scholarly journals Function Trumps Form in Two Sugar Symporters, LacY and vSGLT

2021 ◽  
Vol 22 (7) ◽  
pp. 3572
Author(s):  
Jeff Abramson ◽  
Ernest M. Wright
Keyword(s):  
Binding Site ◽  
Sugar Transport ◽  
Electrochemical Potential ◽  
Inverted Repeats ◽  
Side Chains ◽  
Transmembrane Helices ◽  
Central Cavity ◽  
Potential Gradients ◽  
Sodium Binding ◽  
Major Facilitator

Active transport of sugars into bacteria occurs through symporters driven by ion gradients. LacY is the most well-studied proton sugar symporter, whereas vSGLT is the most characterized sodium sugar symporter. These are members of the major facilitator (MFS) and the amino acid-Polyamine organocation (APS) transporter superfamilies. While there is no structural homology between these transporters, they operate by a similar mechanism. They are nano-machines driven by their respective ion electrochemical potential gradients across the membrane. LacY has 12 transmembrane helices (TMs) organized in two 6-TM bundles, each containing two 3-helix TM repeats. vSGLT has a core structure of 10 TM helices organized in two inverted repeats (TM 1–5 and TM 6–10). In each case, a single sugar is bound in a central cavity and sugar selectivity is determined by hydrogen- and hydrophobic- bonding with side chains in the binding site. In vSGLT, the sodium-binding site is formed through coordination with carbonyl- and hydroxyl-oxygens from neighboring side chains, whereas in LacY the proton (H3O+) site is thought to be a single glutamate residue (Glu325). The remaining challenge for both transporters is to determine how ion electrochemical potential gradients drive uphill sugar transport.

scholarly journals Bridging the gap between structure and kinetics of human SGLT1

2012 ◽  
Vol 302 (9) ◽  
pp. C1293-C1305 ◽  
Author(s):  
Monica Sala-Rabanal ◽  
Bruce A. Hirayama ◽  
Donald D. F. Loo ◽  
Vincent Chaptal ◽  
Jeff Abramson ◽  
...  
Keyword(s):  
Ligand Binding ◽  
Binding Site ◽  
Sugar Transport ◽  
Gene Families ◽  
Structural Studies ◽  
Sugar Binding ◽  
Substituted Cysteine Accessibility ◽  
Biochemical Assays ◽  
Functional Consequences ◽  
Binding Residues

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, K0.5); e.g., mutating sugar binding residues increases the glucose K0.5 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 ( Ki) are proportional to the changes in sugar K0.5, except in the case of F101C, where phlorizin Ki increases by orders of magnitude without a change in glucose K0.5. 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.

scholarly journals Snorkeling of lysine side chains in transmembrane helices: how easy can it get?

FEBS Letters ◽  
2003 ◽  
Vol 544 (1-3) ◽  
pp. 69-73 ◽  
Author(s):  
Erik Strandberg ◽  
J.Antoinette Killian
Keyword(s):  
Side Chains ◽  
Transmembrane Helices

scholarly journals Evaluation of the rate constants of sugar transport through maltoporin (LamB) of Escherichia coli from the sugar-induced current noise.

1995 ◽  
Vol 105 (3) ◽  
pp. 385-401 ◽  
Author(s):  
C Andersen ◽  
M Jordy ◽  
R Benz
Keyword(s):  
Escherichia Coli ◽  
Binding Site ◽  
Outer Membrane ◽  
Rate Constants ◽  
Sugar Transport ◽  
Current Noise ◽  
Induced Current ◽  
Lipid Bilayer Membranes ◽  
Sugar Binding ◽  
Different Temperatures

LamB (maltoporin) of Escherichia coli outer membrane was reconstituted into artificial lipid bilayer membranes. The channel contains a binding site for sugars and is blocked for ions when the site is occupied by a sugar. The on and off reactions of sugar binding cause an increase of the noise of the current through the channel. The sugar-induced current noise of maltoporin was used for the evaluation of the sugar-binding kinetics for different sugars of the maltooligosaccharide series and for sucrose. The on rate constant for sugar binding was between 10(6) and 10(7) M-1.s-1 for the maltooligosaccharides and corresponds to the movement of the sugars from the aqueous phase to the central binding site. The off rate (corresponding to the release of the sugars from the channel) decreased with increasing number of glucose residues in the maltooligosaccharides from approximately 2,000 s-1 for maltotriose to 180 s-1 for maltoheptaose. The kinetics for sucrose movement was considerably slower. The activation energies of the stability constant and of the rate constants for sugar binding were evaluated from noise experiments at different temperatures. The role of LamB in the transport of maltooligosaccharides across the outer membrane is discussed.

scholarly journals Evolution of chemokine receptors is driven by mutations in the sodium binding site

2018 ◽  
Vol 14 (6) ◽  
pp. e1006209 ◽  
Author(s):  
Bruck Taddese ◽  
Madeline Deniaud ◽  
Antoine Garnier ◽  
Asma Tiss ◽  
Hajer Guissouma ◽  
...  
Keyword(s):  
Binding Site ◽  
Chemokine Receptors ◽  
Sodium Binding

scholarly journals Transfer of TRPV1 Sodium Binding Site into TRPV2

2017 ◽  
Vol 112 (3) ◽  
pp. 114a
Author(s):  
Katherine E. Huffer ◽  
Andrés Jara-Oseguera ◽  
Kenton J. Swartz
Keyword(s):  
Binding Site ◽  
Sodium Binding

scholarly journals Caffeine inhibits glucose transport by binding at the GLUT1 nucleotide-binding site

2015 ◽  
Vol 308 (10) ◽  
pp. C827-C834 ◽  
Author(s):  
Jay M. Sage ◽  
Anthony J. Cura ◽  
Kenneth P. Lloyd ◽  
Anthony Carruthers
Keyword(s):  
Binding Site ◽  
Glucose Transport ◽  
Glucose Transporter ◽  
Cytochalasin B ◽  
Sugar Transport ◽  
Nucleotide Binding ◽  
Nucleotide Binding Site ◽  
Sugar Uptake ◽  
Glucose Transporter 1 ◽  
Intracellular Atp

Glucose transporter 1 (GLUT1) is the primary glucose transport protein of the cardiovascular system and astroglia. A recent study proposes that caffeine uncompetitive inhibition of GLUT1 results from interactions at an exofacial GLUT1 site. Intracellular ATP is also an uncompetitive GLUT1 inhibitor and shares structural similarities with caffeine, suggesting that caffeine acts at the previously characterized endofacial GLUT1 nucleotide-binding site. We tested this by confirming that caffeine uncompetitively inhibits GLUT1-mediated 3- O-methylglucose uptake in human erythrocytes [ Vmax and Km for transport are reduced fourfold; Ki(app) = 3.5 mM caffeine]. ATP and AMP antagonize caffeine inhibition of 3- O-methylglucose uptake in erythrocyte ghosts by increasing Ki(app) for caffeine inhibition of transport from 0.9 ± 0.3 mM in the absence of intracellular nucleotides to 2.6 ± 0.6 and 2.4 ± 0.5 mM in the presence of 5 mM intracellular ATP or AMP, respectively. Extracellular ATP has no effect on sugar uptake or its inhibition by caffeine. Caffeine and ATP displace the fluorescent ATP derivative, trinitrophenyl-ATP, from the GLUT1 nucleotide-binding site, but d-glucose and the transport inhibitor cytochalasin B do not. Caffeine, but not ATP, inhibits cytochalasin B binding to GLUT1. Like ATP, caffeine renders the GLUT1 carboxy-terminus less accessible to peptide-directed antibodies, but cytochalasin B and d-glucose do not. These results suggest that the caffeine-binding site bridges two nonoverlapping GLUT1 endofacial sites—the regulatory, nucleotide-binding site and the cytochalasin B-binding site. Caffeine binding to GLUT1 mimics the action of ATP but not cytochalasin B on sugar transport. Molecular docking studies support this hypothesis.

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