Interaction of KLAKLAK-NH2 and Analogs with Biomimetic Membrane Models.

BACKGROUND: Specifically designed peptide mimetics offer higher selectivity regarding their toxicity to mammalian cells. In addition to the α-helix conformation, the specific activity is related to the peptide's ability to penetrate the cell membrane. The alterations in lipid membrane properties were addressed in the presence of the peptide KLAKLAK-NH2 and analogs containing ß-alanine, strengthening the antibacterial activity and/or naphtalimide with proven anticancer properties. METHODS: The molecular interactions of the peptide mimetics with POPC bilayers were studied using FTIR-ATR spectroscopy. The thermal shape fluctuation analysis of quasispherical unilamellar vesicles was applied to probe the membrane bending elasticity. The impedance characteristics of bilayer lipid membranes were measured using fast Fourier-transform electrochemical impedance spectroscopy. RESULTS: A lateral peptide association with the membrane is reported for ß-alanine-containing peptides. The most pronounced membrane softening is found for the NphtG-KLßAKLßAK-NH2 analog containing both active groups that corroborate with the indications for 1,8-naphthalimide penetration in the lipid hydrophobic area obtained from the FTIR-ATR spectra analysis. The ß-alanine substitution induces strong membrane-rigidifying properties even at very low concentrations of both ß-alanine-containing peptides. CONCLUSIONS: The reported results are expected to advance the progress in tailoring the pharmacokinetic properties of antimicrobial peptides with strengthened stability towards enzymatic degradation. The investigation of the nonspecific interactions of peptides with model lipid membranes is featured as a useful tool to assess the antitumor and antimicrobial potential of new peptide mimetics.

Valorphins alter physicochemical characteristics of phosphatidylcholine membranes: Datasets on lipid packing, bending rigidity, specific electrical capacitance, dipole potential, vesicle size.

Endogenous hemorphins are being intensively investigated as therapeutic agents in neuropharmacology, and also as biomarkers in mood regulation, inflammation and oncology. The datasets collected herein report physicochemical parameters of 1-palmitoyl-2-oleoyl-sn-glycero-3-phosphocholine membranes in the presence of VV-hemorphin-5 (Val-Val-Tyr-Pro-Trp-Thr-Gln) and analogues, modified at position 1 and 7 by the natural amino acid isoleucine or the non-proteinogenic 2-aminoisobutyric, 2,3-diaminopropanoic or 2,4-diaminobutanoic amino acids. These peptides have been previously screened for nociceptive activity and were chosen accordingly. The present article contains fluorescence spectroscopy data of Laurdan- and di-8-ANEPPS- labelled large unilamellar vesicles (LUV) providing the degree of hydration and dipole potential of lipid bilayers in the presence of VV-hemorphin-5 analogues. Lipid packing is accessible from Laurdan intensity profiles and generalized polarization datasets reported herein. The data presented on fluorescence intensity ratios of di-8-ANEPPS dye provide dipole potential values of phosphatidylcholine-valorphin membranes. Vesicle size and electrophoretic mobility datasets included refer to the effect of valorphins on the size distribution and ζ -potential of POPC LUVs. Investigation of physicochemical properties of peptides such as diffusion coefficients and heterogeneous rate constant relates to elucidation of transport mechanisms in living cells. Voltammetric data of valorphins are presented together with square-wave voltammograms of investigated peptides for calculation of their heterogeneous electron transfer rate constants. Datasets from the thermal shape fluctuation analysis of quasispherical 'giant' unilamellar vesicles (GUV) are provided to quantify the influence of hemorphin incorporation on the membrane bending elasticity. Isothermal titration calorimetric data on the thermodynamics of peptide-lipid interactions and the binding affinity of valorphin analogues to phosphatidylcholine membranes are reported. Data of frequency-dependent deformation of GUVs in alternating electric field are included together with the values of the specific electrical capacitance of POPC-valorphin membranes. The datasets reported in this article can underlie the formulation and implementation of peptide-based strategies in pharmacology and biomedicine.

Interaction of new VV-hemorphin-5 analogues with cell membrane models.

New analogues of the endogenous heptapeptide VV-hemorphin-5 (valorphin) synthesised by amino acid replacement allow for tailoring the peptide activity in vivo. Investigation of hemorphin-induced alterations of lipid bilayers' physicochemical parameters unravels membrane-mediated mechanisms of interaction with cells and subcellular structures. We studied the effect of modified valorphins with nociceptive activity on the structure, mechanical and electrical properties of lipid membrane models. Lower bending rigidity and higher specific capacitance of phosphatidylcholine bilayers were found in the presence of VV-hemorphin-5 analogues. Peptide partition constants for the transfer from the aqueous solution into the membrane were determined by isothermal titration calorimetry. It was found that the inclusion of non-proteinogenic acids with different number of methylene groups lead to alterations of hemorphin-membrane binding. The highest membrane affinity was obtained for a hemorphin derivative with dose-dependent variable effects on visceral nociception in mice. The valorphin analogue with the most pronounced anti-nociceptive effect in vivo induced the highest dipole and zeta potential change without significantly affecting the lipid packing at glycerol level in phosphatidylcholine bilayers.

Dielectric Properties of Phosphatidylcholine Membranes and the Effect of Sugars.

Simple carbohydrates are associated with the enhanced risk of cardiovascular disease and adverse changes in lipoproteins in the organism. Conversely, sugars are known to exert a stabilizing effect on biological membranes, and this effect is widely exploited in medicine and industry for cryopreservation of tissues and materials. In view of elucidating molecular mechanisms involved in the interaction of mono- and disaccharides with biomimetic lipid systems, we study the alteration of dielectric properties, the degree of hydration, and the rotational order parameter and dipole potential of lipid bilayers in the presence of sugars. Frequency-dependent deformation of cell-size unilamellar lipid vesicles in alternating electric fields and fast Fourier transform electrochemical impedance spectroscopy are applied to measure the specific capacitance of phosphatidylcholine lipid bilayers in sucrose, glucose and fructose aqueous solutions. Alteration of membrane specific capacitance is reported in sucrose solutions, while preservation of membrane dielectric properties is established in the presence of glucose and fructose. We address the effect of sugars on the hydration and the rotational order parameter for 1-palmitoyl-2-oleoyl-sn-glycero-3- phosphocholine (POPC) and 1-stearoyl-2-oleoyl-sn-glycero-3- phosphocholine (SOPC). An increased degree of lipid packing is reported in sucrose solutions. The obtained results provide evidence that some small carbohydrates are able to change membrane dielectric properties, structure, and order related to membrane homeostasis. The reported data are also relevant to future developments based on the response of lipid bilayers to external physical stimuli such as electric fields and temperature changes.

Synthesis, characterization and anticonvulsant activity of new azobenzene-containing VV-hemorphin-5 bio photoswitch.

A novel analog of VV-hemorphin-5 containing azobenzene moiety has been synthesized and investigated for anticonvulsant activity in relation to its E → Z photophysical properties activated by long wavelength light at 365 nm. The synthesis was achieved by a modified SPPS by Fmoc-dimerization strategy. The electrochemical behavior before and after UV illumination was investigated using different voltammetric modes. The number of electrons transferred, heterogenic rate constant and diffusion coefficient for E- and Z-isomers were also evaluated. Revealing the governing principles involved in signaling and nerve pulse propagation requires the detailed characterization of the electrical properties of cell membranes. For probing the effect of synthesized azo-peptide on the membrane electrical properties, we measured the specific capacitance of lipid bilayers, representing a basic physical model of biomembranes with their simple reproducibility in laboratory conditions at controlled membrane composition and physicochemical parameters of the surrounding aqueous medium. Our results have shown reduced membrane capacitance in the presence of the azo-peptide, thus providing evidences for possible alterations in the dielectric permittivity of the bilayer. The (Val-Val-Tyr-Pro-Trp-Thr-Gln)2Azo peptide was explored also in vivo for preliminary anticonvulsant activity by using the 6-Hz seizure test and pentylenetetrazol (PTZ) seizure test in mice. The Z-isomer has exhibited higher potency compared to E-isomer most pronouncedly in the 6 Hz test for psychomotor seizures where the compound had activity at all three tested doses. It was found that the Z-isomer decrease the latency for onset of clonic seizures induced by PTZ. These results demonstrate that the Z-isomer deserves further evaluation in other screening tests for anticonvulsant activity.

Electric-field-induced shape transition of nematic tactoids.

The occurrence of new textures of liquid crystals is an important factor in tuning their optical and photonics properties. Here, we show, both experimentally and by numerical computation, that under an electric field chitin tactoids (i.e., nematic droplets) can stretch to aspect ratios of more than 15, leading to a transition from a spindlelike to a cigarlike shape. We argue that the large extensions occur because the elastic contribution to the free energy is dominated by the anchoring. We demonstrate that the elongation involves hydrodynamic flow and is reversible: the tactoids return to their original shapes upon removing the field.

Aging in glassy polymer-liquid-crystal layers.

We present in this Rapid Communication experimental evidence of an acceleration of the zenithal easy-axis dynamics of a nematic liquid crystal (NLC) with the age of a NLC-polymer layer. The comparison with other hard alignment layers strongly indicates that the polymer softness and its ability to reorient in the nematic ordering field is at the origin of the measured dynamics. The unusual acceleration of the dynamics with the polymer age is discussed in terms of this unique coupling with the NLC order. The NLC behaves like a physical plasticizer as a result of the coupling between the NLC and the polymer orders.

Zenithal gliding of the easy axis of a nematic liquid crystal.

We present experimental evidence of zenithal gliding of the nematic easy axis on a polyimide surface. The reorientation dynamics of the easy axis under external torque, and its relaxation, are extremely slow processes which cannot be described by a single exponential time. They show similarities with aging phenomena previously encountered in glassy systems. At last, the adsorption-desorption-readsorption process which empirically justifies the azimuthal easy axis gliding may also explain our observations.