MOLECULAR MECHANISMS OF INTESTINAL TRANSPORT

Summary

Principal Investigator: ERNEST WRIGHT
Affiliation: University of California
Country: USA
Abstract: The goal of this project is to understand the molecular mechanism of intestinal glucose and sodium transport. The intestine is responsible for the absorption of dietary carbohydrate and more than 4 liters of fluid per day. The brush border Na/glucose cotransporter (SGLT1) is responsible for absorbing 180 grams of glucose and 115 grams of sodium and is also directly or indirectly involved in the absorption of water. Oral Rehydration Therapy, credited with saving thousands of infants a day from infectious diarrhea, is based on the coupling of glucose, salt and water transport by SGLT1. The goal of this project is to understand how human SGLT1 actively transports glucose from the gut into the intestinal epithelium across the brush border membrane. Our previous studies have determined that glucose transport is driven by the sodium and electrical gradients across the brush border and now we wish to explain how glucose and sodium transport are coupled. The human SGLT1 gene will be expressed in cultured cells and biophysical methods will be used to measure the kinetics of Na/glucose co transport. These methods include electrical and optical assays to determine both the steady-state kinetics and the conformational changes of the protein that underlie coupled transport. We have determined the crystal structure of SGLTs, identified a sugar and sodium binding sites, and obtained structural insight into the active transport. The structure will be used as a guide in our biophysical experiments to determine how glucose binds and is transported through the protein molecule. Our objective is to explain the kinetics and sugar selectivity of Na/glucose cotransport in terms of the structural dynamics of SGLT1. SGLT structures will provide clues about the differences in functional properties between the brush border Na/glucose cotransport and the glucosensor (SGLT3) found in the enteric nervous system. The results will also provide a structural basis for the interaction of natural products in our diet with SGLT1 and hopefully explain how these glycosides either blunt glucose absorption or how they are absorbed. Many such glycosides, components of folk medicines, are used to treat a variety of ailments including diabetes, obesity and aging. On a broader scale our work is also relevant to the function of other members of the SGLT gene family (SLC5), e.g. the Na/iodide and SGLT2, and the structurally related serotonin reuptake transporter (SERT) in brain and enteric nervous systems. PUBLIC HEALTH RELEVANCE: This study is to determine how SGLTs transport glucose and sodium across the brush border membrane of the small intestine. The results of our studies may have a large impact on our understanding of glucose absorption in normal healthy subjects and the use of Oral Rehydration Therapy in the treatment of diarrhea. Our structural studies may also account for the differences in function between SGLT transporters and glucose sensors expressed in the GI tract and this will aid in the design of selective agonists and antagonists for the sensors. Some 21 SGLT drugs are currently in clinical trial for the treatment of diabetes. This will enhance therapies designed to regulate glucose absorption in diabetic and obese patients. Furthermore, our unexpected finding that the glucose and neurotransmitter transporters share a common structure has broad implications for transporters expressed in the enteric and central nervous systems.
Funding Period: ----------------1976 - ---------------2014-
more information: NIH RePORT

Top Publications

  1. ncbi A reinvestigation of the secondary structure of functionally active vSGLT, the vibrio sodium/galactose cotransporter
    Eric Turk
    Department of Physiology, David Geffen School of Medicine at UCLA, University of California, 90095 1751, USA
    Biochemistry 45:1470-9. 2006
  2. pmc Functional identification and characterization of sodium binding sites in Na symporters
    Donald D F Loo
    Department of Physiology, David Geffen School of Medicine, University of California, Los Angeles, CA 90095 1751
    Proc Natl Acad Sci U S A 110:E4557-66. 2013
  3. doi Glucose transport families SLC5 and SLC50
    Ernest M Wright
    Department of Physiology, David Geffen School of Medicine at UCLA, Los Angeles, CA 90095 1751, USA
    Mol Aspects Med 34:183-96. 2013
  4. pmc Regional distribution of SGLT activity in rat brain in vivo
    Amy S Yu
    Department of Molecular and Medical Pharmacology, David Geffen School of Medicine, University of California, Los Angeles, CA 90095, USA
    Am J Physiol Cell Physiol 304:C240-7. 2013
  5. pmc The importance of being aromatic: π interactions in sodium symporters
    Xuan Jiang
    Department of Physiology, David Geffen School of Medicine at UCLA, Los Angeles, CA 90095 1751, USA
    Biochemistry 51:9480-7. 2012
  6. pmc Regulation of the human Na+-dependent glucose cotransporter hSGLT2
    Chiara Ghezzi
    Department of Physiology, David Geffen School of Medicine, Univeristy of California at Los Angeles, Los Angeles, California 90095 1751, USA
    Am J Physiol Cell Physiol 303:C348-54. 2012
  7. pmc Structural determinants of water permeation through the sodium-galactose transporter vSGLT
    Joshua L Adelman
    Department of Biological Sciences, University of Pittsburgh, Pittsburgh, Pennsylvania
    Biophys J 106:1280-9. 2014
  8. pmc The crystal structure of a sodium galactose transporter reveals mechanistic insights into Na+/sugar symport
    Salem Faham
    Department of Physiology, David Geffen School of Medicine, University of California, Los Angeles, CA 90095 1751, USA
    Science 321:810-4. 2008
  9. pmc Molecular interactions between dipeptides, drugs and the human intestinal H+ -oligopeptide cotransporter hPEPT1
    Monica Sala-Rabanal
    Department of Physiology, David Geffen School of Medicine at UCLA, 10833 Le Conte Avenue, 53 330 CHS, Los Angeles, California 90095 1751, USA
    J Physiol 574:149-66. 2006
  10. ncbi How drugs interact with transporters: SGLT1 as a model
    Donald D F Loo
    Department of Physiology, David Geffen School of Medicine at UCLA, 10833 LeConte Avenue, Los Angeles, CA 90095 1751, USA
    J Membr Biol 223:87-106. 2008

Scientific Experts

  • ERNEST WRIGHT
  • JEFFREY ABRAMSON
  • Bruce A Hirayama
  • Donald D F Loo
  • Monica Sala-Rabanal
  • Charles S Hummel
  • Xuan Jiang
  • Eric Turk
  • Akira Watanabe
  • Ana Diez-Sampedro
  • Andrew A Voss
  • Joshua L Adelman
  • Amy S Yu
  • Vladimir Kepe
  • Jie Liu
  • Jorge R Barrio
  • Michael Grabe
  • Seungho Choe
  • John M Rosenberg
  • Chiara Ghezzi
  • Chuan Lu
  • Vincent Chaptal
  • Salem Faham
  • Anne Kristine Meinild
  • Ying Sheng
  • Gerald Timbol
  • Sung Cheng Huang
  • Edurne Gorraitz
  • Nagichettiar Satyamurthy
  • Chiari Ghezzi
  • Gabriel Mercado Besserer
  • Duilio Cascio
  • Alexandre Specht
  • Daisy W Leung
  • Mary Lai-Bing
  • Seren Lanza
  • Oktay K Gasymov
  • Movses H Karakossian
  • Joseph Horwitz

Detail Information

Publications21

  1. ncbi A reinvestigation of the secondary structure of functionally active vSGLT, the vibrio sodium/galactose cotransporter
    Eric Turk
    Department of Physiology, David Geffen School of Medicine at UCLA, University of California, 90095 1751, USA
    Biochemistry 45:1470-9. 2006
    ....
  2. pmc Functional identification and characterization of sodium binding sites in Na symporters
    Donald D F Loo
    Department of Physiology, David Geffen School of Medicine, University of California, Los Angeles, CA 90095 1751
    Proc Natl Acad Sci U S A 110:E4557-66. 2013
    ..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. ..
  3. doi Glucose transport families SLC5 and SLC50
    Ernest M Wright
    Department of Physiology, David Geffen School of Medicine at UCLA, Los Angeles, CA 90095 1751, USA
    Mol Aspects Med 34:183-96. 2013
    ..The SWEETs are found mostly in plants where they appear to be responsible for sugar efflux and are targeted by pathogens and symbionts for nutrition...
  4. pmc Regional distribution of SGLT activity in rat brain in vivo
    Amy S Yu
    Department of Molecular and Medical Pharmacology, David Geffen School of Medicine, University of California, Los Angeles, CA 90095, USA
    Am J Physiol Cell Physiol 304:C240-7. 2013
    ..The expression of SGLTs in the brain raises questions about the potential effects of SGLT inhibitors under development for the treatment of diabetes...
  5. pmc The importance of being aromatic: π interactions in sodium symporters
    Xuan Jiang
    Department of Physiology, David Geffen School of Medicine at UCLA, Los Angeles, CA 90095 1751, USA
    Biochemistry 51:9480-7. 2012
    ..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...
  6. pmc Regulation of the human Na+-dependent glucose cotransporter hSGLT2
    Chiara Ghezzi
    Department of Physiology, David Geffen School of Medicine, Univeristy of California at Los Angeles, Los Angeles, California 90095 1751, USA
    Am J Physiol Cell Physiol 303:C348-54. 2012
    ..hSGLT1 was relatively insensitive to insulin. We conclude that hSGLT1 and hSGLT2 are regulated by different mechanisms and suggest that insulin is an SGLT2 agonist in vivo...
  7. pmc Structural determinants of water permeation through the sodium-galactose transporter vSGLT
    Joshua L Adelman
    Department of Biological Sciences, University of Pittsburgh, Pittsburgh, Pennsylvania
    Biophys J 106:1280-9. 2014
    ..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. ..
  8. pmc The crystal structure of a sodium galactose transporter reveals mechanistic insights into Na+/sugar symport
    Salem Faham
    Department of Physiology, David Geffen School of Medicine, University of California, Los Angeles, CA 90095 1751, USA
    Science 321:810-4. 2008
    ..Modeling the outward-facing conformation based on the LeuT structure, in conjunction with biophysical data, provides insight into structural rearrangements for active transport...
  9. pmc Molecular interactions between dipeptides, drugs and the human intestinal H+ -oligopeptide cotransporter hPEPT1
    Monica Sala-Rabanal
    Department of Physiology, David Geffen School of Medicine at UCLA, 10833 Le Conte Avenue, 53 330 CHS, Los Angeles, California 90095 1751, USA
    J Physiol 574:149-66. 2006
    ....
  10. ncbi How drugs interact with transporters: SGLT1 as a model
    Donald D F Loo
    Department of Physiology, David Geffen School of Medicine at UCLA, 10833 LeConte Avenue, Los Angeles, CA 90095 1751, USA
    J Membr Biol 223:87-106. 2008
    ..Our results indicate that competition between substrates and drugs should be taken into consideration when targeting transporters as drug delivery systems...
  11. ncbi Imino sugars are potent agonists of the human glucose sensor SGLT3
    Andrew A Voss
    David Geffen School of Medicine at UCLA, Department of Physiology, 10833 Le Conte Avenue, 53 263 Center for Health Sciences, Los Angeles, CA 90095 1751, USA
    Mol Pharmacol 71:628-34. 2007
    ..This work provides insights into hSGLT3 and -1 substrate binding interactions, establishes a pharmacological profile to study endogenous hSGLT3, and may have important ramifications for the clinical application of imino sugars...
  12. pmc Conformational dynamics of hSGLT1 during Na+/glucose cotransport
    Donald D F Loo
    Department of Physiology, David Geffen School of Medicine at UCLA, University of California, Los Angeles, CA 90095, USA
    J Gen Physiol 128:701-20. 2006
    ..The high affinity blocker phlorizin locks the cotransporter in an inactive conformation...
  13. ncbi Sodium-dependent reorganization of the sugar-binding site of SGLT1
    Bruce A Hirayama
    Department of Physiology, The David Geffen School of Medicine at UCLA, 10833 Le Conte Avenue, Los Angeles, California 90095 1751, USA
    Biochemistry 46:13391-406. 2007
    ..Arranging the four TMHs to account for Na-dependent accessibility and potential for sugar interaction allows us to propose a testable model for the SGLT1 sugar binding site...
  14. doi Molecular mechanism of dipeptide and drug transport by the human renal H+/oligopeptide cotransporter hPEPT2
    Monica Sala-Rabanal
    Dept of Physiology, David Geffen School of Medicine at UCLA, 10833 Le Conte Ave, 53 330 CHS, Los Angeles, CA 90095 1751, USA
    Am J Physiol Renal Physiol 294:F1422-32. 2008
    ..No functional differences were found between the common variants hPEPT2*1 and hPEPT2*2...
  15. pmc Structure and function of Na(+)-symporters with inverted repeats
    Jeff Abramson
    Department of Physiology, David School of Medicine at UCLA, Los Angeles, CA 90095 1751, USA
    Curr Opin Struct Biol 19:425-32. 2009
    ..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...
  16. pmc Bridging the gap between structure and kinetics of human SGLT1
    Monica Sala-Rabanal
    Department of Physiology, The Geffen School of Medicine at University of California, Los Angeles, California 90095 1751, USA
    Am J Physiol Cell Physiol 302:C1293-305. 2012
    ..Overall, the present results provide a bridge between kinetics and structural studies of cotransporters...
  17. pmc Structural selectivity of human SGLT inhibitors
    Charles S Hummel
    Department of Physiology, David Geffen School of Medicine at UCLA, Los Angeles, CA 90095 1751, USA
    Am J Physiol Cell Physiol 302:C373-82. 2012
    ..Therefore, the pharmacophore must include variations in both the structure of the sugar and the aglycone...
  18. doi Biology of human sodium glucose transporters
    Ernest M Wright
    Department of Physiology, David Geffen School of Medicine at University of California Los Angeles, Los Angeles, California 90095 1751, USA
    Physiol Rev 91:733-94. 2011
    ..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...
  19. pmc The mechanism of sodium and substrate release from the binding pocket of vSGLT
    Akira Watanabe
    Department of Physiology, University of California, Los Angeles, Los Angeles, California 90095 1759, USA
    Nature 468:988-91. 2010
    ..Additionally, we identify an allosteric pathway between the sodium-binding sites, the unwound portion of transmembrane helix 1 and the substrate-binding site that is essential in the coupling of co-transport...
  20. pmc Glucose transport by human renal Na+/D-glucose cotransporters SGLT1 and SGLT2
    Charles S Hummel
    Department of Physiology, David Geffen School of Medicine at UCLA, Los Angeles, CA 90095 1751, USA
    Am J Physiol Cell Physiol 300:C14-21. 2011
    ..Our electrophysiological study provides groundwork for a molecular understanding of how hSGLT inhibitors affect renal glucose reabsorption...