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

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. 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. 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

Adding Salt to an Aqueous Solution of t-Butanol: Is Hydrophobic Association Enhanced or Reduced?

Recent neutron scattering experiments on aqueous salt solutions of amphiphilic t-butanol by Bowron and Finney [Phys. Rev. Lett. {\bf 89}, 215508 (2002); J. Chem. Phys. {\bf 118}, 8357 (2003)] suggest the formation of t-butanol pairs, bridged by a chloride ion via ${O}-{H}...{Cl}^-$ hydrogen-bonds, and leading to a reduced number of intermolecular hydrophobic butanol-butanol contacts. Here we present a joint experimental/theoretical study on the same system, using a combination of molecular dynamics simulations and nuclear magnetic relaxation measurements. Both theory and experiment clearly support the more intuitive scenario of an enhanced number of hydrophobic contacts in the presence of the salt, as it would be expected for purely hydrophobic solutes [J. Phys. Chem. B {\bf 107}, 612 (2003)]. Although our conclusions arrive at a structurally completely distinct scenario, the molecular dynamics simulation results are within the experimental errorbars of the Bowron and Finney work.Comment: 15 pages twocolumn revtex, 11 figure

Experimental treatment of stroke in spontaneously hypertensive rats by CD34+ and CD34- cord blood cells

Human umbilical cord blood as a source of stem cells has recently been reported in experimental treatment of cerebral disorders. However, little is known about the nature of cells and cellular mechanisms leading to neurofunctional improvement. Here we investigated the potential of separated CD34+ versus CD34- human umbilical cord blood cells (HUCBC) to promote functional recovery following stroke. The experiments were performed in spontaneously hypertensive (SH) rats, known for a risk profile comparable to stroke patients

Cell-specific synaptic plasticity induced by network oscillations

Gamma rhythms are known to contribute to the process of memory encoding. However, little is known about the underlying mechanisms at the molecular, cellular and network levels. Using local field potential recording in awake behaving mice and concomitant field potential and whole-cell recordings in slice preparations we found that gamma rhythms lead to activity-dependent modification of hippocampal networks, including alterations in sharp wave- ripple complexes. Network plasticity, expressed as long-lasting increases in sharp wave-associated synaptic currents, exhibits enhanced excitatory synaptic strength in pyramidal cells that is induced postsynaptically and depends on metabotropic glutamate receptor-5 activation. In sharp contrast, alteration of inhibitory synaptic strength is independent of postsynaptic activation and less pronounced. Further, we found a cell type-specific, directionally biased synaptic plasticity of two major types of GABAergic cells, parvalbumin- and cholecystokinin-expressing interneurons. Thus, we propose that gamma frequency oscillations represent a network state that introduces long-lasting synaptic plasticity in a cell-specific manner

Heterologous expression of a recombinant lactobacillal -galactosidase in Lactobacillus plantarum: effect of different parameters on the sakacin P-based expression system

Background: Two overlapping genes lacL and lacM (lacLM) encoding for heterodimeric -galactosidase from Lactobacillus reuteri were previously cloned and over-expressed in the food-grade host strain Lactobacillus plantarum WCFS1, using the inducible lactobacillal pSIP expression system. In this study, we analyzed different factors that affect the production of recombinant L. reuteri -galactosidase. Results: Various factors related to the cultivation, i.e. culture pH, growth temperature, glucose concentration, as well as the induction conditions, including cell concentration at induction point and inducer concentration, were tested. Under optimal fermentation conditions, the maximum -galactosidase levels obtained were 130 U/mg protein and 3540 U/ml of fermentation broth corresponding to the formation of approximately 200 mg of recombinant protein per litre of fermentation medium. As calculated from the specific activity of the purified enzyme (190 U/mg), -galactosidase yield amounted to roughly 70% of the total soluble intracellular protein of the host organism. It was observed that pH and substrate (glucose) concentration are the most prominent factors affecting the production of recombinant -galactosidase. Conclusions: The over-expression of recombinant L. reuteri -galactosidase in a food-grade host strain was optimized, which is of interest for applications of this enzyme in the food industry. The results provide more detailed insight into these lactobacillal expression systems and confirm the potential of the pSIP system for efficient, tightly controlled expression of enzymes and proteins in lactobacilli.(VLID)90704

Low-Temperature and High-Pressure Induced Swelling of a Hydrophobic Polymer-Chain in Aqueous Solution

We report molecular dynamics simulations of a hydrophobic polymer-chain in aqueous solution between $260 {K}$ and $420 {K}$ at pressures of $1 {bar}$, $3000 {bar}$, and $4500 {bar}$. The simulations reveal a hydrophobically collapsed state at low pressures and high temperatures. At $3000 {bar}$ and about $260 {K}$ and at $4500 {bar}$ and about $260 {K}$, however, a transition to a swelled state is observed. The transition is driven by a smaller volume and a remarkably strong lower enthalpy of the swelled state, indicating a steep positive slope of the corresponding transition line. The swelling is stabilized almost completely by the energetically favorable state of water in the polymers hydrophobic first hydration shell at low temperatures. Although surprising, this finding is consistent with the observation of a positive heat capacity of hydrophobic solvation. Moreover, the slope and location of the observed swelling transition for the collapsed hydrophobic chain coincides remarkably well with the cold denaturation transition of proteins.Comment: 9 pages, 9 figures, twocolumn revte