Heterogeneous Membrane Systems Research Articles

Antibacterial activity of the CAP18 peptide against Xanthomonas citri ssp. citri, the causative agent of citrus canker, as evaluated by in vitro and in silico studies

AbstractThe bacterium Xanthomonas citri ssp. citri (Xcc), causing citrus canker disease, poses a severe threat to citrus production worldwide. New approaches for managing the disease are required because of the limited number of bactericides available, reported pathogen resistance to copper pesticides, and the side effects of such compounds on citrus trees and the environment. In this study, the bacterium was isolated from a Mexican lime tree showing typical disease symptoms and identified as Xcc using conventional biochemical tests and specific PCR. The antibacterial activity of the recombinant peptide CAP18 (rCAP18) against the Xcc bacterium was assessed. Measuring the MIC parameter showed that purified rCAP18 caused bacterial growth inhibition by 90% at a concentration of 4.5 μM. Furthermore, a heterogeneous membrane system consisting of POPE:POPG:TOCL (5:1:3) was created using molecular dynamics simulation. The interaction effect of the oligomeric structure of rCAP18 (rCAP18OLIGO) on the components of a lipid bilayer membrane was determined by measuring the membrane thickness, the order parameter of the acyl chains and the area of each phospholipid. The results obtained from simulation and measurement of order parameters showed that, among the three phospholipids, rCAP18OLIGO more affected the orientation of carbon atoms in POPG. Fluctuations of average area per lipid for each phospholipid showed that rCAP18OLIGO had more interactions with POPG > TOCL > POPE, respectively, in the outer half of the membrane. The results obtained from in silico studies confirmed that the penetration of rCAP18OLIGO into the lipid bilayer membrane reduced the membrane thickness and caused its deformation during the simulation time. This mechanism is possibly the leading factor of Xcc growth inhibition by rCAP18 in vitro. Therefore, the rCAP18 peptide as an antibacterial agent can provide a way to develop a new approach to control the citrus canker disease.

Strategies to Improve PFSA Membrane Durability: Benefits and Challenges

The durability of ionomer membranes is an important factor affecting the lifetime of proton exchange membrane fuel cells. Degradation of ionomer membrane causes performance losses that accelerate with time and result in catastrophic MEA failure. Membrane instability has two main origins mechanical fatigue and chemical degradation. Both modes strongly depend on the operating conditions applied: temperature, relative humidity, humidity cycling, reactant pressure, applied voltage and properties of the membrane, mainly the ionomer type and equivalent weight (EW), and membrane thickness. Thin membranes (<<20 µm) with low equivalent weight (<<800 EW) are required to achieve industry targets for FCEV however they are also more prone to undergo accelerated degradation. This work focuses on the development and evaluation of different methods to increase durability through the development of a highly heterogeneous membrane system comprising a reinforcing component, radical scavenger and/or hydrogen peroxide decomposition catalyst and in which the architecture of the membrane is designed at the nano- to micro-metric length scales, the latter facilitated by the use of solution casting processes. Electrospun nanofibres provide mechanical strength, ensure low membrane swelling when exposed to humidity cycles, and also provide an appropriate distribution medium for radical scavenging species. This presentation will discuss benefits and remaining challenges associated with efficiency and stability of mechanical and chemical reinforcements. Acknowledgement: This project has received funding from the Fuel Cells and Hydrogen 2 Joint Undertaking under grant agreement No 671465 VOLUMETRIQ. This Joint Undertaking receives support from the European Union’s Horizon 2020 research and innovation programme.

Localization of amyloid beta (Aβ1-42) protofibrils in membrane lateral compartments: Effect of cholesterol and 7-Ketocholesterol

Cholesterol plays an important role in the interaction of Alzheimer’s amyloid beta (Aβ) with cell membranes, an important event in Aβ-induced cytotoxicity. However, it is not fully understood how cholesterol influences the association of Aβ with membrane lateral compartments. We have shown that by modulating membrane fluidity, cholesterol decreased peptide localization in solid-ordered domains and increased that in liquid-ordered domains. It changed the amount of Aβ associating with liquid-disordered (Ld) phase with different tendencies depending on the composition of heterogeneous membrane systems. 7-Ketocholesterol, an oxidized derivative of cholesterol, majorly enhanced the fluidity of and Aβ interaction with Ld phase. These findings are useful for clarifying the impact of cholesterol and its oxidation in Aβ-induced toxicity.

Comparative Antioxidant Properties of Some Gabaergic Phenols and Related Compounds, Determined for Homogeneous and Membrane Systems

Some phenols, like propofol, thymol and related compounds, have been shown to act on the GABA(A) receptor. Several compounds with GABAergic activity have displayed neuroprotective effects attributed mainly to the potentiation of GABA(A)-mediated inhibition of synaptic transmission. It has also been found that compounds containing a phenolic OH group can scavenge reactive oxygen species, as in the case of propofol, among others. Thus, the neuroprotective action mechanism of GABAergic phenols would involve both effects, their pharmacological activity on GABA(A) and their intrinsic antioxidant ability. In this context, the study of the antioxidant properties of phenolic compounds included in the present work will enable these capacities to be correlated with their eventual pharmacological activities. The assays chosen in this study included determination of antioxidant ability in homogeneous isotropic systems (DPPH reduction, FRAP and hydrogen peroxide scavenging) and in heterogeneous membrane systems (inhibition of lipid peroxidation of phospholipid SUVs). The comparative evaluation of the results showed some differences between the relative order of antioxidant potency among all assayed compounds determined by using both types of systems. This analysis supports the conclusion that the antioxidant values obtained in homogeneous non-membrane systems, for phenols or other lipophilic compounds, should be revised according to their capacity of interaction with membranes (i.e. Log P in membrane-buffer system) in order to obtain antioxidant potency values more approximate to those actually occurring in biological systems. These results are essential to understand the actual neuroprotective action mechanism exerted by phenolic compounds involving a pharmacological activity, an antioxidant effect or both actions exerted mutually.

Grape Berry Vacuole: A Complex and Heterogeneous Membrane System Specialized in the Accumulation of Solutes

Vacuoles fulfill highly specialized functions depending on cell type and tissue and plant developmental stage. This complex and dynamic organelle is the main reservoir of grape berry cells, playing a major role during fruit development and ripening. Berry development is accompanied by modifications in size, composition, color, texture, flavor, and pathogen susceptibility, primarily because of changes in vacuolar content. Most aroma and flavor compounds are not evenly distributed in the berry, and the number and type of vacuoles may vary depending on the tissue (skin, flesh, and seeds). Together with the lytic and protein storage vacuoles widely distributed in plant cells, phenolic vacuoles are also implicated in cellular storage in grape cells. After veraison, when grape berry growth exclusively results from cell enlargement, tonoplast transporter proteins mediate a massive sugar import and water intake into the vacuole, leading to a large vacuolar expansion. The V-ATPase and V-PPase pumps create a proton electrochemical gradient across the tonoplast, which, in turn, energizes the uptake of charged and uncharged solutes. Several tonoplast proteins mediating the uptake of sugars, organic acids, water, ions, and anthocyanins have been cloned and some have been functionally characterized. The present review focuses on the storage function of vacuoles and on their structure and diversity in relation to development and ripening of the grape berry.

Membrane microheterogeneity: Förster resonance energy transfer characterization of lateral membrane domains

Lateral membrane heterogeneity, in the form of lipid rafts and microdomains, is currently implicated in cell processes including signal transduction, endocytosis, and cholesterol trafficking. Various biophysical techniques have been used to detect and characterize lateral membrane domains. Among these, Förster resonance energy transfer (FRET) has the crucial advantage of being sensitive to domain sizes smaller than 50-100 nm, below the resolution of optical microscopy but, apparently, similar to those of rafts in cell membranes. In the last decade, several formalisms for the analysis of FRET in heterogeneous membrane systems have been derived and applied to the study of microdomains. They are critically described and illustrated here.

Oxidation of liposomal membrane suppressed by flavonoids: Quantitative structure–activity relationship

Antioxidant activity of the set of 12 flavonoids in heterogeneous membrane system of dioleoyl phosphatidylcholine liposomes stressed by peroxidative damage induced by 2,2′-azobis-(2-amidinopropane)hydrochloride azoiniciator and evaluated by the thiocyanate method was assessed. Antioxidant activity (pIC 50) was correlated with 19 molecule parameters calculated for the minimum energy conformers of the compounds tested. The linear regression analysis revealed that the parameter of hydration energy E HYDR ( R = −0.747) was the best predictor of antioxidant activity in a liposomal system.

Antiradical and antioxidant activities of alkaloids isolated from Mahonia aquifolium. Structural aspects

The antioxidant activities of three alkaloids isolated from Mahonia aquifolium––berberine, jatrorrhizine, and magnoflorine––were studied with respect to their structural aspects, particularly the presence and the position of –OH groups, steric conditions of unpaired electron delocalization and parameters of lipophilicity and hydration energy. The antiradical activities of the compounds tested were evaluated as the reactivities toward free stable α,α′-diphenyl-β-picrylhydrazyl radical (DPPH). The antioxidant features of the alkaloids tested were investigated in heterogeneous membrane system of DOPC liposomes stressed by peroxidative damage induced by AAPH azoinitiator. Both alkaloids bearing free phenolic groups––jatrorrhizine and magnoflorine––showed better activities in both systems used than berberine not bearing any readily abstractable hydrogen on its skeleton. The former two showed antiperoxidative efficiency in DOPC liposomal membrane comparable to that of an effective scavenger of peroxyl radicals––stobadine–and higher than that of Trolox. We conclude that the favorable antioxidant features of the hydroxylated alkaloids are most probably ensured by the combination of reasonably high antiradical reactivity with high lipophilicity, however, the solvation process was found to markedly interfere with these beneficial effects.

Nonisothermal matter transport in sodium chloride and potassium chloride aqueous solutions. 2. Heterogeneous membrane system (thermodialysis)

Nonisothermal membrane transport has been experimentally studied in the system sodium chloride and potassium chloride aqueous solutions/AP-20 Millipore porous partition. Anomalous behavior is found in both solvent and solute fluxes. The concentration dependence of these fluxes exhibits sharp minima and maxima, respectively. The anomalous regions occur in concentration ranges strongly influenced by the nature of the cation and by (average) temperature. When these results are compiled with the ones relative to thermal diffusion in the same solutions, stringent proof of the close affinity of processes of heat-flux-mediated matter transport in homogeneous and nonhomogeneous (membrane) systems is obtained. The physical cause of the observed anomalies can be tentatively imputed to solute-solvent interactions and to their dependence on solute nature and concentration and on solution temperature. 8 figures, 1 table.