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The recently developed mRNA‐based coronavirus SARS‐CoV‐2 vaccines highlighted the great therapeutic potential of the mRNA technology. Although the lipid nanoparticles used for the delivery of the mRNA are very efficient, they showed, in some cases, the induction of side effects as well as the production of antibodies directed against particle components. Thus, the development of alternative delivery systems is of great interest in the pursuit of more effective mRNA treatments. In the present work, we evaluated the mRNA transfection capacities of a series of cationic histidine‐rich amphipathic peptides derived from LAH4. We found that while the LAH4‐A1 peptide was an efficient carrier for mRNA, its activity was highly serum sensitive. Interestingly, modification of this cell penetrating peptide at the N‐terminus with two tyrosines or with salicylic acid allowed to confer serum resistance to the carrier. [ABSTRACT FROM AUTHOR]

Thickness of lipid bilayer membranes is a key physical parameter determining membrane permeability and stability with respect to formation of through pores. Most membrane inclusions or impurities like amphipathic peptides, transmembrane peptides, lipid inclusions of a different molecular shape, lipid domains, and protein-lipid domains, locally deform the membrane. The detailed structure of the locally deformed region of the membrane is a kind of "fingerprint" for the inclusion type. However, most experimental methods allow determining only averaged parameters of membranes with incorporated inclusions, thus preventing the direct obtaining of the characteristics of the inclusion. Here we developed a model that allows the obtaining of characteristic parameters of three types of membrane inclusions (amphipathic peptides, transmembrane peptides, monolayer lipid patches) from experimentally observable dependencies of the average thickness of lipid bilayer on the surface concentration of the inclusions. In the case of amphipathic peptides, the model provided the peptide parameters that were in qualitative agreement with the available experimental data. [ABSTRACT FROM AUTHOR]

Antimicrobial activity of some amphipathic peptides is associated with the formation of through pores in bacterial membranes. Antimicrobial peptides (AMPs) specifically bind to the plasma membrane by incorporating their hydrophobic regions into the outer lipid monolayer. The membrane is inevitably deformed. Many AMPs form so-called toroidal pores, the edge of which is partially lined with peptide molecules. The edge of the pore is characterized by significant deformations. In this work, we calculated the energy of the pore edge, with amphipathic peptides located on the pore equator, as well as the energy of deformations induced by AMP in a planar lipid bilayer. It was shown that for certain physicochemical and geometric characteristics of the AMP molecule the energy of the pore, on the equator of which two or more peptide molecules are located, can be lower than the energy of deformations induced in the planar bilayer by the same number of peptide molecules. Thus, two AMP molecules can, in principle, form a through pore in the membrane, although this is possible only in a fairly narrow range of physicochemical and geometric characteristics of the peptides. [ABSTRACT FROM AUTHOR]

During the final step of the bacteriophage infection cycle, the cytoplasmic membrane of host cells is disrupted by small membrane proteins called holins. The function of holins in cell lysis is carried out by forming a highly ordered structure called lethal lesion, in which the accumulation of holins in the cytoplasmic membrane leads to the sudden opening of a hole in the middle of this oligomer. Previous studies showed that dimerization of holins is a necessary step to induce their higher order assembly. However, the molecular mechanism underlying the holin-mediated lesion formation is not well understood. In order to elucidate the functions of holin, we first computationally constructed a structural model for our testing system: the holin S105 from bacteriophage lambda. All atom molecular dynamic simulations were further applied to refine its structure and study its dynamics as well as interaction in lipid bilayer. Additional simulations on association between two holins provide supportive evidence to the argument that the C-terminal region of holin plays a critical role in regulating the dimerization. In detail, we found that the adhesion of specific nonpolar residues in transmembrane domain 3 (TMD3) in a polar environment serves as the driven force of dimerization. Our study therefore brings insights to the design of binding interfaces between holins, which can be potentially used to modulate the dynamics of lesion formation. [ABSTRACT FROM AUTHOR]

The antimicrobial peptides Ocellatin-LB1, -LB2 and -F1, isolated from frogs, are identical from residue 1 to 22, which correspond to the -LB1 sequence, whereas -LB2 carries an extra N and -F1 additional NKL residues at their C-termini. Despite the similar sequences, previous investigations showed different spectra of activities and biophysical investigations indicated a direct correlation between both membrane-disruptive properties and activities, i.e., ocellatin-F1 > ocellatin-LB1 > ocellatin-LB2. This study presents experimental evidence as well as results from theoretical studies that contribute to a deeper understanding on how these peptides exert their antimicrobial activities and how small differences in the amino acid composition and their secondary structure can be correlated to these activity gaps. Solid-state NMR experiments allied to the simulation of anisotropic NMR parameters allowed the determination of the membrane topologies of these ocellatins. Interestingly, the extra Asn residue at the Ocellatin-LB2 C-terminus results in increased topological flexibility, which is mainly related to wobbling of the helix main axis as noticed by molecular dynamics simulations. Binding kinetics and thermodynamics of the interactions have also been assessed by Surface Plasmon Resonance and Isothermal Titration Calorimetry. Therefore, these investigations allowed to understand in atomic detail the relationships between peptide structure and membrane topology, which are in tune within the series -F1 > > -LB1 ≥ -LB2, as well as how peptide dynamics can affect membrane topology, insertion and binding. [ABSTRACT FROM AUTHOR]

In the plasma membranes of eukaryotic cells, relatively ordered lipid–protein domains can be formed. The characteristics of the interaction of domains can have a significant effect on the processes that require the co-localization of several membrane proteins. The ordered lipid bilayer is thicker than the surrounding disordered membrane. Therefore, it is expected that elastic deformations arise at the boundary of ordered domains, aiming at smoothing the jump in bilayer thickness. The typical length of the deformations equals several nanometers, and, as two domains approach each other, the deformations induced by their boundaries begin to overlap, thereby leading to the effective lateral interaction. In this work, we theoretically considered the influence of amphipathic peptides, adsorbed on the membrane, on the interaction energy of ordered domains. Amphipathic peptides can partially incorporate into the membrane, inducing elastic deformations therein. We used the theory of lipid membrane elasticity to analyze the deformation energy of various configurations of ordered domains and amphipathic peptides. In a membrane without peptides, it is necessary to overcome some energy barrier to bring two parallel boundaries of ordered domains into contact with each other. According to the results of our calculations, the presence of amphipathic peptides in a membrane leads to a severalfold increase in the height of this energy barrier. Thus, amphipathic peptides should significantly hinder the fusion of ordered domains and thereby contribute to the stabilization of the ensemble of nano-domains. [ABSTRACT FROM AUTHOR]

The lateral distribution of integral and peripheral proteins, as well as lipids in the plasma membranes of mammalian cells is extremely heterogeneous. It is believed that various lipid-protein domains are formed in membranes. Domains enriched in sphingomyelin and cholesterol are called rafts. It is assumed that the distribution of proteins into rafts is largely related to the presence in their primary sequence of a specific amino acid region called the CRAC motif, which is responsible for cholesterol binding. In this work, the interaction of two peptides containing CRAC motifs in their structure with membranes of different compositions was studied by means of molecular dynamics. It has been shown that the average number of lipid molecules in contact with each peptide is proportional to the mole fraction of lipid in the membrane. The predominant interaction of peptides with cholesterol was not observed. In addition, cholesterol did not form long-lived contacts with any amino acid or amino acid sequence. We suppose that in some cases the predominant lateral distribution of peptides and proteins containing CRAC motifs into rafts may be due to amphipathicity of the CRAC motif rather than due to specific strong binding of cholesterol. [ABSTRACT FROM AUTHOR]

Biological membranes include various lipids. A heterogeneity of lipid composition can lead to phase separation resulting in the formation of ordered lipid domains, which differ in lipid composition from the other (disordered) part of the membrane. Membrane deformations, which occur at the domain boundary, can affect the lateral distribution of various membrane inclusions. In this paper, in the framework of theory of elasticity of lipid membranes, the influence of the boundaries of lipid domains on the lateral distribution of amphipathic peptides adsorbed on the membrane is considered. Such peptides can cause the formation of through pores. We showed that with an increase in the concentration of amphipathic peptides on the membrane, they first line up near the boundary of the domain parallel to it, thus losing the ability to induce pore formation. Then, as the domain boundary is completely occupied, new peptides stand parallel to the line of peptides that are already at the boundary, at a distance of about 5 nm from the boundary. In this configuration, the probability of formation of through pores in the membrane is increased. Besides, it is shown that the spontaneous curvature of monolayers of the ordered domain and disordered membrane determines the energy of incorporation of peptides into the membrane and their distribution between the phases. However, the spontaneous curvature scarcely influences the interaction of amphipathic peptides with the boundary of the ordered domain. [ABSTRACT FROM AUTHOR]

Amphipathic alpha-helical peptides are perspective antimicrobial drugs. These peptides are partially embedded into the membrane to a shallow depth so that the longitudinal axis of the helix is parallel to the plane of the membrane or deviates from it by a small angle. In the framework of theory of elasticity of liquid crystals, adapted to lipid membranes, we calculated the energy of deformations occurring near the peptides partially embedded into the membrane. The energy of deformations is minimal when two peptides are parallel to each other and stay at a distance of about 5 nm. This configuration is stable with respect to small parallel displacements of the peptides and with respect to small variation of the angle between their axes both in the plane of the membrane and in the perpendicular direction. As a result of deformation the average thickness of the membrane decreases. The distribution of the elastic energy density has a maximum in the middle between the peptides. This region is the most likely place for formation of the through pores in the membrane. Since the equilibrium distance between the peptides is relatively large, it is assumed that the originally appearing pore should be purely lipidic. [ABSTRACT FROM AUTHOR]

ABSTRACT Amphipathic peptides composed of alternating hydrophobic and hydrophilic amino acids are a privileged class of peptide, which have a high propensity to self-assemble into β-sheet fibrils. The Ac-(FKFE)2-NH2 peptide has been extensively studied and forms putative β-sheet bilayer fibrils in which the hydrophobic Phe side chains are organized to a single face of each constituent sheet; upon bilayer formation, these hydrophobic benzyl groups are sequestered in the hydrophobic core of the resulting fibril. In order for the Phe side chains to be uniformly displayed on one face of Ac-(FKFE)2-NH2 β-sheets, an antiparallel packing orientation in which one amino acid residue is unpaired must be adopted. Based on molecular models, we hypothesized that truncated seven amino acid derivatives of Ac-(FKFE)2-NH2 in which either the N-terminal Phe residue (Ac-KFEFKFE-NH2) or the C-terminal Glu residue (Ac-FKFEFKF-NH2) is eliminated should readily self-assemble into β-sheet bilayers in which all hydrogen bond and hydrophobic/charge interactions are satisfied. We found, however, that these minute changes in peptide sequence have unanticipated and dramatic effects on the self-assembly of each peptide. Ac-FKFEFKF-NH2 self-assembled into fibrils with unique morphology relative to the parent peptide, whereas the Ac-KFEFKFE-NH2 peptide had a strongly reduced propensity to self-assemble, even failing to self-assemble altogether under some conditions. These findings provide significant insight into the effect of sequence length and strand registry as well as hydrophobicity and charge on the self-assembly of simple amphipathic peptides to illuminate the possibility of tuning self-assembly processes and the resulting structures with minute changes to peptide sequence. © 2013 Wiley Periodicals, Inc. Biopolymers (Pept Sci) 100: 738-750, 2013. [ABSTRACT FROM AUTHOR]

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Amphipathic peptides composed of alternating polar and nonpolar residues have a strong tendency to self-assemble into one-dimensional, amyloid-like fibril structures. Fibrils derived from peptides of general (XZXZ) n sequence in which X is hydrophobic and Z is hydrophilic adopt a putative β-sheet bilayer. The bilayer configuration allows burial of the hydrophobic X side chain groups in the core of the fibril and leaves the polar Z side chains exposed to solvent. This architectural arrangement provides fibrils that maintain high solubility in water and has facilitated the recent exploitation of self-assembled amphipathic peptide fibrils as functional biomaterials. This article is a critical review of the development and application of self-assembling amphipathic peptides with a focus on the fundamental insight these types of peptides provide into peptide self-assembly phenomena. © 2011 Wiley Periodicals, Inc. Biopolymers (Pept Sci) 98: 169-184, 2012. [ABSTRACT FROM AUTHOR]

Membrane proteins comprise a significant fraction of the proteomes of sequenced organisms and are the targets of approximately half of marketed drugs. However, in spite of their prevalence and biomedical importance, relatively few experimental structures are available due to technical challenges. Computational simulations can potentially address this deficit by providing structural models of membrane proteins. Solvation within the spatially heterogeneous membrane/solvent environment provides a major component of the energetics driving protein folding and association within the membrane. We have developed an implicit solvation model for membranes that is both computationally efficient and accurate enough to enable molecular mechanics predictions for the folding and association of peptides within the membrane. We derived the new atomic solvation model parameters using an unbiased fitting procedure to experimental data and have applied it to diverse problems in order to test its accuracy and to gain insight into membrane protein folding. First, we predicted the positions and orientations of peptides and complexes within the lipid bilayer and compared the simulation results with solid-state NMR structures. Additionally, we performed folding simulations for a series of host-guest peptides with varying propensities to form alpha helices in a hydrophobic environment and compared the structures with experimental measurements. We were also able to successfully predict the structures of amphipathic peptides as well as the structures for dimeric complexes of short hexapeptides that have experimentally characterized propensities to form beta sheets within the membrane. Finally, we compared calculated relative transfer energies with data from experiments measuring the effects of mutations on the free energies of translocon-mediated insertion of proteins into lipid bilayers and of combined folding and membrane insertion of a beta barrel protein. [ABSTRACT FROM AUTHOR]

The article presents a study on the antimicrobial activity and amphipathic linear peptide of the venom from the scorpion Isometrus maculatus. The study used bioassay-guided fractionation of the venom to isolate a novel insect toxin, Im-1. Moreover, it mentions the isolation of several antimicrobial peptides from the venoms in addition to the neurotoxins.

An amphipathic α-helical peptide (C5A) derived from the membrane anchor domain of the hepatitis C virus (HCV) NS5A protein is virocidal for HCV at submicromolar concentrations in vitro. C5A prevents de novo HCV infection and suppresses ongoing infection by inactivating both extra- and intracellular infectious particles, and it is nontoxic in vitro and in vivo at doses at least 100-fold higher than required for antiviral activity. Mutational analysis indicates that C5A's amphipathic α-helical structure is necessary but not sufficient for its virocidal activity, which depends on its amino acid composition but not its primary sequence or chirality. In addition to HCV, C5A inhibits infection by selected flaviviruses, paramyxoviruses, and HIV. These results suggest a model in which C5A destabilizes viral membranes based on their lipid composition, offering a unique therapeutic approach to HCV and other viral infections. [ABSTRACT FROM AUTHOR]

This article reviews the membrane interactions of a variety of peptides including alamethicin, melittin, cecropins, magainins, and defensins. The biological activities of the peptides are discussed and correlated to results from biophysical and structural studies. A picture emerges that allows one to understand the mechanisms of lysis and the regulation of the peptides' activities. Specific peptide-lipid interactions are particularly important in the case of antibiotic peptides, which affect the functionality of bacterial membranes, fungal membranes, or both but leave the bilayers of higher organisms, including those of the host cells, intact. Several models are presented and discussed in view of the ensemble of experimental data. These include the barrel stave, the wormhole, the carpet, and the detergent-like model. [ABSTRACT FROM AUTHOR]

An amphipathic class A peptide, Ac-18A-NH[sub 2], has been employed in modeling the α-helical lipid-binding site of apolipoprotein A-I (apoA-I). To gain insight into the nature of protein–lipid interactions responsible for the ability of apoA-I to promote the efflux of intracellular cholesterol, the peptide disposition in model membranes composed of phosphatidylcholine (PC) and its mixture with cholesterol (Chol) has been characterized. By examining resonance energy transfer between the peptide Trp as a donor and anthrylvinyl-labeled PC as an acceptor it was found that Chol inclusion is conducive to shallower bilayer location of the Ac-18A-NH[sub 2] α-helix. The limits for the Trp distance from the membrane center were estimated to be 1.5–1.7 nm (PC) and 1.9–2.1 nm (PC:Chol), indicating that in the PC bilayer the Trp resides at the level of the glycerol backbone and carbonyl groups while the region of the phosphocholine moieties is preferable for Trp location in the PC:Chol bilayer. These findings suggest that Chol can modulate the interactions between apoA-I and membrane lipids via reducing the depth of α-helix bilayer penetration. [ABSTRACT FROM AUTHOR]

Two novel pore-forming peptides have been isolated from the venom of the South-African scorpion Opistophtalmus carinatus . These peptides, designated opistoporin 1 and 2, differ by only one amino acid and belong to a group of α-helical, cationic peptides. For the first time, a comparison of the primary structures of α-helical pore-forming peptides from scorpion venom was undertaken. This analysis revealed that peptides in the range of 40–50 amino acids contain a typical scorpion conserved sequence S(x)3 KxWxS(x)5 L. An extensive study of biological activity of synthesized opistoporin 1 and parabutoporin, a pore-forming peptide previously isolated from the venom of the South-African scorpion Parabuthus schlechteri , was undertaken to investigate an eventual cell-selective effect of the peptides. Opistoporin 1 and parabutoporin were most active in inhibiting growth of Gram-negative bacteria (1.3–25 µm), while melittin and mastoparan, two well-known cytolytic peptides, were more effective against Gram-positive bacteria in the same concentration range. In addition, the peptides showed synergistic activity with some antibiotics commonly used in therapy. Opistoporin 1 and parabutoporin had hemolytic activity intermediate between the least potent mastoparan and the highly lytic melittin. Furthermore, all peptides inhibited growth of fungi. Experiments with SYTOX green suggested that this effect is related to membrane permeabilization. [ABSTRACT FROM AUTHOR]

Cell membranes are heterogeneous in lipid composition which leads to the phase separation with the formation of nanoscopic liquid-ordered domains, also called rafts. There are multiple cell processes whereby the clustering of these domains into a larger one might be involved, which is responsible for such important processes as signal transduction, polarized sorting, or immune response. Currently, antimicrobial amphipathic peptides are considered promising antimicrobial, antiviral, and anticancer therapeutic agents. Here, within the framework of the classical theory of elasticity adapted for lipid membranes, we investigate how the presence of the peptides in a phase-separated membrane influences the fusion of the domains. We show that the peptides tend to occupy the boundaries of liquid-ordered domains and significantly increase the energy barrier of the domain-domain fusion, which might lead to misregulation of raft clustering and adverse consequences for normal cell processes. [ABSTRACT FROM AUTHOR]

A class of peptides that associate with lipids, known as oblique-orientated peptides, was recently described [Brasseur R., Pillot, T., Lins, L., Vandekerckhove, J. & Rosseneu, M. (1997) Trends Biochem. Sci. 22, 167-171]. Due to an asymmetric distribution of hydrophobic residues along the axis of the α-helix, such peptides adopt an oblique orientation which can destabilise membranes or lipid cores. Variants of these oblique peptides, designed to have an homogeneous distribution of hydrophobic and hydrophilic residues along the helical axis, are classified as regular amphipathic peptides. These peptides are expected to lie parallel to the polar/apolar interface with their hydrophobic residues directed towards the apolar and their hydrophilic residues towards the polar phase. An hydrophobic, oblique-orientated peptide was identified at residues 56-68 in the sequence of the lecithin-cholesterol acyltransferase (LCAT), enzyme. This peptide is predicted to penetrate a lipid bilayer at an angle of 40+ through its more hydrophobic C-terminal end and thereby induce the destabilisation of a membrane or a lipid core. The LCAT-(56-68) wild-type peptide was synthesised together with the LCAT-(56-68, 0+) variant, in which the hydrophobicity gradient was abolished through residue permutations. In two other variants, designed to keep their oblique orientation, the W61 residue was shifted either towards the more hydrophilic N-terminal at residue 57, or to position 68 at the hydrophobic C-terminal end of the peptide. Peptide-induced vesicle fusion was demonstrated by fluorescence measurements using pyrene-labeled vesicles and by monitoring of vesicle size by gel filtration. The interaction between peptides and lipids was monitored by measurement of the intrinsic tryptophan fluorescence emission of the peptides. Fluorescence polarisation measurements, using diphenyl hexatriene, were carried out to follow changes in the lipid fluidity. The LCAT-(56-68) wild-type peptide and... [ABSTRACT FROM AUTHOR]

Background: Recent approvals of gene therapies by the FDA and the EMA for treatment of inherited disorders have further opened the door for assessment of nucleic acid pharmaceuticals for clinical usage. Arising from the presence of damaged or inappropriate DNA, cancer is a condition particularly suitable for genetic intervention. The RALA peptide has been shown to be a potent non-viral delivery platform for nucleic acids. This study examines the use of RALA to deliver a plasmid encoding inducible nitric oxide synthase (iNOS) as an anti-cancer treatment.Methods: The physiochemical properties of the RALA/DNA nanoparticles were characterized via dynamic light scattering and transmission electron microscopy. The nanoparticles were labelled with fluorophores and tracked over time using confocal microscopy with orthogonal sections to determine cellular location. In vitro studies were employed to determine functionality of the nanoparticles both for pEGFP-N1 and CMV-iNOS. Nanoparticles were injected intravenously into C57/BL6 mice with blood and serum samples analysed for immune response. PC3-luc2M cells were injected into the left ventricle of SCID mice followed by treatment with RALA/CMV-iNOS nanoparticles to evaluate the tumour response in a metastatic model of prostate cancer.Results: Functional cationic nanoparticles were produced with gene expression in PC-3 prostate cancer cells. Furthermore, repeated administrations of RALA/DNA nanoparticles into immunocompetent mice did not produce any immunological response: neutralization of the vector or release of inflammatory mediators. RALA/CMV-iNOS reduced the clonogenicity of PC-3 cells in vitro, and in an in vivo model of prostate cancer metastasis, systemically delivered RALA/CMV-iNOS significantly improved the survival of mice.Conclusion: These studies further validate RALA as a genetic cargo delivery vehicle and iNOS as a potent therapy for the treatment of cancer. [ABSTRACT FROM AUTHOR]