Outer Membrane Surface Research Articles

Acinetobacter baumannii Can Survive with an Outer Membrane Lacking Lipooligosaccharide Due to Structural Support from Elongasome Peptidoglycan Synthesis.

ABSTRACTGram-negative bacteria resist external stresses due to cell envelope rigidity, which is provided by two membranes and a peptidoglycan layer. The outer membrane (OM) surface contains lipopolysaccharide (LPS; contains O-antigen) or lipooligosaccharide (LOS). LPS/LOS are essential in most Gram-negative bacteria and may contribute to cellular rigidity. Acinetobacter baumannii is a useful tool for testing these hypotheses as it can survive without LOS. Previously, our group found that strains with naturally high levels of penicillin binding protein 1A (PBP1A) could not become LOS deficient unless the gene encoding it was deleted, highlighting the relevance of peptidoglycan biosynthesis and suggesting that high PBP1A levels were toxic during LOS deficiency. Transposon sequencing and follow-up analysis found that axial peptidoglycan synthesis by the elongasome and a peptidoglycan recycling enzyme, ElsL, were vital in LOS-deficient cells. The toxicity of high PBP1A levels during LOS deficiency was clarified to be due to a negative impact on elongasome function. Our data suggest that during LOS deficiency, the strength of the peptidoglycan specifically imparted by elongasome synthesis becomes essential, supporting that the OM and peptidoglycan contribute to cell rigidity.

In situ formation of tannic (TA)-aminopropyltriethoxysilane (APTES) nanospheres on inner and outer surface of polypropylene membrane toward enhanced dye removal capacity

Tannic acid (TA) − 3-aminopropyltriethoxysilane (APTES) coating (TA-APTES coating) composed of abundant nanospheres with secondary reaction sites has many distinct advantages for surface modification. Herein, an in-situ growth method is proposed to generate TA-APTES nanospheres on both the outer and inner surface of polypropylene (PP) membrane. Compared with previous reported TA-APTES nano spheres coating just on the outer surface of the membrane (named PP-Su-NPs), TA-APTES nano spheres on both outer and inner surfaces prepared with this method (named PP-En-NPs) exhibits much better functional performance after secondary reactions. As a proof of concept, the TA-APTES nanospheres is functionalized by tannic acid, polyethyleneimine (PEI) and Fe3+ to carry positive charges for absorbing anionic dyes, and the dye adsorption performance of the PP-En-NPs after the secondary reactions is 7–8 times higher than that of PP-Su-NPs. Interestingly, the functionalized coating can not only absorb anionic dyes, but also cationic dyes, and selective desorption is also realized for this functionalized coating. The possible mechanism is revealed in this study. This study will accelerate the development of the TA-APTES coating, and make it become a powerful tool for membrane modification.

Preparation of electrically enhanced forward osmosis (FO) membrane by two-dimensional MXenes for organic fouling mitigation

In this work, a conductive thin film composite forward osmosis (TFC-FO) membrane was firstly prepared via vacuum filtering MXenes nanolayer on the outer surface of polyethersulfone membrane followed by interfacial polymerization in the other side. Moreover, its feasibility of mitigating organic fouling under electric field was evaluated. Results indicated that the addition of MXenes greatly reduced the electric resistance of membrane from 2.1 × 1012 Ω to 46.8 Ω, enhanced the membrane porosity and promoted the membrane performance in terms of the ratio of water flux to reverse salt flux. The modified TFC-FO membrane presented the optimal performance with 0.47 g/m2 loading amount of MXenes. Organic fouling experiments using sodium alginate (SA) and bovine serum albumin (BSA) as representative demonstrated that the introduction of MXenes could effectively enhance the anti-fouling ability of TFC-FO membrane under the electric field of 2 V. The interelectron repulsion hindered organic foulants attaching into membrane surface and thus effectively alleviated the membrane fouling. More importantly, the modified TFC-FO membrane showed good stability during the fouling experiment of 10 h. In all, our work proved that introducing MXenes into the porous layer of support is feasible to alleviate organic fouling of FO membrane.

TIO2-ENABLED POLYVYNYLIDENE FLUORIDE FOR PALM OIL MILL EFFLUENT TREATMENT: EFFECTS OF MEMBRANE MORPHOLOGY AND AERATION ON FLUX AND SUSPENDED SOLID REMOVAL

A polyvinylidene fluoride-based mixed matrix membrane (PVDF- MMM) has been developed to treat palm oil mill effluent (POME). The addition of TiO2 into PVDF membrane was conducted. Hollow fibers were spun from a dope solution containing PVDF/PVP 30K/DMAc/additives by using a dry-jet wet spinning process at different air gaps. AFM image demonstrated that wet spun hollow fiber had a rougher outer surface than that of dry-jet wet spun fibers and exhibited symmetric cross-section structure. Experimental results showed that hydrophilicity of membranes increased with adding of TiO2 particles and the varied air gap length influenced the characteristic of membrane pore size and outer membrane surface roughness. In addition, aeration could increase the turbulence and flux and reduce membrane fouling. The values of flux and suspended solids removal were 92.04 L/m2.hr and 94.86 %, respectively, with the varied aeration flow rate of 2.0, 3.0 and 4.0 mL/min and bubble size distribution of 4.0 µm. Overall, this study has proven that PVDF-based MMM could achieve expected performance for POME treatment.

Turn-folded magainin lipopeptide analog induces cytoplasmic vacuoles in MDA-MB-231 cells through G2-phase arrest

Selective induced non-canonical programmed deaths in the lipid raft type 1-enriched MDA-MB-231 is a promising treatment approach. Cationic amphiphilic peptides conjugated to relatively long fatty acyl chains that tend to self-aggregate are prone to upregulate necroptotic and paraptotic signaling. We investigated the toxic effects of an N-terminally palmitoylated magainin derivate (P1MK5E) in the MDA-MB-231 cells in relation to its structure at molecular level. The modeling showed that the palmitoylation reinforces a turn-like structural motif in the lipopeptide which is likely required for its activity. P1MK5E triggered intracellular generation of reactive oxygen species (ROS), G2-phase arrest, mitochondrial membrane potential (ΔΨmt) disturbance and presumable flopping of phosphatidylserine (PtdSer) to the cancer cell membrane outer surface in a comparable manner to doxorubicin (DOX) that induces apoptotic signaling. Despite forming extensive congregates of different sizes at the cell surface, P1MK5E had little impacts on the MDA-MB-231 membrane integrity. The cell death upon exposure to the lipopeptide was, however, caspase 3 independent and characterized by cytoplasmic vacuolation and no distinct nuclear fragmentation that is to be privileged in the treatment of apoptotic resistance pathways in triple-negative breast cancers (TNBCs).

Genetic, cellular, and structural characterization of the membrane potential-dependent cell-penetrating peptide translocation pore.

Cell-penetrating peptides (CPPs) allow intracellular delivery of bioactive cargo molecules. The mechanisms allowing CPPs to enter cells are ill-defined. Using a CRISPR/Cas9-based screening, we discovered that KCNQ5, KCNN4, and KCNK5 potassium channels positively modulate cationic CPP direct translocation into cells by decreasing the transmembrane potential (Vm). These findings provide the first unbiased genetic validation of the role of Vm in CPP translocation in cells. In silico modeling and live cell experiments indicate that CPPs, by bringing positive charges on the outer surface of the plasma membrane, decrease the Vm to very low values (-150 mV or less), a situation we have coined megapolarization that then triggers formation of water pores used by CPPs to enter cells. Megapolarization lowers the free energy barrier associated with CPP membrane translocation. Using dyes of varying dimensions in CPP co-entry experiments, the diameter of the water pores in living cells was estimated to be 2 (-5) nm, in accordance with the structural characteristics of the pores predicted by in silico modeling. Pharmacological manipulation to lower transmembrane potential boosted CPP cellular internalization in zebrafish and mouse models. Besides identifying the first proteins that regulate CPP translocation, this work characterized key mechanistic steps used by CPPs to cross cellular membranes. This opens the ground for strategies aimed at improving the ability of cells to capture CPP-linked cargos in vitro and in vivo.

Hydrophilic carbon nanotube membrane enhanced interfacial evaporation for desalination

Carbon nanotube-based (CNT-based) interfacial evaporation material is one of the most potential materials for solar desalination. Here, we studied the evaporation rate of the CNT-based membranes with different hydrophilic and hydrophobic chemical modified surfaces using molecular dynamic simulations. We found that the hydrogen bonding density among water molecules at the interface is a key factor in enhancing the evaporation rate. For a hydrophilic CNT-based membrane, the strong interactions between the membrane outer surface and the water molecules can destroy the water-water hydrogen bonding interactions at the interface, resulting in the reduction of the hydrogen bonding density, leading to an enhancement effect in evaporation rate. We also found that there is an optimal thickness for evaporation membrane. These findings could provide some theoretical guidance for designing and exploring advanced CNT-based systems with more beneficial performance in water desalination.

Mechanism of LolCDE as a molecular extruder of bacterial triacylated lipoproteins

Lipoproteins are important for bacterial growth and antibiotic resistance. These proteins use lipid acyl chains attached to the N-terminal cysteine residue to anchor on the outer surface of cytoplasmic membrane. In Gram-negative bacteria, many lipoproteins are transported to the outer membrane (OM), a process dependent on the ATP-binding cassette (ABC) transporter LolCDE which extracts the OM-targeted lipoproteins from the cytoplasmic membrane. Lipid-anchored proteins pose a unique challenge for transport machinery as they have both hydrophobic lipid moieties and soluble protein component, and the underlying mechanism is poorly understood. Here we determined the cryo-EM structures of nanodisc-embedded LolCDE in the nucleotide-free and nucleotide-bound states at 3.8-Å and 3.5-Å resolution, respectively. The structural analyses, together with biochemical and mutagenesis studies, uncover how LolCDE recognizes its substrate by interacting with the lipid and N-terminal peptide moieties of the lipoprotein, and identify the amide-linked acyl chain as the key element for LolCDE interaction. Upon nucleotide binding, the transmembrane helices and the periplasmic domains of LolCDE undergo large-scale, asymmetric movements, resulting in extrusion of the captured lipoprotein. Comparison of LolCDE and MacB reveals the conserved mechanism of type VII ABC transporters and emphasizes the unique properties of LolCDE as a molecule extruder of triacylated lipoproteins.

Modification of PVDF hollow fiber membrane by co-deposition of PDA/MPC-co-AEMA for membrane distillation application with anti-fouling and anti-scaling properties

In this study, a self-prepared polyvinylidene fluoride (PVDF) hollow fiber membrane with a hierarchical structure was used for facile modification by co-deposition of polydopamine (PDA) and poly(MPC-co-2-aminoethyl methacrylate hydrochloride) (MPC-co-AEMA) for application in direct contact membrane distillation (DCMD). The facile formation of the PDA/MPC-co-AEMA layer on the membrane outer surface drastically changed the chemical and physical properties of the membrane surface. Although the membrane became hydrophilic and smooth with a low porosity and small pore size, the bulk structure of the membrane remained almost intact. For a saline solution including protein and Ca2+ as organic fouling and scaling agents, the deposition of the hydrophilic PDA/MPC-co-AEMA layer on hydrophobic PVDF led to the alleviation of the membrane fouling and scaling during long-term DCMD application. Whereas the formation of a hydrated layer on the membrane surface avoided BSA fouling by avoiding hydrophobic–hydrophobic interactions, a combination of several chemo-physical properties of the modified membrane surface resulted in anti-scaling properties.

MEMBRANES FUNCTIONALIZED WITH 1d, 2d and 3d CARBON MATERIALS

Modification of polymer and ceramic mem­branes by modern one-, two- and three- di­men­sional carbon nanomaterials (carbon nano­tubes, fullerenes and their derivatives, oxi­dized and reduced graphene) is consi­dered. It is shown that carbon materials can be incorporated into membrane matrices both as independent components and as a part of multicomponent modifier. The main methods of modification are the addition of modifiers to the polymer solution with subsequent making of polymer membranes, incorporation of nanoparticles of carbon nanomaterials into the pristine membranes, deposition on the outer membrane surface, formation of nanoparticles directly in the pores of the ceramic matrix. Composite membranes containing carbon nanoparticles are used for pervaporation, gas separation, baromembrane processes and low-temperature fuel cells. The addition of carbon nanomaterials to polymers provides better mechanical strength of the membranes. Hydrophilic carbon modifiers increase the resistance of membranes to fouling by organic substan­ces and biofouling, improves their separation ability. Ion-exchange membranes modified with fullerenol and oxidized graphene maintain high proton conductivity at elevated temperatures and low humidity. Сarbon additives increase membrane productivity in baromembrane processes. This effect is especially evident for materials modified with nanotubes: their smooth surface ensures fast liquid transport. These carbon nanomaterials are characterized by antibacterial activity. Composites consisting of nanotubes and an ion-exchange biopolymer, and composites with oxidized graphene and inorganic ion exchanger, give to membranes selectivity to inorganic ions. Ceramic membranes modified with carbon nanoparticles that were formed in the pores of matrices by carbonization of synthetic polymers and polysaccharides have the same properties. Besides, these composites reject organic dyes too. The separating ability of composite membranes ocuures due to both dimensional and charge effects. Carbon or composite nano­particles block the pores of the membranes. The pores formed by the modifier prevent pene­tration of large particles of organic substances, for example, protein macromolecules. The charge effect is realized due to the functional groups of the modifier. For membranes modified with fullerenols, the retaining of low molecular weight organic substances occurs due to adsorption. Fullerene-modified gas sepa­ration and pervaporation membranes show increased permeability and selectivity.

Remote Performance Modulation of Ultrafiltration Membranes by Magnetically and Thermally Responsive Polymer Chains.

Ultrafiltration membranes, that respond to an external magnetic field and local temperature have been developed. Surface-initiated activator-generated electron transfer (AGET) atom transfer radical polymerization (ATRP) has been used to graft poly(N-isopropylacrylamide) (PNIPAm) from the surface of 300 kDa regenerated cellulose membranes. The polymerization initiator was selectively attached to the entire membrane surface, only the outer membrane surface or only the inner pore surface. A superparamagnetic nanoparticle was attached to the end of the polymer chain. The DI water flux as well as the flux and rejection of bovine serum albumin were investigated in the absence and presence of a 20 and 1000 Hz oscillating magnetic field. In an oscillating magnetic field, the tethered superparamagnetic nanoparticles can cause movement of the PNIPAm chains or induce heating. A 20 Hz magnetic field maximizes movement of the chains. A 1000 Hz magnetic field leads to greater induced heating. PNIPAm displays a lower critical solution temperature at 32 °C. Heating leads to collapse of the PNIPAm chains above their Lower Critical Solution Temperature (LCST). This work highlights the versatility of selectively grafting polymer chains containing a superparamagnetic nanoparticle from specific membrane locations. Depending on the frequency of the oscillating external magnetic field, membrane properties may be tuned.

Determination of Blood Parameters using Scanning Electron Microscopy as a Prototype Model for Evaluating the Effectiveness of Radiation Therapy for Cervical Cancer

Using the method of SEM in patients with cervical cancer (CC) during radiation therapy (RT) revealed differences in the size and morphology of nanoparticles (NP) localized on the outer surface of the erythrocyte membrane. We found that NP-V (“viruses”) objects localized on the surface of the erythrocyte membrane of CC patients before RT have more distinct contours and are smaller in comparison with the number of NP-EV (extracellular vesicles) arising during RT. Our previous study showed that NP-V objects are evenly distributed not only on the surface of erythrocytes but also in blood plasma, and that during the RT the amount of NP-V decreases, while NP-EV both increases and decreases. The linear size of the NP-EV is characterized by a Gaussian distribution, while the NP-V has a normal size distribution in certain ranges with different mean values. We found that the number of NP-Vs having different linear dimensions differ significantly. Using X-ray radiation, we established characteristic elemental composition of NP. The PCR method was used to determine the HPV DNA in blood samples from CC patients. The revealed differences in the morphology and composition of NP, as well as the data of PCR analysis, possibly indicate their different nature and can be used as a criterion for assessing the effectiveness of RT and the recovery period.

Effect of LED Lighting on Morphogenesis and Content of Ascorbic Acid, P, K, and Ca in Eruca sativa Plants

The effect of light emitting diode (LED) light sources with different spectra on Eruca sativa Mill., cv. Dikovina plant development was investigated. Experiments were conducted with four types of LED lamps of our own assembly: solar box (SB), red-green-blue (RGB), red-blue (FS), and warm white (WW) used as a control with an energy ratio in the blue-green-red range of 14% : 48% : 38%. Spectra of SB (26% : 41% : 33%), RGB (32% : 19% : 49%), and FS (27% : 11% : 62%) lamps were used to obtain nine different types of lighting ensuring modification of spectra in the course of growing. The plants exposed to FS-RGB, SB-FS, and RGB-SB light sources were characterized with the greatest values of the shoot fresh weight. Transfer of plants to SB resulted in a decrease in development of the plants root system. Transformation of leaf mesostructure after transfer to SB showed that light conditions therein promoted the formation of leaf structure with lower membrane indexes and deformed mesophyll cells. At the same time, cultivation of plants for 2 weeks in SB with subsequent transfer to FS for 4 more weeks stimulated development of internal assimilatory surface of the leaf with the greatest integral indexes of the outer membrane surface of leaf cells (Ames/A) and chloroplasts (Achl/A) as compared with other treatments. As a result, SB-FS plants produced maximal dry shoots and roots biomass. Without alteration of the lighting pattern, plants from box FS were inferior to control plants (module WW) in parameters of leaf mesostructure and ranked second among other types of treatment. The greatest accumulation of P and Ca was observed in FS-RGB where a maximal percentage of shoots and roots dry matter and the greatest concentration of ascorbic acid were found. Transfer of plants from other boxes to FS caused a decrease in accumulation of macroelements in E. sativa plants. Thus, the dynamic lighting applied for growing of E. sativa plants affected their characteristics and could be used for optimization of plant cultivation.

Symbiont Transmission onto the Cell Surface of Early Oocytes in the Deep-Sea Clam Phreagena okutanii.

Symbiotic associations with beneficial microorganisms endow a variety of host animals with adaptability to the environment. Stable transmission of symbionts across host generations is a key event in the maintenance of symbiotic associations through evolutionary time. However, our understanding of the mechanisms of symbiont transmission remains fragmentary. The deep-sea clam Phreagena okutanii harbors chemoautotrophic intracellular symbiotic bacteria in gill epithelial cells, and depends on these symbionts for nutrition. In this study, we focused on the association of these maternally transmitted symbionts with ovarian germ cells in juvenile female clams. First, we established a sex identification method for small P. okutanii individuals, and morphologically classified female germ cells observed in the ovary. Then, we investigated the association of the endosymbiotic bacteria with germ cells. We found that the symbionts were localized on the outer surface of the cell membrane of primary oocytes and not within the cluster of oogonia. Based on our findings, we discuss the processes and mechanisms of symbiont vertical transmission in P. okutanii.

Highly Rectifying Fluidic Diodes Based on Asymmetric Layer-by-Layer Nanofilms on Nanochannel Membranes.

Nanochannel-based fluidic diodes display ion selectivity and ion current rectification (ICR), which may prove to be important in energy-harvesting devices and biosensors. This paper reports asymmetric functionalization of the outer surface of a flexible nanochannel polymer membrane to create fluidic diodes that give ICR. Layer-by-layer (LbL) adsorption with cross-linking of only the underlying part of the polyelectrolyte nanofilm leads to a porosity step across the film. The combination of a high effective surface charge density and the porosity step in the film leads to a remarkable maximum ICR factor of ∼200 with a pH gradient across the film. Incorporation of pH-sensitive polyelectrolyte components enables the ICR factor to increase an order of magnitude on going from pH 8 to pH 3. Moreover, the coated membrane shows excellent anion selectivity. Thus, LbL adsorption with partial cross-linking provides a simple method for creating coated nanochannel membranes that serve as pH-responsive ionic diodes for potential chemical/biosensors.

Bexarotene inhibits cell proliferation by inducing oxidative stress, DNA damage and apoptosis via PPARγ/ NF-κB signaling pathway in C6 glioma cells.

Gliomas are one of the most aggressive brain tumors with a poor prognosis in the central nervous system. Bexarotene is a third-generation retinoid X receptor agonist that is promising in the treatment of both cancer and neurodegenerative diseases. In this study, we aimed to investigate the cytotoxic and anti-proliferative effects of bexarotene in C6 glioma cells through the PPARγ/NF-κB pathway. In the study, first cytotoxic bexarotene concentrations for C6 cells were detected, and then apoptosis profile, reactive oxygen species (ROS), total antioxidant (TAS), 8-hydroxy-2'-deoxyguanosine (8-OHdG) and nuclear factor-κB (NF-κB) levels in the cells were determined. In addition, peroxisome proliferator-activated receptor γ (PPARγ) mRNA expression analysis was carried out. As a result, we detected concentration- and time-dependent antiproliferative effects of bexarotene on C6 cells. We found that bexarotene treatment decreased NF-κB and TAS levels and increased PPARγ and 8-OHdG levels in C6 cells. Bexarotene enhanced PPARγ expression in a dose-dependent manner when compared to the control group (P < 0.01). Furthermore, we determined that bexarotene-induced apoptotic C6 cells enhanced through Annexin V-FITC/PI staining and caspase-3/-7 activation analyses since phosphatidylserine level on the outer surface of the cell membrane and caspase-3/-7 activities were increased in the cells treated with bexarotene. In conclusion, bexarotene treatment in C6 glioma cells could modulate apoptosis profile, DNA damage, ROS production, and reduction of TAS levels through inhibition of NF-κB by enhancing PPARγ expression.

Surface Modification of Polytetrafluoroethylene Hollow Fiber Membrane for Direct Contact Membrane Distillation through Low-Density Polyethylene Solution Coating.

Membrane distillation (MD) is an attractive technology for the separation of highly saline water used with a polytetrafluoroethylene (PTFE) hollow fiber (HF) membrane. A hydrophobic coating of low-density polyethylene (LDPE) coats the outer surface of the PTFE membrane to resolve membrane wetting as well as increase membrane permeability flux and salt rejection, a critical problem regarding the MD process. LDPE concentrations in coating solution have been studied and optimized. Consequently, the LDPE layer altered membrane morphology by forming a fine nanostructure on the membrane surface that created a hydrophobic layer, a high roughness of membrane, and a uniform LDPE network. The membrane coated with different concentrations of LDPE exhibited high water contact angles of 135.14 ± 0.24 and 138.08 ± 0.01° for membranes M-3 and M-4, respectively, compared to the pristine membrane. In addition, the liquid entry pressure values of LDPE-incorporated PTFE HF membranes (M-1 to M-5) were higher than that of the uncoated membrane (M-0) with a small decrease in the percentage of porosity. The M-3 and M-4 membranes demonstrated higher flux values of 4.12 and 3.3 L m–2 h–1 at 70 °C, respectively. On the other hand, the water permeation flux of 1.95 L m–2 h–1 for M-5 further decreased when LDPE concentration is increased.

Binding, Unbinding and Aggregation of Crescent-Shaped Particles on Tubular Membranes

The binding of crescent-shaped nanoparticles (CNPs) on nanoscale tubular membranes is investigated through systematic coarse-grained molecular dynamics simulations of an implicit-solvent model. The CNPs adhere through their concave side to the outer surface of the tubular membrane. The binding/unbinding transitions are found to be irreversible, with the threshold binding energy, Eb, being higher than that of the unbinding threshold, Eu. Furthermore, the difference Eb-Eu increases with increasing either the CNP’s arclength, Lnp, or curvature mismatch, m=Rt/Rnp, where Rnp is the CNP’s radius of curvature and Rt is the tube’s radius. We also investigated the arrangement of a CNP on the tube and found that for m smaller than a Lnp-dependent m∗, the CNP lies perpendicularly to the tubule. However, for m<m∗<1, the CNP is tilted with respect to the tubule’s axis, with the tilt angle that increases with decreasing m. for m>1 (or m<m) and high Lnp, the NPs self-assemble into chains.

CHARMM-GUI Supports Hydrogen Mass Repartitioning and Different Protonation States of Phosphates in Lipopolysaccharides.

Hydrogen mass repartitioning (HMR) that permits time steps of all-atom molecular dynamics simulation up to 4 fs by increasing the mass of hydrogen atoms has been used in protein and phospholipid bilayers simulations to improve conformational sampling. Molecular simulation input generation via CHARMM-GUI now supports HMR for diverse simulation programs. In addition, considering ambiguous pH at the bacterial outer membrane surface, different protonation states, either -2e or -1e, of phosphate groups in lipopolysaccharides (LPS) are also supported in CHARMM-GUI LPS Modeler. To examine the robustness of HMR and the influence of protonation states of phosphate groups on LPS bilayer properties, eight different LPS-type all-atom systems with two phosphate protonation states are modeled and simulated utilizing both OpenMM 2-fs (standard) and 4-fs (HMR) schemes. Consistency in the conformational space sampled by standard and HMR simulations shows the reliability of HMR even in LPS, one of the most complex biomolecules. For systems with different protonation states, similar conformations are sampled with a PO41- or PO42- group, but different phosphate protonation states make slight impacts on lipid packing and conformational properties of LPS acyl chains. Systems with PO41- have a slightly smaller area per lipid and thus slightly more ordered lipid A acyl chains compared to those with PO42-, due to more electrostatic repulsion between PO42- even with neutralizing Ca2+ ions. HMR and different protonation states of phosphates of LPS available in CHARMM-GUI are expected to be useful for further investigations of biological systems of diverse origin.

Activation of Nanocomposite Liposomal Capsules in a Conductive Water Medium by Ultra-Short Electric Exposure

In a system that simulates aquatic biological media, the possibility of activating nanocomposite liposomal capsules (NLCs) containing spherical electrically conductive nanoparticles on the outer and inner surfaces of the liposomal membrane, using an external ultrashort electric action, has been shown. The decapsulation effect was registrated by fluorimetry methods. The key role of conducting nanoparticles in increasing the sensitivity of NLCs to external ultrashort electrical impact is shown. A theoretical model of nonthermal interaction of NLCs with ultrashort electric pulses is constructed, within the frame of which an expression is obtained for the critical value of the electric field strength, which determines the threshold for the appearance of the decapsulation effect in a conducting medium. The described mechanism of decapsulation explains the selective nature of ultrashort pulsed electrical impact on the NLCs.