, and shed light on water permeability of SGLT1. These results provide insights into the multifaceted functions of SGLTs.
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Affiliation(s)
- Lei Han
- Department of Molecular and Cellular Physiology, Stanford University School of Medicine, Stanford, CA, USA
| | - Qianhui Qu
- Department of Molecular and Cellular Physiology, Stanford University School of Medicine, Stanford, CA, USA.,Department of Structural Biology, Stanford University School of Medicine, Stanford, CA, USA.,Shanghai Stomatological Hospital, Institutes of Biomedical Science, Department of Systems Biology for Medicine, Fudan University, Shanghai, China
| | - Deniz Aydin
- Department of Molecular and Cellular Physiology, Stanford University School of Medicine, Stanford, CA, USA.,Department of Structural Biology, Stanford University School of Medicine, Stanford, CA, USA.,Department of Computer Science, Stanford University, Stanford, CA, USA.,Institute for Computational and Mathematical Engineering, Stanford University, Stanford, CA, USA
| | - Ouliana Panova
- Department of Molecular and Cellular Physiology, Stanford University School of Medicine, Stanford, CA, USA.,Department of Structural Biology, Stanford University School of Medicine, Stanford, CA, USA
| | - Michael J Robertson
- Department of Molecular and Cellular Physiology, Stanford University School of Medicine, Stanford, CA, USA.,Department of Structural Biology, Stanford University School of Medicine, Stanford, CA, USA
| | - Yan Xu
- Department of Molecular and Cellular Physiology, Stanford University School of Medicine, Stanford, CA, USA
| | - Ron O Dror
- Department of Molecular and Cellular Physiology, Stanford University School of Medicine, Stanford, CA, USA.,Department of Structural Biology, Stanford University School of Medicine, Stanford, CA, USA.,Department of Computer Science, Stanford University, Stanford, CA, USA.,Institute for Computational and Mathematical Engineering, Stanford University, Stanford, CA, USA
| | - Georgios Skiniotis
- Department of Molecular and Cellular Physiology, Stanford University School of Medicine, Stanford, CA, USA. .,Department of Structural Biology, Stanford University School of Medicine, Stanford, CA, USA.
| | - Liang Feng
- Department of Molecular and Cellular Physiology, Stanford University School of Medicine, Stanford, CA, USA. .,Department of Structural Biology, Stanford University School of Medicine, Stanford, CA, USA.
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8
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Lostao MP, Loo DD, Hernell O, Meeuwisse G, Martin MG, Wright EM. The Molecular Basis of Glucose Galactose Malabsorption in a Large Swedish Pedigree. FUNCTION (OXFORD, ENGLAND) 2021; 2:zqab040. [PMID: 34485913 PMCID: PMC8410129 DOI: 10.1093/function/zqab040] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Received: 07/11/2021] [Revised: 08/10/2021] [Accepted: 08/12/2021] [Indexed: 01/12/2023]
Abstract
Glucose-galactose malabsorption (GGM) is due to mutations in the gene coding for the intestinal sodium glucose cotransporter SGLT1 (SLC5A1). Here we identify the rare variant Gln457Arg (Q457R) in a large pedigree of patients in the Västerbotten County in Northern Sweden with the clinical phenotype of GGM. The functional effect of the Q457R mutation was determined in protein expressed in Xenopus laevis oocytes using biophysical and biochemical methods. The mutant failed to transport the specific SGLT1 sugar analog α-methyl-D-glucopyranoside (αMDG). Q457R SGLT1 was synthesized in amounts comparable to the wild-type (WT) transporter. SGLT1 charge measurements and freeze-fracture electron microscopy demonstrated that the mutant protein was inserted into the plasma membrane. Electrophysiological experiments, both steady-state and presteady-state, demonstrated that the mutant bound sugar with an affinity lower than the WT transporter. Together with our previous studies on Q457C and Q457E mutants, we established that the positive charge on Q457R prevented the translocation of sugar from the outward-facing to inward-facing conformation. This is contrary to other GGM cases where missense mutations caused defects in trafficking SGLT1 to the plasma membrane. Thirteen GGM patients are now added to the pedigree traced back to the late 17th century. The frequency of the Q457R variant in Västerbotten County genomes, 0.0067, is higher than in the general Swedish population, 0.0015, and higher than the general European population, 0.000067. This explains the high number of GGM cases in this region of Sweden.
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Affiliation(s)
| | - Donald D Loo
- Department of Physiology, The Geffen School of Medicine, UCLA, USA
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9
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Ferté L, Marino A, Battault S, Bultot L, Van Steenbergen A, Bol A, Cumps J, Ginion A, Koepsell H, Dumoutier L, Hue L, Horman S, Bertrand L, Beauloye C. New insight in understanding the contribution of SGLT1 in cardiac glucose uptake: evidence for a truncated form in mice and humans. Am J Physiol Heart Circ Physiol 2021; 320:H838-H853. [PMID: 33416451 PMCID: PMC8082801 DOI: 10.1152/ajpheart.00736.2019] [Citation(s) in RCA: 10] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 12/13/2019] [Revised: 12/17/2020] [Accepted: 12/17/2020] [Indexed: 01/10/2023]
Abstract
Although sodium glucose cotransporter 1 (SGLT1) has been identified as one of the major SGLT isoforms expressed in the heart, its exact role remains elusive. Evidence using phlorizin, the most common inhibitor of SGLTs, has suggested its role in glucose transport. However, phlorizin could also affect classical facilitated diffusion via glucose transporters (GLUTs), bringing into question the relevance of SGLT1 in overall cardiac glucose uptake. Accordingly, we assessed the contribution of SGLT1 in cardiac glucose uptake using the SGLT1 knockout mouse model, which lacks exon 1. Glucose uptake was similar in cardiomyocytes isolated from SGLT1-knockout (Δex1KO) and control littermate (WT) mice either under basal state, insulin, or hyperglycemia. Similarly, in vivo basal and insulin-stimulated cardiac glucose transport measured by micro-PET scan technology did not differ between WT and Δex1KO mice. Micromolar concentrations of phlorizin had no impact on glucose uptake in either isolated WT or Δex1KO-derived cardiomyocytes. However, higher concentrations (1 mM) completely inhibited insulin-stimulated glucose transport without affecting insulin signaling nor GLUT4 translocation independently from cardiomyocyte genotype. Interestingly, we discovered that mouse and human hearts expressed a shorter slc5a1 transcript, leading to SGLT1 protein lacking transmembrane domains and residues involved in glucose and sodium bindings. In conclusion, cardiac SGLT1 does not contribute to overall glucose uptake, probably due to the expression of slc5a1 transcript variant. The inhibitory effect of phlorizin on cardiac glucose uptake is SGLT1-independent and can be explained by GLUT transporter inhibition. These data open new perspectives in understanding the role of SGLT1 in the heart.NEW & NOTEWORTHY Ever since the discovery of its expression in the heart, SGLT1 has been considered as similar as the intestine and a potential contributor to cardiac glucose transport. For the first time, we have demonstrated that a slc5a1 transcript variant is present in the heart that has no significant impact on cardiac glucose handling.
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Affiliation(s)
- Laura Ferté
- Pôle de Recherche Cardiovasculaire, Institut de Recherche Expérimentale et Clinique, Université catholique de Louvain, Brussels, Belgium
| | - Alice Marino
- Pôle de Recherche Cardiovasculaire, Institut de Recherche Expérimentale et Clinique, Université catholique de Louvain, Brussels, Belgium
| | - Sylvain Battault
- Pôle de Recherche Cardiovasculaire, Institut de Recherche Expérimentale et Clinique, Université catholique de Louvain, Brussels, Belgium
| | - Laurent Bultot
- Pôle de Recherche Cardiovasculaire, Institut de Recherche Expérimentale et Clinique, Université catholique de Louvain, Brussels, Belgium
| | - Anne Van Steenbergen
- Pôle de Recherche Cardiovasculaire, Institut de Recherche Expérimentale et Clinique, Université catholique de Louvain, Brussels, Belgium
| | - Anne Bol
- Center of Molecular Imaging, Radiotherapy and Oncology, Institut de Recherche Expérimentale et Clinique, Université Catholique de Louvain, Brussels, Belgium
| | - Julien Cumps
- Pôle de Recherche Cardiovasculaire, Institut de Recherche Expérimentale et Clinique, Université catholique de Louvain, Brussels, Belgium
| | - Audrey Ginion
- Pôle de Recherche Cardiovasculaire, Institut de Recherche Expérimentale et Clinique, Université catholique de Louvain, Brussels, Belgium
| | - Hermann Koepsell
- Department of Molecular Plant Physiology and Biophysics, Julius von Sachs Institute, University of Würzburg, Würzburg, Germany
| | - Laure Dumoutier
- Médecine Expérimentale, Institut de Duve, Université Catholique de Louvain, Brussels, Belgium
| | - Louis Hue
- Pôle de Recherche Cardiovasculaire, Institut de Recherche Expérimentale et Clinique, Université catholique de Louvain, Brussels, Belgium
- Institut de Duve, Université Catholique de Louvain, Brussels, Belgium
| | - Sandrine Horman
- Pôle de Recherche Cardiovasculaire, Institut de Recherche Expérimentale et Clinique, Université catholique de Louvain, Brussels, Belgium
| | - Luc Bertrand
- Pôle de Recherche Cardiovasculaire, Institut de Recherche Expérimentale et Clinique, Université catholique de Louvain, Brussels, Belgium
| | - Christophe Beauloye
- Pôle de Recherche Cardiovasculaire, Institut de Recherche Expérimentale et Clinique, Université catholique de Louvain, Brussels, Belgium
- Division of Cardiology, Cliniques Universitaires Saint-Luc, Université Catholique de Louvain, Brussels, Belgium
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10
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Elferink H, Bruekers JPJ, Veeneman GH, Boltje TJ. A comprehensive overview of substrate specificity of glycoside hydrolases and transporters in the small intestine : "A gut feeling". Cell Mol Life Sci 2020; 77:4799-4826. [PMID: 32506169 PMCID: PMC7658089 DOI: 10.1007/s00018-020-03564-1] [Citation(s) in RCA: 21] [Impact Index Per Article: 5.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/10/2020] [Revised: 05/21/2020] [Accepted: 05/25/2020] [Indexed: 02/07/2023]
Abstract
The human body is able to process and transport a complex variety of carbohydrates, unlocking their nutritional value as energy source or as important building block. The endogenous glycosyl hydrolases (glycosidases) and glycosyl transporter proteins located in the enterocytes of the small intestine play a crucial role in this process and digest and/or transport nutritional sugars based on their structural features. It is for these reasons that glycosidases and glycosyl transporters are interesting therapeutic targets to combat sugar related diseases (such as diabetes) or to improve drug delivery. In this review we provide a detailed overview focused on the molecular structure of the substrates involved as a solid base to start from and to fuel research in the area of therapeutics and diagnostics.
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Affiliation(s)
- Hidde Elferink
- Institute for Molecules and Materials, Radboud University, Heyendaalseweg 135, 6525, Nijmegen, The Netherlands
| | - Jeroen P J Bruekers
- Institute for Molecules and Materials, Radboud University, Heyendaalseweg 135, 6525, Nijmegen, The Netherlands
| | | | - Thomas J Boltje
- Institute for Molecules and Materials, Radboud University, Heyendaalseweg 135, 6525, Nijmegen, The Netherlands.
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11
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Wang X, Guo K, Huang B, Lin Z, Cai Z. Role of Glucose Transporters in Drug Membrane Transport. Curr Drug Metab 2020; 21:947-958. [PMID: 32778021 DOI: 10.2174/1389200221666200810125924] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/31/2020] [Revised: 05/12/2020] [Accepted: 06/01/2020] [Indexed: 11/22/2022]
Abstract
BACKGROUND Glucose is the main energy component of cellular activities. However, as a polar molecule, glucose cannot freely pass through the phospholipid bilayer structure of the cell membrane. Thus, glucose must rely on specific transporters in the membrane. Drugs with a similar chemical structure to glucose may also be transported through this pathway. METHODS This review describes the structure, distribution, action mechanism and influencing factors of glucose transporters and introduces the natural drugs mediated by these transporters and drug design strategies on the basis of this pathway. RESULTS The glucose transporters involved in glucose transport are of two major types, namely, Na+-dependent and Na+-independent transporters. Glucose transporters can help some glycoside drugs cross the biological membrane. The transmembrane potential is influenced by the chemical structure of drugs. Glucose can be used to modify drugs and improve their ability to cross biological barriers. CONCLUSION The membrane transport mechanism of some glycoside drugs may be related to glucose transporters. Glucose modification may improve the oral bioavailability of drugs or achieve targeted drug delivery.
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Affiliation(s)
- Xin Wang
- Guangdong Provincial Key Laboratory of New Drug Screening, School of Pharmaceutical Sciences, Southern Medical University, Guangzhou, China
| | - Kunkun Guo
- Guangdong Provincial Key Laboratory of New Drug Screening, School of Pharmaceutical Sciences, Southern Medical University, Guangzhou, China
| | - Baolin Huang
- Guangdong Provincial Key Laboratory of New Drug Screening, School of Pharmaceutical Sciences, Southern Medical University, Guangzhou, China
| | - Zimin Lin
- Guangdong Provincial Key Laboratory of New Drug Screening, School of Pharmaceutical Sciences, Southern Medical University, Guangzhou, China
| | - Zheng Cai
- Guangdong Provincial Key Laboratory of New Drug Screening, School of Pharmaceutical Sciences, Southern Medical University, Guangzhou, China
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12
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Gyimesi G, Pujol-Giménez J, Kanai Y, Hediger MA. Sodium-coupled glucose transport, the SLC5 family, and therapeutically relevant inhibitors: from molecular discovery to clinical application. Pflugers Arch 2020; 472:1177-1206. [PMID: 32767111 PMCID: PMC7462921 DOI: 10.1007/s00424-020-02433-x] [Citation(s) in RCA: 44] [Impact Index Per Article: 11.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/04/2020] [Revised: 06/24/2020] [Accepted: 07/02/2020] [Indexed: 02/06/2023]
Abstract
Sodium glucose transporters (SGLTs) belong to the mammalian solute carrier family SLC5. This family includes 12 different members in human that mediate the transport of sugars, vitamins, amino acids, or smaller organic ions such as choline. The SLC5 family belongs to the sodium symporter family (SSS), which encompasses transporters from all kingdoms of life. It furthermore shares similarity to the structural fold of the APC (amino acid-polyamine-organocation) transporter family. Three decades after the first molecular identification of the intestinal Na+-glucose cotransporter SGLT1 by expression cloning, many new discoveries have evolved, from mechanistic analysis to molecular genetics, structural biology, drug discovery, and clinical applications. All of these advances have greatly influenced physiology and medicine. While SGLT1 is essential for fast absorption of glucose and galactose in the intestine, the expression of SGLT2 is largely confined to the early part of the kidney proximal tubules, where it reabsorbs the bulk part of filtered glucose. SGLT2 has been successfully exploited by the pharmaceutical industry to develop effective new drugs for the treatment of diabetic patients. These SGLT2 inhibitors, termed gliflozins, also exhibit favorable nephroprotective effects and likely also cardioprotective effects. In addition, given the recent finding that SGLT2 is also expressed in tumors of pancreas and prostate and in glioblastoma, this opens the door to potential new therapeutic strategies for cancer treatment by specifically targeting SGLT2. Likewise, further discoveries related to the functional association of other SGLTs of the SLC5 family to human pathologies will open the door to potential new therapeutic strategies. We furthermore hope that the herein summarized information about the physiological roles of SGLTs and the therapeutic benefits of the gliflozins will be useful for our readers to better understand the molecular basis of the beneficial effects of these inhibitors, also in the context of the tubuloglomerular feedback (TGF), and the renin-angiotensin system (RAS). The detailed mechanisms underlying the clinical benefits of SGLT2 inhibition by gliflozins still warrant further investigation that may serve as a basis for future drug development.
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Affiliation(s)
- Gergely Gyimesi
- Membrane Transport Discovery Lab, Department of Nephrology and Hypertension, and Department of Biomedical Research, Inselspital, University of Bern, Kinderklinik, Office D845, Freiburgstrasse 15, CH-3010, Bern, Switzerland
| | - Jonai Pujol-Giménez
- Membrane Transport Discovery Lab, Department of Nephrology and Hypertension, and Department of Biomedical Research, Inselspital, University of Bern, Kinderklinik, Office D845, Freiburgstrasse 15, CH-3010, Bern, Switzerland
| | - Yoshikatsu Kanai
- Department of Bio-system Pharmacology, Graduate School of Medicine, Osaka University, Osaka, Japan
| | - Matthias A Hediger
- Membrane Transport Discovery Lab, Department of Nephrology and Hypertension, and Department of Biomedical Research, Inselspital, University of Bern, Kinderklinik, Office D845, Freiburgstrasse 15, CH-3010, Bern, Switzerland.
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13
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Zhekova HR, Sakuma T, Johnson R, Concilio SC, Lech PJ, Zdravkovic I, Damergi M, Suksanpaisan L, Peng KW, Russell SJ, Noskov S. Mapping of Ion and Substrate Binding Sites in Human Sodium Iodide Symporter (hNIS). J Chem Inf Model 2020; 60:1652-1665. [PMID: 32134653 DOI: 10.1021/acs.jcim.9b01114] [Citation(s) in RCA: 4] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Abstract
The human sodium iodide symporter (hNIS) is a theranostic reporter gene which concentrates several clinically approved SPECT and PET radiotracers and plays an essential role for the synthesis of thyroid hormones as an iodide transporter in the thyroid gland. Development of hNIS mutants which could enhance translocation of the desired imaging ions is currently underway. Unfortunately, it is hindered by lack of understanding of the 3D organization of hNIS and its relation to anion transport. There are no known crystal structures of hNIS in any of its conformational states. Homology modeling can be very effective in such situations; however, the low sequence identity between hNIS and relevant secondary transporters with available experimental structures makes the choice of a template and the generation of 3D models nontrivial. Here, we report a combined application of homology modeling and molecular dynamics refining of the hNIS structure in its semioccluded state. The modeling was based on templates from the LeuT-fold protein family and was done with emphasis on the refinement of the substrate-ion binding pocket. The consensus model developed in this work is compared to available biophysical and biochemical experimental data for a number of different LeuT-fold proteins. Some functionally important residues contributing to the formation of putative binding sites and permeation pathways for the cotransported Na+ ions and I- substrate were identified. The model predictions were experimentally tested by generation of mutant versions of hNIS and measurement of relative (to WT hNIS) 125I- uptake of 35 hNIS variants.
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Affiliation(s)
- Hristina R Zhekova
- Centre for Molecular Simulation, Department of Biological Sciences, University of Calgary, Calgary, AB T2N 1N4, Canada
| | - Toshie Sakuma
- Imanis Life Sciences, Rochester, Minnesota 55901, United States.,Department of Molecular Medicine, Mayo Clinic, Rochester, Minnesota 55902, United States
| | - Ryan Johnson
- Imanis Life Sciences, Rochester, Minnesota 55901, United States
| | - Susanna C Concilio
- Department of Molecular Medicine, Mayo Clinic, Rochester, Minnesota 55902, United States.,Mayo Clinic Graduate School of Biomedical Sciences, Mayo Clinic, Rochester, Minnesota 55902, United States
| | - Patrycja J Lech
- Imanis Life Sciences, Rochester, Minnesota 55901, United States
| | - Igor Zdravkovic
- Centre for Molecular Simulation, Department of Biological Sciences, University of Calgary, Calgary, AB T2N 1N4, Canada
| | - Mirna Damergi
- Centre for Molecular Simulation, Department of Biological Sciences, University of Calgary, Calgary, AB T2N 1N4, Canada
| | | | - Kah-Whye Peng
- Imanis Life Sciences, Rochester, Minnesota 55901, United States.,Department of Molecular Medicine, Mayo Clinic, Rochester, Minnesota 55902, United States
| | - Stephen J Russell
- Imanis Life Sciences, Rochester, Minnesota 55901, United States.,Department of Molecular Medicine, Mayo Clinic, Rochester, Minnesota 55902, United States
| | - Sergei Noskov
- Centre for Molecular Simulation, Department of Biological Sciences, University of Calgary, Calgary, AB T2N 1N4, Canada
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14
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Phospholipid effects on SGLT1-mediated glucose transport in rabbit ileum brush border membrane vesicles. BIOCHIMICA ET BIOPHYSICA ACTA-BIOMEMBRANES 2019; 1861:182985. [PMID: 31082355 DOI: 10.1016/j.bbamem.2019.05.007] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Received: 11/16/2018] [Revised: 04/23/2019] [Accepted: 05/08/2019] [Indexed: 11/20/2022]
Abstract
In small intestine, sodium-glucose cotransporter SGLT1 provides the main mechanism for sugar uptake. We investigated the effect of membrane phospholipids (PL) on this transport in rabbit ileal brush border membrane vesicles (BBMV). For this, PL of different charge, length, and saturation were incorporated into BBMV. Transport was measured related to (i) membrane surface charge (membrane-bound MC540 fluorescence), (ii) membrane thickness (PL incorporation of different acyl chain length), and (iii) membrane fluidity (r12AS, fluorescence anisotropy of 12-AS). Compared to phosphatidylcholine (PC) carrying a neutral head group, inhibition of SGLT1 increased considerably with the acidic phosphatidic acid (PA) and phosphatidylinositol (PI) that increase membrane negative surface charge. The order of PL potency was PI>PA > PE = PS > PC. Inhibition by acidic PA-oleate was 5-times more effective than with neutral PE (phosphatidylethanolamine)-oleate. Lineweaver-Burk plot indicated uncompetitive inhibition of SGLT1 by PA. When membrane thickness was increased by neutral PC of varying acyl chain length, transport was increasingly inhibited by 16:1 PC to 22:1 PC. Even more pronounced inhibition was observed with mono-unsaturated instead of saturated acyl chains which increased membrane fluidity (indicated by decreased r12AS). In conclusion, sodium-dependent glucose transport of rabbit ileal BBMV is modulated by (i) altered membrane surface charge, (ii) length of acyl chains via membrane thickness, and (iii) saturation of PL acyl chains altering membrane fluidity. Transport was attenuated by charged PL with longer and unsaturated acyl residues. Alterations of PL may provide a principle for attenuating dietary glucose uptake.
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15
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Inhibitor binding mode and allosteric regulation of Na +-glucose symporters. Nat Commun 2018; 9:5245. [PMID: 30532032 PMCID: PMC6286348 DOI: 10.1038/s41467-018-07700-1] [Citation(s) in RCA: 30] [Impact Index Per Article: 5.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/09/2018] [Accepted: 11/14/2018] [Indexed: 12/22/2022] Open
Abstract
Sodium-dependent glucose transporters (SGLTs) exploit sodium gradients to transport sugars across the plasma membrane. Due to their role in renal sugar reabsorption, SGLTs are targets for the treatment of type 2 diabetes. Current therapeutics are phlorizin derivatives that contain a sugar moiety bound to an aromatic aglycon tail. Here, we develop structural models of human SGLT1/2 in complex with inhibitors by combining computational and functional studies. Inhibitors bind with the sugar moiety in the sugar pocket and the aglycon tail in the extracellular vestibule. The binding poses corroborate mutagenesis studies and suggest a partial closure of the outer gate upon binding. The models also reveal a putative Na+ binding site in hSGLT1 whose disruption reduces the transport stoichiometry to the value observed in hSGLT2 and increases inhibition by aglycon tails. Our work demonstrates that subtype selectivity arises from Na+-regulated outer gate closure and a variable region in extracellular loop EL5. Sodium-dependent glucose transporters (SGLTs) transport sugars across the plasma membrane and play important roles in renal sugar reabsorption. Here authors develop structural models of human SGLT1/2 (hSGLT1/2) in complex with inhibitors which helps to understand inhibitor subtype selectivity.
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16
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Intestinal Saturated Long-Chain Fatty Acid, Glucose and Fructose Transporters and Their Inhibition by Natural Plant Extracts in Caco-2 Cells. Molecules 2018; 23:molecules23102544. [PMID: 30301205 PMCID: PMC6222386 DOI: 10.3390/molecules23102544] [Citation(s) in RCA: 16] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/05/2018] [Revised: 09/29/2018] [Accepted: 10/04/2018] [Indexed: 02/07/2023] Open
Abstract
The intestinal absorption of fatty acids, glucose and fructose is part of the basic requirements for the provision of energy in the body. High access of saturated long-chain fatty acids (LCFA), glucose and fructose can facilitate the development of metabolic diseases, particularly the metabolic syndrome and type-2 diabetes mellitus (T2DM). Research has been done to find substances which decelerate or inhibit intestinal resorption of these specific food components. Promising targets are the inhibition of intestinal long-chain fatty acid (FATP2, FATP4), glucose (SGLT1, GLUT2) and fructose (GLUT2, GLUT5) transporters by plant extracts and by pure substances. The largest part of active components in plant extracts belongs to the group of polyphenols. This review summarizes the knowledge about binding sites of named transporters and lists the plant extracts which were tested in Caco-2 cells regarding uptake inhibition.
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17
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Ghezzi C, Loo DDF, Wright EM. Physiology of renal glucose handling via SGLT1, SGLT2 and GLUT2. Diabetologia 2018; 61:2087-2097. [PMID: 30132032 PMCID: PMC6133168 DOI: 10.1007/s00125-018-4656-5] [Citation(s) in RCA: 184] [Impact Index Per Article: 30.7] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 03/27/2018] [Accepted: 04/23/2018] [Indexed: 12/12/2022]
Abstract
The concentration of glucose in plasma is held within narrow limits (4-10 mmol/l), primarily to ensure fuel supply to the brain. Kidneys play a role in glucose homeostasis in the body by ensuring that glucose is not lost in the urine. Three membrane proteins are responsible for glucose reabsorption from the glomerular filtrate in the proximal tubule: sodium-glucose cotransporters SGLT1 and SGLT2, in the apical membrane, and GLUT2, a uniporter in the basolateral membrane. 'Knockout' of these transporters in mice and men results in the excretion of filtered glucose in the urine. In humans, intravenous injection of the plant glucoside phlorizin also results in excretion of the full filtered glucose load. This outcome and the finding that, in an animal model, phlorizin reversed the symptoms of diabetes, has stimulated the development and successful introduction of SGLT2 inhibitors, gliflozins, in the treatment of type 2 diabetes mellitus. Here we summarise the current state of our knowledge about the physiology of renal glucose handling and provide background to the development of SGLT2 inhibitors for type 2 diabetes treatment.
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Affiliation(s)
- Chiara Ghezzi
- Department of Physiology, Geffen School of Medicine at UCLA, Los Angeles, CA, 90095-1751, USA
| | - Donald D F Loo
- Department of Physiology, Geffen School of Medicine at UCLA, Los Angeles, CA, 90095-1751, USA
| | - Ernest M Wright
- Department of Physiology, Geffen School of Medicine at UCLA, Los Angeles, CA, 90095-1751, USA.
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18
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Wright EM, Ghezzi C, Loo DDF. Novel and Unexpected Functions of SGLTs. Physiology (Bethesda) 2017; 32:435-443. [PMID: 29021363 PMCID: PMC5817162 DOI: 10.1152/physiol.00021.2017] [Citation(s) in RCA: 41] [Impact Index Per Article: 5.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/03/2017] [Revised: 08/25/2017] [Accepted: 08/25/2017] [Indexed: 12/13/2022] Open
Abstract
It has been 30 years since the intestinal sodium glucose cotransporter SGLT1 was cloned, and, in the intervening years, there have been many advances that have influenced physiology and medicine. Among the first was that SGLT1 is the founding member of the human gene family SLC5, containing 11 diverse transporters and a glucose sensor. Equally surprising was that SGLTs are members of a structural family of cotransporters and exchangers in different gene families. This led to the conclusion that these proteins operate by a mechanism where transport involves the opening and closing of external and internal gates. The mechanism is shared by a wide variety of transporters in different structural families, e.g., the human facilitated glucose transporters (SLC2) in the huge major facilitator superfamily (MFS). Not surprising is the finding that mutations in Sglt genes cause the rare diseases glucose-galactose-malabsorption (GGM) and familial renal glucosuria (FRG). However, it was not envisaged that SGLT inhibitors would be used to treat diabetes mellitus, and these drugs may be able to treat cancer. Finally, in 2017, we have just learned that SGLT1 may be required to resist infection and to avoid recurrent pregnancy loss.
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Affiliation(s)
- Ernest M Wright
- Department of Physiology, David Geffen School of Medicine at UCLA, Los Angeles, California
| | - Chiara Ghezzi
- Department of Physiology, David Geffen School of Medicine at UCLA, Los Angeles, California
| | - Donald D F Loo
- Department of Physiology, David Geffen School of Medicine at UCLA, Los Angeles, California
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19
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Abstract
Site-directed fluorometry was used to understand conformational changes of the Na+/glucose symporter. SGLT1 functions by a mechanism where the substrate-binding site alternates between the two faces of the membrane, but little is known about the underlying conformational changes. Rhodamines were covalently inserted into the substrate cavity, and changes of fluorescence were measured in real time with the opening and closing of the outer gate as SGLT1 was driven between inward and outward conformations using voltage jumps. Structural modeling indicated that the quenching with gating opening was due to an increased solvation of rhodamine and an increase in polar residues lining the wall of the cavity. This experimental approach will lead to a better understanding of the mechanism of membrane transport. In the human sodium glucose cotransporter (hSGLT1) cycle, the protein undergoes conformational changes where the sugar-binding site alternatively faces the external and internal surfaces. Functional site-directed fluorometry was used to probe the conformational changes at the sugar-binding site. Residues (Y290, T287, H83, and N78) were mutated to cysteines. The mutants were expressed in Xenopus laevis oocytes and tagged with environmentally sensitive fluorescent rhodamines [e.g., tetramethylrhodamine (TMR)-thiols]. The fluorescence intensity was recorded as the mutants were driven into different conformations using voltage jumps. Sugar binding and transport by the fluorophore-tagged mutants were blocked, but Na+ binding and the voltage-dependent conformational transitions were unaffected. Structural models indicated that external Na+ binding opened a large aqueous vestibule (600 Å3) leading to the sugar-binding site. The fluorescence of TMR covalently linked to Y290C, T287C, and H83C decreased as the mutant proteins were driven from the inward to the outward open Na+-bound conformation. The time courses of fluorescence changes (milliseconds) were close to the SGLT1 capacitive charge movements. The quench in rhodamine fluorescence indicated that the environment of the chromophores became more polar with opening of the external gates as the protein transitioned from the inward to outward facing state. Structural analyses showed an increase in polar side chains and a decrease in hydrophobic side chains lining the vestibule, and this was reflected in solvation of the chromophore. The results demonstrate the opening and closing of external gates in real time, with the accompanying changes of polarity of the sugar vestibule.
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20
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Calabrese AN, Jackson SM, Jones LN, Beckstein O, Heinkel F, Gsponer J, Sharples D, Sans M, Kokkinidou M, Pearson AR, Radford SE, Ashcroft AE, Henderson PJF. Topological Dissection of the Membrane Transport Protein Mhp1 Derived from Cysteine Accessibility and Mass Spectrometry. Anal Chem 2017; 89:8844-8852. [PMID: 28726379 PMCID: PMC5588088 DOI: 10.1021/acs.analchem.7b01310] [Citation(s) in RCA: 18] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/08/2017] [Accepted: 07/20/2017] [Indexed: 01/01/2023]
Abstract
Cys accessibility and quantitative intact mass spectrometry (MS) analyses have been devised to study the topological transitions of Mhp1, the membrane protein for sodium-linked transport of hydantoins from Microbacterium liquefaciens. Mhp1 has been crystallized in three forms (outward-facing open, outward-facing occluded with substrate bound, and inward-facing open). We show that one natural cysteine residue, Cys327, out of three, has an enhanced solvent accessibility in the inward-facing (relative to the outward-facing) form. Reaction of the purified protein, in detergent, with the thiol-reactive N-ethylmalemide (NEM), results in modification of Cys327, suggesting that Mhp1 adopts predominantly inward-facing conformations. Addition of either sodium ions or the substrate 5-benzyl-l-hydantoin (L-BH) does not shift this conformational equilibrium, but systematic co-addition of the two results in an attenuation of labeling, indicating a shift toward outward-facing conformations that can be interpreted using conventional enzyme kinetic analyses. Such measurements can afford the Km for each ligand as well as the stoichiometry of ion-substrate-coupled conformational changes. Mutations that perturb the substrate binding site either result in the protein being unable to adopt outward-facing conformations or in a global destabilization of structure. The methodology combines covalent labeling, mass spectrometry, and kinetic analyses in a straightforward workflow applicable to a range of systems, enabling the interrogation of changes in a protein's conformation required for function at varied concentrations of substrates, and the consequences of mutations on these conformational transitions.
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Affiliation(s)
| | | | | | - Oliver Beckstein
- Department of Physics, Arizona State University , Tempe, Arizona 85287-1504, United States
| | - Florian Heinkel
- Centre for High-Throughput Biology, University of British Columbia , Vancouver, British Columbia, Canada V6T 1Z4
| | - Joerg Gsponer
- Centre for High-Throughput Biology, University of British Columbia , Vancouver, British Columbia, Canada V6T 1Z4
| | | | - Marta Sans
- Hamburg Centre for Ultrafast Imaging, Institute for Nanostructure and Solid State Physics, Universität Hamburg , Hamburg 22761, Germany
| | - Maria Kokkinidou
- Hamburg Centre for Ultrafast Imaging, Institute for Nanostructure and Solid State Physics, Universität Hamburg , Hamburg 22761, Germany
| | - Arwen R Pearson
- Hamburg Centre for Ultrafast Imaging, Institute for Nanostructure and Solid State Physics, Universität Hamburg , Hamburg 22761, Germany
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21
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Affiliation(s)
- Patricia L Brubaker
- Departments of Physiology and Medicine, University of Toronto, Toronto, Ontario, Canada
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22
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Soták M, Marks J, Unwin RJ. Putative tissue location and function of the SLC5 family member SGLT3. Exp Physiol 2017; 102:5-13. [DOI: 10.1113/ep086042] [Citation(s) in RCA: 25] [Impact Index Per Article: 3.6] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/15/2016] [Accepted: 11/08/2016] [Indexed: 01/29/2023]
Affiliation(s)
- Matúš Soták
- Cardiovascular and Metabolic Diseases; Innovative Medicines and Early Development Biotech Unit; AstraZeneca; Mölndal Sweden
| | - Joanne Marks
- Department of Neuroscience; Physiology and Pharmacology; University College London; London UK
| | - Robert J. Unwin
- Cardiovascular and Metabolic Diseases; Innovative Medicines and Early Development Biotech Unit; AstraZeneca; Mölndal Sweden
- Department of Neuroscience; Physiology and Pharmacology; University College London; London UK
- Department of Physiology and Neuroscience; University of Gothenburg; Gothenburg Sweden
- Centre for Nephrology; University College London; London UK
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23
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Zeuthen T, Gorraitz E, Her K, Wright EM, Loo DDF. Structural and functional significance of water permeation through cotransporters. Proc Natl Acad Sci U S A 2016; 113:E6887-E6894. [PMID: 27791155 PMCID: PMC5098644 DOI: 10.1073/pnas.1613744113] [Citation(s) in RCA: 32] [Impact Index Per Article: 4.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022] Open
Abstract
Membrane transporters, in addition to their major role as specific carriers for ions and small molecules, can also behave as water channels. However, neither the location of the water pathway in the protein nor their functional importance is known. Here, we map the pathway for water and urea through the intestinal sodium/glucose cotransporter SGLT1. Molecular dynamics simulations using the atomic structure of the bacterial transporter vSGLT suggest that water permeates the same path as Na+ and sugar. On a structural model of SGLT1, based on the homology structure of vSGLT, we identified and mutated residues lining the sugar transport pathway to cysteine. The mutants were expressed in Xenopus oocytes, and the unitary water and urea permeabilities were determined before and after modifying the cysteine side chain with reversible methanethiosulfonate reagents. The results demonstrate that water and urea follow the sugar transport pathway through SGLT1. The changes in permeability, increases or decreases, with side-chain modifications depend on the location of the mutation in the region of external or internal gates, or the sugar binding site. These changes in permeability are hypothesized to be due to alterations in steric hindrance to water and urea, and/or changes in protein folding caused by mismatching of side chains in the water pathway. Water permeation through SGLT1 and other transporters bears directly on the structural mechanism for the transport of polar solutes through these proteins. Finally, in vitro experiments on mouse small intestine show that SGLT1 accounts for two-thirds of the passive water flow across the gut.
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Affiliation(s)
- Thomas Zeuthen
- Department of Cellular and Molecular Medicine, The Panum Institute, University of Copenhagen, DK 2200N, Copenhagen, Denmark;
| | - Edurne Gorraitz
- Department of Physiology, David Geffen School of Medicine at University of California, Los Angeles, CA 90095-1751
| | - Ka Her
- Department of Physiology, David Geffen School of Medicine at University of California, Los Angeles, CA 90095-1751
| | - Ernest M Wright
- Department of Physiology, David Geffen School of Medicine at University of California, Los Angeles, CA 90095-1751
| | - Donald D F Loo
- Department of Physiology, David Geffen School of Medicine at University of California, Los Angeles, CA 90095-1751
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24
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Abstract
The sodium/iodide symporter (NIS) mediates active I(-) transport in the thyroid-the first step in thyroid hormone biosynthesis-with a 2 Na(+): 1 I(-) stoichiometry. The two Na(+) binding sites (Na1 and Na2) and the I(-) binding site interact allosterically: when Na(+) binds to a Na(+) site, the affinity of NIS for the other Na(+) and for I(-) increases significantly. In all Na(+)-dependent transporters with the same fold as NIS, the side chains of two residues, S353 and T354 (NIS numbering), were identified as the Na(+) ligands at Na2. To understand the cooperativity between the substrates, we investigated the coordination at the Na2 site. We determined that four other residues-S66, D191, Q194, and Q263-are also involved in Na(+) coordination at this site. Experiments in whole cells demonstrated that these four residues participate in transport by NIS: mutations at these positions result in proteins that, although expressed at the plasma membrane, transport little or no I(-) These residues are conserved throughout the entire SLC5 family, to which NIS belongs, suggesting that they serve a similar function in the other transporters. Our findings also suggest that the increase in affinity that each site displays when an ion binds to another site may result from changes in the dynamics of the transporter. These mechanistic insights deepen our understanding not only of NIS but also of other transporters, including many that, like NIS, are of great medical relevance.
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25
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Abstract
Secondary active transporters, such as those that adopt the leucine-transporter fold, are found in all domains of life, and they have the unique capability of harnessing the energy stored in ion gradients to accumulate small molecules essential for life as well as expel toxic and harmful compounds. How these proteins couple ion binding and transport to the concomitant flow of substrates is a fundamental structural and biophysical question that is beginning to be answered at the atomistic level with the advent of high-resolution structures of transporters in different structural states. Nonetheless, the dynamic character of the transporters, such as ion/substrate binding order and how binding triggers conformational change, is not revealed from static structures, yet it is critical to understanding their function. Here, we report a series of molecular simulations carried out on the sugar transporter vSGLT that lend insight into how substrate and ions are released from the inward-facing state of the transporter. Our simulations reveal that the order of release is stochastic. Functional experiments were designed to test this prediction on the human homolog, hSGLT1, and we also found that cytoplasmic release is not ordered, but we confirmed that substrate and ion binding from the extracellular space is ordered. Our findings unify conflicting published results concerning cytoplasmic release of ions and substrate and hint at the possibility that other transporters in the superfamily may lack coordination between ions and substrate in the inward-facing state.
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26
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Bracher S, Guérin K, Polyhach Y, Jeschke G, Dittmer S, Frey S, Böhm M, Jung H. Glu-311 in External Loop 4 of the Sodium/Proline Transporter PutP Is Crucial for External Gate Closure. J Biol Chem 2016; 291:4998-5008. [PMID: 26728461 DOI: 10.1074/jbc.m115.675306] [Citation(s) in RCA: 9] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/30/2015] [Indexed: 12/17/2022] Open
Abstract
The available structural information on LeuT and structurally related transporters suggests that external loop 4 (eL4) and the outer end of transmembrane domain (TM) 10' participate in the reversible occlusion of the outer pathway to the solute binding sites. Here, the functional significance of eL4 and the outer region of TM10' are explored using the sodium/proline symporter PutP as a model. Glu-311 at the tip of eL4, and various amino acids around the outer end of TM10' are identified as particularly crucial for function. Substitutions at these sites inhibit the transport cycle, and affect in part ligand binding. In addition, changes at selected sites induce a global structural alteration in the direction of an outward-open conformation. It is suggested that interactions between the tip of eL4 and the peptide backbone at the end of TM10' participate in coordinating conformational alterations underlying the alternating access mechanism of transport. Together with the structural information on LeuT-like transporters, the results further specify the idea that common design and functional principles are maintained across different transport families.
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Affiliation(s)
- Susanne Bracher
- From the Department of Biology 1, Division of Microbiology, Ludwig Maximilians University Munich, Grosshaderner Strasse 2-4, 82152 Martinsried, Germany and
| | - Kamila Guérin
- the ETH Zurich, Laboratory of Physical Chemistry, Vladimir-Prelog-Weg 2, 8093 Zurich, Switzerland
| | - Yevhen Polyhach
- the ETH Zurich, Laboratory of Physical Chemistry, Vladimir-Prelog-Weg 2, 8093 Zurich, Switzerland
| | - Gunnar Jeschke
- the ETH Zurich, Laboratory of Physical Chemistry, Vladimir-Prelog-Weg 2, 8093 Zurich, Switzerland
| | - Sophie Dittmer
- From the Department of Biology 1, Division of Microbiology, Ludwig Maximilians University Munich, Grosshaderner Strasse 2-4, 82152 Martinsried, Germany and
| | - Sabine Frey
- From the Department of Biology 1, Division of Microbiology, Ludwig Maximilians University Munich, Grosshaderner Strasse 2-4, 82152 Martinsried, Germany and
| | - Maret Böhm
- From the Department of Biology 1, Division of Microbiology, Ludwig Maximilians University Munich, Grosshaderner Strasse 2-4, 82152 Martinsried, Germany and
| | - Heinrich Jung
- From the Department of Biology 1, Division of Microbiology, Ludwig Maximilians University Munich, Grosshaderner Strasse 2-4, 82152 Martinsried, Germany and
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27
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Bisha I, Magistrato A. The molecular mechanism of secondary sodium symporters elucidated through the lens of the computational microscope. RSC Adv 2016. [DOI: 10.1039/c5ra22131e] [Citation(s) in RCA: 11] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/26/2023] Open
Abstract
Transport of molecules across cellular membranes is a key biological process for normal cell function. In this review we describe current state-of-the-art knowledge on molecular mechanism of secondary active transporters obtained by molecular simulations studies.
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Affiliation(s)
- Ina Bisha
- Theoretical Chemical Biology and Protein Modelling Group
- Technische Universität München
- 85354 Freising
- Germany
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28
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Raja M, Puntheeranurak T, Gruber HJ, Hinterdorfer P, Kinne RKH. The role of transporter ectodomains in drug recognition and binding: phlorizin and the sodium–glucose cotransporter. MEDCHEMCOMM 2016. [DOI: 10.1039/c5md00572h] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 11/21/2022]
Abstract
This article reviews the role of segments of SLCs located outside the plasma membrane bilayer (ectodomains) using the inhibition of SGLTs (SLC5 family) by the aromatic glucoside phlorizin as a model system.
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Affiliation(s)
- M. Raja
- Max Planck Institute of Molecular Physiology
- Dortmund
- Germany
| | - T. Puntheeranurak
- Department of Biology
- Center of Nanoscience
- Faculty of Science
- Mahidol University
- Bangkok
| | - H. J. Gruber
- Institute for Biophysics
- Christian Doppler Laboratory of Nanoscopic Methods in Biophysics
- Johannes Kepler University of Linz and Center for Advanced Bioanalysis GmbH (CBL)
- Linz
- Austria
| | - P. Hinterdorfer
- Institute for Biophysics
- Christian Doppler Laboratory of Nanoscopic Methods in Biophysics
- Johannes Kepler University of Linz and Center for Advanced Bioanalysis GmbH (CBL)
- Linz
- Austria
| | - R. K. H. Kinne
- Max Planck Institute of Molecular Physiology
- Dortmund
- Germany
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29
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Pontremoli C, Mozzi A, Forni D, Cagliani R, Pozzoli U, Menozzi G, Vertemara J, Bresolin N, Clerici M, Sironi M. Natural Selection at the Brush-Border: Adaptations to Carbohydrate Diets in Humans and Other Mammals. Genome Biol Evol 2015; 7:2569-84. [PMID: 26319403 PMCID: PMC4607523 DOI: 10.1093/gbe/evv166] [Citation(s) in RCA: 14] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/06/2023] Open
Abstract
Dietary shifts can drive molecular evolution in mammals and a major transition in human history, the agricultural revolution, favored carbohydrate consumption. We investigated the evolutionary history of nine genes encoding brush-border proteins involved in carbohydrate digestion/absorption. Results indicated widespread adaptive evolution in mammals, with several branches experiencing episodic selection, particularly strong in bats. Many positively selected sites map to functional protein regions (e.g., within glucosidase catalytic crevices), with parallel evolution at SI (sucrase-isomaltase) and MGAM (maltase-glucoamylase). In human populations, five genes were targeted by positive selection acting on noncoding variants within regulatory elements. Analysis of ancient DNA samples indicated that most derived alleles were already present in the Paleolithic. Positively selected variants at SLC2A5 (fructose transporter) were an exception and possibly spread following the domestication of specific fruit crops. We conclude that agriculture determined no major selective event at carbohydrate metabolism genes in humans, with implications for susceptibility to metabolic disorders.
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Affiliation(s)
- Chiara Pontremoli
- Bioinformatics, Scientific Institute IRCCS E.MEDEA, Bosisio Parini, Italy
| | - Alessandra Mozzi
- Bioinformatics, Scientific Institute IRCCS E.MEDEA, Bosisio Parini, Italy
| | - Diego Forni
- Bioinformatics, Scientific Institute IRCCS E.MEDEA, Bosisio Parini, Italy
| | - Rachele Cagliani
- Bioinformatics, Scientific Institute IRCCS E.MEDEA, Bosisio Parini, Italy
| | - Uberto Pozzoli
- Bioinformatics, Scientific Institute IRCCS E.MEDEA, Bosisio Parini, Italy
| | - Giorgia Menozzi
- Bioinformatics, Scientific Institute IRCCS E.MEDEA, Bosisio Parini, Italy
| | - Jacopo Vertemara
- Bioinformatics, Scientific Institute IRCCS E.MEDEA, Bosisio Parini, Italy
| | - Nereo Bresolin
- Bioinformatics, Scientific Institute IRCCS E.MEDEA, Bosisio Parini, Italy Dino Ferrari Centre, Department of Physiopathology and Transplantation, University of Milan, Fondazione Ca' Granda IRCCS Ospedale Maggiore Policlinico, Italy
| | - Mario Clerici
- Department of Physiopathology and Transplantation, University of Milan, Italy Don C. Gnocchi Foundation ONLUS, IRCCS, Milan, Italy
| | - Manuela Sironi
- Bioinformatics, Scientific Institute IRCCS E.MEDEA, Bosisio Parini, Italy
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30
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Gallo LA, Wright EM, Vallon V. Probing SGLT2 as a therapeutic target for diabetes: basic physiology and consequences. Diab Vasc Dis Res 2015; 12:78-89. [PMID: 25616707 PMCID: PMC5886707 DOI: 10.1177/1479164114561992] [Citation(s) in RCA: 264] [Impact Index Per Article: 29.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 12/25/2022] Open
Abstract
Traditional treatments for type 1 and type 2 diabetes are often associated with side effects, including weight gain and hypoglycaemia that may offset the benefits of blood glucose lowering. The kidneys filter and reabsorb large amounts of glucose, and urine is almost free of glucose in normoglycaemia. The sodium-dependent glucose transporter (SGLT)-2 in the early proximal tubule reabsorbs the majority of filtered glucose. Remaining glucose is reabsorbed by SGLT1 in the late proximal tubule. Diabetes enhances renal glucose reabsorption by increasing the tubular glucose load and the expression of SGLT2 (as shown in mice), which maintains hyperglycaemia. Inhibitors of SGLT2 enhance urinary glucose excretion and thereby lower blood glucose levels in type 1 and type 2 diabetes. The load-dependent increase in SGLT1-mediated glucose reabsorption explains why SGLT2 inhibitors in normoglycaemic conditions enhance urinary glucose excretion to only ~50% of the filtered glucose. The role of SGLT1 in both renal and intestinal glucose reabsorption provides a rationale for the development of dual SGLT1/2 inhibitors. SGLT2 inhibitors lower blood glucose levels independent of insulin and induce pleiotropic actions that may be relevant in the context of lowering cardiovascular risk. Ongoing long-term clinical studies will determine whether SGLT2 inhibitors have a safety profile and exert cardiovascular benefits that are superior to traditional agents.
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MESH Headings
- Animals
- Blood Glucose/drug effects
- Blood Glucose/metabolism
- Diabetes Mellitus, Type 1/blood
- Diabetes Mellitus, Type 1/diagnosis
- Diabetes Mellitus, Type 1/drug therapy
- Diabetes Mellitus, Type 1/physiopathology
- Diabetes Mellitus, Type 2/blood
- Diabetes Mellitus, Type 2/diagnosis
- Diabetes Mellitus, Type 2/drug therapy
- Diabetes Mellitus, Type 2/physiopathology
- Humans
- Hypoglycemic Agents/adverse effects
- Hypoglycemic Agents/therapeutic use
- Kidney Tubules, Proximal/drug effects
- Kidney Tubules, Proximal/metabolism
- Kidney Tubules, Proximal/physiopathology
- Molecular Targeted Therapy
- Renal Elimination/drug effects
- Renal Reabsorption/drug effects
- Sodium-Glucose Transporter 1/antagonists & inhibitors
- Sodium-Glucose Transporter 1/metabolism
- Sodium-Glucose Transporter 2/metabolism
- Sodium-Glucose Transporter 2 Inhibitors
- Treatment Outcome
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Affiliation(s)
- Linda A Gallo
- Glycation and Diabetes Complications Research Group, Mater Research Institute - University of Queensland, Translational Research Institute, Woolloongabba, QLD, Australia
| | - Ernest M Wright
- Department of Physiology, David Geffen School of Medicine, University of California, Los Angeles, Los Angeles, CA, USA
| | - Volker Vallon
- Departments of Medicine and Pharmacology, University of California, San Diego, La Jolla, CA, USA VA San Diego Healthcare System, San Diego, CA, USA
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31
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Bisha I, Rodriguez A, Laio A, Magistrato A. Metadynamics simulations reveal a Na+ independent exiting path of galactose for the inward-facing conformation of vSGLT. PLoS Comput Biol 2014; 10:e1004017. [PMID: 25522004 PMCID: PMC4270436 DOI: 10.1371/journal.pcbi.1004017] [Citation(s) in RCA: 19] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/09/2014] [Accepted: 10/31/2014] [Indexed: 11/25/2022] Open
Abstract
Sodium-Galactose Transporter (SGLT) is a secondary active symporter which accumulates sugars into cells by using the electrochemical gradient of Na+ across the membrane. Previous computational studies provided insights into the release process of the two ligands (galactose and sodium ion) into the cytoplasm from the inward-facing conformation of Vibrio parahaemolyticus sodium/galactose transporter (vSGLT). Several aspects of the transport mechanism of this symporter remain to be clarified: (i) a detailed kinetic and thermodynamic characterization of the exit path of the two ligands is still lacking; (ii) contradictory conclusions have been drawn concerning the gating role of Y263; (iii) the role of Na+ in modulating the release path of galactose is not clear. In this work, we use bias-exchange metadynamics simulations to characterize the free energy profile of the galactose and Na+ release processes toward the intracellular side. Surprisingly, we find that the exit of Na+ and galactose is non-concerted as the cooperativity between the two ligands is associated to a transition that is not rate limiting. The dissociation barriers are of the order of 11–12 kcal/mol for both the ion and the substrate, in line with kinetic information concerning this type of transporters. On the basis of these results we propose a branched six-state alternating access mechanism, which may be shared also by other members of the LeuT-fold transporters. Membrane proteins are crucial for the communication of the cell with the environment. Among these, symporters are in charge of the transport of molecules (like sugars, amino acids, osmolytes) inside the cells, exploiting the concentration gradient of an ion to perform the task. Here we investigate by atomistic simulations the transport mechanism of the Sodium-Galactose symporter. Our results allow constructing a detailed and quantitative model of the release process of the two ligands. Surprisingly, we find that the galactose is released to the cytosol independently from the ion, unambiguously indicating that the coupling in their transport mechanism is associated to the steps preceding the release process. A large family of symporters shares the same fold and potentially the same transport mechanism. As such our results are important also because they can provide insights on common mechanistic features of these transporters.
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Affiliation(s)
| | | | | | - Alessandra Magistrato
- CNR-IOM-Democritos National Simulation Center, SISSA, Trieste, Italy
- * E-mail: mailto: (AL); mailto: (AM)
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32
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Conformational cycle and ion-coupling mechanism of the Na+/hydantoin transporter Mhp1. Proc Natl Acad Sci U S A 2014; 111:14752-7. [PMID: 25267652 DOI: 10.1073/pnas.1410431111] [Citation(s) in RCA: 64] [Impact Index Per Article: 6.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/14/2022] Open
Abstract
Ion-dependent transporters of the LeuT-fold couple the uptake of physiologically essential molecules to transmembrane ion gradients. Defined by a conserved 5-helix inverted repeat that encodes common principles of ion and substrate binding, the LeuT-fold has been captured in outward-facing, occluded, and inward-facing conformations. However, fundamental questions relating to the structural basis of alternating access and coupling to ion gradients remain unanswered. Here, we used distance measurements between pairs of spin labels to define the conformational cycle of the Na(+)-coupled hydantoin symporter Mhp1 from Microbacterium liquefaciens. Our results reveal that the inward-facing and outward-facing Mhp1 crystal structures represent sampled intermediate states in solution. Here, we provide a mechanistic context for these structures, mapping them into a model of transport based on ion- and substrate-dependent conformational equilibria. In contrast to the Na(+)/leucine transporter LeuT, our results suggest that Na(+) binding at the conserved second Na(+) binding site does not change the energetics of the inward- and outward-facing conformations of Mhp1. Comparative analysis of ligand-dependent alternating access in LeuT and Mhp1 lead us to propose that different coupling schemes to ion gradients may define distinct conformational mechanisms within the LeuT-fold class.
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33
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Neundlinger I, Puntheeranurak T, Wildling L, Rankl C, Wang LX, Gruber HJ, Kinne RKH, Hinterdorfer P. Forces and dynamics of glucose and inhibitor binding to sodium glucose co-transporter SGLT1 studied by single molecule force spectroscopy. J Biol Chem 2014; 289:21673-83. [PMID: 24962566 DOI: 10.1074/jbc.m113.529875] [Citation(s) in RCA: 16] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
Single molecule force spectroscopy was employed to investigate the dynamics of the sodium glucose co-transporter (SGLT1) upon substrate and inhibitor binding on the single molecule level. CHO cells stably expressing rbSGLT1 were probed by using atomic force microscopy tips carrying either thioglucose, 2'-aminoethyl β-d-glucopyranoside, or aminophlorizin. Poly(ethylene glycol) (PEG) chains of different length and varying end groups were used as tether. Experiments were performed at 10, 25 and 37 °C to address different conformational states of SGLT1. Unbinding forces between ligands and SGLT1 were recorded at different loading rates by changing the retraction velocity, yielding binding probability, width of energy barrier of the binding pocket, and the kinetic off rate constant of the binding reaction. With increasing temperature, width of energy barrier and average life time increased for the interaction of SGLT1 with thioglucose (coupled via acrylamide to a long PEG) but decreased for aminophlorizin binding. The former indicates that in the membrane-bound SGLT1 the pathway to sugar translocation involves several steps with different temperature sensitivity. The latter suggests that also the aglucon binding sites for transport inhibitors have specific, temperature-sensitive conformations.
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Affiliation(s)
- Isabel Neundlinger
- From the Institute for Biophysics, Johannes Kepler University of Linz, Gruberstrasse 40, 4020 Linz, Austria
| | - Theeraporn Puntheeranurak
- From the Institute for Biophysics, Johannes Kepler University of Linz, Gruberstrasse 40, 4020 Linz, Austria, Department of Biology, Faculty of Science, Mahidol University and Nanotec-MU Center of Excellence on Intelligent Materials and Systems, 272 Rama VI, Ratchathewi, Bangkok 10400, Thailand
| | - Linda Wildling
- From the Institute for Biophysics, Johannes Kepler University of Linz, Gruberstrasse 40, 4020 Linz, Austria
| | | | - Lai-Xi Wang
- Institute of Human Virology and Department of Biochemistry and Molecular Biology, University of Maryland School of Medicine, Baltimore, Maryland 21201, and
| | - Hermann J Gruber
- From the Institute for Biophysics, Johannes Kepler University of Linz, Gruberstrasse 40, 4020 Linz, Austria
| | - Rolf K H Kinne
- Max Planck Institute of Molecular Physiology, Otto-Hahn Strasse 11, 44227 Dortmund, Germany
| | - Peter Hinterdorfer
- From the Institute for Biophysics, Johannes Kepler University of Linz, Gruberstrasse 40, 4020 Linz, Austria,
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34
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Simmons KJ, Jackson SM, Brueckner F, Patching SG, Beckstein O, Ivanova E, Geng T, Weyand S, Drew D, Lanigan J, Sharples DJ, Sansom MSP, Iwata S, Fishwick CWG, Johnson AP, Cameron AD, Henderson PJF. Molecular mechanism of ligand recognition by membrane transport protein, Mhp1. EMBO J 2014; 33:1831-44. [PMID: 24952894 PMCID: PMC4195764 DOI: 10.15252/embj.201387557] [Citation(s) in RCA: 50] [Impact Index Per Article: 5.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/05/2023] Open
Abstract
The hydantoin transporter Mhp1 is a sodium-coupled secondary active transport protein of the nucleobase-cation-symport family and a member of the widespread 5-helix inverted repeat superfamily of transporters. The structure of Mhp1 was previously solved in three different conformations providing insight into the molecular basis of the alternating access mechanism. Here, we elucidate detailed events of substrate binding, through a combination of crystallography, molecular dynamics, site-directed mutagenesis, biochemical/biophysical assays, and the design and synthesis of novel ligands. We show precisely where 5-substituted hydantoin substrates bind in an extended configuration at the interface of the bundle and hash domains. They are recognised through hydrogen bonds to the hydantoin moiety and the complementarity of the 5-substituent for a hydrophobic pocket in the protein. Furthermore, we describe a novel structure of an intermediate state of the protein with the external thin gate locked open by an inhibitor, 5-(2-naphthylmethyl)-L-hydantoin, which becomes a substrate when leucine 363 is changed to an alanine. We deduce the molecular events that underlie acquisition and transport of a ligand by Mhp1.
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Affiliation(s)
- Katie J Simmons
- School of Chemistry and Astbury Centre for Structural Molecular Biology, University of Leeds, Leeds, UK
| | - Scott M Jackson
- School of Biomedical Sciences and Astbury Centre for Structural Molecular Biology, University of Leeds, Leeds, UK
| | - Florian Brueckner
- Membrane Protein Laboratory, Diamond Light Source Harwell Science and Innovation Campus, Chilton, Didcot, UK Division of Molecular Biosciences, Membrane Protein Crystallography Group Imperial College, London, UK Rutherford Appleton Laboratory, Research Complex at Harwell, Harwell, Oxford, Didcot, UK
| | - Simon G Patching
- School of Biomedical Sciences and Astbury Centre for Structural Molecular Biology, University of Leeds, Leeds, UK
| | - Oliver Beckstein
- Department of Physics, Arizona State University, Tempe, AZ, USA Department of Biochemistry, University of Oxford, Oxford, UK
| | - Ekaterina Ivanova
- School of Biomedical Sciences and Astbury Centre for Structural Molecular Biology, University of Leeds, Leeds, UK
| | - Tian Geng
- Membrane Protein Laboratory, Diamond Light Source Harwell Science and Innovation Campus, Chilton, Didcot, UK Division of Molecular Biosciences, Membrane Protein Crystallography Group Imperial College, London, UK Rutherford Appleton Laboratory, Research Complex at Harwell, Harwell, Oxford, Didcot, UK
| | - Simone Weyand
- Membrane Protein Laboratory, Diamond Light Source Harwell Science and Innovation Campus, Chilton, Didcot, UK Division of Molecular Biosciences, Membrane Protein Crystallography Group Imperial College, London, UK Rutherford Appleton Laboratory, Research Complex at Harwell, Harwell, Oxford, Didcot, UK
| | - David Drew
- Division of Molecular Biosciences, Membrane Protein Crystallography Group Imperial College, London, UK
| | - Joseph Lanigan
- School of Chemistry and Astbury Centre for Structural Molecular Biology, University of Leeds, Leeds, UK
| | - David J Sharples
- School of Biomedical Sciences and Astbury Centre for Structural Molecular Biology, University of Leeds, Leeds, UK
| | - Mark S P Sansom
- Department of Biochemistry, University of Oxford, Oxford, UK
| | - So Iwata
- Membrane Protein Laboratory, Diamond Light Source Harwell Science and Innovation Campus, Chilton, Didcot, UK Division of Molecular Biosciences, Membrane Protein Crystallography Group Imperial College, London, UK Rutherford Appleton Laboratory, Research Complex at Harwell, Harwell, Oxford, Didcot, UK
| | - Colin W G Fishwick
- School of Chemistry and Astbury Centre for Structural Molecular Biology, University of Leeds, Leeds, UK
| | - A Peter Johnson
- School of Chemistry and Astbury Centre for Structural Molecular Biology, University of Leeds, Leeds, UK
| | - Alexander D Cameron
- Membrane Protein Laboratory, Diamond Light Source Harwell Science and Innovation Campus, Chilton, Didcot, UK Division of Molecular Biosciences, Membrane Protein Crystallography Group Imperial College, London, UK School of Life Sciences, University of Warwick, Coventry, UK
| | - Peter J F Henderson
- School of Biomedical Sciences and Astbury Centre for Structural Molecular Biology, University of Leeds, Leeds, UK
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35
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Ghezzi C, Gorraitz E, Hirayama BA, Loo DDF, Grempler R, Mayoux E, Wright EM. Fingerprints of hSGLT5 sugar and cation selectivity. Am J Physiol Cell Physiol 2014; 306:C864-70. [PMID: 24573086 DOI: 10.1152/ajpcell.00027.2014] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Abstract
Sodium glucose cotransporters (SGLTs) mediate the translocation of carbohydrates across the brush border membrane of different organs such as intestine, kidney, and brain. The human SGLT5 (hSGLT5), in particular, is localized in the kidney were it is responsible for mannose and fructose reabsorption from the glomerular filtrate as confirmed by more recent studies on hSGLT5 knockout mice. Here we characterize the functional properties of hSGLT5 expressed in a stable T-Rex-HEK-293 cell line using biochemical and electrophysiological assays. We confirmed that hSGLT5 is a sodium/mannose transporter that is blocked by phlorizin. Li(+) and H(+) ions were also able to drive mannose transport, and transport was electrogenic. Our results moreover indicate that substrates require a pyranose ring with an axial hydroxyl group (-OH) on carbon 2 (C-2). Compared with Na(+)/glucose cotransport, the level of function of Na(+)/mannose cotransport in rat kidney slices was low.
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Affiliation(s)
- Chiara Ghezzi
- Department of Physiology, Geffen School of Medicine, University of California, Los Angeles, California; and
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36
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Adelman JL, Sheng Y, Choe S, Abramson J, Wright EM, Rosenberg JM, Grabe M. Structural determinants of water permeation through the sodium-galactose transporter vSGLT. Biophys J 2014; 106:1280-9. [PMID: 24655503 PMCID: PMC3984995 DOI: 10.1016/j.bpj.2014.01.006] [Citation(s) in RCA: 23] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/31/2013] [Revised: 12/19/2013] [Accepted: 01/02/2014] [Indexed: 01/26/2023] Open
Abstract
Sodium-glucose transporters (SGLTs) facilitate the movement of water across the cell membrane, playing a central role in cellular homeostasis. Here, we present a detailed analysis of the mechanism of water permeation through the inward-facing state of vSGLT based on nearly 10 μs of molecular dynamics simulations. These simulations reveal the transient formation of a continuous water channel through the transporter that permits water to permeate the protein. Trajectories in which spontaneous release of galactose is observed, as well as those in which galactose remains in the binding site, show that the permeation rate, although modulated by substrate occupancy, is not tightly coupled to substrate release. Using a, to our knowledge, novel channel-detection algorithm, we identify the key residues that control water flow through the transporter and show that solvent gating is regulated by side-chain motions in a small number of residues on the extracellular face. A sequence alignment reveals the presence of two insertion sites in mammalian SGLTs that flank these outer-gate residues. We hypothesize that the absence of these sites in vSGLT may account for the high water permeability values for vSGLT determined via simulation compared to the lower experimental estimates for mammalian SGLT1.
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Affiliation(s)
- Joshua L Adelman
- Department of Biological Sciences, University of Pittsburgh, Pittsburgh, Pennsylvania
| | - Ying Sheng
- Department of Biological Sciences, University of Pittsburgh, Pittsburgh, Pennsylvania
| | - Seungho Choe
- School of Basic Science, College of Convergence, Daegu Gyeongbuk Institute of Science & Technology, Daegu, Korea
| | - Jeff Abramson
- Department of Physiology, University of California, Los Angeles, California
| | - Ernest M Wright
- Department of Physiology, University of California, Los Angeles, California
| | - John M Rosenberg
- Department of Biological Sciences, University of Pittsburgh, Pittsburgh, Pennsylvania.
| | - Michael Grabe
- Department of Biological Sciences, University of Pittsburgh, Pittsburgh, Pennsylvania; Cardiovascular Research Institute, Department of Pharmaceutical Chemistry, University of California, San Francisco, California.
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37
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Functional identification and characterization of sodium binding sites in Na symporters. Proc Natl Acad Sci U S A 2013; 110:E4557-66. [PMID: 24191006 DOI: 10.1073/pnas.1319218110] [Citation(s) in RCA: 32] [Impact Index Per Article: 2.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/19/2023] Open
Abstract
Sodium cotransporters from several different gene families belong to the leucine transporter (LeuT) structural family. Although the identification of Na(+) in binding sites is beyond the resolution of the structures, two Na(+) binding sites (Na1 and Na2) have been proposed in LeuT. Na2 is conserved in the LeuT family but Na1 is not. A biophysical method has been used to measure sodium dissociation constants (Kd) of wild-type and mutant human sodium glucose cotransport (hSGLT1) proteins to identify the Na(+) binding sites in hSGLT1. The Na1 site is formed by residues in the sugar binding pocket, and their mutation influences sodium binding to Na1 but not to Na2. For the canonical Na2 site formed by two -OH side chains, S392 and S393, and three backbone carbonyls, mutation of S392 to cysteine increased the sodium Kd by sixfold. This was accompanied by a dramatic reduction in the apparent sugar and phlorizin affinities. We suggest that mutation of S392 in the Na2 site produces a structural rearrangement of the sugar binding pocket to disrupt both the binding of the second Na(+) and the binding of sugar. In contrast, the S393 mutations produce no significant changes in sodium, sugar, and phlorizin affinities. We conclude that the Na2 site is conserved in hSGLT1, the side chain of S392 and the backbone carbonyl of S393 are important in the first Na(+) binding, and that Na(+) binding to Na2 promotes binding to Na1 and also sugar binding.
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38
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Zhao C, Noskov SY. The molecular mechanism of ion-dependent gating in secondary transporters. PLoS Comput Biol 2013; 9:e1003296. [PMID: 24204233 PMCID: PMC3812048 DOI: 10.1371/journal.pcbi.1003296] [Citation(s) in RCA: 44] [Impact Index Per Article: 4.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/28/2013] [Accepted: 09/08/2013] [Indexed: 11/29/2022] Open
Abstract
LeuT-like fold Na-dependent secondary active transporters form a large family of integral membrane proteins that transport various substrates against their concentration gradient across lipid membranes, using the free energy stored in the downhill concentration gradient of sodium ions. These transporters play an active role in synaptic transmission, the delivery of key nutrients, and the maintenance of osmotic pressure inside the cell. It is generally believed that binding of an ion and/or a substrate drives the conformational dynamics of the transporter. However, the exact mechanism for converting ion binding into useful work has yet to be established. Using a multi-dimensional path sampling (string-method) followed by all-atom free energy simulations, we established the principal thermodynamic and kinetic components governing the ion-dependent conformational dynamics of a LeuT-like fold transporter, the sodium/benzyl-hydantoin symporter Mhp1, for an entire conformational cycle. We found that inward-facing and outward-facing states of Mhp1 display nearly the same free energies with an ion absent from the Na2 site conserved across the LeuT-like fold transporters. The barrier separating an apo-state from inward-facing or outward-facing states of the transporter is very low, suggesting stochastic gating in the absence of ion/substrate bound. In contrast, the binding of a Na2 ion shifts the free energy stabilizing the outward-facing state and promoting substrate binding. Our results indicate that ion binding to the Na2 site may also play a key role in the intracellular thin gate dynamics modulation by altering its interactions with the transmembrane helix 5 (TM5). The Potential of Mean Force (PMF) computations for a substrate entrance displays two energy minima that correspond to the locations of the main binding site S1 and proposed allosteric S2 binding site. However, it was found that substrate's binds to the site S1 ∼5 kcal/mol more favorable than that to the site S2 for all studied bound combinations of ions and a substrate.
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Affiliation(s)
- Chunfeng Zhao
- Center for Molecular Simulations, Department of Biological Sciences, University of Calgary, Calgary, Canada
| | - Sergei Yu. Noskov
- Center for Molecular Simulations, Department of Biological Sciences, University of Calgary, Calgary, Canada
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Wright EM. Glucose transport families SLC5 and SLC50. Mol Aspects Med 2013; 34:183-96. [DOI: 10.1016/j.mam.2012.11.002] [Citation(s) in RCA: 141] [Impact Index Per Article: 12.8] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/14/2012] [Accepted: 10/04/2012] [Indexed: 01/15/2023]
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40
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Jiang X, Loo DDF, Hirayama BA, Wright EM. The importance of being aromatic: π interactions in sodium symporters. Biochemistry 2012; 51:9480-7. [PMID: 23116249 DOI: 10.1021/bi301329w] [Citation(s) in RCA: 16] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Abstract
In the LeuT family of sodium solute symporters, 13-17% of the residues in transmembrane domains are aromatic. The unique properties of aromatic amino acids allow them to play specialized roles in proteins, but their function in membrane transporters is underappreciated. Here we analyze the π bonding pattern in the LeuT (5TMIR) family and then describe the role of a triad of aromatic residues in sodium-dependent sugar cotransporters (SGLTs). In SLC5 symporters, three aromatic residues in TM6 (SGLT1 W289, Y290, and W291) are conserved in only those transporting sugars and inositols. We used biophysical analysis of mutants to discover their functional roles, which we have interpreted in terms of CH-π, π-π, and cation-π bonding. We discovered that (1) glucose binding involves CH-π stacking with Y290, (2) π T-stacking interactions between Y290 and W291 and H-bonding between Y290 and N78 (TM1) are essential to form the sodium and sugar binding sites, (3) the Na(+):sugar stoichiometry is determined by these residues, and (4) W289 may be important in stabilizing the structure through H-bonding to TM3. We also find that the WYW triad plays a role in Na(+) coordination at the Na1 site, possibly through cation-π interactions. Surprisingly, this Na(+) is not necessarily coupled to glucose translocation. Our analysis of π interactions in other LeuT proteins suggests that they also contribute to the structure and function in this whole family of transporters.
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Affiliation(s)
- Xuan Jiang
- Department of Physiology, David Geffen School of Medicine at UCLA, Los Angeles, CA 90095-1751, USA
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Raja M, Puntheeranurak T, Hinterdorfer P, Kinne R. SLC5 and SLC2 transporters in epithelia-cellular role and molecular mechanisms. CURRENT TOPICS IN MEMBRANES 2012. [PMID: 23177983 DOI: 10.1016/b978-0-12-394316-3.00002-8] [Citation(s) in RCA: 14] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 12/21/2022]
Abstract
Members of the SLC5 and SLC2 family are prominently involved in epithelial sugar transport. SGLT1 (sodium-glucose transporter) and SGLT2, as representatives of the former, mediate sodium-dependent uptake of sugars into intestinal and renal cells. GLUT2 (glucose transporter), as representative of the latter, facilitates the sodium-independent exit of sugars from cells. SGLT has played a major role in the formulation and experimental proof for the existence of sodium cotransport systems. Based on the sequence data and biochemical and biophysical analyses, the role of extramembranous loops in sugar and inhibitor binding can be delineated. Crystal structures and homology modeling of SGLT reveal that the sugar translocation involves operation of two hydrophobic gates and intermediate exofacial and endofacial occluded states of the carrier in an alternating access model. The same basic model is proposed for GLUT1. Studies on GLUT1 have pioneered the isolation of eukaryotic transporters by biochemical methods and the development of transport kinetics and transporter models. For GLUT1, results from extensive mutagenesis, cysteine substitution and accessibility studies can be incorporated into a homology model with a barrel-like structure in which accessibility to the extracellular and intracellular medium is altered by pinching movements of some of the helices. For SGLT1 and GLUT1, the extensive hydrophilic and hydrophobic interactions between sugars and binding sites of the various intramembrane helices occur and lead to different substrate specificities and inhibitor affinities of the two transporters. A complex network of regulatory steps adapts the transport activity to the needs of the body.
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Affiliation(s)
- Mobeen Raja
- Max Planck Institute of Molecular Physiology, Dortmund, Germany
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