Characterization Of Plasma Membrane Research Articles

Engineered surface design of recognition site-ordered biomimetic sensor for efficient detection of circulating tumor cells

The oriented assembly of cell membrane coating plays an important role in advancing the application of this strategy in biomedical fields, particularly in detecting circulating tumor cells (CTCs). Unfortunately, there is a formidable challenge in achieving effective membrane orientation during the coating process owing to the asymmetric properties of cell membranes. Herein, magnetic vesicles released by tumor cells were designed to break down these barriers in the same way that microvesicles are actively secreted from cells, which completely inherited the orientation and characteristics of the parent cell membranes, exhibiting a satisfactory self-targeting ability for homologous cells. To cope with the complex application environment, spatially ordered aptamers were integrated into magnetic vesicles and combined with catalytic hairpin assembly (CHA) technology to construct a recognition site-ordered biomimetic sensor for high-performance detection of CTCs. In this strategy, the ordered arrangement of membrane proteins and aptamers markedly improved capture efficiency of traditional biomimetic strategy for CTCs. Additionally, CHA-induced fluorescence and colorimetric analysis ensured the detection accuracy and sensitivity, with a linear range of 0 to 104 cells mL−1 and a low detection limit of 3 cells mL−1 for fluorometry and 6 cells mL−1 for colorimetry. Overall, the biomimetic sensor offered broader possibilities for detecting rare CTCs and provided new insight to expand the application of cell membrane biomimetic strategies in biomedicine.

Serum lipidomic profiling of dairy calves fed milk replacers containing animal or vegetable fats

Vegetable fat blends are commonly used as fat sources in milk replacers (MR) for calves, but their composition differs considerably from that of bovine milk fat. The aim of this study was to investigate the serum lipid profile of preweaning calves fed twice-daily MR containing 30% fat (% DM). Upon arrival, 30 male Holstein-Friesian calves (BW = 45.6 ± 4.0 kg, age = 2.29 ± 0.8 d) were randomly assigned to 2 experimental diets (n = 15 per treatment): one MR was derived from either vegetable fats (VG; 65% rapeseed and 35% coconut fats) or animal fats (AN; 65% packers lard and 35% dairy cream). The 2 MR formulas contained 30% fat, 24% CP, and 36% lactose. Calves were housed indoors in individual pens with ad libitum access to chopped straw and water. Daily milk allowances were 6.0 L from d 1 to 5, 7.0 L from d 6 to 9, and 8.0 L from d 10 to 35, divided into 2 equal meals and prepared at 13.5% solids. An untargeted liquid chromatography-quadrupole time-of-flight mass spectrometry (LC-QTOF-MS) method was employed to analyze the lipid profiles in the serum of calves sampled from the jugular vein at 35 d of age. In total, 594 lipids were characterized, comprising 25 different lipid classes. Principal component analysis (PCA) showed significant separation between VG and AN, indicating different lipid profiles in the serum. An orthogonal partial least squares discriminant analysis (OPLS-DA) classification model was used to further validate the distinction between the 2 treatment groups. The model exhibited a robust class separation and high predictive accuracy. Using a volcano plot (fold change threshold ≥1.5 and false discovery rate ≤0.05), it was observed that calves fed AN had higher levels of 39 lipid species in serum than calves fed VG, whereas 171 lipid species were lower in the AN group. Lipid classes, such as phosphatidylcholine (PC), phosphatidylethanolamine (PE), sphingomyelin (SM), triglycerides (TG), lysophosphatidylcholine (LPC), and lysophosphatidylethanolamine (LPE), were different. In particular, PC and PE were observed at lower levels in calves fed AN, possibly indicating shifts in cell membrane characteristics, intracellular signaling, and liver functions. In addition, a decrease in certain triglyceride (TG) species was observed in calves fed AN, including a decrease in TG species such as TG 36:0 and TG 38:0, possibly related to variations in the content of certain fatty acids within the AN MR, such as C10:0, C12:0, C14:0, and C18:0, compared with the VG MR. Calves fed AN had lower levels of LPC and LPE, and lysophosphatidylinositol, SM, and phosphatidylinositol species than calves fed VG, suggesting shifts in lipoprotein and lipid metabolic pathways. In conclusion, these results deepen the understanding of how lipid sources in MR can modulate the serum lipidome profiles of dairy calves.

Non-Invasive Bio-impedance Diagnostics: Delving into Signal Frequency and Electrode Placement Effects

Electrical characterization of biological tissues offers a promising non-invasive approach to understanding tissue properties. This research rigorously examines how bio-impedance values are influenced by the frequency of the input signal and the strategic placement of electrodes. Utilizing the capabilities of the AD5933 evaluation board by Analog Devices, the study spanned a frequency range from 1KHz to 200 KHz. The results highlighted a significant decrease in impedance with increasing frequency, a trend attributed to the capacitive characteristics of cell membranes. Moreover, the specific distance between electrodes was identified as a crucial factor affecting measurement accuracy. Given these findings, the adaptation of this technique in healthcare settings, particularly in diagnostics, could offer enhanced precision, underscoring its potential relevance in clinical practice.

Genetically programmable cell membrane-camouflaged nanoparticles for targeted combination therapy of colorectal cancer

Cell membrane-camouflaged nanoparticles possess inherent advantages derived from their membrane structure and surface antigens, including prolonged circulation in the bloodstream, specific cell recognition and targeting capabilities, and potential for immunotherapy. Herein, we introduce a cell membrane biomimetic nanodrug platform termed MPB-3BP@CM NPs. Comprising microporous Prussian blue nanoparticles (MPB NPs) serving as both a photothermal sensitizer and carrier for 3-bromopyruvate (3BP), these nanoparticles are cloaked in a genetically programmable cell membrane displaying variants of signal regulatory protein α (SIRPα) with enhanced affinity to CD47. As a result, MPB-3BP@CM NPs inherit the characteristics of the original cell membrane, exhibiting an extended circulation time in the bloodstream and effectively targeting CD47 on the cytomembrane of colorectal cancer (CRC) cells. Notably, blocking CD47 with MPB-3BP@CM NPs enhances the phagocytosis of CRC cells by macrophages. Additionally, 3BP, an inhibitor of hexokinase II (HK2), suppresses glycolysis, leading to a reduction in adenosine triphosphate (ATP) levels and lactate production. Besides, it promotes the polarization of tumor-associated macrophages (TAMs) towards an anti-tumor M1 phenotype. Furthermore, integration with MPB NPs-mediated photothermal therapy (PTT) enhances the therapeutic efficacy against tumors. These advantages make MPB-3BP@CM NPs an attractive platform for the future development of innovative therapeutic approaches for CRC. Concurrently, it introduces a universal approach for engineering disease-tailored cell membranes for tumor therapy.

Inactivation of Carotenogenic-Biosynthesizing Genes Altered Lipids Composition and Intensity in Cronobacter sakazakii.

Cronobacter sakazakii, an opportunistic milk-borne pathogen responsible for severe neonatal meningitis and bacteremia, can synthesize yellow pigment (various carotenoids) benefiting for bacterial survival, while little literature was available about the influence of various carotenoids on bacterial resistance to a series of stresses and the characteristics of cell membrane, obstructing the development of novel bactericidal strategies overcoming the strong tolerance of C. sakazakii. Thus in this study, for the first time, five carotenogenic genes of C. sakazakii BAA-894 were inactivated, respectively, to construct a series of mutants producing various carotenoids and their effects on the cell membrane properties, and resistances to food- and host-related stresses, were investigated systematically. Furthermore, to explore its possible mode of action, comparative lipidomics analysis was performed to reveal the change of lipids that were mainly located at cell membranes. The results showed that five mutants (ΔcrtB, ΔcrtI, ΔcrtY, ΔcrtZ, and ΔcrtX) displayed negligible change in growth rate but higher permeability of the outer membrane and lower fluidity of cell membrane compared to the wild type. Besides, these mutants exhibited poorer ability of biofilm formation and lower resistances to acid, oxidative, osmotic, and desiccation stresses, indicating that different carotenoid composition significantly affected environmental tolerance of C. sakazakii. To discover the possible causes, lipidomics analysis of C. sakazakii was conducted and more than 500 lipid species belonging to 27 classes had been identified at first. Compared to that of BAA-894, the composition and relative intensity of lipid species in five mutants varied significantly, especially the monounsaturated and biunsaturated phosphatidylethanolamine. The evidence presented in this study demonstrated that the varied composition of carotenoids in C. sakazakii significantly altered the lipid profile and intensity, which maybe a crucial means to influencing the characteristics of cell membranes and resistance to environmental stresses.

Lipid bilayer fluidity and degree of order regulates small EVs adsorption on model cell membrane

Small extracellular vesicles (sEVs) are known to play an important role in the communication between distant cells and to deliver biological information throughout the body. To date, many studies have focused on the role of sEVs characteristics such as cell origin, surface composition, and molecular cargo on the resulting uptake by the recipient cell. Yet, a full understanding of the sEV fusion process with recipient cells and in particular the role of cell membrane physical properties on the uptake are still lacking. Here we explore this problem using sEVs from a cellular model of triple-negative breast cancer fusing to a range of synthetic planar lipid bilayers both with and without cholesterol, and designed to mimic the formation of ‘raft’-like nanodomains in cell membranes. Using time-resolved Atomic Force Microscopy we were able to track the sEVs interaction with the different model membranes, showing the process to be strongly dependent on the local membrane fluidity. The strongest interaction and fusion is observed over the less fluid regions, with sEVs even able to disrupt ordered domains at sufficiently high cholesterol concentration. Our findings suggest the biophysical characteristics of recipient cell membranes to be crucial for sEVs uptake regulation.

The Changes of Phenotypic Characteristics of Shewanella putrefaciens under Cold Adaptation

Shewanella putrefaciens (S. putrefaciens) is frequently detected as a serious threat to food safety because it causes spoilage of aquatic products during cold chain transportation. Here, we studied phenotypic changes in S. putrefaciens at low temperatures to discuss the specific behavior of its spoiled aquatic products. S. putrefaciens was found to grow considerably through the growth curve at 0–30°C. In order to investigate the strong putrefaction of aquatic significant amounts under cold storage at 0–10°C, SEM was used to examine the microstructure of S. putrefaciens that had been cultivated at various temperatures. At low temperatures, it was discovered that the cell membrane surface of S. putrefaciens was smoother. FITC-labeled fluorescence microscope was used to view the results. Analysis of S. putrefaciens cultivated at various temperatures revealed that the integrity and permeability of the cell membrane deteriorated with the drop of culture temperature; however, the downward trend slowed down when the temperature was below 10°C. In addition, as the temperature continued to drop below 10°C, the capacity of S. putrefaciens to build biofilms did not diminish noticeably. The findings demonstrate that S. putrefaciens’s cold adaptation mechanism at low temperatures involves modifications to the morphological and phenotypic characteristics of cell membranes, plays a significant role in the organism’s ability to corrode aquatic products at low temperatures, and provides an important target for prevention and control of S. putrefaciens’ ability to contaminate aquatic products and cause financial losses.

Cellular Membrane Components-mediated Cancer ImmunotherapeuticPlatforms.

Immune cell engineering is an active field of ongoing research that can be easily applied to nanoscale biomedicine as an alternative to overcoming limitations of nanoparticles. Cell membrane coating and artificial nanovesicle technology have been reported as representative methods with an advantage of good biocompatibility for biomimetic replication of cell membrane characteristics. Cell membrane-mediated biomimetic technique provides properties of natural cell membrane and enables membrane-associated cellular/molecular signaling. Thus, coated NPs and artificial nanovesicles can achieve effective and extended in vivo circulation, enabling execution of target functions. While coated NPs and artificial nanovesicles provide clear advantages, much work remains before clinical application. In this review, we first provide a comprehensive overview of cell membrane coating techniques and artificial nanovesicles. Next, we summarize the function and application of various immune cell membrane types. This article is protected by copyright. All rights reserved.

Effect of Pd2Spermine on Mice Brain-Liver Axis Metabolism Assessed by NMR Metabolomics.

Cisplatin (cDDP)-based chemotherapy is often limited by severe deleterious effects (nephrotoxicity, hepatotoxicity and neurotoxicity). The polynuclear palladium(II) compound Pd2Spermine (Pd2Spm) has emerged as a potential alternative drug, with favorable pharmacokinetic/pharmacodynamic properties. This paper reports on a Nuclear Magnetic Resonance metabolomics study to (i) characterize the response of mice brain and liver to Pd2Spm, compared to cDDP, and (ii) correlate brain-liver metabolic variations. Multivariate and correlation analysis of the spectra of polar and lipophilic brain and liver extracts from an MDA-MB-231 cell-derived mouse model revealed a stronger impact of Pd2Spm on brain metabolome, compared to cDDP. This was expressed by changes in amino acids, inosine, cholate, pantothenate, fatty acids, phospholipids, among other compounds. Liver was less affected than brain, with cDDP inducing more metabolite changes. Results suggest that neither drug induces neuronal damage or inflammation, and that Pd2Spm seems to lead to enhanced brain anti-inflammatory and antioxidant mechanisms, regulation of brain bioactive metabolite pools and adaptability of cell membrane characteristics. The cDDP appears to induce higher extension of liver damage and an enhanced need for liver regeneration processes. This work demonstrates the usefulness of untargeted metabolomics in evaluating drug impact on multiple organs, while confirming Pd2Spm as a promising replacement of cDDP.

The effect of fermentation conditions (temperature, salt concentration, and pH) with lactobacillus strains for producing Short Chain Fatty Acids

Short-Chain Fatty Acids are one of the vital metabolites generated by the fermentation of dietary fiber in the gastrointestinal tract through bacterial fermentation and play an essential role in human health. This a study aimed to evaluate the effects of different fermentation conditions, including temperature (30, 42 °C), salt concentrations (2, 4 and 6%), pH (4.5, 5 and 6), and their interaction effects on the production of short-chain fatty acids (acetic acid, propionic acid, isobutyric acid, butyric acid, isovaleric acid, valeric acid) by Lactobacillus fermentum ATCC 9338, Lactobacillus fermentum 19SH and Lactobacillus acidophilus ATCC 4356. Once grown under different fermentation conditions, supernatants and pellets of fermentation media were separated, and then SCFAs were measured using Gas chromatography/mass spectrometry (GC-MS). Results revealed that fatty acid content was altered in each fermentation condition, and the highest amount after lactic acid belonged to propionic acid. Accordingly, Lb. Fermentum 19sh, Lb. Fermentum ATCC9938, and Lb. Acidophilus ATCC4356 produced the highest levels of isovaleric acid, acetic acid, propionic acid, isobutyric acid, butyric acid, and valeric acids, respectively. The results indicated a relationship between the production of short-chain fatty acids and the growth of bacterial strains and cell membrane characteristics.

Understanding electrochemical properties of supported lipid bilayers interfaced with organic electronic devices

Native and synthetic membranes can be electrically monitored by creating supported lipid bilayers on top of conducting polymer electrodes. Cell membrane characteristics, e.g. the function of transmembrane proteins, are studied in this paper, along with device sensitivity.

Cell Membrane Adaptations Mediate β-Lactam-Induced Resensitization of Daptomycin-Resistant (DAP-R) Staphylococcus aureus In Vitro.

The reversal of daptomycin resistance in MRSA to a daptomycin-susceptible phenotype following prolonged passage in selected β-lactams occurs coincident with the accumulation of multiple point mutations in the mprF gene. MprF regulates surface charge by modulating the content and translocation of the positively charged cell membrane phospholipid, lysyl-phosphatidylglycerol (LPG). The precise cell membrane adaptations accompanying such β-lactam-induced mprF perturbations are unknown. This study examined key cell membrane metrics relevant to antimicrobial resistance among three daptomycin-resistant MRSA clinical strains, which became daptomycin-susceptible following prolonged exposure to cloxacillin (‘daptomycin-resensitized’). The causal role of such secondary mprF mutations in mediating daptomycin resensitization was confirmed through allelic exchange strategies. The daptomycin-resensitized strains derived either post-cloxacillin passage or via allelic exchange (vs. their respective daptomycin-resistant strains) showed the following cell membrane changes: (i) enhanced BODIPY-DAP binding; (ii) significant reductions in LPG content, accompanied by significant increases in phosphatidylglycerol content (p < 0.05); (iii) no significant changes in positive cell surface charge; (iv) decreased cell membrane fluidity (p < 0.05); (v) enhanced carotenoid content (p < 0.05); and (vi) lower branched chain fatty acid profiles (antiso- vs. iso-), resulting in increases in saturated fatty acid composition (p < 0.05). Overall, the cell membrane characteristics of the daptomycin-resensitized strains resembled those of parental daptomycin-susceptible strains. Daptomycin resensitization with selected β-lactams results in both definable genetic changes (i.e., mprF mutations) and a number of key cell membrane phenotype modifications, which likely facilitate daptomycin activity.

Effect of NaCl addition on the production of welan gum with the UV mutant of Sphingomonas sp

Because of its excellent stability, non-toxicity, biodegradability and unique rheology, welan gum can be widely used in various fields, such as petroleum, biomedicine and food products. In this study, a high-yield mutant strain FM01-S09 was screened through two rounds of UV mutagenesis. Remarkably, the production of welan gum could be further increased by adding 4 mM NaCl at 32 h fermentation, reaching 30.12 ± 0.25 g/L (28.66% higher than no adding), and the NaCl-WG solution had stronger structural, impact resistance, and temperature resistance than H2O2-WG and WG solutions. Furthermore, the mechanism by which NaCl promotes welan gum synthesis was also investigated. It was found that cell membrane characteristics, intracellular microenvironment makeup, and key enzyme gene expression levels were significantly altered in different fermentation stages. Therefore, the addition of NaCl could effectively promote the growth and fermentation performance of Sphingomonas sp., providing a novel strategy for cost-effective welan gum production.

Dimethyl phthalate damages Staphylococcus aureus by changing the cell structure, inducing oxidative stress and inhibiting energy metabolism

Dimethyl phthalate (DMP), used as a plasticizer in industrial products, exists widely in air, water and soil. Staphylococcus aureus is a typical model organism representing Gram-positive bacteria. The molecular mechanisms of DMP toxicology in S. aureus were researched by proteomic and transcriptomic analyses. The results showed that the cell wall, membrane and cell surface characteristics were damaged and the growth was inhibited in S. aureus by DMP. Oxidative stress was induced by DMP in S. aureus. The activities of succinic dehydrogenase (SDH) and ATPase were changed by DMP, which could impact energy metabolism. Based on proteomic and transcriptomic analyses, the oxidative phosphorylation pathway was enhanced and the glycolysis/gluconeogenesis and pentose phosphate pathways were inhibited in S. aureus exposed to DMP. The results of real-time reverse transcription quantitative PCR (RT-qPCR) further confirmed the results of the proteomic and transcriptomic analyses. Lactic acid, pyruvic acid and glucose were reduced by DMP in S. aureus, which suggested that DMP could inhibit energy metabolism. The results indicated that DMP damaged the cell wall and membrane, induced oxidative stress, and inhibited energy metabolism and activation in S. aureus.

Membrane Derived Vesicles as Biomimetic Carriers for Targeted Drug Delivery System.

Extracellular vesicles (EVs) are membrane vesicles (MVs) playing important roles in various cellular and molecular functions in cell-to-cell signaling and transmitting molecular signals to adjacent as well as distant cells. The preserved cell membrane characteristics in MVs derived from live cells, give them great potential in biological applications. EVs are nanoscale particulates secreted from living cells and play crucial roles in several important cellular functions both in physiological and pathological states. EVs are the main elements in intercellular communication in which they serve as carriers for various endogenous cargo molecules, such as RNAs, proteins, carbohydrates, and lipids. High tissue tropism capacity that can be conveniently mediated by surface molecules, such as integrins and glycans, is a unique feature of EVs that makes them interesting candidates for targeted drug delivery systems. The cell-derived giant MVs have been exploited as vehicles for delivery of various anticancer agents and imaging probes and for implementing combinational phototherapy for targeted cancer treatment. Giant MVs can efficiently encapsulate therapeutic drugs and deliver them to target cells through the membrane fusion process to synergize photodynamic/photothermal treatment under light exposure. EVs can load diagnostic or therapeutic agents using different encapsulation or conjugation methods. Moreover, to prolong the blood circulation and enhance the targeting of the loaded agents, a variety of modification strategies can be exploited. This paper reviews the EVs-based drug delivery strategies in cancer therapy. Biological, pharmacokinetics and physicochemical characteristics, isolation techniques, engineering, and drug loading strategies of EVs are discussed. The recent preclinical and clinical progresses in applications of EVs and oncolytic virus therapy based on EVs, the clinical challenges and perspectives are discussed.

Experimental evolution reveals nitrate tolerance mechanisms in Desulfovibrio vulgaris.

Elevated nitrate in the environment inhibits sulfate reduction by important microorganisms of sulfate-reducing bacteria (SRB). Several SRB may respire nitrate to survive under elevated nitrate, but how SRB that lack nitrate reductase survive to elevated nitrate remains elusive. To understand nitrate adaptation mechanisms, we evolved 12 populations of a model SRB (i.e., Desulfovibrio vulgaris Hildenborough, DvH) under elevated NaNO3 for 1000 generations, analyzed growth and acquired mutations, and linked their genotypes with phenotypes. Nitrate-evolved (EN) populations significantly (p < 0.05) increased nitrate tolerance, and whole-genome resequencing identified 119 new mutations in 44 genes of 12 EN populations, among which six functional gene groups were discovered with high mutation frequencies at the population level. We observed a high frequency of nonsense or frameshift mutations in nitrosative stress response genes (NSR: DVU2543, DVU2547, and DVU2548), nitrogen regulatory protein C family genes (NRC: DVU2394-2396, DVU2402, and DVU2405), and nitrate cluster (DVU0246-0249 and DVU0251). Mutagenesis analysis confirmed that loss-of-functions of NRC and NSR increased nitrate tolerance. Also, functional gene groups involved in fatty acid synthesis, iron regulation, and two-component system (LytR/LytS) known to be responsive to multiple stresses, had a high frequency of missense mutations. Mutations in those gene groups could increase nitrate tolerance through regulating energy metabolism, barring entry of nitrate into cells, altering cell membrane characteristics, or conferring growth advantages at the stationary phase. This study advances our understanding of nitrate tolerance mechanisms and has important implications for linking genotypes with phenotypes in DvH.

Variable Membrane Dielectric Polarization Characteristic in Individual Live Cells.

Investigation of the dielectric properties of cell membranes plays an important role in understanding the biological activities that sustain cellular life and realize cellular functionalities. Herein, the variable dielectric polarization characteristics of cell membranes are reported. In controlling the dielectric polarization of a cell using dielectrophoresis force spectroscopy, different cellular crossover frequencies were observed by modulating both the direction and sweep rate of the frequency. The crossover frequencies were used for the extraction of the variable capacitance, which is involved in the dielectric polarization across the cell membranes. In addition, this variable phenomenon was investigated by examining cells whose membranes were cholesterol-depleted with methyl-β-cyclodextrin, which verified a strong correlation between the variable dielectric polarization characteristics and membrane composition changes. This study presented the dielectric polarization properties in live cells' membranes that can be modified by the regulation of external stimuli and provided a powerful platform to explore cellular membrane dielectric polarization.

C18:1 Improves the Freeze-Drying Resistance of Lactobacillus plantarum by Maintaining the Cell Membrane.

Increasing knowledge about lactic acid bacteria as fermentation starters and probiotics to improve health has led to a growing awareness of their application potential. Despite a long history of applying cryoprotectants, the maintenance of probiotic viability is still a major challenge. In this study, we implemented a strategy and explored its mechanisms in detail. We found that the survival rates after freeze-drying were positively correlated with the relative concentration of the octadecenoic acid (C18:1) and with the ratio of unsaturated to saturated FAs (U/S ratio). The addition of C18:1 significantly improved the survival of L. plantarum after freeze-drying. Contrary to the most commonly used cryoprotectants, the addition of C18:1 did not affect the glass transition temperature or collapse temperature. We predicted that the cell membrane characteristics would be significantly degraded during the drying stage, but C18:1 can effectively maintain the cell membrane integrity and fluidity. Our experiments confirmed those predictions, and simultaneously found that the enzyme activities of key enzymes of glucose metabolism were increased compared with the control group. These finding indicate that C18:1 might serve as a lyoprotectant to maintain the cell membrane integrity and fluidity, and thereby increasing the survival rate of L. plantarum after freeze-drying. This study constitutes a strategy to safeguard bacterial viability.

Enhanced resolution impedimetric analysis of cell responses from the distribution of relaxation times

A universal strategy for the sensitive investigation of cell responses to external stimuli, in particular nanosecond pulsed electric fields (nsPEFs), was developed based on electrical impedance spectroscopy (EIS) in combination with a multi-peak analysis for the distribution of relaxation times (DRT). The DRT method provides high resolution for the identification of different polarization processes without a priori assumptions, as they are needed by more conventional approaches, such as an evaluation by equivalent circuit models. Accordingly, the physical properties of cells and their changes due to external stimuli can be uncovered and visualized and dispersion mechanisms introduced by Schwan et al. clearly identified. These are in particular relaxation processes at about 100 kHz that are associated with cell membrane characteristics and dominating respective changes of the distribution function for epithelial cell monolayers after exposure. A relatively moderate evolution at about 10 kHz may represent the polarization of extracellular matrices. Relaxation processes at around 1 MHz were suggested to be associated with intracellular changes. Conversely, the distribution of relaxation times can aid the optimization of the experimental design with respect to intended responses by an external stimulus.

A steady-state modeling approach for simulation of antimicrobial peptide-cell membrane interaction

Antimicrobial Peptides (AMPs) are host defense molecules that initiate microbial death by binding to the membrane. On membrane binding, AMPs undergo changes in conformation and aggregation state to enable killing action. Depending on the AMP and cell membrane characteristics, the nature of binding can be aggregating or non-aggregating, with high/low cooperativity, at single or multiple sites with high/low affinity leading to a unique killing action that needs to be studied individually. In the present study, a steady-state model that simulates AMP-membrane interaction was developed and was used to predict the mechanism of AMP binding. The predictions obtained from the model were validated with experimentally deciphered values available in literature. The model was further used to predict the mechanism for a set of designed AMPs with high sequence similarity to Myeloid Antimicrobial Peptide (MAP) family. Depending on the predicted mechanism, a unique half saturation constant and steepness of response (Hill coefficient) was obtained which was further validated with available data from literature. The model could reliably predict the mechanism, the half saturation constant and the Hill coefficient values. Further based on the analysis, it was observed that aggregation and oligomerization result in drastic killing action in a short range of peptide concentration owing to high Hill coefficient values. Mechanisms such as monomers binding at multiple sites with/without cooperativity result in antimicrobial activity at low half saturation constant though the killing action may not be steep. Thus, the methodology developed here can be used to develop hypothesis for studying AMP-membrane interaction mechanisms.