Asymmetric PI Research Articles

Single-molecule imaging of PI(4,5)P2 and PTEN in vitro reveals a positive feedback mechanism for PTEN membrane binding

PTEN, a 3-phosphatase of phosphoinositide, regulates asymmetric PI(3,4,5)P3 signaling for the anterior-posterior polarization and migration of motile cells. PTEN acts through posterior localization on the plasma membrane, but the mechanism for this accumulation is poorly understood. Here we developed an in vitro single-molecule imaging assay with various lipid compositions and use it to demonstrate that the enzymatic product, PI(4,5)P2, stabilizes PTEN’s membrane-binding. The dissociation kinetics and lateral mobility of PTEN depended on the PI(4,5)P2 density on artificial lipid bilayers. The basic residues of PTEN were responsible for electrostatic interactions with anionic PI(4,5)P2 and thus the PI(4,5)P2-dependent stabilization. Single-molecule imaging in living Dictyostelium cells revealed that these interactions were indispensable for the stabilization in vivo, which enabled efficient cell migration by accumulating PTEN posteriorly to restrict PI(3,4,5)P3 distribution to the anterior. These results suggest that PI(4,5)P2-mediated positive feedback and PTEN-induced PI(4,5)P2 clustering may be important for anterior-posterior polarization.

Predictive membrane transport models for Organic Solvent Nanofiltration: How complex do we need to be?

From feasibility tests at laboratory scale to large industrial scale processes, modelling can be applied to Organic Solvent Nanofiltration (OSN) for two purposes: (i) parameter estimation, when experimental data for standard solute + solvent systems are available, and it is desired to estimate relevant parameters for as yet uncharacterised systems, and (ii) prediction, when the model parameters for the solvent–solute are available, and modelling can be applied to describe the performance of a different solute + solvent system or operations at a different process scale. Both estimation and prediction require the choice of a transport model, to carry out regression and simulation, respectively. This paper reports a systematic comparison of a range of different transport models (irreversible thermodynamics, solution–diffusion, pore-flow and transient transport models, such as the solution–diffusion with imperfections model) using selected experimental data for various solutes and solvents through polymeric OSN membranes with different physico-chemical properties. Commercial integrally skinned asymmetric polyimide (PI, glassy) and thin film composite silicone-coated PI (rubbery) membranes from Evonik® MET were systematically tested in this study, with styrene oligomers and Safranin-O dye in different organic solvents under uniform operating conditions (temperature, pressure, cross-flow velocity and solute concentration). In addition, experimental data from the literature were taken for non-commercial thin film composite silicone-coated PI, glassy poly[1-(trimethylsilyl)-1-propyne] (PTMSP) and poly[4methyl2pentyne] (PMP) membranes, to include a broad spectrum of positive and negative rejection values. The different transport models were used to perform regression of experimental data and prediction at different pressure values, based on the regressed model parameters. The models were then compared in terms of regression performance and experimental/numerical effort required to use them for parameter estimation. Negative rejection data was used to further discriminate among the models. Solution–diffusion-based models gave a better description of permeation through flexible-chain glassy membranes than pore-flow models. On the other hand, pore-flow-based models gave a better description of permeation through glassy PTMSP and PMP membranes. For integrally skinned asymmetric PI membranes, the prediction of a concentration process using the best performing regression models (i.e. the Maxwell–Stefan and the classical solution–diffusion model) was also performed. Interestingly, no significant difference was observed between the two models for both a membrane with complete solute rejection (Duramem® 200) and a membrane with partial solute rejection (Duramem® 500). Process modelling by accounting for a classical solution–diffusion-type transport mechanism is therefore sufficient to obtain a reliable transport description for this membrane family.

The Simulation Research of Maximum Power Point Tracking Based on Asymmetric Fuzzy-PI Control for Photovoltaic Grid-Connected System

According to the characteristics of photovoltaic array, a novel asymmetric fuzzy PI control method is introduced for MPPT of photovoltaic system. Photovoltaic energy generation system can track the maximum power of PV cell rapidly by using asymmetric fuzzy control. On the base of asymmetric fuzzy control, an added PI control is used to eliminate the power oscillation around maximum power point. Simulation results have verified the good performance of the proposed method

Branching fractions forΥ(3S)→π0hbandψ(2S)→π0hc

Using e^+e^- collision data corresponding to 5.88M Y(3S) [25.9M psi(2S)] decays and acquired by the CLEO III [CLEO-c] detectors operating at CESR, we study the single-pion transitions from Y(3S) [psi(2S)] to the respective spin-singlet states h_{b[c]}. Utilizing only the momentum of suitably selected transition-pi^0 candidates, we obtain the upper limit B(Y(3S) -> pi^0 h_b) < 1.2\times 10^{-3} at 90% confidence level, and measure B(psi(2S) -> pi^0 h_c) = (9.0+-1.5+-1.3)\times 10^{-4}. Signal sensitivities are enhanced by excluding very asymmetric pi^0 -> gamma gamma candidates.

Asymmetric PI(3,4,5)P3and Akt Signaling Mediates Chemotaxis of Axonal Growth Cones

The action of many extracellular guidance cues on axon pathfinding requires Ca2+ influx at the growth cone (Hong et al., 2000; Nishiyama et al., 2003; Henley and Poo, 2004), but how activation of guidance cue receptors leads to opening of plasmalemmal ion channels remains largely unknown. Analogous to the chemotaxis of amoeboid cells (Parent et al., 1998; Servant et al., 2000), we found that a gradient of chemoattractant triggered rapid asymmetric PI(3,4,5)P3 accumulation at the growth cone's leading edge, as detected by the translocation of a GFP-tagged binding domain of Akt in Xenopus laevis spinal neurons. Growth cone chemoattraction required PI(3,4,5)P3 production and Akt activation, and genetic perturbation of polarized Akt activity disrupted axon pathfinding in vitro and in vivo. Furthermore, patch-clamp recording from growth cones revealed that exogenous PI(3,4,5)P3 rapidly activated TRP (transient receptor potential) channels, and asymmetrically applied PI(3,4,5)P3 was sufficient to induce chemoattractive growth cone turning in a manner that required downstream Ca2+ signaling. Thus, asymmetric PI(3,4,5)P3 elevation and Akt activation are early events in growth cone chemotaxis that link receptor activation to TRP channel opening and Ca2+ signaling. Altogether, our findings reveal that PI(3,4,5)P3 elevation polarizes to the growth cone's leading edge and can serve as an early regulator during chemotactic guidance.

Investigation of Asymmetric PI Controller using Hardware-in-the-loop Simulation System

The algorithm for control of processes with the asymmetric dynamics, which is employed in the designed digital asymmetric PI (aPI) controller, has been proposed. The investigation technique of designed aPI controller using hardware-in-the-loop (HIL) simulation system and software Simulink have been presented. The special-purpose multifunctional PC board, which includes the A/D and D/A converters, implements the link between the actual aPI controller and virtual asymmetric process realized using software Simulink and developed model of process with the asymmetric dynamics. The controller is based on the microcontroller AT89C51AC3. It is intended to use for the feedback control of air pressure of advanced energy-saving industrial ventilation systems. The designed aPI controller allows us to improve the control quality of analyzed concrete process with the asymmetric dynamics as compared with the case when popular in industry PI controller is used. Ill. 6, bibl. 7 (in English; summaries in English, Russian and Lithuanian).

Asymmetric PI Controller for Mechatronic Systems

An asymmetric PI (aPI) controller based on a control algorithm, which is the modification of the PI control method, has been suggested. The principal characteristic feature of the aPI controller is that different values of proportional and integral constants are used at positive and at negative errors. Contrary to the classical PI controller, the proposed controller allows us to improve the positive disturbance rejection of control systems without sacrificing the unit step response dynamics. Results of the investigation of the concrete control systems based on the aPI controller are also presented. Using the dynamic system simulation program Simulink performed the investigation.

Golgi polarization in a strong electric field

Directional cell migration requires proper cell polarization. The redistribution of the Golgi apparatus is an important event in the polarization and migration of many types of cells, as a polarized Golgi supplies membrane components for leading edge protrusion. Direct current electric fields induce directional cell migration in a wide variety of cells. Here we show that electric fields of 300 mV/mm induce robust Golgi polarization and directional cell migration in CHO cells. Asymmetric Src and PI 3-kinase signalling as well as actin polymerization are essential for electric field-induced Golgi polarization and directional cell migration. The Golgi polarizes at the same time as cells change morphology and migrate directionally in response to an electric field. Golgi polarization in turn significantly reinforces and maintains optimal electrotaxis. It is not known whether electrical signals, when contradicting other directional cues, are still able to polarize cells and direct cell migration. Most strikingly, Golgi polarization and cell migration simply follow the direction of an applied electric field and ignore all other cues generated by wounding a monolayer of CHO cells. Thus, an electric field of 300 mV/mm is the predominant cue to polarize the Golgi and direct cell migration mediated by PI 3-kinase and Src signalling.

Dihapto coordination of carboxylic acid derivatives with an asymmetric rhenium pi-base: a new mechanism for amide isomerization?

The asymmetric pi basic metal fragment [TpRe(CO)(MeIm)] (Tp = hydridotris(pyrazolyl)borate, MeIm = 1-methylimidazole) forms thermally stable complexes with ethyl acetate, acetic anhydride, N-methylsuccinimide, N-acetylpyrrole, and N-methylmaleimide in which the metal binds a carbonyl group in a pi fashion. In all cases a single diastereomer is observed, indicating that one enantioface of the carbonyl is selectively coordinated. X-ray and NMR data for the compound TpRe(CO)(MeIm)(eta(2)-N-methylsuccinimide) indicate that metal coordination effectively removes the pi interaction between the bound carbonyl and the nitrogen of the succinimide ring.