Peptide-membrane Interactions Research Articles

Unveiling Plant-Based Antimicrobial Peptides by In Silico Tools

Background:Bacterial vaginosis (BV) arises from a disruption in the vaginal microbiome, primarily characterized by a decrease in Lactobacilli and an overgrowth of bacteria like Gardnerella vaginalis. These findings highlight the potential of plant-derived AMPs as novel, effective treatments for BV, offering a pathway to combat antimicrobial resistance and recurrence. Methods:Insilico study was conducted to screen and characterize AMPs from Thymbracapitata and Zataria multiflora, two plants with well-documented medicinal propertiesdesigned to target the ABC transporter permease protein in G. vaginalis, a key contributor to antimicrobial resistance. Structural and physicochemical analyses were conducted to assess peptide stability, hydrophilicity, and membrane interaction potential. Result:Analysis revealed that TCCP-1, a peptide from Thymbracapitata, is more stable and hydrophilic, while ZMLP-2 from Zatariamultiflora exhibits higher hydrophobicity, making it more suited for membrane interactions. These characteristics suggest that these plant-derived peptides have properties favorable for treating BV. Conclusion:Plant-derived antimicrobial peptides (AMPs), especially those from Thymbracapitata and Zataria multiflora, show potential as innovative treatments for bacterial vaginosis (BV), offering a holistic and effective approach while mitigating antimicrobial resistance and recurrence. In silico analysis suggests that the identified transporter in Gardnerella vaginalis is likely an integral membrane protein, a critical insight for docking studies as interactions with membrane-bound proteins differ from those in the cytoplasm or extracellular space. Targeting this protein with AMPs could disrupt cellular transport and division, impairing the pathogen's ability to survive and propagate.

De Novo Design of Tryptophan Containing Broad-Spectrum Cationic Antimicrobial Octapeptides.

With the advent of antibiotic resistant organisms, development of alternate classes of molecules other than antibiotics to combat microbial infections, have become extremely important. In this context, antimicrobial peptides have taken center stage of antimicrobial therapeutic research. In this work, we have reported two cationic antimicrobial octapeptides WRL and LWRF, with broad spectrum antimicrobial activities against several strains of ESKAPE pathogens. Both the peptides were membrane associative and induced microbial cell death through membranolysis, being selective towards microbial membranes over mammalian membranes. The AMPs were unstructured in water, adopting partial helical conformation in the presence of microbial membrane mimics. Electrostatic interaction formed the primary basis of peptide-membrane interactions. WRL was more potent, salt tolerant and faster acting of the two AMPs, owing to the presence of two tryptophan residues against that of one in LWRF. Increased tryptophan number in WRL enhanced its membrane association ability, resulting in higher antimicrobial potency but lower selectivity. This experimental and computational work, established that an optimum number of tryptophan residues and their position was critical for obtaining high antimicrobial potency and selectivity simultaneously in the designed cationic AMPs. Understanding the peptide membrane interactions in atomistic details can lead to development of better antimicrobial therapeutics in future.

Computational investigation of the effect of BODIPY labelling on peptide-membrane interaction

Optical monitoring of peptide binding to live cells is hampered by the abundance of naturally occurring fluorophores such as tryptophan. Unnatural amino acids incorporating synthetic fluorophores such as BODIPY overcome these optical limitations. A drawback to using fluorophores in lipid binding peptide design is their propensity to override other interactions, potentially causing the peptides to lose their binding selectivity. Here, the binding strength of a selection of peptides incorporating a variety of BODIPY derivatized amino acids has been studied via molecular dynamics simulations to quantify the impact of BODIPY incorporation on peptide-membrane binding behaviour.

Origin of Secondary Structure Transitions and Peptide Self-Assembly Propensity in Trifluoroethanol-Water Mixtures.

Membrane-peptide interactions are key to the formation of helical intermediates in the early stages of amyloidogenesis. Aqueous solutions of 2,2,2-trifluoroethanol (TFE) provide a membrane-mimetic environment capable of promoting and stabilizing local peptide interactions. Uperin 3.5 (U3.5), a 17-residue and amidated antimicrobial peptide, is unstructured in water but self-assembles into fibrils in the presence of salt. Secondary structure transitions linked to U3.5 self-assembly were investigated in TFE/water mixtures, in both the absence and presence of salt, to assess the role of membrane-peptide interactions on peptide self-assembly and amyloid formation. A 5-to-7-fold increase in fibril yield of U3.5 was observed at low TFE concentrations (10% TFE/water v/v) compared with physiological buffer but only in the presence of salt. No aggregation was observed in salt-free TFE/water mixtures. Circular dichroism spectra showed that partial helical structures, initially stabilized by TFE, transitioned to β-sheet-rich aggregates in a saline buffer. Molecular dynamics simulations confirmed that TFE and salt act synergistically to enhance peptide-peptide interactions, resulting in β-sheet-rich U3.5 oligomers at low TFE concentrations. Specifically, TFE stabilized amphipathic, helical intermediates, leading to increased peptide-peptide attraction through hydrophobic interactions. The presence of salt further enhanced the peptide-peptide interactions by screening positively charged residues. Thus, the study revealed the role of a membrane mimic in stabilizing helical intermediates on the pathway to amyloid formation in the antimicrobial U3.5 peptide.

Molecular Dynamics Simulations Help Determine the Molecular Mechanisms of Lasioglossin-III and Its Variant Peptides' Membrane Interfacial Interactions.

Lasioglossin-III (LL-III) is a potent broad-spectrum antimicrobial peptide used in diverse antimicrobial applications. In this work, coarse-grained and all-atom molecular dynamics simulation strategies were used in tandem to interpret the molecular mechanisms involved in the interfacial dynamics of LL-III and its recombinant variants during interactions with diverse cell membrane systems. Our results indicate that the membrane charges act as the driving force for initiating the membrane-peptide interactions, while the hydrophobic or van der Waals forces help to reinforce the membrane-peptide bindings. The optimized charge-hydrophobicity ratio of the LL-III peptides helps ensure their high specificity toward bacterial membranes compared to mammalian membrane systems, which also helps explain our experimental observations. Overall, we hope that our work gives new insight into the antimicrobial action of LL-III peptides and that the adopted simulation strategy will help other scientists and engineers extract maximal information from complex molecular simulations using minimal computational power.

Assessment of membrane labelling mechanisms with exogenous fatty acids and detergents in bacteria

Labelling of bacterial membranes using exogenous fatty acids has proven to be a valuable tool to investigate molecular interactions by in-cell solid-state nuclear magnetic resonance (ssNMR) spectroscopy, notably with antimicrobial peptides. However, the mechanism by which this labelling takes place in non-mutated bacteria has not yet been investigated. In this work, we propose a rapid method to assess the fate of the fatty acids during the labelling of bacteria, involving two different methylation schemes and gas chromatography coupled to mass spectrometry. We applied this approach to Gram(+) and Gram(−) bacteria grown with deuterated palmitic acid under different conditions. We assessed the extent of labelling, then the resulting membrane rigidity by 2H ssNMR. Our results reveal that the labelling mechanism depends on the detergent used to micellize the fatty acids. This labelling can be either active or passive, whether the fatty acids are metabolized and used in the phospholipids biosynthesis, or remain unmodified in the membrane. We discuss the best labelling protocol for studying peptide-membrane interactions.

How antimicrobial peptide indolicidin and its derivatives interact with phospholipid membranes: Molecular dynamics simulation

Infections by drug-resistant bacteria pose a growing threat to human health, so developing new antimicrobial drugs is becoming an increasingly urgent requirement. Antimicrobial peptides are an important part of the innate immune system of many organisms, which have a broad spectrum of antimicrobial activity and little likelihood to trigger resistance, so they are considered good candidates for developing new antimicrobial drugs. In this paper, the interaction of indolicidin (IR13) and its derived peptides CP10A, CP-11 and cycloCP-11 with Gram-negative bacterial model membranes is investigated using coarse-grained molecular dynamics approach. The aim is to analyse the behaviour of these antimicrobial peptides when interacting with Gram-negative bacterial membranes. The widely studied phospholipid bilayer consisting of POPC and POPG is used as a Gram-negative bacterial membrane model in the simulations. The results show that the derived peptides CP-11 and cycloCP-11 are more active against Gram-negative bacteria than IR13 and CP10A. The dynamic behaviour of the four antimicrobial peptides on the membrane is different, and the peptide-membrane interactions induce changes in the thickness and surface area of the phospholipid bilayer, diminish membrane mobility, and so on. The present study provides important insights into the mechanism of interaction between antimicrobial peptides and phospholipid membranes by analysing them at the molecular level, and is therefore informative for designing new derivative peptides.

Vesicle protrusion induced by antimicrobial peptides suggests common carpet mechanism for short antimicrobial peptides

Short-cationic alpha-helical antimicrobial peptides (SCHAMPs) are promising candidates to combat the growing global threat of antimicrobial resistance. They are short-sequenced, selective against bacteria, and have rapid action by destroying membranes. A full understanding of their mechanism of action will provide key information to design more potent and selective SCHAMPs. Molecular Dynamics (MD) simulations are invaluable tools that provide detailed insights into the peptide-membrane interaction at the atomic- and meso-scale level. We use atomistic and coarse-grained MD to look into the exact steps that four promising SCHAMPs—BP100, Decoralin, Neurokinin-1, and Temporin L—take when they interact with membranes. Following experimental set-ups, we explored the effects of SCHAMPs on anionic membranes and vesicles at multiple peptide concentrations. Our results showed all four peptides shared similar binding steps, initially binding to the membrane through electrostatic interactions and then flipping on their axes, dehydrating, and inserting their hydrophobic moieties into the membrane core. At higher concentrations, fully alpha-helical peptides induced membrane budding and protrusions. Our results suggest the carpet mode of action is fit for the description of SCHAMPs lysis activity and discuss the importance of large hydrophobic residues in SCHAMPs design and activity.

Stabilization of Prebiotic Vesicles by Peptides Depends on Sequence and Chirality: A Mechanism for Selection of Protocell-Associated Peptides.

Cells require oligonucleotides and polypeptides with specific, homochiral sequences to perform essential functions, but it is unclear how such oligomers were selected from random sequences at the origin of life. Cells were probably preceded by simple compartments such as fatty acid vesicles, and oligomers that increased the stability, growth, or division of vesicles could have thereby increased in frequency. We therefore tested whether prebiotic peptides alter the stability or growth of vesicles composed of a prebiotic fatty acid. We find that three of 15 dipeptides tested reduce salt-induced flocculation of vesicles. All three contain leucine, and increasing their length increases the efficacy. Also, leucine-leucine but not alanine-alanine increases the size of vesicles grown by multiple additions of micelles. In a molecular simulation, leucine-leucine docks to the membrane, with the side chains inserted into the hydrophobic core of the bilayer, while alanine-alanine fails to dock. Finally, the heterochiral forms of leucine-leucine, at a high concentration, rapidly shrink the vesicles and make them leakier and less stable to high pH than the homochiral forms do. Thus, prebiotic peptide-membrane interactions influence the flocculation, growth, size, leakiness, and pH stability of prebiotic vesicles, with differential effects due to sequence, length, and chirality. These differences could lead to a population of vesicles enriched for peptides with beneficial sequence and chirality, beginning selection for the functional oligomers that underpin life.

Milk Antiviral Proteins and Derived Peptides against Zoonoses.

Milk is renowned for its nutritional richness but also serves as a remarkable reservoir of bioactive compounds, particularly milk proteins and their derived peptides. Recent studies have showcased several robust antiviral activities of these proteins, evidencing promising potential within zoonotic viral diseases. While several publications focus on milk's bioactivities, antiviral peptides remain largely neglected in reviews. This knowledge is critical for identifying novel research directions and analyzing potential nutraceuticals within the One Health context. Our review aims to gather the existing scientific information on milk-derived antiviral proteins and peptides against several zoonotic viral diseases, and their possible mechanisms. Overall, in-depth research has increasingly revealed them as a promising and novel strategy against viruses, principally for those constituting a plausible pandemic threat. The underlying mechanisms of the bioactivity of milk's proteins include inhibiting viral entry and attachment to the host cells, blocking replication, or even viral inactivation via peptide-membrane interactions. Their marked versatility and effectiveness stand out compared to other antiviral peptides and can support future research and development in the post-COVID-19 era. Overall, our review helps to emphasize the importance of potentially effective milk-derived peptides, and their significance for veterinary and human medicines, along with the pharmaceutical, nutraceutical, and dairy industry.

Binding-induced lipid domains: Peptide-membrane interactions with PIP2 and PS

Binding-induced lipid domains: Peptide-membrane interactions with PIP2 and PS

Aggregation, structure and water permeability of membrane-embedded helical Aβ oligomers.

It is widely recognized that membranes can facilitate the aggregation of amyloid-β (Aβ) peptides, while Aβ can in turn cause membrane damage. Many studies focus on the peptide-membrane interactions of Aβ oligomers with β-rich structures. However, the exact aggregation and toxicity mechanism of the membrane-embedded helical Aβ oligomers remain ambiguous. Herein, the molecular dynamics simulations were performed on membrane-embedded helical Aβ42 peptides. Initiated by eight Aβ42 monomers embedded in a lipid bilayer, the monomers aggregate into oligomers with stable transmembrane helix structures. With the aggregation of peptides, the membrane perturbations caused by Aβ aggregates decrease. The molecular architectures of oligomers were characterized and a helix-rich octamer stabilized by an annular network of hydrogen bonds was observed. The oligomers demonstrate the capability to assist transmembrane water transport. Our study may provide new insights for the investigation of transmembrane Aβ oligomers.

Application of singular value decomposition analysis: Insights into the complex mechanisms of amyloidogenesis

Amyloidogenesis, with its multifaceted nature spanning from peptide self-assembly to membrane-mediated structural transitions, presents a significant challenge for the interdisciplinary scientific community. Here, we emphasize on how Singular Value Decomposition (SVD) can be employed to reveal hidden patterns and dominant modes of interaction that govern the complex process of amyloidogenesis. We first utilize SVD analysis on Circular Dichroism (CD) spectral datasets to identify the intermediate structural species emerging during peptide-membrane interactions and to determine binding constants more precisely than conventional methods. We investigate the monomer loss kinetics associated with peptide self-assembly using Nuclear Magnetic Resonance (NMR) dataset and determine the global kinetic parameters through SVD. Furthermore, we explore the seeded growth of amyloid fibrils by analyzing a time-dependent NMR dataset, shedding light on the kinetic intricacies of this process. Our analysis uncovers two distinct states in the aggregation of Aβ40 and pinpoints key residues responsible for this seeded growth. To strengthen our findings and enhance their robustness, we validate those using simulated data, thereby highlighting the physical interpretations derived from SVD. Overall, SVD analysis offers a model-free, global kinetic perspective, enabling the selection of optimal kinetic models. This study not only contributes valuable insights into the dynamics but also highlights the versatility of SVD in unravelling complex processes of amyloidogenesis.

Molecular Dynamics Simulation Studies of the Orientation and Mechanism of Action of Magainin in Water and DPPC Membrane Environments

Abstract: Antimicrobial peptides (AMPs) function as defense mediators that can act against microbial invasion in their primary host. Magainin-2 is an antimicrobial peptide with 23 amino acids isolated from the African clawed frog Xenopus laevis. This study employed the molecular dynamics (MD) simulation technique to investigate the structural changes of magainin-2 in an explicit aqueous solution and in a dipalmitoyl¬phos¬phatidyl-choline (DPPC) membrane environment with a view to understanding the dynamics of the antimicrobial peptide, the nature of the peptide-membrane interactions and the structural changes of the peptide in both aqueous solvent and membrane during the whole processes. The GROMOS96-53A6 force field and Spc216 water model were employed for the MD simulations under isothermal-isobaric conditions with periodic boundary conditions imposed on x-, y- and z- directions. Structural changes were evaluated by measuring the Radius of Gyration (Rg), Root Mean Square Deviation (RMSD), Root Mean Square Fluctuation (RMSF), hydrogen bonds and Bilayer Thickness. Twenty-six intramolecular hydrogen bonds were found, which confirms the stability of the protein during the simulation. The radius of gyration was computed to determine its compactness with water and DPPC. From the lower value ranges of Rg (0.9–1.16 nm), RMSD (0.3–0.47 nm) and RMSF (0.1–0.6 nm) in DPPC, the Magainin-2 tends to be relatively stable in Membrane environment than in aqueous solution at a conformational state.

Binding-induced lipid domains: Peptide-membrane interactions with PIP2 and PS

Cell signaling is an important process involving complex interactions between lipids and proteins. The myristoylated alanine-rich C-kinase substrate (MARCKS) has been established as a key signaling regulator, serving a range of biological roles. Its effector domain (ED), which anchors the protein to the plasma membrane, induces domain formation in membranes containing phosphatidylinositol 4,5-bisphosphate (PIP2) and phosphatidylserine (PS). The mechanisms governing the MARCKS-ED binding to membranes remain elusive. Here, we investigate the composition-dependent affinity and MARCKS-ED-binding-induced changes in interfacial environments using two-dimensional infrared spectroscopy and fluorescence anisotropy. Both negatively charged lipids facilitate the MARCKS-ED binding to lipid vesicles. Although the hydrogen-bonding structure at the lipid-water interface remains comparable across vesicles with varied lipid compositions, the dynamics of interfacial water show divergent patterns due to specific interactions between lipids and peptides. Our findings also reveal that PIP2 becomes sequestered by bound peptides, while the distribution of PS exhibits no discernible change upon peptide binding. Interestingly, PIP2 and PS become colocalized into domains both in the presence and absence of MARCKS-ED. More broadly, this work offers molecular insights into the effects of membrane composition on binding.

Unraveling the Effects of Cationic Peptides on Vesicle Structures: Insights into Peptide-Membrane Interactions.

Antimicrobial resistance is a pressing global health issue, with millions of lives at risk by 2050, necessitating the development of alternatives with broad-spectrum activity against pathogenic microbes. Antimicrobial peptides provide a promising solution by combating microbes, modulating immunity, and reducing resistance development through membrane and intracellular targeting. PuroA, a synthetic peptide derived from the tryptophan-rich domain of puroindoline A, exhibits potent antimicrobial activity against various pathogens, while the rationally designed P1 peptide demonstrates enhanced antimicrobial activity with its specific composition. This paper investigates the concentration-dependent effects of these cationic peptides on distinct types of vesicles representing strong-negative bacterial cell membranes (S-vesicles), weak-negative bacterial cell membranes (W-vesicles), and mammalian cell membranes (M-vesicles). To investigate the interactions between the peptides and vesicles, small-angle neutron scattering experiments were conducted. The cationic peptides, PuroA and P1, interact with S-vesicles through electrostatic interactions, leading to distinct effects. PuroA accumulates on the vesicle surface, increasing Rcore and Rtotal, aligning with the carpet model. P1 disrupts the vesicle structure at higher concentrations, consistent with the detergent model. Neither peptide significantly affects W-vesicles, emphasizing the role of charge. In uncharged M-vesicles, both peptides decrease Rcore and Rtotal and increase tshell, indicating peptide insertion and altered bilayer properties. These findings provide valuable insights into peptide-membrane interactions and their impact on vesicle structures. Furthermore, the implications of these findings extend to the potential development of innovative antimicrobial agents and drug delivery systems that specifically target bacterial and mammalian membranes. This research contributes to the advancement of understanding peptide-membrane interactions and lays the foundation for the design of approaches for targeting membranes in various biomedical applications.

Biophysical Insights into the Antitumoral Activity of Crotalicidin against Breast Cancer Model Membranes.

Bioactive peptides have emerged as promising therapeutic agents with antimicrobial, antifungal, antiparasitic, and, recently, antitumoral properties with a mechanism of action based on membrane destabilization and cell death, often involving a conformational change in the peptide. This biophysical study aims to provide preliminary insights into the membrane-level antitumoral mode of action of crotalicidin, a cationic host defense peptide from rattlesnake venom, toward breast cancer cell lines. The lipid composition of breast cancer cell lines was obtained after lipid extraction and quantification to prepare representative cell membrane models. Membrane-peptide interaction studies were performed using differential scanning calorimetry and Fourier-transform infrared spectroscopy. The outcome evidences the potential antitumoral activity and selectivity of crotalicidin toward breast cancer cell lines and suggests a mechanism initiated by the electrostatic interaction of the peptide with the lipid bilayer surface and posterior conformation change with membrane intercalation between the acyl chains in negatively charged lipid systems. This research provides valuable information that clears up the antitumoral mode of action of crotalicidin.

Antimicrobial activity, membrane interaction and structural features of short arginine-rich antimicrobial peptides.

Antimicrobial activity of many AMPs can be improved by lysine-to-arginine substitution due to a more favourable interaction of arginine guanidinium moiety with bacterial membranes. In a previous work, the structural and functional characterization of an amphipathic antimicrobial peptide named RiLK1, including lysine and arginine as the positively charged amino acids in its sequence, was reported. Specifically, RiLK1 retained its β-sheet structure under a wide range of environmental conditions (temperature, pH, and ionic strength), and exhibited bactericidal activity against Gram-positive and Gram-negative bacteria and fungal pathogens with no evidence of toxicity on mammalian cells. To further elucidate the influence of a lysine-to-arginine replacement on RiLK1 conformational properties, antimicrobial activity and peptide-liposome interaction, a new RiLK1-derivative, named RiLK3, in which the lysine is replaced with an arginine residue, was projected and characterised in comparison with its parental compound. The results evidenced that lysine-to-arginine mutation not only did not assure an improvement in the antimicrobial potency of RiLK1 in terms of bactericidal, virucidal and fungicidal activities, but rather it was completely abolished against the hepatitis A virus. Therefore, RiLK1 exhibited a wide range of antimicrobial activity like other cationic peptides, although the exact mechanisms of action are not completely understood. Moreover, tryptophan fluorescence measurements confirmed that RiLK3 bound to negatively charged lipid vesicles with an affinity lower than that of RiLK1, although no substantial differences from the structural and self-assembled point of view were evidenced. Therefore, our findings imply that antimicrobial efficacy and selectivity are affected by several complex and interrelated factors related to substitution of lysine with arginine, such as their relative proportion and position. In this context, this study could provide a better rationalisation for the optimization of antimicrobial peptide sequences, paving the way for the development of novel AMPs with broad applications.

Molecular dynamics simulations of an antifreeze protein at the lipid / water interface

The ability of antifreeze proteins (AFP's) and glycoproteins (AFGP's) to prevent damage to certain organisms under cold stress is well established. These molecules have also been shown to prevent chilling damage in some biological membranes and interaction between membranes and AF(G)P's has been observed during chilling events; however, the exact mechanism of membrane stabilization is still not well understood. Molecular modelling is an ideal technique for probing atomistic information in these systems although modelling studies to date have focused on peptide structure and the site and mode, e.g., insertion, of the peptide-membrane interaction. To provide insight into how AF(G)P's may act to stabilize (or destabilize) membranes during phase transitions, we have conducted molecular dynamics (MD) simulations of a solvated dimyristoylphosphatidylcholine (DMPC) lipid bilayer containing an AFP Type I at the lipid/water interface at several temperatures. We present the analysis of several properties of the phospholipid bilayer that are relevant when considering phase transitions. Possible areas for concentrating future research efforts have been highlighted; namely the acyl chain order and the polar headgroups, both of which have been implicated in experimental studies of the stabilization of model membranes by AF(G)P's.

Synthesis, Conformational Analysis and Antitumor Activity of the Naturally Occurring Antimicrobial Medium-Length Peptaibol Pentadecaibin and Spin-Labeled Analogs Thereof.

Peptaibols are proteolysis-resistant, membrane-active peptides. Their remarkably stable helical 3D-structures are key for their bioactivity. They can insert themselves into the lipid bilayer as barrel staves, or lay on its surface like carpets, depending on both their length and the thickness of the lipid bilayer. Medium-length peptaibols are of particular interest for studying the peptide-membrane interaction because their length allows them to adopt either orientation as a function of the membrane thickness, which, in turn, might even result in an enhanced selectivity. Electron paramagnetic resonance (EPR) is the election technique used to this aim, but it requires the synthesis of spin-labeled medium-length peptaibols, which, in turn, is hampered by the poor reactivity of the Cα-tetrasubstituted residues featured in their sequences. After several years of trial and error, we are now able to give state-of-the-art advice for a successful synthesis of nitroxide-containing peptaibols, avoiding deleted sequences, side reactions and difficult purification steps. Herein, we describe our strategy and itsapplication to the synthesis of spin-labeled analogs of the recently discovered, natural, medium-length peptaibol pentadecaibin. We studied the antitumor activity of pentadecaibin and its analogs, finding potent cytotoxicity against human triple-negative breast cancer and ovarian cancer. Finally, our analysis of the peptide conformational preferences and membrane interaction proved that pentadecaibinspin-labeling does not alter the biological features of the native sequence and is suitable for further EPR studies. The nitroxide-containing pentadecaibins, and their synthetic strategy described herein, will help to shed light on the mechanism of the peptide-membrane interaction of medium-length peptaibols.