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Takeyasu M, Kozai K, Sugita M. Involvement of sodium-glucose cotransporter-1 activities in maintaining oscillatory Cl - currents from mouse submandibular acinar cells. J Comp Physiol B 2024; 194:21-32. [PMID: 38308715 PMCID: PMC10940492 DOI: 10.1007/s00360-024-01532-w] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/15/2023] [Revised: 12/01/2023] [Accepted: 01/04/2024] [Indexed: 02/05/2024]
Abstract
In salivary acinar cells, cholinergic stimulation induces elevations of cytosolic [Ca2+]i to activate the apical exit of Cl- through TMEM16A Cl- channels, which acts as a driving force for fluid secretion. To sustain the Cl- secretion, [Cl-]i must be maintained to levels that are greater than the electrochemical equilibrium mainly by Na+-K+-2Cl- cotransporter-mediated Cl- entry in basolateral membrane. Glucose transporters carry glucose into the cytoplasm, enabling the cells to produce ATP to maintain Cl- and fluid secretion. Sodium-glucose cotransporter-1 is a glucose transporter highly expressed in acinar cells. The salivary flow is suppressed by the sodium-glucose cotransporter-1 inhibitor phlorizin. However, it remains elusive how sodium-glucose cotransporter-1 contributes to maintaining salivary fluid secretion. To examine if sodium-glucose cotransporter-1 activity is required for sustaining Cl- secretion to drive fluid secretion, we analyzed the Cl- currents activated by the cholinergic agonist, carbachol, in submandibular acinar cells while comparing the effect of phlorizin on the currents between the whole-cell patch and the gramicidin-perforated patch configurations. Phlorizin suppressed carbachol-induced oscillatory Cl- currents by reducing the Cl- efflux dependent on the Na+-K+-2Cl- cotransporter-mediated Cl- entry in addition to affecting TMEM16A activity. Our results suggest that the sodium-glucose cotransporter-1 activity is necessary for maintaining the oscillatory Cl- secretion supported by the Na+-K+-2Cl- cotransporter activity in real time to drive fluid secretion. The concerted effort of sodium-glucose cotransporter-1, Na+-K+-2Cl- cotransporter, and apically located Cl- channels might underlie the efficient driving of Cl- secretion in different secretory epithelia from a variety of animal species.
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Affiliation(s)
- Misa Takeyasu
- Department of Physiology and Oral Physiology, Graduate School of Biomedical and Health Sciences, Hiroshima University, Kasumi 1-2-3, Minami-ku, Hiroshima, 734-8553, Japan
- Department of Pediatric Dentistry, Graduate School of Biomedical and Health Sciences, Hiroshima University, Hiroshima, Japan
| | - Katsuyuki Kozai
- Department of Pediatric Dentistry, Graduate School of Biomedical and Health Sciences, Hiroshima University, Hiroshima, Japan
| | - Makoto Sugita
- Department of Physiology and Oral Physiology, Graduate School of Biomedical and Health Sciences, Hiroshima University, Kasumi 1-2-3, Minami-ku, Hiroshima, 734-8553, Japan.
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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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Ginsenoside Rd protects cerebral endothelial cells from oxygen-glucose deprivation/reoxygenation induced pyroptosis via inhibiting SLC5A1 mediated sodium influx. J Ginseng Res 2022; 46:700-709. [PMID: 36090684 PMCID: PMC9459060 DOI: 10.1016/j.jgr.2022.05.006] [Citation(s) in RCA: 3] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/14/2022] [Revised: 04/21/2022] [Accepted: 05/12/2022] [Indexed: 12/03/2022] Open
Abstract
Background Ginsenoside Rd is a natural compound with promising neuroprotective effects. However, the underlying mechanisms are still not well-understood. In this study, we explored whether ginsenoside Rd exerts protective effects on cerebral endothelial cells after oxygen-glucose deprivation/reoxygenation (OGD/R) treatment and its potential docking proteins related to the underlying regulations. Method Commercially available primary human brain microvessel endothelial cells (HBMECs) were used for in vitro OGD/R studies. Cell viability, pyroptosis-associated protein expression and tight junction protein degradation were evaluated. Molecular docking proteins were predicted. Subsequent surface plasmon resonance (SPR) technology was utilized for validation. Flow cytometry was performed to quantify caspase-1 positive and PI positive (caspase-1+/PI+) pyroptotic cells. Results Ginsenoside Rd treatment attenuated OGD/R-induced damage of blood-brain barrier (BBB) integrity in vitro. It suppressed NLRP3 inflammasome activation (increased expression of NLRP3, cleaved caspase-1, IL-1β and GSDMD-N terminal (NT)) and subsequent cellular pyroptosis (caspase-1+/PI + cells). Ginsenoside Rd interacted with SLC5A1 with a high affinity and reduced OGD/R-induced sodium influx and potassium efflux in HBMECs. Inhibiting SLC5A1 using phlorizin suppressed OGD/R-activated NLRP3 inflammasome and pyroptosis in HBMECs. Conclusion Ginsenoside Rd protects HBMECs from OGD/R-induced injury partially via binding to SLC5A1, reducing OGD/R-induced sodium influx and potassium efflux, thereby alleviating NLRP3 inflammasome activation and pyroptosis.
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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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Liang X, Yan F, Gao Y, Xiong M, Wang H, Onxayvieng K, Tang R, Li L, Zhang X, Chi W, Piria M, Fuka MM, Gavrilović A, Li D. Sugar transporter genes in grass carp (Ctenopharyngodon idellus): molecular cloning, characterization, and expression in response to different stocking densities. FISH PHYSIOLOGY AND BIOCHEMISTRY 2020; 46:1039-1052. [PMID: 32062828 DOI: 10.1007/s10695-020-00770-3] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 09/04/2019] [Accepted: 01/24/2020] [Indexed: 06/10/2023]
Abstract
Glucose and fructose play a central role in the metabolism and cellular homeostasis of organisms. Their absorption is co-mediated by two families of glucose transporters, Na+-coupled glucose co-transporters (SGLTs) and facilitative Na+-independent sugar carriers (GLUTs), in the intestine. However, limited information has been available on these transporters in fish. Therefore, we studied glut2, sglt1, and sglt4 genes in grass carp (Ctenopharyngodon idellus). The full-length cDNAs of glut2 was 2308 bp, with an open reading frame (ORF) of 503 amino acids (AAs). The full-length cDNAs of sglt1 was 2890 bp, with an ORF of 658 AAs. Additionally, the full-length cDNAs of sglt4 was 2090 bp, with an ORF encoding 659 AAs. The three deduced AA sequences showed high homology between grass carp and other cyprinid fish species. Based on homology modeling, three-dimensional models of GLUT2, SGLT1, and SGLT4 proteins were created and transmembrane domains were noted. glut2, sglt1, and sglt4 were abundantly expressed in the anterior and mid intestine. In particular, glut2 was markedly expressed in liver (P < 0.05). Additionally, the results indicated that different stocking densities (0.9 or 5.9 kg m-2) did not alter intestinal section-dependent expression patterns of the three transporter genes. However, high stocking density impacted segmental mRNA expression levels. This work demonstrated that mRNA expression of sugar transporter genes in the fish intestine was segment specific, and crowding stress may affect the activity of intestinal sugar transporters. These results provided new insights into the relationship between crowding stress and intestinal sugar transporters in fish.
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Affiliation(s)
- Xiao Liang
- College of Fisheries, Hubei Provincial Engineering Laboratory for Pond Aquaculture, Huazhong Agricultural University, Shizishan Street, Hongshan District, Wuhan, 430070, China
| | - Fengying Yan
- College of Fisheries, Hubei Provincial Engineering Laboratory for Pond Aquaculture, Huazhong Agricultural University, Shizishan Street, Hongshan District, Wuhan, 430070, China
| | - Yu Gao
- College of Animal Science and Technology, Yunnan Agricultural University, Kunming, 650201, China
| | - Mei Xiong
- College of Fisheries, Hubei Provincial Engineering Laboratory for Pond Aquaculture, Huazhong Agricultural University, Shizishan Street, Hongshan District, Wuhan, 430070, China
| | - Haishan Wang
- College of Fisheries, Hubei Provincial Engineering Laboratory for Pond Aquaculture, Huazhong Agricultural University, Shizishan Street, Hongshan District, Wuhan, 430070, China
| | - Kommaly Onxayvieng
- College of Fisheries, Hubei Provincial Engineering Laboratory for Pond Aquaculture, Huazhong Agricultural University, Shizishan Street, Hongshan District, Wuhan, 430070, China
- Department of livestock and fisheries, Ministry of agriculture and forestry, 6644, Vientiane, Laos
| | - Rong Tang
- College of Fisheries, Hubei Provincial Engineering Laboratory for Pond Aquaculture, Huazhong Agricultural University, Shizishan Street, Hongshan District, Wuhan, 430070, China
| | - Li Li
- College of Fisheries, Hubei Provincial Engineering Laboratory for Pond Aquaculture, Huazhong Agricultural University, Shizishan Street, Hongshan District, Wuhan, 430070, China
| | - Xi Zhang
- College of Fisheries, Hubei Provincial Engineering Laboratory for Pond Aquaculture, Huazhong Agricultural University, Shizishan Street, Hongshan District, Wuhan, 430070, China
| | - Wei Chi
- College of Fisheries, Hubei Provincial Engineering Laboratory for Pond Aquaculture, Huazhong Agricultural University, Shizishan Street, Hongshan District, Wuhan, 430070, China
| | - Marina Piria
- University of Zagreb, Faculty of Agriculture, Svetošimunska cesta 25, 10000, Zagreb, Croatia
| | - Mirna Mrkonjić Fuka
- University of Zagreb, Faculty of Agriculture, Svetošimunska cesta 25, 10000, Zagreb, Croatia
| | - Ana Gavrilović
- University of Zagreb, Faculty of Agriculture, Svetošimunska cesta 25, 10000, Zagreb, Croatia
| | - Dapeng Li
- College of Fisheries, Hubei Provincial Engineering Laboratory for Pond Aquaculture, Huazhong Agricultural University, Shizishan Street, Hongshan District, Wuhan, 430070, China.
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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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Schäfer N, Friedrich M, Jørgensen ME, Kollert S, Koepsell H, Wischmeyer E, Lesch KP, Geiger D, Döring F. Functional analysis of a triplet deletion in the gene encoding the sodium glucose transporter 3, a potential risk factor for ADHD. PLoS One 2018; 13:e0205109. [PMID: 30286162 PMCID: PMC6171906 DOI: 10.1371/journal.pone.0205109] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/23/2018] [Accepted: 09/19/2018] [Indexed: 12/19/2022] Open
Abstract
Sodium-glucose transporters (SGLT) belong to the solute carrier 5 family, which is characterized by sodium dependent transport of sugars and other solutes. In contrast, the human SGLT3 (hSGLT3) isoform, encoded by SLC5A4, acts as a glucose sensor that does not transport sugar but induces membrane depolarization by Na+ currents upon ligand binding. Whole-exome sequencing (WES) of several extended pedigrees with high density of attention-deficit/hyperactivity disorder (ADHD) identified a triplet ATG deletion in SLC5A4 leading to a single amino acid loss (ΔM500) in the hSGLT3 protein imperfectly co-segregating with the clinical phenotype of ADHD. Since mutations in homologous domains of hSGLT1 and hSGLT2 were found to affect intestinal and renal function, respectively, we analyzed the functional properties of hSGLT3[wt] and [ΔM500] by voltage clamp and current clamp recordings from cRNA-injected Xenopus laevis oocytes. The cation conductance of hSGLT3[wt] was activated by application of glucose or the specific agonist 1-desoxynojirimycin (DNJ) as revealed by inward currents in the voltage clamp configuration and cell depolarization in the current clamp mode. Almost no currents and changes in membrane potential were observed when glucose or DNJ were applied to hSGLT3[ΔM500]-injected oocytes, demonstrating a loss of function by this amino acid deletion in hSGLT3. To monitor membrane targeting of wt and mutant hSGLT3, fusion constructs with YFP were generated, heterologously expressed in Xenopus laevis oocytes and analyzed for membrane fluorescence by confocal microscopy. In comparison to hSGLT3[wt] the fluorescent signal of mutant [ΔM500] was reduced by 43% indicating that the mutant phenotype might mainly result from inaccurate membrane targeting. As revealed by homology modeling, residue M500 is located in TM11 suggesting that in addition to the core structure (TM1-TM10) of the transporter, the surrounding TMs are equally crucial for transport/sensor function. In conclusion, our findings indicate that the deletion [ΔM500] in hSGLT3 inhibits membrane targeting and thus largely disrupts glucose-induced sodium conductance, which may, in interaction with other ADHD risk-related gene variants, influence the risk for ADHD in deletion carriers.
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Affiliation(s)
- Nadine Schäfer
- Department of Molecular Plant Physiology and Biophysics, Julius-von-Sachs-Institute, University of Würzburg, Würzburg, Germany
| | - Maximilian Friedrich
- Division of Molecular Psychiatry, Center of Mental Health, University Hospital of Würzburg, Würzburg, Germany
| | - Morten Egevang Jørgensen
- Department of Molecular Plant Physiology and Biophysics, Julius-von-Sachs-Institute, University of Würzburg, Würzburg, Germany
| | - Sina Kollert
- Division of Molecular Psychiatry, Center of Mental Health, University Hospital of Würzburg, Würzburg, Germany
- Division of Molecular Electrophysiology, Institute of Physiology, University of Würzburg, Würzburg, Germany
- Laboratory of Psychiatric Neurobiology, Institute of Molecular Medicine, Sechenov First Moscow State Medical University, Moscow, Russia
| | - Hermann Koepsell
- Department of Molecular Plant Physiology and Biophysics, Julius-von-Sachs-Institute, University of Würzburg, Würzburg, Germany
| | - Erhard Wischmeyer
- Division of Molecular Electrophysiology, Institute of Physiology, University of Würzburg, Würzburg, Germany
- Department of Psychiatry, Psychosomatics and Psychotherapy, Center of Mental Health,University Hospital of Würzburg, Würzburg, Germany
| | - Klaus-Peter Lesch
- Division of Molecular Psychiatry, Center of Mental Health, University Hospital of Würzburg, Würzburg, Germany
- Laboratory of Psychiatric Neurobiology, Institute of Molecular Medicine, Sechenov First Moscow State Medical University, Moscow, Russia
- Department of Neuroscience, School for Mental Health and Neuroscience (MHeNS), Maastricht University, Maastricht, The Netherlands
| | - Dietmar Geiger
- Department of Molecular Plant Physiology and Biophysics, Julius-von-Sachs-Institute, University of Würzburg, Würzburg, Germany
| | - Frank Döring
- Division of Molecular Electrophysiology, Institute of Physiology, University of Würzburg, Würzburg, Germany
- Department of Psychiatry, Psychosomatics and Psychotherapy, Center of Mental Health,University Hospital of Würzburg, Würzburg, Germany
- * E-mail:
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Terachi M, Hirono C, Kitagawa M, Sugita M. The biphasic effect of extracellular glucose concentration on carbachol-induced fluid secretion from mouse submandibular glands. Eur J Oral Sci 2018; 126:197-205. [PMID: 29676804 DOI: 10.1111/eos.12417] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/27/2022]
Abstract
Cholinergic agonists evoke elevations of the cytoplasmic free-calcium concentration ([Ca2+ ]i ) to stimulate fluid secretion in salivary glands. Salivary flow rates are significantly reduced in diabetic patients. However, it remains elusive how salivary secretion is impaired in diabetes. Here, we used an ex vivo submandibular gland perfusion technique to characterize the dependency of salivary flow rates on extracellular glucose concentration and activities of glucose transporters expressed in the glands. The cholinergic agonist carbachol (CCh) induced sustained fluid secretion, the rates of which were modulated by the extracellular glucose concentration in a biphasic manner. Both lowering the extracellular glucose concentration to less than 2.5 mM and elevating it to higher than 5 mM resulted in decreased CCh-induced fluid secretion. The CCh-induced salivary flow was suppressed by phlorizin, an inhibitor of the sodium-glucose cotransporter 1 (SGLT1) located basolaterally in submandibular acinar cells, which is altered at the protein expression level in diabetic animal models. Our data suggest that SGLT1-mediated glucose uptake in acinar cells is required to maintain the fluid secretion by sustaining Cl- secretion in real-time. High extracellular glucose levels may suppress the CCh-induced secretion of salivary fluid by altering the activities of ion channels and transporters downstream of [Ca2+ ]i signals.
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Affiliation(s)
- Momomi Terachi
- Department of Physiology and Oral Physiology, Graduate School of Biomedical & Health Sciences, Hiroshima University, Hiroshima, Japan
| | - Chikara Hirono
- Department of Physiology and Oral Physiology, Graduate School of Biomedical & Health Sciences, Hiroshima University, Hiroshima, Japan
| | - Michinori Kitagawa
- Department of Physiology and Oral Physiology, Graduate School of Biomedical & Health Sciences, Hiroshima University, Hiroshima, Japan
| | - Makoto Sugita
- Department of Physiology and Oral Physiology, Graduate School of Biomedical & Health Sciences, Hiroshima University, Hiroshima, Japan
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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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Al-Kurdi ZI, Chowdhry BZ, Leharne SA, Qinna NA, Al Omari MMH, Badwan AA. Influence of glucosamine on the bioactivity of insulin delivered subcutaneously and in an oral nanodelivery system. DRUG DESIGN DEVELOPMENT AND THERAPY 2015; 9:6167-76. [PMID: 26640369 PMCID: PMC4657806 DOI: 10.2147/dddt.s91974] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Indexed: 12/31/2022]
Abstract
The aim of the work reported herein was to study the effect of glucosamine HCl (GlcN·HCl) on the bioactivity (BA) of insulin, administered via subcutaneous (SC) and oral routes, in adult male Sprague Dawley rats. The oral insulin delivery system (insulin-chitosan reverse micelle [IC-RM]) was prepared by solubilizing insulin-chitosan (13 kDa) polyelectrolyte complex in a RM system consisting of oleic acid, PEG-8 caprylic/capric glycerides, and polyglycerol-6-dioleate. The BA of insulin in vivo was evaluated by measuring blood glucose level using a blood glucose meter; the results revealed that the extent of hypoglycemic activity of SC insulin was GlcN·HCl dose dependent when they were administered simultaneously. A significant reduction in blood glucose levels (P<0.05) was found for the insulin:GlcN·HCl at mass ratios of 1:10 and 1:20, whereas lower ratios (eg, 1:1 and 1:4) showed no significant reduction. Furthermore, enhancement of the action of SC insulin was achieved by oral administration of GlcN·HCl for 5 consecutive days prior to insulin injection (P<0.05). For oral insulin administration via the IC-RM system, the presence of GlcN·HCl increased the hypoglycemic activity of insulin (P<0.05). The relative BA were 6.7% and 5.4% in the presence and absence of GlcN·HCl (ie, the increase in the relative BA was approximately 23% due to incorporating GlcN·HCl in the IC-RM system), respectively. The aforementioned findings offer an opportunity to incorporate GlcN·HCl in oral insulin delivery systems in order to enhance a reduction in blood glucose levels.
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Affiliation(s)
- Zakieh I Al-Kurdi
- The Jordanian Pharmaceutical Manufacturing Company (PLC), Naor, Jordan ; Faculty of Engineering and Science, University of Greenwich, Medway Campus, Kent, UK
| | - Babur Z Chowdhry
- Faculty of Engineering and Science, University of Greenwich, Medway Campus, Kent, UK
| | - Stephen A Leharne
- Faculty of Engineering and Science, University of Greenwich, Medway Campus, Kent, UK
| | - Nidal A Qinna
- Department of Pharmacology and Biomedical Sciences, Faculty of Pharmacy and Medical Sciences, University of Petra, Amman, Jordan
| | | | - Adnan A Badwan
- The Jordanian Pharmaceutical Manufacturing Company (PLC), Naor, Jordan
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Li Z, Lee ASE, Bracher S, Jung H, Paz A, Kumar JP, Abramson J, Quick M, Shi L. Identification of a second substrate-binding site in solute-sodium symporters. J Biol Chem 2014; 290:127-41. [PMID: 25398883 DOI: 10.1074/jbc.m114.584383] [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: 12/13/2022] Open
Abstract
The structure of the sodium/galactose transporter (vSGLT), a solute-sodium symporter (SSS) from Vibrio parahaemolyticus, shares a common structural fold with LeuT of the neurotransmitter-sodium symporter family. Structural alignments between LeuT and vSGLT reveal that the crystallographically identified galactose-binding site in vSGLT is located in a more extracellular location relative to the central substrate-binding site (S1) in LeuT. Our computational analyses suggest the existence of an additional galactose-binding site in vSGLT that aligns to the S1 site of LeuT. Radiolabeled galactose saturation binding experiments indicate that, like LeuT, vSGLT can simultaneously bind two substrate molecules under equilibrium conditions. Mutating key residues in the individual substrate-binding sites reduced the molar substrate-to-protein binding stoichiometry to ~1. In addition, the related and more experimentally tractable SSS member PutP (the Na(+)/proline transporter) also exhibits a binding stoichiometry of 2. Targeting residues in the proposed sites with mutations results in the reduction of the binding stoichiometry and is accompanied by severely impaired translocation of proline. Our data suggest that substrate transport by SSS members requires both substrate-binding sites, thereby implying that SSSs and neurotransmitter-sodium symporters share common mechanistic elements in substrate transport.
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Affiliation(s)
- Zheng Li
- From the Department of Physiology and Biophysics, Weill Cornell Medical College, Cornell University, New York, New York 10065
| | - Ashley S E Lee
- the Center for Molecular Recognition and Department of Psychiatry, Columbia University College of Physicians and Surgeons, New York, New York 10032
| | - Susanne Bracher
- the Ludwig Maximilian University of Munich, Biocentre, Microbiology, Grosshaderner Strasse 2-4, Martinsried, D-82152, Germany
| | - Heinrich Jung
- the Ludwig Maximilian University of Munich, Biocentre, Microbiology, Grosshaderner Strasse 2-4, Martinsried, D-82152, Germany
| | - Aviv Paz
- the Department of Physiology, UCLA, Los Angeles, California 90095
| | - Jay P Kumar
- the Institute for Stem Cell Biology and Regenerative Medicine, NCBS Campus, GKVK Post, Bellary Road, Bangalore-560065, Karnataka, India
| | - Jeff Abramson
- the Department of Physiology, UCLA, Los Angeles, California 90095, the Institute for Stem Cell Biology and Regenerative Medicine, NCBS Campus, GKVK Post, Bellary Road, Bangalore-560065, Karnataka, India
| | - Matthias Quick
- the Center for Molecular Recognition and Department of Psychiatry, Columbia University College of Physicians and Surgeons, New York, New York 10032, the Division of Molecular Therapeutics, New York State Psychiatric Institute, New York, New York 10032, and
| | - Lei Shi
- From the Department of Physiology and Biophysics, Weill Cornell Medical College, Cornell University, New York, New York 10065, the Institute for Computational Biomedicine, Weill Cornell Medical College, Cornell University, New York, New York 10021
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12
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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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13
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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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14
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15
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A Microscopic View of the Mechanisms of Active Transport Across the Cellular Membrane. ANNUAL REPORTS IN COMPUTATIONAL CHEMISTRY 2014. [DOI: 10.1016/b978-0-444-63378-1.00004-5] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 02/07/2023]
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16
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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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17
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Darrouzet E, Lindenthal S, Marcellin D, Pellequer JL, Pourcher T. The sodium/iodide symporter: state of the art of its molecular characterization. BIOCHIMICA ET BIOPHYSICA ACTA-BIOMEMBRANES 2013; 1838:244-53. [PMID: 23988430 DOI: 10.1016/j.bbamem.2013.08.013] [Citation(s) in RCA: 59] [Impact Index Per Article: 5.4] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 06/06/2013] [Revised: 08/05/2013] [Accepted: 08/19/2013] [Indexed: 12/30/2022]
Abstract
The sodium/iodide symporter (NIS or SLC5A5) is an intrinsic membrane protein implicated in iodide uptake into thyroid follicular cells. It plays a crucial role in iodine metabolism and thyroid regulation and its function is widely exploited in the diagnosis and treatment of benign and malignant thyroid diseases. A great effort is currently being made to develop a NIS-based gene therapy also allowing the radiotreatment of nonthyroidal tumors. NIS is also expressed in other tissues, such as salivary gland, stomach and mammary gland during lactation, where its physiological role remains unclear. The molecular identity of the thyroid iodide transporter was elucidated approximately fifteen years ago. It belongs to the superfamily of sodium/solute symporters, SSS (and to the human transporter family, SLC5), and is composed of 13 transmembrane helices and 643 amino acid residues in humans. Knowledge concerning NIS structure/function relationship has been obtained by taking advantage of the high resolution structure of one member of the SSS family, the Vibrio parahaemolyticus sodium/galactose symporter (vSGLT), and from studies of gene mutations leading to congenital iodine transport defects (ITD). This review will summarize current knowledge regarding the molecular characterization of NIS.
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Affiliation(s)
- Elisabeth Darrouzet
- SBTN, bât 170, centre de Marcoule, BP 17171, 30207 Bagnols sur Cèze CEDEX, France; Laboratoire TIRO, Faculté de médecine, Université de Nice Sophia-Antipolis, 28 Avenue de Valombrose, 06107 Nice CEDEX, France; CAL, TIRO, F-06107 Nice, France.
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18
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Shaikh S, Li J, Enkavi G, Wen PC, Huang Z, Tajkhorshid E. Visualizing functional motions of membrane transporters with molecular dynamics simulations. Biochemistry 2013; 52:569-87. [PMID: 23298176 PMCID: PMC3560430 DOI: 10.1021/bi301086x] [Citation(s) in RCA: 38] [Impact Index Per Article: 3.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/11/2012] [Revised: 12/21/2012] [Indexed: 01/08/2023]
Abstract
Computational modeling and molecular simulation techniques have become an integral part of modern molecular research. Various areas of molecular sciences continue to benefit from, indeed rely on, the unparalleled spatial and temporal resolutions offered by these technologies, to provide a more complete picture of the molecular problems at hand. Because of the continuous development of more efficient algorithms harvesting ever-expanding computational resources, and the emergence of more advanced and novel theories and methodologies, the scope of computational studies has expanded significantly over the past decade, now including much larger molecular systems and far more complex molecular phenomena. Among the various computer modeling techniques, the application of molecular dynamics (MD) simulation and related techniques has particularly drawn attention in biomolecular research, because of the ability of the method to describe the dynamical nature of the molecular systems and thereby to provide a more realistic representation, which is often needed for understanding fundamental molecular properties. The method has proven to be remarkably successful in capturing molecular events and structural transitions highly relevant to the function and/or physicochemical properties of biomolecular systems. Herein, after a brief introduction to the method of MD, we use a number of membrane transport proteins studied in our laboratory as examples to showcase the scope and applicability of the method and its power in characterizing molecular motions of various magnitudes and time scales that are involved in the function of this important class of membrane proteins.
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Affiliation(s)
- Saher
A. Shaikh
- Department of Biochemistry, Beckman Institute for Advanced
Science and Technology, and Center for Biophysics and Computational
Biology, University of Illinois at Urbana-Champaign, 405 North Mathews Avenue, Urbana, Illinois 61801, United States
| | - Jing Li
- Department of Biochemistry, Beckman Institute for Advanced
Science and Technology, and Center for Biophysics and Computational
Biology, University of Illinois at Urbana-Champaign, 405 North Mathews Avenue, Urbana, Illinois 61801, United States
| | - Giray Enkavi
- Department of Biochemistry, Beckman Institute for Advanced
Science and Technology, and Center for Biophysics and Computational
Biology, University of Illinois at Urbana-Champaign, 405 North Mathews Avenue, Urbana, Illinois 61801, United States
| | - Po-Chao Wen
- Department of Biochemistry, Beckman Institute for Advanced
Science and Technology, and Center for Biophysics and Computational
Biology, University of Illinois at Urbana-Champaign, 405 North Mathews Avenue, Urbana, Illinois 61801, United States
| | - Zhijian Huang
- Department of Biochemistry, Beckman Institute for Advanced
Science and Technology, and Center for Biophysics and Computational
Biology, University of Illinois at Urbana-Champaign, 405 North Mathews Avenue, Urbana, Illinois 61801, United States
| | - Emad Tajkhorshid
- Department of Biochemistry, Beckman Institute for Advanced
Science and Technology, and Center for Biophysics and Computational
Biology, University of Illinois at Urbana-Champaign, 405 North Mathews Avenue, Urbana, Illinois 61801, United States
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20
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Sala-Rabanal M, Hirayama BA, Loo DDF, Chaptal V, Abramson J, Wright EM. Bridging the gap between structure and kinetics of human SGLT1. Am J Physiol Cell Physiol 2011; 302:C1293-305. [PMID: 22159082 DOI: 10.1152/ajpcell.00397.2011] [Citation(s) in RCA: 41] [Impact Index Per Article: 3.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Abstract
The Na(+)-glucose cotransporter hSGLT1 is a member of a class of membrane proteins that harness Na(+) electrochemical gradients to drive uphill solute transport. Although hSGLT1 belongs to one gene family (SLC5), recent structural studies of bacterial Na(+) cotransporters have shown that Na(+) transporters in different gene families have the same structural fold. We have constructed homology models of hSGLT1 in two conformations, the inward-facing occluded (based on vSGLT) and the outward open conformations (based on Mhp1), mutated in turn each of the conserved gates and ligand binding residues, expressed the SGLT1 mutants in Xenopus oocytes, and determined the functional consequences using biophysical and biochemical assays. The results establish that mutating the ligand binding residues produces profound changes in the ligand affinity (the half-saturation concentration, K(0.5)); e.g., mutating sugar binding residues increases the glucose K(0.5) by up to three orders of magnitude. Mutation of the external gate residues increases the Na(+) to sugar transport stoichiometry, demonstrating that these residues are critical for efficient cotransport. The changes in phlorizin inhibition constant (K(i)) are proportional to the changes in sugar K(0.5), except in the case of F101C, where phlorizin K(i) increases by orders of magnitude without a change in glucose K(0.5). We conclude that glucose and phlorizin occupy the same binding site and that F101 is involved in binding to the phloretin group of the inhibitor. Substituted-cysteine accessibility methods show that the cysteine residues at the position of the gates and sugar binding site are largely accessible only to external hydrophilic methanethiosulfonate reagents in the presence of external Na(+), demonstrating that the external sugar (and phlorizin) binding vestibule is opened by the presence of external Na(+) and closes after the binding of sugar and phlorizin. Overall, the present results provide a bridge between kinetics and structural studies of cotransporters.
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Affiliation(s)
- Monica Sala-Rabanal
- Department of Physiology, The Geffen School of Medicine at University of California, Los Angeles, California 90095-1751, USA
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21
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Li J, Tajkhorshid E. A gate-free pathway for substrate release from the inward-facing state of the Na⁺-galactose transporter. BIOCHIMICA ET BIOPHYSICA ACTA-BIOMEMBRANES 2011; 1818:263-71. [PMID: 21978597 DOI: 10.1016/j.bbamem.2011.09.011] [Citation(s) in RCA: 17] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 06/30/2011] [Revised: 09/02/2011] [Accepted: 09/10/2011] [Indexed: 10/17/2022]
Abstract
Employing molecular dynamics (MD) simulations, the pathway and mechanism of substrate unbinding from the inward-facing state of the Na(+)-coupled galactose transporter, vSGLT, have been investigated. During a 200-ns equilibrium simulation, repeated spontaneous unbinding events of the substrate from its binding site have been observed. In contrast to the previously proposed gating role of a tyrosine residue (Y263), the unbinding mechanism captured in the present equilibrium simulation does not rely on the displacement and/or rotation of this side chain. Rather, the unbinding involves an initial lateral displacement of the substrate out of the binding site which allows the substrate to completely emerge from the region covered by the side chain of Y263 without any noticeable conformational changes of the latter. Starting with the snapshots taken from this equilibrium simulation with the substrate outside the binding site, steered MD (SMD) simulations were then used to probe the translocation of the substrate along the remaining of the release pathway within the protein's lumen and to characterize the nature of protein-substrate interactions involved in the process. Combining the results of the equilibrium and SMD simulations, we provide a description of the full translocation pathway for the substrate release from the binding site into the cytoplasm. Residues E68, N142, T431, and N267 facilitate the initial substrate's displacement out of the binding site, while the translocation of the substrate along the remainder of the exit pathway formed between TM6 and TM8 is facilitated by H-bond interactions between the substrate and a series of conserved, polar residues (Y138, N267, R273, S365, S368, N371, S372, and T375). The observed molecular events indicate that no gating is required for the release of the substrate from the crystallographically captured structure of the inward-facing state of SGLT, suggesting that this conformation might represent an open, rather than occluded, state of the transporter. This article is part of a Special Issue entitled: Membrane protein structure and function.
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Affiliation(s)
- Jing Li
- Department of Biochemistry, College of Medicine, Beckman Institute, and Center for Biophysics and Computational Biology, University of Illinois at Urbana-Champaign, Urbana, Illinois 61801, USA
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Abstract
There are two classes of glucose transporters involved in glucose homeostasis in the body, the facilitated transporters or uniporters (GLUTs) and the active transporters or symporters (SGLTs). The energy for active glucose transport is provided by the sodium gradient across the cell membrane, the Na(+) glucose cotransport hypothesis first proposed in 1960 by Crane. Since the cloning of SGLT1 in 1987, there have been advances in the genetics, molecular biology, biochemistry, biophysics, and structure of SGLTs. There are 12 members of the human SGLT (SLC5) gene family, including cotransporters for sugars, anions, vitamins, and short-chain fatty acids. Here we give a personal review of these advances. The SGLTs belong to a structural class of membrane proteins from unrelated gene families of antiporters and Na(+) and H(+) symporters. This class shares a common atomic architecture and a common transport mechanism. SGLTs also function as water and urea channels, glucose sensors, and coupled-water and urea transporters. We also discuss the physiology and pathophysiology of SGLTs, e.g., glucose galactose malabsorption and familial renal glycosuria, and briefly report on targeting of SGLTs for new therapies for diabetes.
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Affiliation(s)
- Ernest M Wright
- Department of Physiology, David Geffen School of Medicine at University of California Los Angeles, Los Angeles, California 90095-1751, USA.
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Simon RR, Marks V, Leeds AR, Anderson JW. A comprehensive review of oral glucosamine use and effects on glucose metabolism in normal and diabetic individuals. Diabetes Metab Res Rev 2011; 27:14-27. [PMID: 21218504 PMCID: PMC3042150 DOI: 10.1002/dmrr.1150] [Citation(s) in RCA: 56] [Impact Index Per Article: 4.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 03/26/2010] [Revised: 10/01/2010] [Accepted: 10/14/2010] [Indexed: 01/05/2023]
Abstract
Glucosamine (GlcN) is a widely utilized dietary supplement that is used to promote joint health. Reports that oral GlcN supplementation at usual doses adversely affects glucose metabolism in subjects with impaired glucose tolerance have raised concerns that GlcN should be contraindicated in individuals with diabetes and those at risk for developing it. This review addresses its potential, when used at typical doses, to affect glucose metabolism and insulin sensitivity in healthy individuals and those with diabetes or 'pre-diabetes'. Publicly available scientific information and data on GlcN were systematically compiled using the electronic search tool, Dialog , and reviewed with special emphasis on human studies. In long-term clinical trials, including those containing subjects with type 2 diabetes or 'pre-diabetes', GlcN produced a non-significant lowering of fasting blood glucose concentrations in all groups of subjects treated for periods of up to 3 years. Owing to limitations in study design, conclusions based on studies that report adverse affects of GlcN on insulin sensitivity and glucose tolerance in pre-diabetic subjects are suspect. However, no definitive long-term studies of GlcN use for individuals with pre-diabetes are available. Nevertheless, based on available evidence, we conclude that GlcN has no effect on fasting blood glucose levels, glucose metabolism, or insulin sensitivity at any oral dose level in healthy subjects, individuals with diabetes, or those with impaired glucose tolerance.
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Affiliation(s)
- R R Simon
- Cantox Health Sciences International, Mississauga, ON, Canada
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Boudry G, David ES, Douard V, Monteiro IM, Le Huërou-Luron I, Ferraris RP. Role of intestinal transporters in neonatal nutrition: carbohydrates, proteins, lipids, minerals, and vitamins. J Pediatr Gastroenterol Nutr 2010; 51:380-401. [PMID: 20808244 DOI: 10.1097/mpg.0b013e3181eb5ad6] [Citation(s) in RCA: 47] [Impact Index Per Article: 3.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 01/19/2023]
Abstract
To support rapid growth and a high metabolic rate, infants require enormous amounts of nutrients. The small intestine must have the complete array of transporters that absorb the nutrients released from digested food. Failure of intestinal transporters to function properly often presents symptoms as "failure to thrive" because nutrients are not absorbed and as diarrhea because unabsorbed nutrients upset luminal osmolality or become substrates of intestinal bacteria. We enumerate the nutrients that constitute human milk and various infant milk formulas, explain their importance in neonatal nutrition, then describe for each nutrient the transporter(s) that absorbs it from the intestinal lumen into the enterocyte cytosol and from the cytosol to the portal blood. More than 100 membrane and cytosolic transporters are now thought to facilitate absorption of minerals and vitamins as well as products of digestion of the macronutrients carbohydrates, proteins, and lipids. We highlight research areas that should yield information needed to better understand the important role of these transporters during normal development.
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Affiliation(s)
- Gaëlle Boudry
- Institut National de Recherche Agronomique, UMR1079 Système d'Elevage, Nutrition, Animale et Humaine, St-Gilles, France
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Yu AS, Hirayama BA, Timbol G, Liu J, Basarah E, Kepe V, Satyamurthy N, Huang SC, Wright EM, Barrio JR. Functional expression of SGLTs in rat brain. Am J Physiol Cell Physiol 2010; 299:C1277-84. [PMID: 20826762 DOI: 10.1152/ajpcell.00296.2010] [Citation(s) in RCA: 87] [Impact Index Per Article: 6.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Abstract
This work provides evidence of previously unrecognized uptake of glucose via sodium-coupled glucose transporters (SGLTs) in specific regions of the brain. The current understanding of functional glucose utilization in brain is largely based on studies using positron emission tomography (PET) with the glucose tracer 2-deoxy-2-[F-18]fluoro-D-glucose (2-FDG). However, 2-FDG is only a good substrate for facilitated-glucose transporters (GLUTs), not for SGLTs. Thus, glucose accumulation measured by 2-FDG omits the role of SGLTs. We designed and synthesized two high-affinity tracers: one, α-methyl-4-[F-18]fluoro-4-deoxy-D-glucopyranoside (Me-4FDG), is a highly specific SGLT substrate and not transported by GLUTs; the other one, 4-[F-18]fluoro-4-deoxy-D-glucose (4-FDG), is transported by both SGLTs and GLUTs and will pass through the blood brain barrier (BBB). In vitro Me-4FDG autoradiography was used to map the distribution of uptake by functional SGLTs in brain slices with a comparable result from in vitro 4-FDG autoradiography. Immunohistochemical assays showed that uptake was consistent with the distribution of SGLT protein. Ex vivo 4-FDG autoradiography showed that SGLTs in these areas are functionally active in the normal in vivo brain. The results establish that SGLTs are a normal part of the physiology of specific areas of the brain, including hippocampus, amygdala, hypothalamus, and cerebral cortices. 4-FDG PET imaging also established that this BBB-permeable SGLT tracer now offers a functional imaging approach in humans to assess regulation of SGLT activity in health and disease.
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Affiliation(s)
- Amy S Yu
- Department of Molecular and Medical Pharmacology, David Geffen School of Medicine, Universityof California Los Angeles, California 90095-1751, USA
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La Ferla B, Spinosa V, D'Orazio G, Palazzo M, Balsari A, Foppoli AA, Rumio C, Nicotra F. Dansyl C-Glucoside as a Novel Agent Against Endotoxic Shock. ChemMedChem 2010; 5:1677-80. [DOI: 10.1002/cmdc.201000282] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/07/2022]
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Roche M, Neti PVSV, Kemp FW, Agrawal A, Attanasio A, Douard V, Muduli A, Azzam EI, Norkus E, Brimacombe M, Howell RW, Ferraris RP. Radiation-induced reductions in transporter mRNA levels parallel reductions in intestinal sugar transport. Am J Physiol Regul Integr Comp Physiol 2009; 298:R173-82. [PMID: 19907007 DOI: 10.1152/ajpregu.00612.2009] [Citation(s) in RCA: 10] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Abstract
More than a century ago, ionizing radiation was observed to damage the radiosensitive small intestine. Although a large number of studies has since shown that radiation reduces rates of intestinal digestion and absorption of nutrients, no study has determined whether radiation affects mRNA expression and dietary regulation of nutrient transporters. Since radiation generates free radicals and disrupts DNA replication, we tested the hypotheses that at doses known to reduce sugar absorption, radiation decreases the mRNA abundance of sugar transporters SGLT1 and GLUT5, prevents substrate regulation of sugar transporter expression, and causes reductions in sugar absorption that can be prevented by consumption of the antioxidant vitamin A, previously shown by us to radioprotect the testes. Mice were acutely irradiated with (137)Cs gamma rays at doses of 0, 7, 8.5, or 10 Gy over the whole body. Mice were fed with vitamin A-supplemented diet (100x the control diet) for 5 days prior to irradiation after which the diet was continued until death. Intestinal sugar transport was studied at days 2, 5, 8, and 14 postirradiation. By day 8, d-glucose uptake decreased by approximately 10-20% and d-fructose uptake by 25-85%. With increasing radiation dose, the quantity of heterogeneous nuclear RNA increased for both transporters, whereas mRNA levels decreased, paralleling reductions in transport. Enterocytes of mice fed the vitamin A supplement had > or = 6-fold retinol concentrations than those of mice fed control diets, confirming considerable intestinal vitamin A uptake. However, vitamin A supplementation had no effect on clinical or transport parameters and afforded no protection against radiation-induced changes in intestinal sugar transport. Radiation markedly reduced GLUT5 activity and mRNA abundance, but high-d-fructose diets enhanced GLUT5 activity and mRNA expression in both unirradiated and irradiated mice. In conclusion, the effect of radiation may be posttranscriptional, and radiation-damaged intestines can still respond to dietary stimuli.
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Affiliation(s)
- Marjolaine Roche
- Department of Pharmacology and Physiology, New Jersey Medical School, NJ, USA
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Abramson J, Wright EM. Structure and function of Na(+)-symporters with inverted repeats. Curr Opin Struct Biol 2009; 19:425-32. [PMID: 19631523 PMCID: PMC3496787 DOI: 10.1016/j.sbi.2009.06.002] [Citation(s) in RCA: 166] [Impact Index Per Article: 11.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/19/2009] [Revised: 06/12/2009] [Accepted: 06/16/2009] [Indexed: 11/19/2022]
Abstract
Symporters are membrane proteins that couple energy stored in electrochemical potential gradients to drive the cotransport of molecules and ions into cells. Traditionally, proteins are classified into gene families based on sequence homology and functional properties, for example the sodium glucose (SLC5 or Sodium Solute Symporter Family, SSS or SSF) and GABA (SLC6 or Neurotransmitter Sodium Symporter Family, NSS or SNF) symporter families [1-4]. Recently, it has been established that four Na(+)-symporter proteins with unrelated sequences have a common structural core containing an inverted repeat of 5 transmembrane (TM) helices [5(**)-8(**)]. Analysis of these four structures reveals that they reside in different conformations along the transport cycle providing atomic insight into the mechanism of sodium solute cotransport.
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Affiliation(s)
- Jeff Abramson
- Department of Physiology, David School of Medicine at UCLA, Los Angeles, CA 90095-1751, USA.
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Liu T, Krofchick D, Silverman M. Effects on conformational states of the rabbit sodium/glucose cotransporter through modulation of polarity and charge at glutamine 457. Biophys J 2009; 96:748-60. [PMID: 19167319 DOI: 10.1016/j.bpj.2008.09.045] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/23/2008] [Accepted: 09/22/2008] [Indexed: 11/17/2022] Open
Abstract
The high affinity sodium/glucose cotransporter (SGLT1) couples transport of Na(+) and glucose. Previous studies established that mutant Q457C human SGLT1 retains full activity, and sugar translocation is abolished in mutant Q457R or in mutant Q457C after reaction with methanethiosulfonate derivatives, but Na(+) and sugar binding remain intact. To explore the mechanism by which modulation of Q457 abolishes transport, Q457C and Q457R of rabbit SGLT1 were studied using chemical modification and the two-electrode voltage-clamp technique. Compared to wild-type SGLT1, Q457C exhibits approximately 20-fold reduction in phloridzin affinity and preferential occupancy of an inward-facing state. Alkylation of Q457C by [(2-trimethylammonium) ethyl] methanethiosulphonate bromide, (MTSET), reverses these changes while blocking transport. Analysis of pre-steady-state currents in the absence of sugar yields three decay constants for each of Q457C, Q457C-MTSET and Q457R. Comparison of Q457C-MTSET and Q457R with Q457C and wild-type, reveals that inhibition of transport is accompanied by a decrease in magnitude and voltage-independence of the slow decay constant at negative potentials. But fast and medium decays remain unchanged. Computer simulation of transient currents suggests that introduction of positive charge at position 457 leads to a predominant outward rather than inward-facing conformational state. Taken together, the results suggest that glutamine 457, in addition to being involved in sugar binding, is a residue that is sensitive to conformational changes of the carrier.
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Affiliation(s)
- Tiemin Liu
- Department of Medicine, University of Toronto, Toronto, Ontario, Canada
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Liu T, Speight P, Silverman M. Reanalysis of structure/function correlations in the region of transmembrane segments 4 and 5 of the rabbit sodium/glucose cotransporter. Biochem Biophys Res Commun 2008; 378:133-8. [PMID: 19013429 DOI: 10.1016/j.bbrc.2008.11.015] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/02/2008] [Accepted: 11/06/2008] [Indexed: 11/17/2022]
Abstract
The predicted topology of the mammalian high-affinity sodium/glucose cotransporter (SGLT1), in the region surrounding transmembrane segments 4 and 5, disagrees with the recent published crystal structure of bacterial SGLT from Vibrio parahaemolyticus (vSGLT). To investigate this issue further, 38 residues from I143 to A180 in the N-terminal half of rabbit SGLT1 were each replaced with cysteine and then expressed in COS-7 cells or Xenopus laevis oocytes. The membrane orientations of the substituted cysteines were determined by treatment with the thiol-specific reagent N-Biotinoylaminoethyl methanethiosulfonate (biotin-MTSEA), combined with the membrane impermeant thiol-specific reagent sodium (2-sulfonatoethyl) methanethiosulfonate (MTSES). The present results combined with previous structure/function studies of SGLT1, suggest that transmembrane domain (TM) 4 of mammalian SGLT1 extends from residue 143-171 and support the topology observed in the crystal structure of vSGLT.
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Affiliation(s)
- Tiemin Liu
- Department of Medicine, University of Toronto, Medical Sciences Building, Room 7336, 1 King's College Circle, Toronto, Ontario, Canada M5S 1A8
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31
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Faham S, Watanabe A, Besserer GM, Cascio D, Specht A, Hirayama BA, Wright EM, Abramson J. The crystal structure of a sodium galactose transporter reveals mechanistic insights into Na+/sugar symport. Science 2008; 321:810-4. [PMID: 18599740 PMCID: PMC3654663 DOI: 10.1126/science.1160406] [Citation(s) in RCA: 412] [Impact Index Per Article: 25.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/15/2022]
Abstract
Membrane transporters that use energy stored in sodium gradients to drive nutrients into cells constitute a major class of proteins. We report the crystal structure of a member of the solute sodium symporters (SSS), the Vibrio parahaemolyticus sodium/galactose symporter (vSGLT). The approximately 3.0 angstrom structure contains 14 transmembrane (TM) helices in an inward-facing conformation with a core structure of inverted repeats of 5 TM helices (TM2 to TM6 and TM7 to TM11). Galactose is bound in the center of the core, occluded from the outside solutions by hydrophobic residues. Surprisingly, the architecture of the core is similar to that of the leucine transporter (LeuT) from a different gene family. Modeling the outward-facing conformation based on the LeuT structure, in conjunction with biophysical data, provides insight into structural rearrangements for active transport.
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Affiliation(s)
- Salem Faham
- Department of Physiology, David Geffen School of Medicine, University of California, Los Angeles, California 90095-1751, USA
| | - Akira Watanabe
- Department of Physiology, David Geffen School of Medicine, University of California, Los Angeles, California 90095-1751, USA
| | - Gabriel Mercado Besserer
- Department of Physiology, David Geffen School of Medicine, University of California, Los Angeles, California 90095-1751, USA
| | - Duilio Cascio
- UCLA-Department of Energy Institute of Genomics and Proteomics, University of California, Los Angeles, CA 90095, USA
| | - Alexandre Specht
- Laboratoire de chimie bioorganique, Université Louis Pasteur / CNRS UMR 7175 LC01, Faculté de Pharmacie, 74 route du Rhin, 67401 Illkirch, France
| | - Bruce A. Hirayama
- Department of Physiology, David Geffen School of Medicine, University of California, Los Angeles, California 90095-1751, USA
| | - Ernest M. Wright
- Department of Physiology, David Geffen School of Medicine, University of California, Los Angeles, California 90095-1751, USA
| | - Jeff Abramson
- Department of Physiology, David Geffen School of Medicine, University of California, Los Angeles, California 90095-1751, USA
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Loo DDF, Hirayama BA, Sala-Rabanal M, Wright EM. How drugs interact with transporters: SGLT1 as a model. J Membr Biol 2008; 223:87-106. [PMID: 18592293 DOI: 10.1007/s00232-008-9116-6] [Citation(s) in RCA: 17] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/01/2008] [Accepted: 05/20/2008] [Indexed: 11/29/2022]
Abstract
Drugs are transported by cotransporters with widely different turnover rates. We have examined the underlying mechanism using, as a model system, glucose and indican (indoxyl-beta-D-glucopyranoside) transport by human Na+/glucose cotransporter (hSGLT1). Indican is transported by hSGLT1 at 10% of the rate for glucose but with a fivefold higher apparent affinity. We expressed wild-type hSGLT1 and mutant G507C in Xenopus oocytes and used electrical and optical methods to measure the kinetics of glucose (using nonmetabolized glucose analogue alpha-methyl-D-glucopyranoside, alphaMDG) and indican transport, alone and together. Indican behaved as a competitive inhibitor of alphaMDG transport. To examine protein conformations, we recorded SGLT1 capacitive currents (charge movements) and fluorescence changes in response to step jumps in membrane voltage, in the presence and absence of indican and/or alphaMDG. In the absence of sugar, voltage jumps elicited capacitive SGLT currents that decayed to steady state with time constants (tau) of 3-20 ms. These transient currents were abolished in saturating alphaMDG but only slightly reduced (10%) in saturating indican. SGLT1 G507C rhodamine fluorescence intensity increased with depolarizing and decreased with hyperpolarizing voltages. Maximal fluorescence increased approximately 150% in saturating indican but decreased approximately 50% in saturating alphaMDG. Modeling indicated that the rate-limiting step for indican transport is sugar translocation, whereas for alphaMDG it is dissociation of Na+ from the internal binding sites. The inhibitory effects of indican on alphaMDG transport are due to its higher affinity and a 100-fold lower translocation rate. Our results indicate that competition between substrates and drugs should be taken into consideration when targeting transporters as drug delivery systems.
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Affiliation(s)
- Donald D F Loo
- Department of Physiology, David Geffen School of Medicine at UCLA, 10833 LeConte Avenue, Los Angeles, CA 90095-1751, USA.
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Liu T, Lo B, Speight P, Silverman M. Transmembrane IV of the high-affinity sodium-glucose cotransporter participates in sugar binding. Am J Physiol Cell Physiol 2008; 295:C64-72. [PMID: 18448629 DOI: 10.1152/ajpcell.90602.2007] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Abstract
Investigation of the structure/function relationships of the sodium-glucose transporter (SGLT1) is crucial to understanding the cotransporter mechanism. In the present study, we used cysteine-scanning mutagenesis and chemical modification by methanethiosulfonate (MTS) derivatives to test whether predicted transmembrane IV participates in sugar binding. Five charged and polar residues (K139, Q142, T156, K157, and D161) and two glucose/galactose malabsorption missense mutations (I147 and S159) were replaced with cysteine. Mutants I147C, T156C, and K157C exhibited sufficient expression to be studied in detail using the two-electrode voltage-clamp method in Xenopus laevis oocytes and COS-7 cells. I147C was similar in function to wild-type and was not studied further. Mutation of lysine-157 to cysteine (K157C) causes loss of phloridzin and alpha-methyl-D-glucopyranoside (alphaMG) binding. These functions are restored by chemical modification with positively charged (2-aminoethyl) methanethiosulfonate hydrobromide (MTSEA). Mutation of threonine-156 to cysteine (T156C) reduces the affinity of alphaMG and phloridzin for T156C by approximately 5-fold and approximately 20-fold, respectively. In addition, phloridzin protects cysteine-156 in T156C from alkylation by MTSEA. Therefore, the presence of a positive charge or a polar residue at 157 and 156, respectively, affects sugar binding and sugar-induced Na(+) currents.
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Affiliation(s)
- Tiemin Liu
- Department of Medicine, University of Toronto, Toronto, Ontario, Canada
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