Asymmetric Substrate Research Articles

System L amino acid transporter LAT1 accumulates O-(2-fluoroethyl)-L-tyrosine (FET).

O-(2-fluoroethyl)-L-tyrosine (FET) labeled with fluorine-18 is an important and specific tracer for diagnostics of glioblastoma via positron emission tomography (PET). However, the mechanism of its quite specific accumulation in tumor tissue has not been understood so far. In this work we demonstrate that [(3)H]L-tyrosine is primarily transported by the system L transporter LAT1 in human LN229 glioblastoma cells. FET reduced tyrosine transport, suggesting that it shares the same uptake pathway. More importantly, accumulation of FET was significantly reduced after siRNA-mediated downregulation of LAT1. Xenopus laevis oocytes expressing human LAT1 together with the glycoprotein 4F2hc (necessary to pull LAT-1 to the plasma membrane) exhibited a similar accumulation of FET as observed in glioblastoma cells. In contrast, no accumulation was observed in control oocytes, not overexpressing an exogenous transporter. Because LAT1 works exclusively as an exchanger of amino acids, substrates at one side of the membrane stimulate exchange against substrates at the other side. Extracellular FET stimulated the efflux of intracellular [(3)H]L-leucine, demonstrating that FETis indeed an influx substrate for LAT1. However, FET injected into oocytes was not able to stimulate uptake of extracellular [(3)H]L-leucine, indicating that FET is not a good efflux substrate. Our data, therefore, suggest that FET is trapped within cells due to the asymmetry of its intra- and extracellular recognition by LAT1. If also found for other transporters in tumor cells, asymmetric substrate recognition may be further exploited for tumor-specific accumulation of PET-tracers and/or other tumor-related drugs.

Compact Multi-Port Power Combination/Distribution With Inherent Bandpass Filter Characteristics

Compact multi-port power combiners and dividers with filter characteristics are introduced. These components advantageously combine the functions of power distribution and filtering in a single component, thus reducing the number of components in a system and improving overall system performance. The design principle, which is entirely based on filter theory, is first presented for a symmetric filtering four-port combiner/divider and is then extended to an eight-port network. Measurements on a symmetric all-metal waveguide four-port prototype show excellent agreement with simulations and validate the general design approach. The experimental response of an asymmetric substrate integrated waveguide eight-port network agrees reasonably well with simulations and demonstrates that the basic four-port element can be extended to very compact multi-port combiner/dividers to cope with a variety of systems requirements.

Improved Body Effect and Analog Characteristics of n-Channel MOSFET With Lateral Asymmetric Substrate Doping

An n-channel MOSFET with lateral asymmetric substrate doping (LASD) is presented in this paper. The proposed LASD device has a p-well on the source side and a p-substrate on the drain side. The LASD MOSFET was designed by the simple p-well layout approach and fabricated using the 0.18 \(\mu \) m standard low-voltage CMOS process without any process modification. The experimental measurements showed the improved analog performances of the LASD MOSFET: higher transconductance (g \(_{\mathbf {m}}\) ), lower drain conductance (g \(_{{\mathrm {ds}}}\) ), lower drain induced barrier lowering, higher transconductance generation factor (g \(_{{\mathrm {m}}}/{\mathrm I}_{{\mathrm {D}}}\) ), and higher Early voltage (V \(_{{\mathrm {EA}}}\) ). In addition, the LASD device showed strong body-effect immunity: smaller V \(_{{\mathrm {T}}}\) shift according to body bias and lower body bias sensitivity factor (g \(_{{\mathrm {mb}}}/{\mathrm g}_{{\mathrm {m}}}\) ).

Expression, purification and reconstitution of the 4-hydroxybenzoate transporter PcaK from Acinetobacter sp. ADP1

The aromatic acid:H+ symporter family of integral membrane proteins play an important role in the microbial metabolism of aromatic compounds. Here, we show that the 4-hydroxybenzoate transporter from Acinetobacter sp. ADP1, PcaK, can be successfully overexpressed in Escherichia coli and purified by affinity chromatography. Affinity-purified PcaK is a stable, monodisperse homotrimer in the detergent n-dodecyl-β-d-maltopyranoside supplemented with cholesteryl hemisuccinate. The purified protein has α-helical secondary structure and can be reconstituted to a functional state in synthetic proteoliposomes. Asymmetric substrate transport was observed when proteoliposomes were energized by applying an electrochemical proton gradient (Δμ‾H+) or a membrane potential (ΔΨ) but not by ΔpH alone. PcaK was selective in transporting 4-hydroxybenzoate and 3,4-dihydroxybenzoate over closely related compounds, confirming previous reports on substrate specificity. However, PcaK also showed an unexpected preference for transporting 2-hydroxybenzoates. These results provide the basis for further detailed studies of the structure and function of this family of transporters.

Photoswitchable ratchet surface topographies based on self-protonating spiropyran-NIPAAM hydrogels.

In this work, self-protonating spiropyran-based poly(N-isopropylacrylamide) polymer networks are prepared. These photoresponsive hydrogel coatings can change their surface topography upon exposure with visible light in a neutral environment. Photoresponsive surface-constrained films have been fabricated for which the swelling behavior can be controlled in a reversible manner. In a first step, symmetrical switchable surface topologies with varying cross-link density are obtained by polymerization-induced diffusion. Under light exposure, the areas with low cross-link density swell more than the areas with high cross-link density, thus forming a corrugated surface. Asymmetric ratchet-like photoresponsive surfaces have been prepared on prestructured asymmetric substrates. As a result of thickness variation of the surface-confined hydrogel layer, an asymmetric swelling behavior is obtained. Depending on the cross-link density of the hydrogel, it is possible to switch between a ratchet and flat surface topography or even an inverse ratchet surface by light.

Structural and biophysical analysis of UCH37: ubiquitin recognition and binding to ADRM1 (952.3)

Ubiquitin C‐terminal hydrolase 37 (UCH37) is a deubiquitinating enzyme capable of dismantling Lys48‐linked polyubiquitin chains when associated with the 26S proteasome. Upon binding to the proteasomal subunit ADRM1, UCH37 is activated for cleavage of the distal monomer in a chain, an exo‐specific activity. Prior to binding with ADRM1, it is thought that UCH37 is inhibited by its own C‐terminal UCHL5‐like domain (ULD). Our interests lie in UCH37’s mechanism of activation by ADRM1 as well as its exo‐specificity. Previously we have reported the crystal structure of T. spiralis UCH37 bound to ubiquitin vinyl methyl ester, which revealed that the ULD domain interacts with ubiquitin’s Lys48, an event we believe accounts for its exo‐specificity. In order to further examine specificity and activation, we have generated a series of ULD mutants of UCH37. To probe exo‐specificity, we are purifying the 19S regulatory particle of the proteasome from rabbit skeletal muscle, will reconstitute each ULD mutant within the 19S, and then test their cleavage with an asymmetric triubiquitin substrate. When mutated, ULD residues involved in ubiquitin recognition may lose exo‐specificity against the asymmetric substrate. Additionally, we have analyzed UCH37 and ADRM1’s biophysical interactions through isothermal titration calorimetry, finding that the two bind with 1:1 stoichiometry and a dissociation constant of 22 nM. Due to this tight binding and our structural data, we hypothesize that ADRM1’s activation of UCH37 may not be due to an enhancement of UCH37’s turnover rate, but rather due to an increase in ubiquitin’s koff rate; that is, the ULD merely slows product dissociation. We hope to characterize this phenomenon through surface plasmon resonance studies of ubiquitin binding to ULD mutants in the presence of ADRM1. These findings should not only provide a better understanding of UCH37’s activation and exo‐specificity, but will further probe the role of deubiquitination at the proteasome.Grant Funding Source: Supported by National Institutes of Health Grant 1R01RR026273 (C.D.)

Saturation effects in ac + dc driven Frenkel–Kontorova model

Properties of the Shapiro steps in different commensurate structures of the ac+dc driven Frenkel–Kontorova model with asymmetric deformable substrate potential have been examined. Deviation from the sinusoidal potential produces appearance of large subharmonic steps. In general, different commensurate structures respond differently to the applied force and have different velocities. The results have shown that after shape parameter gets some critical value, there is no difference in the behavior of Shapiro steps for different commensurate structures. The step size and the critical depinning force for different commensurate structures saturate to the same values, due to reduction of degrees of freedom with the large deformation of potential.

Ceramic hollow fibres catalytic enhanced reactors for glycerol steam reforming

In this study, NiO/MgO/CeO2 catalysts with Ni content from 5% to 30% were synthetized by sol–gel method and tested in a fixed-bed reactor (FBR) in the glycerol steam reforming (GSR) reaction. The catalysts were characterized by N2 adsorption isotherms at −196°C (SBET), X-ray diffraction (XRD), H2 temperature programmed reduction (H2-TPR), transmission electron microscopy (TEM) and energy dispersive X-ray (EDX). The 20% NiO/MgO/CeO2 catalyst, which showed the highest catalytic activity in GSR reaction, was selected to be deposited in the finger-like region of the asymmetric Al2O3 hollow fibre and the sponge-like region of the symmetric Al2O3 hollow fibre in the development of the asymmetric hollow fibre reactor (AHFR) and symmetric hollow fibre reactor (SHFR), respectively. The impregnated ceramic substrates were characterized by scanning electron microscopy (SEM), EDX and TEM. The performances of the AHFR and SHFR were compared with that in a conventional FBR during the GSR reaction. Both AHFR and SHFR were operating at “dead-end” configuration at a temperature range from 250°C to 550°C, atmospheric pressure and in a reactant mixture of steam and glycerol (16:1 molar ratio). At 550°C the glycerol conversion in the AHFR and SHFR was 70% and 46%, respectively, which are 5 and 2 times higher than that obtained in the FBR. The different performances of the AHFR and SHFR could be explained due to the unlike catalyst particle size deposited in the asymmetric and symmetric substrates, 8nm and 3nm, respectively.

Performance and Long-Term Stability of Pd/PSS and Pd/Al2O3 Membranes for Hydrogen Separation.

The present work is focused on the investigation of the performance and long-term stability of two composite palladium membranes under different operating conditions. One membrane (Pd/porous stainless steel (PSS)) is characterized by a ~10 µm-thick palladium layer on a porous stainless steel substrate, which is pretreated by means of surface modification and oxidation; the other membrane (Pd/Al2O3) is constituted by a ~7 µm-thick palladium layer on an asymmetric microporous Al2O3 substrate. The operating temperature and pressure ranges, used for studying the performance of these two kinds of membranes, are 350–450 °C and 200–800 kPa, respectively. The H2 permeances and the H2/N2 selectivities of both membranes were investigated and compared with literature data. At 400 °C and 200 kPa as pressure difference, Pd/PSS and Pd/Al2O3 membranes exhibited an H2/N2 ideal selectivity equal to 11700 and 6200, respectively, showing stability for 600 h. Thereafter, H2/N2 selectivity of both membranes progressively decreased and after around 2000 h, dropped dramatically to 55 and 310 for the Pd/PSS and Pd/Al2O3 membranes, respectively. As evidenced by Scanning Electron Microscope (SEM) analyses, the pinholes appear on the whole surface of the Pd/PSS membrane and this is probably due to release of sulphur from the graphite seal rings.

Preparation and characterization of UZM-5/polyamide thin film nanocomposite membrane for dewaxing solvent recovery

Thin-film nanocomposite (TFN) membrane containing amino-functionalized UZM-5 nanoparticles was synthesized by interfacial polymerization on polyetherimide (PEI)/modified SiO2 asymmetric substrate tailored for organic solvent nanofiltration OSN process. m-Phenylenediamine (MPD) with trimesoyl chloride (TMC) was polymerized to prepare polyamide layer. UZM-5 nanoparticles (~73nm) were synthesized and then functionalized by aminopropylediethoxymethylsilane (APDEMS) and finally incorporated into polyamide (PA) selective layer at concentrations ranging from 0 to 0.2w/v%. The as-prepared TFN membranes were characterized by scanning electron microscopy (SEM), field emission scanning electron microscopy (FESEM), atomic force microscopy (AFM), attenuated total reflection Fourier transform infrared (ATR-FTIR) spectroscopy and contact angle measurements. The performances of membranes were also evaluated through dewaxing solvents (MEK and toluene) recovery from lube oil. FESEM and SEM images clearly confirmed that the polyamide/UZM-5 nanocomposite top layer was formed on the support surface and its morphology was significantly affected by UZM-5 loading. Interaction between functional groups of modified UZM-5 nanoparticles and polyamide matrix was established by ATR-FTIR. AFM results revealed that in the range of 0–0.1w/v% zeolite loading, the surface roughness of TFN membranes decreased due to the change of polyamide structure while at 0.2w/v% of zeolite loading, an increase in surface roughness was observed. It also resulted in enhanced hydrophilicity of TFN membranes in the range of 0–0.1w/v% UZM-5 loading, proved by a decreased water contact angle. The permeation test results indicated that the existence of UZM-5 in the polyamide selective layer improved both oil rejection and permeate flux under optimal concentration (0.02% w/v of UZM-5).

Exploiting large non-isomorphous differences for phase determination of a G-segment invertase–DNA complex

Crystals of the G-segment invertase in complex with a 37-base-pair asymmetric DNA duplex substrate had an unusually high solvent content of 88% and diffracted to a maximal resolution of about 5.0 Å. These crystals exhibited a high degree of non-isomorphism and anisotropy, which presented a serious challenge for structure determination by isomorphous replacement. Here, a procedure of cross-crystal averaging is described that uses large non-isomorphous crystallographic data with a priori information of an approximate molecular boundary as determined from a minimal amount of experimental phase information. Using this procedure, high-quality experimental phases were obtained that have enabled it to be shown that the conformation of the bound substrate DNA duplex significantly differs from those of substrates bound in other serine recombinase-DNA complexes.

Structure and function of an insect α-carboxylesterase (αEsterase7) associated with insecticide resistance

Insect carboxylesterases from the αEsterase gene cluster, such as αE7 (also known as E3) from the Australian sheep blowfly Lucilia cuprina (LcαE7), play an important physiological role in lipid metabolism and are implicated in the detoxification of organophosphate (OP) insecticides. Despite the importance of OPs to agriculture and the spread of insect-borne diseases, the molecular basis for the ability of α-carboxylesterases to confer OP resistance to insects is poorly understood. In this work, we used laboratory evolution to increase the thermal stability of LcαE7, allowing its overexpression in Escherichia coli and structure determination. The crystal structure reveals a canonical α/β-hydrolase fold that is very similar to the primary target of OPs (acetylcholinesterase) and a unique N-terminal α-helix that serves as a membrane anchor. Soaking of LcαE7 crystals in OPs led to the capture of a crystallographic snapshot of LcαE7 in its phosphorylated state, which allowed comparison with acetylcholinesterase and rationalization of its ability to protect insects against the effects of OPs. Finally, inspection of the active site of LcαE7 reveals an asymmetric and hydrophobic substrate binding cavity that is well-suited to fatty acid methyl esters, which are hydrolyzed by the enzyme with specificity constants (∼10(6) M(-1) s(-1)) indicative of a natural substrate.

Asymmetric drag in oscillatory motion: Ratchet effect without an asymmetric potential

Asymmetry of magnetic objects in a fluid under an oscillating magnetic field leads to a wealth of nonequilibrium dynamics phenomena including a novel ratchet effect without an asymmetric substrate. These nonlinear dynamics are explained in the framework of the Stokes' model by a drag coefficient, which depends on the direction of motion. This approach is general and is independent of the physical mechanism responsible for this directional dependence of the drag coefficient as well as the size of the object. The theoretical model is experimentally verified for two systems, a nonrigid magnetic microcoil and a chiral magnetic macroobject immersed in a bounded fluid.

Aspherical anamorphic lens for shaping laser diode beam

We propose a novel method to fabricate aspherical anamorphic lenses at very low costs. A droplet made of UV-curable negative photoresist is placed on an asymmetrical substrate and cured when its surface shape evolves to be aspherical due to electrostatic force and meets the designed optimal shape. Both numerical analysis and experimental results are presented, showing that the fabricated lens has different optical powers in the two transverse directions and can collimate the divergent beam generated by a laser diode in the fast-axis direction with high energy efficiency.

The Effect of Deposition Patterns on the Deformation of Substrates During Direct Laser Fabrication

The deformation of substrate caused by laser scanning pattern during direct laser fabrication (DLF) is ignored in spite of its importance to the final dimension accuracy. In this paper, in order to investigate the effect of deposition pattern on the deformation of substrate during DLF, eight laser scanning patterns are designed to build a cylinder on an asymmetrical IN718 arc substrate, respectively. Deformations of substrates along x, y, z-directions after DLF and heat treatment are compared and discussed. Meanwhile, the maximum displacement in z-direction of each substrate is calculated. Besides, a modified temperature gradient mechanism (TGM) is introduced to understand deformations of substrates under different laser scanning patterns. The results show that the deformation of substrate along z-direction is much larger than other two directions for all scanning patterns. The deformation of substrate strongly depends on x- and y-directional dimension of the substrate when a symmetrical build is fabricated. Compared with contour-offset scanning patterns, raster scanning patterns have distinct directional effect on deformations of substrates. Especially, the deformations of substrates caused by laser fabrication are permanent. In order to improve the fabrication efficiency, to and fro laser scan along the short dimension direction is preferred during DLF for generating the minimum deformation to substrate and reducing unnecessary movements of the working table.

Kink localization under asymmetric double-well potentials

We study diffuse phase interfaces under asymmetric double-well potential energies with degenerate minima and demonstrate that the limiting sharp profile, for small interface energy cost, on a finite space interval is in general not symmetric and its position depends exclusively on the second derivatives of the potential energy at the two minima (phases). We discuss an application of the general result to porous media in the regime of solid-fluid segregation under an applied pressure and describe the interface between a fluid-rich and a fluid-poor phase.

Relativistic Brownian motion on a graphene chip

Relativistic Brownian motion can be inexpensively demonstrated on a graphene chip. The interplay of stochastic and relativistic dynamics, governing the transport of charge carrier in graphene, induces noise-controlled effects such as (i) a stochastic effective mass, detectable as a suppression of the particle mobility with increasing the temperature; (ii) transverse harmonic mixing, whereby electron transport can be controlled by two orthogonal, commensurate ac drives; (iii) a transverse ratchet effect, measurable as a net current orthogonal to an ac drive on an asymmetric substrate, and (iv) chaotic stochastic resonance. Such properties can be of practical applications in the emerging graphene technology.

Symmetry interplay in Brownian photomotors: From a single-molecule device to ensemble transport

Unlike most of Brownian motor models in which the state of a point particle is described by a single scalar fluctuating parameter, we consider light-induced dichotomic fluctuations of electron density distributions in an extended molecule moving in the electrostatic periodic potential of a polar substrate. This model implies that the potential energy profiles of two motor states differ substantially and their symmetry is dictated by the interplay between the symmetries of the substrate potential and of molecular electronic states. As shown, a necessary condition for the occurrence of directed motion, the asymmetry of the potential energy profiles, is satisfied for (i) symmetric electron density distributions in molecules on asymmetric substrates and (ii) asymmetric electron density distributions in molecules on symmetric substrates. In the former case, the average velocity of directed motion is independent of molecular orientations and the ensemble of molecules moves as a whole, whereas in the latter case, oppositely oriented molecules move counterdirectionally thus causing the ensemble to diffuse. Using quantum chemical data for a specific organic-based photomotor as an example, we demonstrate that the behavior of molecular ensembles is controllable by switching on/off resonance laser radiation: they can be transported as a whole or separated into differently oriented molecules depending on the ratio of symmetric and antisymmetric contributions to the substrate electrostatic potential and to the molecular electron density distributions.

Microstructure modifications of CrN coatings by pulsed bias sputtering

This paper investigates the influence of a combined electron and ion bombardment via asymmetric bipolar pulsed substrate bias on the microstructure and mechanical properties of reactively magnetron-sputtered CrN hard coatings for two different ion-to-atom flux ratios.A short ratio of electron-to-ion bombardment duration leads to a preferred (110) orientation of the CrN phase, high residual stress up to −4.1GPa and hardness values up to 17.9GPa. An increased electron-to-ion bombardment ratio promotes a change in preferred orientation from (110) towards (100). Concurrently, residual stress and hardness values are reduced to a few ±100MPa and 15.1GPa, respectively. The texture cross-over from (110) to (100) is shifted to longer electron bombardment duration for higher ion-to-atom flux ratios.

Ratchet composite thin film for low-temperature self-propelled Leidenfrost droplet

The droplet control, especially for the self-propelled Leidenfrost droplet, has attracted many researchers’ attention in applied and fundamental fields. In this paper, the ratchet thin film was fabricated by magnetron sputtering and hybrid ion beams deposition. The micro- and nanoscale structure of the film was characterized by field emission scanning electron microscope. This study reports an interesting phenomenon that the self-propelled Leidenfrost water droplet was initiated at low temperature. The Leidenfrost point of droplets was controlled by the surface wettability and parameters of the asymmetric ratchet substrate. This novel self-propelled interfacial material and preparation technology can be expanded to the manufacture process and constructed a temperature-dependent tubule for microfluidic systems.