Location of Repository

Sucrose- and H+-dependent charge movements associated with the gating of sucrose transporter ZmSUT1

By Armando Carpaneto, Hermann Koepsell, Ernst Bamberg, Rainer Franz Hedrich and Dietmar Geiger

Abstract

Background: In contrast to man the majority of higher plants use sucrose as mobile carbohydrate. Accordingly proton-driven sucrose transporters are crucial for cell-to-cell and long-distance distribution within the plant body. Generally very negative plant membrane potentials and the ability to accumulate sucrose quantities of more than 1 M document that plants must have evolved transporters with unique structural and functional features.\ud \ud Methodology/Principal Findings: To unravel the functional properties of one specific high capacity plasma membrane sucrose transporter in detail, we expressed the sucrose/H+ co-transporter from maize ZmSUT1 in Xenopus oocytes. Application of sucrose in an acidic pH environment elicited inward proton currents. Interestingly the sucrose-dependent H+ transport was associated with a decrease in membrane capacitance (Cm). In addition to sucrose Cm was modulated by the membrane potential and external protons. In order to explore the molecular mechanism underlying these Cm changes, presteady-state currents (Ipre) of ZmSUT1 transport were analyzed. Decay of Ipre could be best fitted by double exponentials. When plotted against the voltage the charge Q, associated to Ipre, was dependent on sucrose and protons. The mathematical derivative of the charge Q versus voltage was well in line with the observed Cm changes. Based on these parameters a turnover rate of 500 molecules sucrose/s was calculated. In contrast to gating currents of voltage dependent-potassium channels the analysis of ZmSUT1-derived presteady-state currents in the absence of sucrose (I = Q/τ) was sufficient to predict ZmSUT1 transport-associated currents.\ud \ud Conclusions: Taken together our results indicate that in the absence of sucrose, ‘trapped’ protons move back and forth between an outer and an inner site within the transmembrane domains of ZmSUT1. This movement of protons in the electric field of the membrane gives rise to the presteady-state currents and in turn to Cm changes. Upon application of external sucrose, protons can pass the membrane turning presteady-state into transport currents

Topics: ddc:570
Year: 2010
OAI identifier: oai:publikationen.ub.uni-frankfurt.de:23768

Suggested articles

Preview

Citations

  1. (1997). A kinetic model with ordered cytoplasmic dissociation for SUC1, an Arabidopsis H +/ sucrose cotransporter expressed in Xenopus oocytes.
  2. (1996). A multi-substrate single-file model for ion-coupled transporters.
  3. (2002). An improved method for real-time monitoring of membrane capacitance in Xenopus laevis oocytes.
  4. (1996). Changes in voltage activation, Cs + sensitivity, and ion permeability in H5 mutants of the plant K + channel KAT1.
  5. (2006). Conformational dynamics of hSGLT1 during Na +/glucose cotransport.
  6. (1992). Electrogenic properties of the cloned Na +/glucose cotransporter: I. Voltage-clamp studies.
  7. (1992). Electrogenic properties of the cloned Na +/glucose cotransporter: II. A transport model under nonrapid equilibrium conditions.
  8. (2004). Electrophysiological insights into the mechanism of ion-coupled cotransporters.
  9. (1975). Evidence for ionic pores in excitable membranes.
  10. (1999). GAT1 (GABA:Na +:Cl 2) cotransport function. Database reconstruction with an alternating access model.
  11. (1999). Ion binding and permeation through the lepidopteran amino acid transporter KAAT1 expressed in Xenopus oocytes.
  12. (1996). Kinetics and stoichiometry of a proton/myo-inositol cotransporter.
  13. (1999). Molecular cloning and expression analysis of a gene for a sucrose transporter in maize (Zea mays L.).
  14. (2007). Molecular physiology of higher plant sucrose transporters.
  15. (2010). Peres A
  16. (2005). Perturbation analysis of the voltage-sensitive conformational changes of the Na +/glucose cotransporter.
  17. (2005). Phloemlocalized, proton-coupled sucrose carrier ZmSUT1 mediates sucrose efflux under the control of the sucrose gradient and the proton motive force.
  18. (1993). Potato sucrose transporter expression in minor veins indicates a role in phloemloading.
  19. (1993). Relaxation kinetics of the Na +/glucose cotransporter.
  20. (2007). Singlemolecule FRET reveals sugar-induced conformational dynamics in LacY.
  21. (2007). Sitedirected alkylation and the alternating access model for LacY.
  22. (1993). Steady states, charge movements, and rates for a cloned GABA transporter expressed in Xenopus oocytes.
  23. (1994). Steady-state and presteady-state kinetics of the H +/hexose cotransporter (STP1) from Arabidopsis thaliana expressed in Xenopus oocytes.
  24. (1989). Structural parts involved in activation and inactivation of the sodium channel.
  25. (1994). SUC1 and SUC2: two sucrose transporters from Arabidopsis thaliana; expression and characterization in baker’s yeast and identification of the histidine-tagged protein.
  26. (2009). Sucrose transporter1 functions in phloem loading in maize leaves.
  27. (1997). Symmetry of H + binding to the intra- and extracellular side of the H +-coupled oligopeptide cotransporter PepT1.
  28. (1994). The kinetics of voltage-gated ion channels.
  29. (2003). The phloem, a miracle of ingenuity.
  30. (1998). The voltage dependence of a cloned mammalian renal type II Na +/Pi cotransporter (NaPi-2).
  31. (1976). The voltage dependence of membrane capacity.
  32. (2000). The voltage sensor in voltage-dependent ion channels.
  33. (1996). Transport mechanism of the cloned potato H +/sucrose cotransporter StSUT1.
  34. (1991). Voltage-clamp studies of the Na +/glucose cotransporter cloned from rabbit small intestine.

To submit an update or takedown request for this paper, please submit an Update/Correction/Removal Request.