The interfacial properties of the peptide Polybia-MP1 and its interaction with DPPC are modulated by lateral electrostatic attractions

Using Carbon Nanotubes to Improve Enzyme Activity and Electroactivity of Fatty Acid Langmuir-Blodgett Film-Incorporated Galactose Oxidase for Sensing and Energy Storage Applications

Incorporating enzymes into nanostructured supercapacitor devices represents a groundbreaking advancement in energy storage. Enzyme catalysis using nanomaterials enhances performance, efficiency, and stability by facilitating precise charge transfer, while the nanostructure provides a high surface area and improved conductivity. This synergy yields eco-friendly, high-performance energy storage solutions crucial for diverse applications, from portable electronics to renewable energy systems. In this study, we harnessed the versatility of Langmuir-Blodgett films to create meticulously organized thin films with specific enzyme properties, coupled with carbon nanotubes, to develop biosupercapacitors. Langmuir monolayers were constructed with stearic acid, carbon nanotubes, and galactose oxidase. Following comprehensive characterization using tensiometric, rheological, morphological, and spectroscopic techniques, the monolayers were transferred to solid supports, yielding Langmuir-Blodgett films. These films exhibited superior performance, with persisting enzyme activity. However, increasing film thickness did not enhance enzymatic activity values, indicating a surface-driven process. Subsequently, we explored the electrochemical properties of the films, revealing stability compatible with supercapacitor applications. The introduction of carbon nanotubes demonstrated a higher capacitance, indicating the potential viability of the films for energy storage applications.

Effect of substituting glutamine with lysine on structural and biological properties of antimicrobial peptide Polybia-MP1

The natural antimicrobial peptide Polybia-MP1 is a promising candidate for developing new treatment therapy for infection and cancer. It showed broad-spectrum antimicrobial and anticancer activity with high safety on healthy cells. However, previous sequence modification usually resulted in at least one of two consequences: a notable increase in hemolytic activity or a considerable decrease in activity against Gram-negative bacteria and cancer cells. Herein, a new approach was applied by replacing the amino acid Glutamine at position 12 with Lysine and generating the MP1-Q12K analog. Our preliminary data suggested an enhancement in antibacterial and antifungal activity, whereas the anticancer and hemolytic activity of the two peptides were comparable. Moreover, MP1-Q12K was found to be less self-assembly than Polybia-MP1, which further supports the enhancement of antimicrobial properties. Hence, this study provides new information regarding the structure-activity relationships of Polybia-MP1 and support for the development of potent, selective antimicrobial peptides.

Interaction mechanism of three egg protein derived ACE inhibitory tri-peptides and DPPC membrane using FS, FTIR, and DSC studies

Understanding the interaction of food derived angiotensin converting enzyme (ACE) inhibitory peptides and intestinal epithelial cell membrane may help to improve their absorption. This research aimed to study the molecular interaction of ACE inhibitory tri-peptides ADF, FGR, and MIR with DPPC membrane during absorption process. The DPPC liposome was prepared and characterized, then used as a model membrane. The permeability of tri-peptides across the membrane was investigated using Fluorescence spectroscopy. The effect of tri-peptides on the structure and dynamics of DPPC bilayers was determined using Fourier transform infrared spectroscopy. The effect of tri-peptides on the phase transition temperature in the DPPC membrane was also analyzed using Differential scanning calorimetry. The results showed that ACE inhibitory tri-peptides ADF, FGR, and MIR can penetrate into both the membrane-water interface and hydrophobic region of DPPC bilayer, and the tri-peptide FGR have higher permeability across the membrane.

Multiple roles of ribosomal antimicrobial peptides in tackling global antimicrobial resistance

In the last century, conventional antibiotics have played a significant role in global healthcare. Antibiotics support the body in controlling bacterial infection and simultaneously increase the tendency of drug resistance. Consequently, there is a severe concern regarding the regression of the antibiotic era. Despite the use of antibiotics, host defence systems are vital in fighting infectious diseases. In fact, the expression of ribosomal antimicrobial peptides (AMPs) has been crucial in the evolution of innate host defences and has been irreplaceable to date. Therefore, this valuable source is considered to have great potential in tackling the antimicrobial resistance (AMR) crisis. Furthermore, the possibility of bacterial resistance to AMPs has been intensively investigated. Here, we summarize all aspects related to the multiple applications of ribosomal AMPs and their derivatives in combating AMR.

Natural Peptides Inducing Cancer Cell Death: Mechanisms and Properties of Specific Candidates for Cancer Therapeutics

Nowadays, cancer has become the second highest leading cause of death, and it is expected to continue to affect the population in forthcoming years. Additionally, treatment options will become less accessible to the public as cases continue to grow and disease mechanisms expand. Hence, specific candidates with confirmed anticancer effects are required to develop new drugs. Among the novel therapeutic options, proteins are considered a relevant source, given that they have bioactive peptides encrypted within their sequences. These bioactive peptides, which are molecules consisting of 2–50 amino acids, have specific activities when administered, producing anticancer effects. Current databases report the effects of peptides. However, uncertainty is found when their molecular mechanisms are investigated. Furthermore, analyses addressing their interaction networks or their directly implicated mechanisms are needed to elucidate their effects on cancer cells entirely. Therefore, relevant peptides considered as candidates for cancer therapeutics with specific sequences and known anticancer mechanisms were accurately reviewed. Likewise, those features which turn certain peptides into candidates and the mechanisms by which peptides mediate tumor cell death were highlighted. This information will make robust the knowledge of these candidate peptides with recognized mechanisms and enhance their non-toxic capacity in relation to healthy cells and further avoid cell resistance.

Natural Peptides Inducing Cancer Cell Death: Mechanisms and Properties of Specific Candidates for Cancer Therapeutics

Nowadays, cancer has become the second highest leading cause of death, and it is expected to continue to affect the population in forthcoming years. Additionally, treatment options will become less accessible to the public as cases continue to grow and disease mechanisms expand. Hence, specific candidates with confirmed anticancer effects are required to develop new drugs. Among the novel therapeutic options, proteins are considered a relevant source, given that they have bioactive peptides encrypted within their sequences. These bioactive peptides, which are molecules consisting of 2–50 amino acids, have specific activities when administered, producing anticancer effects. Current databases report the effects of peptides. However, uncertainty is found when their molecular mechanisms are investigated. Furthermore, analyses addressing their interaction networks or their directly implicated mechanisms are needed to elucidate their effects on cancer cells entirely. Therefore, relevant peptides considered as candidates for cancer therapeutics with specific sequences and known anticancer mechanisms were accurately reviewed. Likewise, those features which turn certain peptides into candidates and the mechanisms by which peptides mediate tumor cell death were highlighted. This information will make robust the knowledge of these candidate peptides with recognized mechanisms and enhance their non-toxic capacity in relation to healthy cells and further avoid cell resistance.

A bactericide peptide changing the static and dilatational surface elasticity properties of zwitterionic lipids at the air-water interface: Relationship with the thermodynamic, structural and morphological properties

In this paper, we studied how different hydrophilicity degrees of the polar groups of the lipids dipalmitoylphosphatidylcholine (DPPC) and dipalmitoyl phosphatidylethanolamine (DPPE) influence the interaction of the antibiotic peptide vancomycin (VC), affecting the physicochemical properties of the monolayers, including thermodynamic, rheological, structural and morphological ones. Lipid Langmuir monolayers were prepared at air-water interfaces with VC aqueous solution as subphase and characterized with tensiometry, Brewster angle microscopy, infrared spectroscopy, dilatational, and interfacial shear rheology. The presence of PC or PE groups as polar head groups of the phospholipid monolayers modulated the interaction of VC adsorbing from the aqueous subphase since for DPPC, vancomycin condenses the monolayer, making it less stable, fluid, and more disordered. In contrast, for DPPE, vancomycin expands the monolayer, making it more stable, keeping the compressibility, and leading to the formation of interfacial aggregates, which are not observed for DPPC. We concluded thatelectrostatic interactions induced the insertion of the peptide into the polar heads of the monolayers (DPPE), while hydrophobic interactions, in addition to ion-dipole interactions, induced the adsorption of the peptide onto the polar head of the monolayers (DPPC).

Chemical approaches in the development of natural nontoxic peptide Polybia-MP1 as a potential dual antimicrobial and antitumor agent

Polybia-MP1 is a well-known natural antimicrobial peptide that has been intensively studied recently due to its therapeutic potential. MP1 exhibited not only potent antibacterial activity but also antifungal and anticancer properties. More importantly, MP1 shows relatively low hemolytic activity compared to other antimicrobial peptides having a similar origin. Thus, besides investigating possible mechanisms of action, great efforts have been invested to develop this peptide to become more "druggable". In this review, we summarized all the chemical approaches, both success and failure, that using MP1 as a lead compound to create modified analogs with better pharmacological properties. As there have been thousands of natural AMPs found and deposited in numerous databases, such useful information in both the success and failure will provide insight into the research and development of antimicrobial peptides and guiding for the next steps.

The effect of acidic pH on the adsorption and lytic activity of the peptides Polybia-MP1 and its histidine-containing analog in anionic lipid membrane: a biophysical study by molecular dynamics and spectroscopy

Antimicrobial peptides (AMPs) are part of the innate immune system of many species. AMPs are short sequences rich in charged and non-polar residues. They act on the lipid phase of the plasma membrane without requiring membrane receptors. Polybia-MP1 (MP1), extracted from a native wasp, is a broad-spectrum bactericide, an inhibitor of cancer cell proliferation being non-hemolytic and non-cytotoxic. MP1 mechanism of action and its adsorption mode is not yet completely known. Its adsorption to lipid bilayer and lytic activity is most likely dependent on the ionization state of its two acidic and three basic residues and consequently on the bulk pH. Here we investigated the effect of bulk acidic (pH 5.5) and neutral pH (7.4) solution on the adsorption, insertion, and lytic activity of MP1 and its analog H-MP1 to anionic (7POPC:3POPG) model membrane. H-MP1 is a synthetic analog of MP1 with lysines replaced by histidines. Bulk pH changes could modulate this peptide efficiency. The combination of different experimental techniques and molecular dynamics (MD) simulations showed that the adsorption, insertion, and lytic activity of H-MP1 are highly sensitive to bulk pH in opposition to MP1. The atomistic details, provided by MD simulations, showed peptides contact their N-termini to the bilayer before the insertion and then lay parallel to the bilayer. Their hydrophobic faces inserted into the acyl chain phase disturb the lipid-packing.

The antimicrobial peptide Polybia-MP1 differentiates membranes with the hopanoid, diplopterol from those with cholesterol

Polybia-MP1 is an antimicrobial peptide that shows a decreased activity in membranes with cholesterol (CHO). Since it is now accepted that hopanoids act as sterol-surrogates in some sterol-lacking bacteria, we here inquire about the impact of Polybia-MP1 on membranes containing the hopanoid diplopterol (DP) in comparison to membranes with CHO. We found that, despite the properties induced on lipid membranes by DP are similar to those induced by CHO, the effect of Polybia-MP1 on membranes with CHO or DP was significantly different. DP did not prevent dye release from LUVs, nor the insertion of Polybia-MP1 into monolayers, and peptide-membrane affinity was higher for those with DP than with CHO. Zeta potentials ( ζ ) for DP-containing LUVs showed a complex behavior at increasing peptide concentration. The effect of the peptide on membrane elasticity, investigated by nanotube retraction experiments, showed that peptide addition softened all membrane compositions, but membranes with DP got stiffer at long times. Considering this, and the ζ results, we propose that peptides accumulate at the interface adopting different arrangements, leading to a non-monotonic behavior. Possible correlations with cell membranes were inquired testing the antimicrobial activity of Polybia-MP1 against hopanoid-lacking bacteria pre-incubated with DP or CHO. The fraction of surviving cells was lower in cultures incubated with DP compared to those incubated with CHO. We propose that the higher activity of Polybia-MP1 against some bacteria compared to mammalian cells is not only related to membrane electrostatics, but also the composition of neutral lipids, particularly the hopanoids, could be important.

The Spectrum of Design Solutions for Improving the Activity-Selectivity Product of Peptide Antibiotics against Multidrug-Resistant Bacteria and Prostate Cancer PC-3 Cells

The link between the antimicrobial and anticancer activity of peptides has long been studied, and the number of peptides identified with both activities has recently increased considerably. In this work, we hypothesized that designed peptides with a wide spectrum of selective antimicrobial activity will also have anticancer activity, and tested this hypothesis with newly designed peptides. The spectrum of peptides, used as partial or full design templates, ranged from cell-penetrating peptides and putative bacteriocin to those from the simplest animals (placozoans) and the Chordata phylum (anurans). We applied custom computational tools to predict amino acid substitutions, conferring the increased product of bacteriostatic activity and selectivity. Experiments confirmed that better overall performance was achieved with respect to that of initial templates. Nine of our synthesized helical peptides had excellent bactericidal activity against both standard and multidrug-resistant bacteria. These peptides were then compared to a known anticancer peptide polybia-MP1, for their ability to kill prostate cancer cells and dermal primary fibroblasts. The therapeutic index was higher for seven of our peptides, and anticancer activity stronger for all of them. In conclusion, the peptides that we designed for selective antimicrobial activity also have promising potential for anticancer applications.

Biophysical approaches for exploring lipopeptide-lipid interactions

In recent years, lipopeptides (LPs) have attracted a lot of attention in the pharmaceutical industry due to their broad-spectrum of antimicrobial activity against a variety of pathogens and their unique mode of action. This class of compounds has enormous potential for application as an alternative to conventional antibiotics and for pest control. Understanding how LPs work from a structural and biophysical standpoint through investigating their interaction with cell membranes is crucial for the rational design of these biomolecules. Various analytical techniques have been developed for studying intramolecular interactions with high resolution. However, these tools have been barely exploited in lipopeptide-lipid interactions studies. These biophysical approaches would give precise insight on these interactions. Here, we reviewed these state-of-the-art analytical techniques. Knowledge at this level is indispensable for understanding LPs activity and particularly their potential specificity, which is relevant information for safe application. Additionally, the principle of each analytical technique is presented and the information acquired is discussed. The key challenges, such as the selection of the membrane model are also been briefly reviewed.

Structural Plasticity of EAK-16 Peptide Inducing Vesicle Membrane Leakage

BACKGROUND

Ionic complementary peptide EAK-16 has been studies for anticancer drug delivery application. This is a 16 residues, short sequence peptide has ability to trosnform into micro/nanoparticle via self-assembly. However, it is still not clear that how this can bind with cell membrane to induce membrane leakage or delivering their cargo inside cell membrane.

OBJECTIVE

The main objective of this work was to understand behaviour of secondary structure conformation of peptide in solution and at lipid membrane interfaces and membrane permeability of synthetic ionic complementary peptide EAK-16. The corresponding secondary structure conformation was evaluated.

METHODS

We performed biophysical investigation to probe the interaction of synthesised ionic complementary peptide (EAK-16) with dimyristoylphospholcholine (DMPC) and dimyristoylphosphoserine (DMPS) membrane interfaces. The folding behaviours of EAK-16 were studied with Circular Dichroism (CD) spectroscopy. Membrane leakage with peptide was confirmed with calcein leakage assay.

RESULTS

Our finding of this study showed that in aqueous phase EAK-16 was predominantly folded into β-sheets. The temperature could alter the β-sheets. However, in DMPC and DMPS membrane interfaces, EAK-16 adopted helical conformation. EAK-16 has preference in perturbing anionic compared Zwitterionic lipid vesicles. This study proposed that hydrophobic grooves of EAK-16 might be a key in the association with lipid bilayers. Secondly, a charge distribution of ionic residues would also support the orientation at lipid bilayers. This peptide membrane association would facilitate the membrane destabilisation.

CONCLUSION

This study demonstrated the supporting evidence that EAK-16 could interact with lipid membranes and conforming to helical structure, while the helical conformation induced the lipid membrane leakage. Overall, this study provides a physical rationale that ionic complementary peptide can be a useful tool for designing and development of novel antibiotics and anticancer agents along its previous drug delivery applications.

The effect of pH on the lytic activity of a synthetic mastoparan-like peptide in anionic model membranes

Peptide sequences containing acidic and basic residues could potentially have their net charges modulated by bulk pH with a possible influence on their lytic activity in lipid vesicles. The present study reports on a biophysical investigation of these modulatory effects on the synthetic mastoparan-like peptide L1A (IDGLKAIWKKVADLLKNT-NH2). At pH 10.0 L1A was 6 times more efficient in lysing large anionic (1-palmitoyl-oleoyl-sn-glycero-3-phosphocholine (POPC):1-palmitoyl-2-oleoyl-sn-glycero-3-phosphoglycerol (POPG)/(8:2)) unilamellar vesicles (LUVs) than at pH 4.0. Despite the reduction of 60% in the L1A net charge in basic pH its affinity for this vesicle was almost insensitive to pH. On the other hand, L1A insertion into monolayers was dramatically influenced by subphase condition, showing that, in the neutral and basic subphases, the peptide induced surface pressure changes that surpassed the membrane lateral pressure, being able to destabilize a bilayer structure. In addition, in the basic subphase, visualization of the compression isotherms of co-spread 1,2-dipalmitoyl-sn-glycero-3-phosphocholine (DPPC):POPG (8:2) + 4.8 mol% L1A showed that the peptide induced significant changes in solid lipid domains, indicating its capability in perturbing lipid-packing. An insight into L1A lytic activity was also obtained in giant unilamellar vesicles (GUVs) using phase contrast microscopy. The suppression of L1A lytic activity at acidic pH is in keeping with its lower insertion capability and ability to disturb the lipid monolayer. The lytic activity observed under neutral and basic conditions showed a quick and stochastic leakage following a lag-time. The permeability and the leakage-time averaged over at least 14 single GUVs were dependent on the bulk condition. At basic pH, permeability is higher and quicker than in a neutral medium in good accordance with the lipid-packing perturbation.

Fluorinated CdSe/ZnS quantum dots: Interactions with cell membrane

Fluorescent inorganic quantum dots are highly promising for biomedical applications as sensing and imaging agents. However, the low internalization of the quantum dots, as well as for most of the nanoparticles, by living cells is a critical issue which should be solved for success in translational research. In order to increase the internalization rate of inorganic CdSe/ZnS quantum dots, they were functionalized with a fluorinated organic ligand. The fluorinated quantum dots displayed an enhanced surface activity, leading to a significant cell uptake as demonstrated by in vitro experiments with HeLa cells. We combined the experimental and computational results of Langmuir monolayers of the DPPC phospholipid as a model cell membrane with in vitro experiments for analyzing the mechanism of internalization of the fluorinated CdSe/ZnS quantum dots. Surface pressure-molecular area isotherms suggested that the physical state of the DPPC molecules was greatly affected by the quantum dots. UV-vis reflection spectroscopy and Brewster Angle Microscopy as in situ experimental techniques further confirmed the significant surface concentration of quantum dots. The disruption of the ordering of the DPPC molecules was assessed. Computer simulations offered detailed insights in the interaction between the quantum dots and the phospholipid, pointing to a significant modification of the physical state of the hydrophobic region of the phospholipid molecules. This phenomenon appeared as the most relevant step in the internalization mechanism of the fluorinated quantum dots by cells. Thus, this work sheds light on the role of fluorine on the surface of inorganic nanoparticles for enhancing their cellular uptake.

Regulation of phase boundaries and phase-segregated patterns in model membranes

Demixing of components has long been described in model membranes. It is a consequence of non-ideal lateral interactions between membrane components, and it causes the presence of segregated phases, forming patches (domains) of different properties, thus introducing heterogeneity into the membrane. In the present review we first describe the processes through which domains are generated, how they grow, and why they are rounded, striped or fractal-like, as well as why they get distributed forming defined patterns. Next, we focus on the effect of an additive on a lipid mixture, which usually induces shifts in demixing points, thus stabilizing or destabilizing the phase-segregated state. Results found for different model membranes are summarized, detailing the ways in which phase segregation and the generated patterns may be modulated. We focus on which are, from our viewpoint, the most relevant regulating factors affecting the surface texture observed in model membranes. This article is part of a Special Issue entitled: Emergence of Complex Behavior in Biomembranes edited by Marjorie Longo.

Effect of N-terminal acetylation on lytic activity and lipid-packing perturbation induced in model membranes by a mastoparan-like peptide

L1A (IDGLKAIWKKVADLLKNT-NH2) is a peptide that displays a selective antibacterial activity to Gram-negative bacteria without being hemolytic. Its lytic activity in anionic lipid vesicles was strongly enhanced when its N-terminus was acetylated (ac-L1A). This modification seems to favor the perturbation of the lipid core of the bilayer by the peptide, resulting in higher membrane lysis. In the present study, we used lipid monolayers and bilayers as membrane model systems to explore the impact of acetylation on the L1A lytic activity and its correlation with lipid-packing perturbation. The lytic activity investigated in giant unilamellar vesicles (GUVs) revealed that the acetylated peptide permeated the membrane at higher rates compared with L1A, and modified the membrane's mechanical properties, promoting shape changes. The peptide secondary structure and the changes in the environment of the tryptophan upon adsorption to large unilamellar vesicles (LUVs) were monitored by circular dichroism (CD) and red-edge excitation shift experiments (REES), respectively. These experiments showed that the N-terminus acetylation has an important effect on both, peptide secondary structure and peptide insertion into the bilayer. This was also confirmed by experiments of insertion into lipid monolayers. Compression isotherms for peptide/lipid mixed films revealed that ac-L1A dragged lipid molecules to the more disordered phase, generating a more favorable environment and preventing the lipid molecules from forming stiff films. Enthalpy changes in the main phase transition of the lipid membrane upon peptide insertion suggested that the acetylated peptide induced higher impact than the non-acetylated one on the thermotropic behavior of anionic vesicles.

Lipid-packing perturbation of model membranes by pH-responsive antimicrobial peptides

The indiscriminate use of conventional antibiotics is leading to an increase in the number of resistant bacterial strains, motivating the search for new compounds to overcome this challenging problem. Antimicrobial peptides, acting only in the lipid phase of membranes without requiring specific membrane receptors as do conventional antibiotics, have shown great potential as possible substituents of these drugs. These peptides are in general rich in basic and hydrophobic residues forming an amphipathic structure when in contact with membranes. The outer leaflet of the prokaryotic cell membrane is rich in anionic lipids, while the surface of the eukaryotic cell is zwitterionic. Due to their positive net charge, many of these peptides are selective to the prokaryotic membrane. Notwithstanding this preference for anionic membranes, some of them can also act on neutral ones, hampering their therapeutic use. In addition to the electrostatic interaction driving peptide adsorption by the membrane, the ability of the peptide to perturb lipid packing is of paramount importance in their capacity to induce cell lysis, which is strongly dependent on electrostatic and hydrophobic interactions. In the present research, we revised the adsorption of antimicrobial peptides by model membranes as well as the perturbation that they induce in lipid packing. In particular, we focused on some peptides that have simultaneously acidic and basic residues. The net charges of these peptides are modulated by pH changes and the lipid composition of model membranes. We discuss the experimental approaches used to explore these aspects of lipid membranes using lipid vesicles and lipid monolayer as model membranes.

The insertion of Polybia-MP1 peptide into phospholipid monolayers is regulated by its anionic nature and phase state

Polybia-MP1 or simply MP1 (IDWKKLLDAAKQIL-NH₂) is a peptide with broad-spectrum bactericidal activity and a strong inhibitory effect against cancer cells. The aim of this work was to evaluate the effect of biophysical properties such as membrane texture and film thickness on MP1 interaction with neutral and anionic lipid membranes. For this purpose, we first explored the peptide's surface behavior. MP1 showed high surface activity, adsorbing onto bare air/aqueous interfaces up to higher surface pressures than the collapse pressure of MP1 Langmuir films. The MP1-lipid membrane interaction was studied using Langmuir phosphatidylcholine and phosphatidylserine (PS) monolayers as model membrane systems. PS was chosen since this negatively charged lipid was found predominantly on the outer leaflet of tumor cells, and it enhances MP1 activity for PS-containing membranes to a greater extent than for other negatively charged lipids. MP1 incorporated into anionic PS monolayers, which show a liquid-expanded (LE) phase or LE-liquid-condensed (LC) phase coexistence, up to lipid-packing densities higher than those of cell membranes. The mixed lipid/MP1 films were explored by Brewster angle microscopy and atomic force microscopy. MP1 partitioned preferentially into the LE phase state of PS films, and were thus excluded from the coexisting LC phase. This interaction had strong electrostatic bases: in pure water, the lipid-peptide interaction was strong enough to induce formation of reversible lipid-peptide 3D structures associated with the interface. MP1 incorporation into the LE phase was accompanied by a shift of the phase transition pressure to higher values and a thinning of the lipid film. These results showed a clear correlation between peptide penetration capacity and the presence or induction of the thin LE phase. This capacity to regulate membrane physical properties may be of relevance in the binding, incorporation and membrane selectivity of this promising antitumor peptide.

How to gather useful and valuable information from protein binding measurements using Langmuir lipid monolayers

This review presents data on the influence of various experimental parameters on the binding of proteins onto Langmuir lipid monolayers. The users of the Langmuir methodology are often unaware of the importance of choosing appropriate experimental conditions to validate the data acquired with this method. The protein Retinitis pigmentosa 2 (RP2) has been used throughout this review to illustrate the influence of these experimental parameters on the data gathered with Langmuir monolayers. The methods detailed in this review include the determination of protein binding parameters from the measurement of adsorption isotherms, infrared spectra of the protein in solution and in monolayers, ellipsometric isotherms and fluorescence micrographs.

Molecular-level insight into the binding of arginine to a zwitterionic Langmuir monolayer

Arginine molecules bind to a DPPC monolayer, altering the interfacial electrostatic potential and the lateral mobility of the lipids, while having little effect on the compression isotherm of the monolayer.

Non-Brownian diffusion in lipid membranes: Experiments and simulations

The dynamics of constituents and the surface response of cellular membranes-also in connection to the binding of various particles and macromolecules to the membrane-are still a matter of controversy in the membrane biophysics community, particularly with respect to crowded membranes of living biological cells. We here put into perspective recent single particle tracking experiments in the plasma membranes of living cells and supercomputing studies of lipid bilayer model membranes with and without protein crowding. Special emphasis is put on the observation of anomalous, non-Brownian diffusion of both lipid molecules and proteins embedded in the lipid bilayer. While single component, pure lipid bilayers in simulations exhibit only transient anomalous diffusion of lipid molecules on nanosecond time scales, the persistence of anomalous diffusion becomes significantly longer ranged on the addition of disorder-through the addition of cholesterol or proteins-and on passing of the membrane lipids to the gel phase. Concurrently, experiments demonstrate the anomalous diffusion of membrane embedded proteins up to macroscopic time scales in the minute time range. Particular emphasis will be put on the physical character of the anomalous diffusion, in particular, the occurrence of ageing observed in the experiments-the effective diffusivity of the measured particles is a decreasing function of time. Moreover, we present results for the time dependent local scaling exponent of the mean squared displacement of the monitored particles. Recent results finding deviations from the commonly assumed Gaussian diffusion patterns in protein crowded membranes are reported. The properties of the displacement autocorrelation function of the lipid molecules are discussed in the light of their appropriate physical anomalous diffusion models, both for non-crowded and crowded membranes. In the last part of this review we address the upcoming field of membrane distortion by elongated membrane-binding particles. We discuss how membrane compartmentalisation and the particle-membrane binding energy may impact the dynamics and response of lipid membranes. This article is part of a Special Issue entitled: Biosimulations edited by Ilpo Vattulainen and Tomasz Róg.