poly-L-lysine Molecules Research Articles

Ultralow Energy Consumption Angstrom-Fluidic Memristor.

The emergence of nanofluidic memristors has made a giant leap to mimic the neuromorphic functions of biological neurons. Here, we report neuromorphic signaling using Angstrom-scale funnel-shaped channels with poly-l-lysine (PLL) assembled at nano-openings. We found frequency-dependent current-voltage characteristics under sweeping voltage, which represents a diode in low frequencies, but it showed pinched current hysteresis as frequency increases. The current hysteresis is strongly dependent on pH values but weakly dependent on salt concentration. We attributed the current hysteresis to the entropy barrier of PLL molecules entering and exiting the Angstrom channels, resulting in reversible voltage-gated open-close state transitions. We successfully emulated the synaptic adaptation of Hebbian learning using voltage spikes and obtained a minimum energy consumption of 2-23 fJ in each spike per channel. Our findings pave a new way to mimic neuronal functions by Angstrom channels in low energy consumption.

Preparation of fluorescent nanoparticles based on broken-rice starch for live-cell imaging

Native broken-rice starch was used to create starch nanoparticles (StNPs) with particle sizes ranging from 100 nm to 800 nm. The fluorescent isothiocyanate poly-l-lysine StNPs (FITC-PLL-StNPs) were created in two steps. First, the StNPs were electrostatically modified by poly-l-lysine (PLL) molecules rich in amino acids. Second, fluorescein isothiocyanate reacted with some amino groups on PLL molecules (FITC). Fluorescence spectrophotometry was used to determine the degree of substitution (DS) and fluorescent properties of fluorescent starches. The study found that FITC-PLL-StNP-200 has higher fluorescence stability, more phagocytic cells, and a better and clearer fluorescence detecting effect than FITC-PLL-St, FITC-PLL-StNP-100, FITC-PLL-StNP-400, and FITC-PLL-StNP-800. The biological evaluation results showed that FITC-PLL-StNP-200 did not affect the viability of HeLa cells at the lysosome labeling concentration. These findings suggest that FITC-PLL-StNP-200 has strong and stable fluorescence, indicating that FITC-PLL-StNP-200 can be used as a fluorescent probe and lysosome marker in a variety of applications, particularly in biomedicine.

Poly-L-lysine/hyaluronan nanocarriers as a novel nanosystem for gene delivery.

The present research comes up with a novel DNA-loaded poly-L-lysine (PLL)/hyaluronan (HA) nanocarrier (DNA-loaded PLL/HA NCs) for gene delivery applications, as a promising candidate for gene delivery into diverse cells. A straightforward approach was employed to prepare such a nanosystem through masking DNA-loaded PLL molecules by HA. Fourier-transform infrared (FTIR) spectroscopy, dynamic light scattering (DLS), field emission-scanning electron microscopy(FE-SEM) and transmission electron microscopy (TEM) were used to analyse the interaction of the molecules as well as the physicochemical properties of the NCs. The NCs showed a negative charge of -24 ± 3mV, with an average size of 138 ± 6 nm, in an ellipsoid-shape with smooth surfaces. The DNA loading efficiency (LE) measured by DNA absorbance was around 95 %. The MTT assay showed that the developed NCs are non-toxic to the cells. Furthermore, the uptake of the DNA-loaded PLL/HA NCs by the human embryonic kidney (HEK)-293T cells was evaluated by a flow cytometry method, and demonstrated high potential cellular uptake over 90% for transferring the gene to HEK-293T cells at the optimised conditions. Therefore, the DNA-loaded PLL/HA NCs are the potent strategy for developing nanosystems for gene delivery applications.

Influence of phenothiazine molecules on the interactions between positively charged poly-l-lysine and negatively charged DPPC/DPPG membranes.

Phenothiazines are very effective antipsychotic drugs, which also have anticancer and antimicrobial activities. Despite being used in human treatment, the molecular mechanism of the biological actions of these molecules is not yet understood in detail. The role of the interactions between phenothiazines and proteins or lipid membranes has been much discussed. Herein, fourier-transform infrared (FTIR) spectroscopic studies were used to investigate the effect of three phenothiazines: fluphenazine (FPh); chlorpromazine (ChP); and propionylpromazine (PP) on the structures of a positively charged poly-l-lysine (PLL) peptide, a negatively charged dipalmitoylphosphatidylcholine/dipalmitoylphosphatidylglycerol (DPPC/DPPG) membrane, and on the mutual interactions between electrostatically associated PLL molecules and DPPC/DPPG membranes. Phenothiazine-induced alterations in the secondary structure of PLL, the conformational state (trans/gauche) of the hydrocarbon lipid chains, and the hydration of the DPPC/DPPG membrane interface were studied on the basis of amide I' vibrations, antisymmetric and symmetric stretching vibrations of the CH2 groups of the lipid hydrocarbon chains (νsCH2), and stretching vibrations of the lipid C=O groups (νC = O), respectively. It was shown that in the presence of negatively charged DPPC/DPPG membranes, the phenothiazines were able to modify the secondary structure of charged PLL molecules. Additionally, the effect of PLL on the structure of DPPC/DPPG membranes was also altered by the presence of the phenothiazine molecules.

Detection of Amyloid β Using a Poly-L-Lysine Mediated Nanobiosensor.

Amyloid β (Aβ) peptide is secreted from the outside of neural cell by a neural signal pathway and it accumulated each other results in the highly toxicity amyloid plaque which is a critical causative factor in the pathogenesis of Alzheimer's Disease (AD). The peptide is considered to be a potential biomarker to diagnose AD. Here we introduce a novel poly-L-lysine (PLL) mediated nanobiosensor to detect Aβ in vitro. The PLL molecules were utilized as a signal amplifier of Aβ detection. The indirect enzyme-linked immunosorbent assay (ELISA) method and the sandwich ELISA method have tried to the detection of Aβ. A commercially available ELISA plate was modified by PLL using a chemical agent and the amplified amino groups were activated by a functional group for the binding of Aβ. The bound Aβ was further modified with a primary antibody and fluorescence molecules conjugated secondary antibody by the traditional immunochemistry. In the result, the fluorescence intensity was increased by the increasing concentration of Aβ, and the best Aβ detection results were obtained in the PLL mediated indirect ELISA nanobiosensor. We expected that the present method would be optimized and applied for the detection of Aβ in human fluid.

Impact of molecular linker size on physicochemical properties of assembled gold nanoparticle mono-/multi-layers and their applicability for functional binding of biomolecules

In this work the impact of molecular inter-linker size on gold nanoparticle (AuNP) mono-/multilayer structural properties, density and homogeneity has been investigated. These characteristics are of great importance for functional binding of biomolecules. Positively charged high or low molecular weight inter-linkers, poly-L-lysine (PLL) or N-(6-mercapto)hexylpyridinium (MHP), were used to attach negatively charged AuNPs on a planar gold surface as well as to further interlink into a multilayer structure via layer-by-layer deposition. The inter-particle interaction within the assembled AuNP films was adjusted by the ionic strength in the AuNPs dispersions. The AuNP layer density and structural/viscoelastic properties were evaluated by the quartz crystal microbalance with dissipation (QCM-D) technique. The validity of the commercial Voigt model, specifically developed for quantitative QCM-D data analysis of homogeneous viscoelastic films, was evaluated by a model independent analysis when comparing the assembled AuNP films with a homogeneous layer of a mucin from bovine submaxillary glands. Both AuNP mono- and multilayers, attached/interlinked via long flexible PLL molecules assembled to denser and more soft/viscous structures compared to those interlinked by short MHP compounds. Thus, PLL-interlinked AuNP mono-/multilayer structures were further investigated as a platform for laccase enzyme functional adsorption via qualitative assessment of bioelectrochemical characteristics of the enzyme.

Conformations of Poly-l-lysine Molecules in Electrolyte Solutions: Modeling and Experimental Measurements

Physicochemical properties of poly-l-lysine (PLL) hydrobromide were determined by molecular dynamics (MD) modeling and a variety of experimental techniques. Primarily, the density, the chain diameter, the monomer length, and the PLL molecule conformations were theoretically calculated. These results were applied for the interpretation of experimental data acquired for the PLL sample of average molar mass equal to 122 kg/mol. They comprised the diffusion coefficient, the hydrodynamic diameter, and the electrophoretic mobility of molecules determined for the ionic strength ranging from 2 × 10–5 to 0.15 M and pH 5.6. Using these data, the electrokinetic charge and the effective ionization degree of PLL molecules were determined as a function of ionic strength. Additionally, precise dynamic viscosity measurements for dilute PLL solutions were performed yielding the intrinsic viscosity, which decreased from 2420 to 120 for ionic strengths of 2 × 10–5 and 0.15 M, respectively. This confirmed that PLL molecules ...

The PPII-to-α-helix transition of poly-l-lysine in methanol/water solvent mixtures accompanied by fibrillar self-aggregation: An influence of fluphenazine molecules

Fourier-transform infrared, vibrational circular dichroism spectroscopy and transmission electron microscopy are used to follow the structural changes of pure and fluphenazine (FPh)-mixed poly-l-lysine (PLL) triggered by variations of the methanol to water ratio in solvent mixtures. FPh molecules are used as an effective psychotic drug but with a strong Parkinson's-related side effect. To answer the question whether FPh molecules can modify the fibril development, the PLL polypeptide was used as a model of α-helix- and PPII-rich fibrils. It was stated that the presence of FPh molecules did not inhibit the creation of both types of PLL fibrils with clustering features. The methanol-poor aqueous solutions promote the formation of extended polyproline II (PPII) helices; however, the methanol-rich aqueous solutions induce the development of α-helices of both pure and FPh-mixed PLL. Unpredicted and interesting features of PLL fibrillogenesis are evidenced by the formation of uncommon fibrillar aggregates, which are developed in methanol/water solvents from PLL molecules rich in either α-helix or PPII structures. Possibility of PLL molecules to form β-sheet-, α-helix- and PPII-rich fibrils demonstrating that fibrillogenesis is a common phenomenon, and fibrillar aggregates can be based on all of the basic protein secondary structures.

Alpha-helix to beta-sheet transition in long-chain poly-l-lysine: Formation of alpha-helical fibrils by poly-l-lysine

The temperature-induced α-helix to β-sheet transition in long-chain poly-l-lysine (PLL), accompanied by the gauche-to-trans isomerization of CH2 groups in the hydrocarbon side chains of Lys amino acid residues, and formation of β-sheet as well as α-helix fibrillar aggregates of PLL have been studied using Fourier-transform infrared (FT-IR) and vibrational circular dichroism (VCD) spectroscopy, and transmission electron microscopy (TEM). In a low-temperature alkaline water solution or in a methanol-rich water mixture, the secondary structure of PLL is represented by α-helical conformations with unordered and gauche-rich hydrocarbon side chains. Under these conditions, PLL molecules aggregate into α-helical fibrils. PLLs dominated by extended antiparallel β-sheet structures with highly ordered trans-rich hydrocarbon side chains are formed in a high-temperature range at alkaline pD and aggregate into fibrillar, protofibrillar, and spherical forms. Presented data support the idea that fibrillar aggregation is a varied phenomenon possible in repetitive structural elements with not only a β-sheet-rich conformation, but also an α-helical-rich conformation.

Devising Self-Assembled-Monolayers for Surface-Enhanced Infrared Spectroscopy of pH-Driven Poly-l-lysine Conformational Changes

Surface-enhanced infrared absorption spectroscopy (SEIRA) is applied to study protein conformational changes. In general, the appropriate functionalization of metal surfaces with biomolecules remains a challenge if the conformation and activity of the biomolecule shall be preserved. Here we present a SEIRA study to monitor pH-induced conformational changes of poly-l-lysine (PLL) covalently bound to a thin gold layer via self-assembled monolayers (SAMs). We demonstrate that the composition of the SAM is crucial. A SAM of 11-mercaptoundecanonic acid (MUA) can link PLL to the gold layer, but pH-driven conformational transitions were hindered compared to poly-l-lysine in solution. To address this problem, we devised a variety of SAMs, i.e., mixed SAMs of MUA with either octanethiol (OT) or 11-mercapto-1-undecanol (MUoL) and furthermore SAMs of MT(PEG)4 and NHS-PEG10k-SH. These mixed SAMs modify the surface properties by changing the polarity and the morphology of the surface present to nearby PLL molecules. Our experiments reveal that mixed SAMs of MUA-MUoL and SAMs of NHS-PEG10k-SH-MT(PEG)4 are suitable to monitor pH-driven conformational changes of immobilized PLL. These SAMs might be applicable for chemoselective protein immobilization in general.

Biophysical characteristics of neurotensin polyplex for in vitro and in vivo gene transfection

Previously we improved the neurotensin (NT)-polyplex by the coupling of HA2 fusogenic peptide (FP) and Vp1 SV40 karyophilic peptide (KP). We now report the proportion of [ 125I]-NT, [ 3H]-FP, and poly- l-lysine (PLL) in the NT-polyplex, and some of its biophysical properties. We concluded that the most efficient NT-polyplex comprised 1 NT, 4 FP, and 2 PLL molecules. Electrophoresis revealed that high acidity is detrimental for NT-polyplex stability. Electron microscopy and electrophoresis studies showed that 6 μM KP and 1% serum condensed the plasmid DNA (pDNA) before the appearance of toroid structures. Four plasmids were used to evaluate the transfection efficiency. In vitro, maximum expression was produced at molar ratios (pDNA : [ 125I]-NT-[ 3H]-FP-PLL conjugate) of 1:34 for pEGFP-N1 and 1:27 for pECFP-Nuc. Cotransfection of those plasmids was attained at their optimum molar ratios. In vivo, maximum expression of the pDAT-BDNF-flag in dopamine neurons was produced at a 1:45 molar ratio, whereas that of pDAT-EGFP was at 1:20. The NT-polyplex in the presence of 1 μM SR-48692, an NT-receptor specific antagonist, and untargeted polyplex did not cause transfection in vivo demonstrating the specificity of gene transfer via NT-receptor endocytosis. This information is essential for synthesizing an efficient NT-polyplex that can provide a useful tool for specific gene transfection.

Microencapsulating Hepatocytes

Background Because standardization of the cell microencapsulation procedure has not yet been achieved, we performed hepatocyte microencapsulation using alginate (ALG)–poly- l-lysine (PLL)–ALG (APA) polymer. Methods Hepatocytes were microencapsulated using a binozzle air-jet droplet generator. Our study aims were to: (1) clarify how ALG concentration affects the quality of ALG beads; (2) determine how the PLL concentration affects the quality of microcapsules (MCs); (3) ascertain the influence of liquefaction time by sodium citrate (SC) on the quality of the MCs; (4) and clarify how temperature and solution pH, respectively, affect the viability of the hepatocytes inside the MCs. Results The concentration of ALG must be ≥ 3% (w/v) to generate droplets with satisfactory homogeneity in size and roundness ( P < .01). The total quantity of PLL molecules is the essential component for MCs ( P < .01). As our results show, the numeric ratio of PLL (milligrams) to MCs (milliliters) is roughly 25:1. SC incubation for 8 minutes resulted in the proper thickness of the MC wall; however, the time varied according to the size of the MCs ( P < .05). Temperature and pH, although both difficult to control, exerted great influences on cell viability: 4°C and pH 7.2 were found to be optimal by this study ( P < .05). Conclusions Concentrations of ALG and PLL exerted decisive effects on the quality and strength of MCs. Higher concentrations were suggested. Because temperature and pH greatly affected cell viability, they must be properly monitored.

Construction and deconstruction of PLL/DNA multilayered films for DNA delivery: Effect of ionic strength

Through the layer-by-layer (LbL) self-assembly technique, DNA was incorporated into the multilayered films with poly- l-lysine (PLL). The effect of ionic strength on the construction and deconstruction of the PLL/DNA films was investigated. It was found that the salt concentration of the deposition solution had a significant effect on the construction of the films, which might attribute to the effect of salt ions on the conformation of polyelectrolytes and interaction between PLL and DNA molecules. A salt-induced deconstruction of the PLL/DNA films was observed. The extent of the deconstruction increased with the salt concentration in the incubation solution. The mechanism of the deconstruction was discussed. Taking the advantages of the LbL technique, the erasable PLL/DNA films could deposit onto a variety of surfaces, such as vascular stent, intervention catheter and tissue engineering scaffold, to serve as a novel DNA delivery system.

Physicochemical model of alginate–poly- l-lysine microcapsules defined at the micrometric/nanometric scale using ATR-FTIR, XPS, and ToF-SIMS

Alginate–poly- l-lysine–alginate (APA) microcapsules are currently being investigated as a means to immuno-isolate transplanted cells, but their biocompatibility is limited. In this study, we verified the hypothesis that poly- l-lysine (PLL), which is immunogenic when unbound, is exposed at the APA microcapsule surface. To do so, we analysed the microcapsule membrane at the micrometric/nanometric scale using attenuated total reflectance Fourier transform infrared spectroscopy, X-ray photoelectron spectroscopy, and time-of-flight secondary ion mass spectrometry. The results indicate that PLL and alginate molecules interact within the membrane. PLL exists in considerable amounts near the surface, contributing to the majority of the carbon within the outermost 100 Å of the membrane. PLL was also detected at the true surface (the outermost monolayer) of the microcapsules. The exposure of PLL does not appear to result from defects in the outer alginate coating. This physicochemical model of APA microcapsules could explain their immunogenicity and will play an important role in the optimization of the microcapsule design.

Effect of secondary structure on the potential of mean force for poly- l-lysine in the α-helix and β-sheet conformations

Because poly- l-lysine (PLL) can exist in the α-helix or β-sheet conformation depending on solution preparation and solution conditions, PLL is a suitable candidate to probe the dependence of protein interactions on secondary structure. The osmotic second virial coefficient and weight-average molecular weight are reported from low-angle laser-light scattering measurements for PLL as a function of NaCl concentration, pH, and α-helix or β-sheet content. Interactions between PLL molecules become more attractive as salt concentration increases due to screening of PLL charge by salt ions and at low salt concentration become more attractive as pH increases due to decreased net charge on PLL. The experimental results show that interactions are stronger for the β-sheet conformation than for the α-helix conformation. A spherically-symmetric model for the potential of mean force is used to account for specific interactions not described by DLVO theory and to show how differences in secondary structure affect PLL interactions.

Interaction of poly-L-lysine with photosynthetic reaction center for the Langmuir–Blodgett film preparation

The interaction between poly-L-lysine (PLL) and photosynthetic reaction center (RC) from Rodopseudomonas viridis was studied with special interest for the Langmuir–Blodgett (LB) film preparation. PLL of low concentration (0.5mM) in the subphase of the LB trough as a counterion stabilized the protein at the air/water interface and enhanced the protein deposition efficiency onto the substrate. PLLs of various degree of polymerization ( n=1, 5, 10, 15 and 20) were synthesized and the effect of each PLL was examined. Enhancement of the deposition of RC was observed using high n peptide ( n=10, 15 and 20) but not using low n one ( n=1 and 5). When PLL ( n=1, 5, 10, 15 and 20) was added to the RC solution, the protein–protein association and the subsequent precipitation of RC occurred. Highly polymerized PLLs were effective on both RC deposition and RC precipitation suggesting that RCs spread at air/water interface were linked by PLL. The number of PLL molecules which were adsorbed on one RC molecule was 9.0 (±1.5) and 6.6 (±0.5) in the case of n=10 and 20 of PLL, respectively.

Characterization of poly-L-lysine adsorption onto alkanethiol-modified gold surfaces with polarization-modulation Fourier transform infrared spectroscopy and surface plasmon resonance measurements

The electrostatic adsorption of poly-L-lysine molecules onto a vapor-deposited gold film modified with a carboxylic acid-terminated alkanethiol monolayer is monitored with the spectroscopic techniques of polarization-modulation Fourier transform infrared (PM-FTIR) spectroscopy and surface plasmon resonance (SPR). The PM-ITIR spectrum of a monolayer of poly-L-lysine (PL) adsorbed onto a self-assembled monolayer of 11-mercaptoundecanoic acid (MUA) indicates that the lysine residues and the MUA carboxylic acid moieties form ammonium-carboxylate ion pairs which electrostatically bind the polypeptide to the surface. The PL molecules can be desorbed from the surface by rinsing with a buffer solution at a pH that destroys the ion pairing (pH 12). Measurements of the shift in the SPR angle upon adsorption were used to determine the thicknesses of the adsorbed monolayers; the MUA and PL monolayers were found to be 17.0 and 10.5 A thick, respectively. These thickness results suggest that the poly-L-lysine monolayer adsorbs onto the packed MUA surface in an extended conformation with the PL backbone lying parallel to the surface. Subsequent exposure ofthe PL monolayer to a solution ofiron phthalocyanine tetracarboxylic acid (FePc) resulted in the adsorption of a third layer onto the surface. The ability of the adsorbed PL molecules to interact with FePc indicates the presence of free lysine residues available for interaction with molecules other than the MUA monolayer.

Interaction between poly-L-lysine and synthetic chrysotile asbestos

The adsorption of poly-L-lysine (PLL) on synthetic chrysotile asbestos in aqueous solutions has been studied at 25°C. Adsorbed amount (mg g −1) of randomly coiled PLL (pH 8.5) was independent of its molecular weight (3900–47 000) and of the charge density of PLL and chrysotile. The adsorbed amount of helical PLL at pH 11 was five times more than that of randomly coiled PLL and its adsorbed amount increased with increasing molecular weight of PLL. The adsorbed amount of PLL increased linearly with increasing helix content, irrespective of pH and molecular weight. This suggests that ϵ-amino groups in the side-chains which are free from helical cores may be responsible for PLL adsorption. Nitrogen adsorption on a chrysotile sample with pre-adsorbed PLL at pH 11 indicated that PLL molecules in helical form would be also adsorbed on the inner surface of chrysotile.

Interactions between Oppositely Charged Polypeptides

Conformation-directing interactions between poly(L- or poly(D-glutamic acid)) (PLG or PDG) and poly-L-lysine (PLL) in aqueous media were investigated as functions of pH by using the optical rotatory dispersion and circular dichroism spectroscopies. The results indicate that at pH <4 PLL molecules surround the core of the right-handed α-helix of PLG, and at pH about 7, the polyelectrolyte complex formed may be in a scramble-salt form, whereas at pH >8, complexes of PLG—PLL are in a form close to β-structure. On the other hand, with PDG—PLL systems, in the low pH region, the left-handed α-helical structure of PDG is markedly disrupted by the presence of PLL, and in the high pH region, the complexes may be in a form of a scramble-salt aggregate composed of β-structures.

Thermodynamic parameters of helix-coil transition in polypeptide chains. II. Poly-L-lysine.

AbstractThe helix–coil transitions for poly‐L‐lysine (PL) were investigated by the methods of spectropolarimetry, viscometry and potentiometric titration in 0.2M NaCl at different temperatures as well as in 0.2MNaBr, 1MKCl, and in mixtures of 0.2MNaCl or NaBr with methanol at room temperature. The enthalpy and entropy differences between the helical and coillike states of uncharged PL molecules in 0.2.M NaCl were determined from the potentiometric titration curves. The cooperativity parameters σ for PL in different solvents were determined by two methods (from the sharpness of the transition and from the dependence of the intrinsic viscosity on the helical content in the transition region). In 0.2MNaCl σ has a value of (2.3 ± 0.5) × 10−4 and does not depend on temperature, i.e., the cooperativity of the helix‐coil transition, as for PGA, is mainly of an entropy origin (the initiating of the helical region is accompanied by the entropy decrease ΔSi = −12 eu/mole of helical regions). A comparison of the obtained results for PGA and PL with the molecular theories of the helix‐coil transitions shows that the role of dipole‐dipole interactions of nonneighboring peptide groups is greatly overestimated in these theories, leading to a considerable enthalpy contribution to the free energy of initiating helical regions which is not observed in the experiment.