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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]

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.

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]

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]

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]

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]

Junyi Qian,1,2 Ningze Xu,1,2 Xu Zhou,1,2 Kaihong Shi,1,2 Qian Du,1,2 Xiaoxing Yin,1,2 Ziming Zhao1,2 1Department of Pharmacy, Xuzhou Medical University, Xuzhou 221004, People’s Republic of China; 2Jiangsu Key Laboratory of New Drug Research and Clinical Pharmacy, Xuzhou Medical University, Xuzhou 221004, People’s Republic of ChinaCorrespondence: Ziming Zhao; Xiaoxing YinDepartment of Pharmacy, Xuzhou Medical University, 209 Tongshan Road, Xuzhou 221004, People’s Republic of ChinaTel +86 516 8326 2139Fax +86 516 8326 2257Email zmzhao@xzhmu.edu.cn; yinxxgood@126.comBackground: Low density lipoprotein (LDL) has been regarded as a promising antitumor drug vehicle. However some problems, such as rare source, difficulty of large-scale production, and potential safety concerns, hinder its clinical application.Purpose: The objective of this study is to develop a biomimetic LDL nanocarrier by replacing the native apolipoprotein B-100 (apoB-100) with an artificial amphipathic peptide and demonstrate its antitumor efficacy.Methods: The amphipathic hybrid peptide (termed as FPL) consisting of a lipid binding motif of apoB-100 (LBMapoB)-polyethylene glycol (PEG)-folic acid (FA) was synthesized and characterized by 1H NMR and circular dichroism. FPL decorated lipoprotein-mimic nanoparticles (termed as FPLM NPs) were prepared by a modified solvent emulsification method. Paclitaxel (PTX) was incorporated into NPs and its content was quantified by HPLC analysis. The morphology of NPs was observed by transmission electron microscopy (TEM), and the particle size and zeta potential of NPs were determined by dynamic light scattering (DLS). The colloidal stability of FPLM NPs was evaluated in PBS containing bovine serum albumin (BSA). In vitro release of PTX loaded FPLM NPs was evaluated using the dialysis method. Cellular uptake and cytotoxity assayswere evaluated on human cervical cancer cells (HeLa) and lung cancer cells (A549). Tumor inhibition in vivo was investigated in M109 tumor-bearing mice via tail vein injection of Taxol formulation and PTX loaded NPs.Results: The composition of FPLM NPs, including cholesteryl oleate, glyceryl trioleate, cholesterol, 1,2-dioleoyl-sn-glycero-3-phosphoethanolamine (DOPE), and FPL peptides, was optimized to be 5:1:1:3:10 (w/w). FPLM NPs had a spherical shape with a mean diameter of 83 nm and a negative charge (-12 mV). FPLM NPs with optimum formulation had good colloidal stability in BSA solution.The release of PTX from FPLM NPs was slow and sustained. The uptake of FPLM NPs was higher in folate receptor (FR) overexpressing tumor cells (HeLa cells) than in FR deficient tumor cells (A549 cells). The intracellular distribution indicated that FPLM NPs had the lysosome escape capacity. The internalization mechanism of FPLM NPs was involved with clathrin- and caveolae-mediated endocytosis and FR played a positive role in the internalization of FPLM NPs. The CCK-8 assay demonstrated that FPLM NPs exhibited notably better anti-tumor effect than Taxol formulation in vitro. Moreover, PTX loaded FPLM NPs produced very marked anti-tumor efficiency in M109 tumor-bearing mice in vivo.Conclusion: FPLM NPs is a promising nanocarrier which can improve the therapeutic effect and reduce the side effects of antitumor drugs.Keywords: LDL mimic nanoparticles, amphipathic peptide, folic acid, paclitaxel, tumor targeting

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]

Abstract 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.

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]

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.

Molecules interfering with lipid bilayer function exhibit strong antiviral activity against a broad range of enveloped viruses, with a lower risk of resistance development than that for viral protein-targeting drugs. Amphipathic peptides are rich sources of such membrane-interacting antivirals. Here, we report that influenza viruses were effectively inactivated by M2 AH, an amphipathic peptide derived from the M2 protein of the influenza virus. Although overall hydrophobicity () of M2 AH was not related to antiviral activity, modification of the hydrophobic moment (<μH>) of M2 AH dramatically altered the antiviral activity of this peptide. M2 MH, a derivative of M2 AH with a <μH> of 0.874, showed a half maximal inhibitory concentration (IC 50) of 53.3 nM against the A/PR/8/34 strain (H1N1), which is 16-times lower than that of M2 AH. The selectivity index (IC 50 /CC 50), where CC 50 is the half maximal cytotoxic concentration, was 360 for M2 MH and 81 for M2 AH. Dynamic light scattering spectroscopy and electron microscopy revealed that M2 AH-derived peptides did not disrupt liposomes but altered the shape of viruses. This result suggests that the shape of virus envelope was closely related to its activity. Thus, we propose that deforming without rupturing the membranes may achieve a high selectivity index for peptide antivirals. • M2 AH is an amphipathic peptide derived from influenza virus M2 protein. • M2 MH with elevated hydrophobic moment was a strong antiviral with low toxicity. • M2 AH and MH did not disrupt membrane but simply deformed the shape of virus. • Deformation of viral envelope may achieve a high selectivity index for peptide antivirals. [ABSTRACT FROM AUTHOR]

Peptides able to translocate cell membranes while carrying macromolecular cargo, as cell-penetrating peptides (CPPs), can contribute to the field of drug delivery by enabling the transport of otherwise membrane impermeable molecules. Formation of non-covalent complexes between amphipathic peptides and oligonucleotides is driven by electrostatic and hydrophobic interactions. Here we investigate and quantify the coexistence of distinct molecular species in multiple equilibria, namely peptide monomer, peptide self-aggregates and peptide/oligonucleotide complexes. As a model for the complexes, we used a stearylated peptide from the PepFect family, PF14 and siRNA. PF14 has a cationic part and a lipid part, resembling some characteristics of cationic lipids. Fluorescence correlation spectroscopy (FCS) and fluorescence cross-correlation spectroscopy (FCCS) were used to detect distinct molecular entities in solution and at the plasma membrane of live cells. For that, we labeled the peptide with carboxyrhodamine 6G and the siRNA with Cyanine 5. We were able to detect fluorescent entities with diffusional properties characteristic of the peptide monomer as well as of peptide aggregates and peptide/oligonucleotide complexes. Strategies to avoid peptide adsorption to solid surfaces and self-aggregation were developed and allowed successful FCS measurements in solution and at the plasma membrane. The ratio between the detected molecular species was found to vary with pH, peptide concentration and the proximity to the plasma membrane. The present results suggest that the diverse cellular uptake mechanisms, often reported for amphipathic CPPs, might result from the synergistic effect of peptide monomers, self-aggregates and cargo complexes, distributed unevenly at the plasma membrane. [ABSTRACT FROM AUTHOR]

Gene transfer using lentiviral vectors has therapeutic applications spanning from monogenic and infectious diseases to cancer. Such gene therapy has to be improved by enhancing the levels of viral infection of target cells and/or reducing the amount of lentivirus for greater safety and reduced costs. Vectofusin-1, a recently developed cationic amphipathic peptide with a pronounced capacity to enhance such viral transduction, strongly promotes the entry of several retroviral pseudotypes into target cells when added to the culture medium. To clarify the molecular basis of its action the peptide was investigated on a molecular and a supramolecular level by a variety of biophysical approaches. We show that in culture medium vectofusin-1 rapidly forms complexes in the 10 nm range that further assemble into annular and extended nanofibrils. These associate with viral particles allowing them to be easily pelleted for optimal virus-cell interaction. Thioflavin T fluorescence, circular dichroism and infrared spectroscopies indicate that these fibrils have a unique α-helical structure whereas most other viral transduction enhancers form β-amyloid fibrils. A vectofusin-1 derivative (LAH2-A4) is inefficient in biological assays and does not form nanofibrils, suggesting that supramolecular assembly is essential for transduction enhancement. Our observations define vectofusin-1 as a member of a new class of α-helical enhancers of lentiviral infection. Its fibril formation is reversible which bears considerable advantages in handling the peptide in conditions well-adapted to Good Manufacturing Practices and scalable gene therapy protocols. [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]

The intracellular delivery of functionally active transcription factor proteins is emerging as a promising technique for artificial regulation of cellular functions. However, in addition to the cell membrane, which acts as a barrier to macromolecules, the aggregation-favored properties of structurally flexible transcription factor proteins limit the application of this method. In-cell folding technique can be used to overcome these issues. This technique solubilizes denatured protein by reversible alkyl-disulfide cationization ( S -cationization), and simultaneously endows efficient intracellular delivery and folding to the biologically active conformation in the reducing environment of the cytosol. Because cationized protein is internalized into cells by adsorption-mediated endocytosis, endosomal escape is crucial for this technique. In this study, we utilized a sensitive luciferase reporter gene assay to quantitatively evaluate in-cell folding of the artificial transcription factor GAL4-VP16. Although the cationic moiety of S -cationized protein was slightly affected, co-transduction of amphipathic peptide Endo-PORTER dramatically improved in-cell folding efficiency. Live cell imaging of fluorescent-labeled GAL4-VP16 revealed that some of the proteins diffused into the cytosol and nucleus through co-transduction with Endo-PORTER. Real-time monitoring of light output of luciferase revealed the kinetics of in-cell folding, supporting that endosomal-release assisted by Endo-PORTER was stimulated by endosome acidification. Because this method can transduce proteins uniformly and repeatedly into living cells, S -cationized transcription factor proteins are widely applicable for the artificial regulation of cellular functions. [ABSTRACT FROM AUTHOR]

The lipid membranes of living cells are composed of a large number of lipid types and can undergo phase separation with the formation of nanometer-scale liquid-ordered lipid domains, also called rafts. Raft coalescence, i.e., the fusion of lipid domains, is involved in important cell processes, such as signaling and trafficking. In this work, within the framework of the theory of elasticity of lipid membranes, we explore how amphipathic peptides adsorbed on lipid membranes may affect the domain-domain fusion processes. We show that the elastic deformations of lipid membranes drive amphipathic peptides to the boundary of lipid domains, which leads to an increase in the average energy barrier of the domain-domain fusion, even if the surface concentration of amphipathic peptides is low and the domain boundaries are only partially occupied by the peptides. This inhibition of the fusion of lipid domains may lead to negative side effects of using amphipathic peptides as antimicrobial agents.

Helical amphipathic peptides containing cationic and hydrophobic amino acid residues can possess potent antimicrobial activity against both Gram-positive and Gram-negative bacteria. In this study, several amphipathic peptides with enhanced helical structures containing nonproteinogenic amino acids were designed, and the relationships between the antimicrobial activity, hemolytic activity, and cytotoxicity were evaluated. In particular, the effect on the antimicrobial activity and cytotoxicity of the number and position of stapling structures introduced into the sequence was investigated. Peptide stp1 containing α,α-disubstituted amino acids showed potent antimicrobial activity against multidrug-resistant bacteria (MDRP, SP45, and Staphylococcus aureus ) without causing appreciable hemolytic activity or cytotoxicity. The cytotoxicity was found to be somewhat correlated to the hydrophobicity of the peptides.

A synthetic LDL (sLDL) has been prepared by combining a lipid microemulsion with amphipathic peptides containing the apoprotein B receptor domain. The biological properties of sLDL have been investigated using the U937 in vitro cell proliferation assay. sLDL exhibits a concentration dependent and saturable stimulation of U937 proliferation. By utilizing different amphipathic peptides, variable proliferation is achieved, indicating a specific interaction between sLDL and the U937 LDL receptor are possible. U937 proliferation is reduced by the addition of an anti-LDL receptor antibody, indicating that sLDL is assimilated via the LDL receptor pathway. The behavior of sLDL mimics that of native LDL, and this approach represents a viable technique for the production of an sLDL particle on a large scale for research and general application. —Baillie, G., M. D. Owens, and G. W. Halbert. A synthetic low density lipoprotein particle capable of supporting U937 proliferation in vitro. J. Lipid Res. 2002. 43: 69–73.

Diverse organisms secrete amphipathic biomolecules for competitive gains. However, how cells cope with producing these membrane-permeabilizing molecules is unclear. We focused on the PSM family of secreted amphipathic peptides in the pathogen Staphylococcus aureus that uses two ABC transporters, PmtCD and AbcA, to export peptides across the bacterial cell membrane. We found that increased peptide hydrophobicity favors PSM secretion through PmtCD over AbcA and that only PmtCD protected cells against amphipathic peptides. We propose a two-system model in which PmtCD and AbcA independently export PSMs from either membrane or cytosolic environments, respectively. Our model provides a rationale for the encoding of multiple transport systems on diverse biosynthetic gene clusters used to produce distinct amphipathic molecules. In addition, our data serve as a guide for selectively blocking PSM secretion to achieve antimicrobial or antivirulence approaches and to disrupt established roles of PSM-mediated virulence.

A new antimicrobial peptide, herein named Stigmurin, was selected based on a transcriptomic analysis of the Brazilian yellow scorpion Tityus stigmurus venom gland, an underexplored source for toxic peptides with possible biotechnological applications. Stigmurin was investigated in silico , by circular dichroism (CD) spectroscopy, and in vitro. The CD spectra suggested that this peptide interacts with membranes, changing its conformation in the presence of an amphipathic environment, with predominance of random coil and beta-sheet structures. Stigmurin exhibited antibacterial and antifungal activity, with minimal inhibitory concentrations ranging from 8.7 to 69.5 μM. It was also showed that Stigmurin is toxic against SiHa and Vero E6 cell lines. The results suggest that Stigmurin can be considered a potential anti-infective drug. [ABSTRACT FROM AUTHOR]

The design of a non-viral gene delivery vehicle capable of delivering and releasing a functional nucleic acid cargo intracellularly remains a formidable challenge. For systemic gene therapy to be successful a delivery vehicle is required that protects the nucleic acid cargo from enzymatic degradation, extravasates from the vasculature, traverses the cell membrane, disrupts the endosomal vesicles and unloads the cargo at its destination site, namely the nucleus for the purposes of gene delivery. This manuscript reports the extensive investigation of a novel amphipathic peptide composed of repeating RALA units capable of overcoming the biological barriers to gene delivery both in vitro and in vivo. Our data demonstrates the spontaneous self-assembly of cationic DNA-loaded nanoparticles when the peptide is complexed with pDNA. Nanoparticles were < 100 nm, were stable in the presence of serum and were fusogenic in nature, with increased peptide α-helicity at a lower pH. Nanoparticles proved to be non-cytotoxic, readily traversed the plasma membrane of both cancer and fibroblast cell lines and elicited reporter-gene expression following intravenous delivery in vivo. The results of this study indicate that RALA presents an exciting delivery platform for the systemic delivery of nucleic acid therapeutics. [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]

Abstract: Most fatalities from trauma occur due to severe blood loss. There is a need for improved hemostatic biomaterials that can address this problem. The aim of this study was to determine the in vivo efficacy of nanofibrous microspheres (NFM) loaded with hemostatic peptides, specifically ideal amphipathic peptides (IAP) that have been demonstrated to possess both procoagulant and antifibrinolyic activities. We demonstrate that IAP can be coupled to NFM (IAP-NFM) to form matrices that exhibit substantial hemostatic activity. IAP-NFM matrices were compared to a commercial zeolitic hemostatic biomaterial (QuikClot) and have superior efficacy in reducing bleeding in vivo. In both a murine tail transection and a murine hepatic injury model, bleeding times were significantly reduced (P <0.05) with the use of IAP-NFM as compared with equal masses of either QuikClot or NFM alone, or no treatment. Importantly, histological examination revealed no tissue injury when IAP-NFM or NFM were applied to hepatic lacerations. In contrast, QuikClot caused widespread hepatocyte degeneration and necrosis, with higher average injury zone thickness as determined by semiquantitative analysis. In summary, NFM was able to maintain the pro-coagulant properties of IAP in our preclinical model, caused no observable tissue damage at the site of application and had better performance than QuikClot controls. [Copyright &y& Elsevier]

Abstract: We describe a simple but sensitive fluorescence method to accurately detect the esterification activity of lecithin:cholesterol acyltransferase (LCAT). The new assay protocol employs a convenient mix, incubate, and measure scheme. This is possible by using the fluorescent sterol dehydroergosterol (DHE) in place of cholesterol as the LCAT substrate. The assay method is further enhanced by incorporation of an amphiphilic peptide in place of apolipoprotein A-I as the lipid emulsifier and LCAT activator. Specific fluorescence detection of DHE ester synthesis is achieved by employing cholesterol oxidase to selectively render unesterified DHE nonfluorescent. The assay accurately detects LCAT activity in buffer and in plasma that is depleted of apolipoprotein B lipoproteins by selective precipitation. Analysis of LCAT activity in plasmas from control subjects and sickle cell disease (SCD) patients confirms previous reports of reduced LCAT activity in SCD and demonstrates a strong correlation between plasma LCAT activity and LCAT content. The fluorescent assay combines the sensitivity of radiochemical assays with the simplicity of nonradiochemical assays to obtain accurate and robust measurement of LCAT esterification activity. [Copyright &y& Elsevier]

Highlights: [•] Three novel antimicrobial peptides (Pantinin-1, Pantinin-2 and Pantinin-3) were identified from Pandinus imperator. [•] The three peptides have relatively strong antimicrobial activities against Gram-positive bacteria. [•] Pantinin-3 has great potential to be applied in the treatment of VRE infections. [•] We found that hydrophobicity of the hydrophilic region significantly affects the activity of antimicrobial peptides. [Copyright &y& Elsevier]

Short-chain amphipathic peptides are promising components in the new generation of engineered biomaterials. The model 14-residue leucine-lysine peptide Ac-LKKLLKLLKKLLKL-NH2 (LKα) is one such amphipathic peptide. In dilute aqueous solution (<0.05 mmol/L), it was previously proposed, using CD spectroscopic data, that LKα existed in a cooperative monomeric (unstructured) - tetrameric (α-helical) equilibrium that shifted towards the tetramer at high NaCl and peptide concentrations. Here, at similar peptide concentrations, CD spectroscopy shows that LKα readily adopts α-helical structure in the presence of 2,2,2-trifluoroethanol (TFE) and 1,1,1,3,3,3-hexafluoroisopropanol (HFIP) with maximal helical character in 20% TFE and ∼10% HFIP ( v/ v). The helical character in fluorinated alcohols suggested by the CD data at low peptide concentrations (0.06 mmol/L) is corroborated at high peptide concentrations (1.5 mmol/L) by NMR NOE data that also show that 1.5 mmol/L LKα is helical in 100% water. Size exclusion chromatography and estimations of rotational correlation times ( τc) showed that the self-assembled LKα complexes contained three to five peptides. Removing the N-terminal acetyl group prevents LKα from forming helices and self-associating at high NaCl and peptide concentrations. This more detailed characterization of the structural and physical properties of LKα over a greater range of peptide concentrations and in the presence of fluorinated alcohols will assist the design of biomaterials containing amphipathic peptides and guide the ability to control self-assembly. [ABSTRACT FROM AUTHOR]

Abstract: Crotamine is a highly basic peptide from the venom of Crotalus durissus terrificus rattlesnake. Its common gene ancestry and structural similarity with the β-defensins, mainly due to an identical disulfide bond pattern, stimulated us to assess the antimicrobial properties of native, recombinant, and chemically synthesized crotamine. Antimicrobial activities against standard strains and clinical isolates were analyzed by the colorimetric microdilution method showing a weak antibacterial activity against both Gram-positive and Gram-negative bacteria [MIC (Minimum Inhibitory Concentration) of 50–>200 μg/mL], with the exception of Micrococcus luteus [MIC ranging from 1 to 2 μg/mL]. No detectable activity was observed for the filamentous fungus Aspergillus fumigatus and Trichophyton rubrum at concentrations up to 125 μg/mL. However, a pronounced antifungal activity against Candida spp., Trichosporon spp., and Cryptococcus neoformans [12.5–50.0 μg/mL] was observed. Chemically produced synthetic crotamine in general displayed MIC values similar to those observed for native crotamine, whereas recombinant crotamine was overridingly more potent in most assays. On the other hand, derived short linear peptides were not very effective apart from a few exceptions. Pronounced ultrastructure alteration in Candida albicans elicited by crotamine was observed by electron microscopy analyses. The peculiar specificity for highly proliferating cells was confirmed here showing potential low cytotoxic effect of crotamine against nontumoral mammal cell lines (HEK293, PC12, and primary culture astrocyte cells) compared to tumoral B16F10 cells, and no hemolytic activity was observed. Taken together these results suggest that, at low concentration, crotamine is a potentially valuable anti-yeast or candicidal agent, with low harmful effects on normal mammal cells, justifying further studies on its mechanisms of action aiming medical and industrial applications. [Copyright &y& Elsevier]

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]

Abstract: Fiber-forming proteins and peptides are being scrutinized as a promising source of building blocks for new nanomaterials. Arabinogalactan-like (AGL) proteins expressed at the symbiotic interface between plant roots and arbuscular mycorrhizal fungi have novel sequences, hypothesized to form polyproline II (PPII) helix structures. The functional nature of these proteins is unknown but they may form structures for the establishment and maintenance of fungal hyphae. Here we show that recombinant AGL1 (rAGL1) and recombinant AGL3 (rAGL3) are extended proteins based upon secondary structural characteristics determined by electronic circular dichroism (CD) spectroscopy and can self-assemble into fibers and microtubes as observed by atomic force microscopy (AFM) and scanning electron microscopy (SEM). CD spectroscopy results of synthetic peptides based on repeat regions in AGL1, AGL2 and AGL3 suggest that the synthetic peptides contain significant amounts of extended PPII helices and that these structures are influenced by ionic strength and, at least in one case, by concentration. Point mutations of a single residue of the repeat region of AGL3 resulted in altered secondary structures. Self-assembly of these repeats was observed by means of AFM and optical microscopy. Peptide (APADGK)6 forms structures with similar morphology to rAGL1 suggesting that these repeats are crucial for the morphology of rAGL1 fibers. These novel self-assembling sequences may find applications as precursors for bioinspired nanomaterials. [Copyright &y& Elsevier]

Abstract: Amphipathic peptides with unusual cellular translocation properties have been used as carriers of different biomolecules. However, the parameters which control the delivery efficiency of a particular cargo by a peptide and the selectivity of cargo delivery are not very well understood. In this work, we have used the known cell penetrating peptide pVEC (derived from VE-cadherin) and systematically changed its amphipathicity (from primary to secondary) as well as the total charge and studied whether these changes influence the plasmid DNA condensation ability, cellular uptake of the peptide–DNA complexes and in turn the efficiency of DNA delivery of the peptide. Our results show that although the efficiency of DNA delivery of pVEC is poor, modification of the same peptide to create a combination of nine arginines along with secondary amphipathicity improves its plasmid DNA delivery efficiency, particularly in presence of an endosomotropic agent like chloroquine. In addition, presence of histidines along with 9 arginines and secondary amphipathicity shows efficient DNA delivery with low toxicity even in absence of chloroquine in multiple cell lines. We attribute these enhancements in transfection efficiency to the differences in the mechanism of complex formation by the different variants of the parent peptide which in turn are related to the chemical nature of the peptide itself. These results exhibit the importance of understanding the physicochemical parameters of the carrier and complex in modulating gene delivery efficiency. Such studies can be helpful in improving peptide design for delivery of different cargo molecules. [Copyright &y& Elsevier]

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]

Abstract: The twin-arginine translocase (Tat) system is used by many bacteria and plants to move folded proteins across the cytoplasmic or thylakoid membrane. In most bacteria, the TatA protein is believed to form a defined pore in the membrane through homo-oligomerization with other TatA protomers. The predicted secondary structure of TatA includes a transmembrane helix, an amphipathic helix, and an unstructured C-terminal region. Here biophysical and structural investigations were performed on a synthetic peptide representing the amphipathic region of TatA (residues 22 to 44, abbreviated TatAH2). The C-terminal region of TatA (residues 44–89) was previously shown to be accessible from both the cytoplasmic and periplasmic sides of the membrane only when the membrane potential was intact, suggesting dependence of its topology on an energized membrane (Chan et al. 2007 Biochemistry 46: 7396–404). Such observation suggests that the TatAH2 region would have unique lipid interactions that may be related to the function of TatA during translocation and thus warranted further investigations. NMR and CD spectroscopy of TatAH2 show that it adopts a predominantly helical structure in a membrane environment while remaining unstructured in aqueous solution. Differential scanning calorimetry studies also reveal that TatAH2 interacts with DPPG lipids but not with DPPC, suggesting that negatively charged phospholipid head groups contribute to the membrane interactions with TatA. [Copyright &y& Elsevier]

Abstract: The multiple physiological characterizations of glucagon-like peptide-1 (GLP-1) make it a promising drug candidate for the treatment of type 2 diabetes. However, in vivo, the half-life of GLP-1 is short, which is caused by the degradation of dipeptidyl peptidase-IV (DPP-IV) and renal clearance. Thus, the stabilization of GLP-1 is critical for its utility in drug development. Peptides known as GLP-1 protectors are predicted to increase the half-life of GLP-1 in vivo. Protecting peptides are able to form stable complexes by non-covalent interactions with human GLP-1. In this study, the stability of the complex was investigated, and the physiological functions of the GLP-1/peptide 1 complex were compared to those of exenatide and liraglutide in animals. The results indicated that the GLP-1/peptide 1 complex remarkably raised the half-life of GLP-1 in vivo and showed better glucose tolerance and higher HbA1c reduction than exenatide and liraglutide in rodents. Based upon these results, it is suggested that the GLP-1/peptide 1 complex might be utilized as a possible potent anti-diabetic drug in the treatment of type 2 diabetes mellitus. [Copyright &y& Elsevier]

Abstract: RTA3 is an α-helical, amphipathic peptide with broad-spectrum activity against Gram-negative bacteria and low mammalian cell toxicity. RTA3 contains a cysteine residue, replacement of which with an alanine or serine (RTA3-C15S) virtually abolishes antimicrobial activity. Much of the activity of RTA3 can be recovered in RTA3-C15L, indicating that the C15 residue functions largely as a bulky hydrophobic side chain promoting target cell membrane interactions. The poorly active RTA3-C15S is a useful variant for assessing the mechanistic aspects of RTA3 activity. Binding and membrane perturbation in vesicles containing different proportions of negative surface charge are analyzed in terms of amino acid-specific free energy contributions to interfacial binding, which likely underlie variations in antimicrobial activity amongst RTA3 variants. Comparison with published free energy scales indicates that the reduced electrostatic contribution to binding to membranes having reduced negative surface charge can be compensated in RTA3 (but not RTA3-C15S) by a slightly deeper insertion of the C-terminus of the peptide to maximize hydrophobic contributions to binding. Analysis of inner membrane (IM)- and outer membrane (OM)-selective permeabilization of E scherichia coli demonstrates a broad similarity between peptide effects on vesicles with low negative surface charge (20% negatively charged lipids), E . coli membrane perturbation, and antimicrobial activity, supporting a role for membrane perturbation in the killing mechanism of RTA3. The results demonstrate that large variations in antimicrobial activity on subtle changes in amino acid sequence in helical amphipathic peptides can be rationalized in terms of the thermodynamics of peptide binding to membranes, allowing a more systematic understanding of antimicrobial activity in these peptides. [Copyright &y& Elsevier]

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.

Abstract: An ideal amphipathic peptide (IAP), composed of simply lysine and leucine residues in a 1:2 ratio (K7L15), specifically prolongs in vitro coagulation assays that use phospholipids, such as the activated partial thromboplastin time (APTT). The main hypothesis of the present work is that IAP’s anticoagulant effect occurs by competing with phospholipid membranes in in vitro coagulation reactions. We verified this hypothesis by employing different phospholipid-dependent coagulation assays, such as the APTT, the dilute prothrombin time (dPT) and the dilute Russell viper venom time (dRVVT) with both low and high amounts of phospholipids. We show that coagulation times are prolonged by IAP in a concentration-dependent manner, and that this prolongation is abrogated by adding excess phospholipid, demonstrating a phospholipid dependence for this inhibition. Using an ELISA-based binding assay, we show IAP inhibits the binding of one of the vitamin K-dependent coagulation factors, factor X, to phospholipid membranes. This is further confirmed with fluorescence spectroscopy, where the interaction of IAP and factor X is inhibited by phospholipid. In summary, this work demonstrates that IAP can act as an anticoagulant by impairing the interaction of coagulation factors with phospholipid membranes and provides a paradigm for the development of novel anticoagulants. [Copyright &y& Elsevier]

Abstract: Apolipoprotein E (apoE) plays a major role in the transport and metabolism of lipid by acting as a ligand for low density lipoprotein-receptors. The amphipathic helical regions of its C-terminal domain are necessary for the lipoprotein binding and assembly of nascent lipoprotein particles. Lipoproteins in the plasma are known to possess a net negative charge, determined by both its protein and lipid components, which regulates the metabolism of lipoproteins. The role of membrane surface charge on the interaction of apoE has not been studied previously. Also the importance of individual amphipathic helical regions of its C-terminal domain in binding to negatively charged lipid membrane is not addressed. In this study we have compared the interaction of four peptide segments of apoE C-terminal domain (apoE(202–223), apoE(223–244), apoE(245–266), and apoE(268–289)) with zwitterionic and negatively charged model membranes by employing UV–visible and fluorescence spectroscopy, circular dichroism, and native PAGE analysis. Our results show that the peptide sequence 202–223, 245–266 and 268–289 of apoE has higher affinity towards negatively charged lipid membrane and are independently capable of forming lipoprotein particles of 17±2 nm Stokes diameter. The results suggest that surface charge of lipoprotein regulates its metabolism possibly by modulating the recruitment of apoE on its surface. [Copyright &y& Elsevier]

Abstract: The physiological function of apolipoprotein E (apoE) includes transport and metabolism of lipids and its C-terminal domain harbors high affinity lipid-binding sites. Although the binding of apoE with non-oxidized phospholipid containing membranes has been characterized earlier, the interaction of apoE or its fragments with oxidized phospholipid containing membrane has never been studied. In this study we have compared the interaction of amphipathic helical peptide sequences derived from the C-terminal domain of apoE with membrane vesicles containing oxidized phospholipid, 1-palmitoyl-2-azelaoyl-sn-glycero-3-phosphocholine (PazePC), with membrane vesicles without PazePC. The interaction was studied by monitoring (a) fluorescence emission maxima of the peptides, (b) acrylamide quenching of the peptides tryptophan residues and (c) by measuring the equilibrium binding constants by resonance energy transfer (RET) analysis. Our result shows that peptide sequence 202–223, 245–266 and 268–289 of apoE has higher affinity towards membrane containing PazePC, compared to membrane without PazePC. Presence of 1mM divalent cation or 50 mM NaCl in the buffer decreased the binding of peptides to PazePC containing membrane vesicles suggesting possible involvement of the electrostatic interaction in the binding. These observations suggest that the preferential binding of apoE to oxidized phospholipid containing membrane may play a role in the anti-oxidative properties of apoE. [Copyright &y& Elsevier]

Abstract: Independently from the cell penetrating peptide uptake mechanism (endocytic or not), the interaction of the peptide with the lipid bilayer remains a common issue that needs further investigation. The cell penetrating or antimicrobial properties of exogenous peptides require probably different preliminary interactions with the plasma membrane. Herein, we have employed 31P NMR, differential scanning calorimetry and CD to study the membrane interaction and perturbation mechanisms of two basic peptides with similar length but distinct charge distribution, penetratin (non-amphipathic) and RL16, a secondary amphipathic peptide. The peptide effects on the thermotropic phase behavior of large multilamellar vesicles of dimyristoylphosphatidylcholine (DMPC), dimyristoylphosphatidylglycerol (DMPG) and dipalmitoleoyl phosphatidylethanolamine (DiPoPE) were investigated. We have found that, even though both peptides are cationic, their interaction with zwitterionic versus anionic lipids is markedly distinct. Penetratin greatly affects the temperature, enthalpy and cooperativity of DMPG main phase transition but does not affect those of DMPC while RL16 presents opposite effects. Additionally, it was found that penetratin induces a negative curvature whereas RL16 induces a positive one, since a decrease in the fluid lamellar to inverted hexagonal phase transition temperature of DiPoPE (T H) was observed for penetratin and an increase for RL16. Contrary to penetratin, 31P NMR of samples containing DMPC MLVs and RL16 shows an isotropic signal indicative of the formation of small vesicles, concomitant with a great decrease in sample turbidity both below and at the phase transition temperature. Opposite effects were also observed on DMPG where both peptides provoke strong aggregation and precipitation. Both CPPs adopt helical structures when contacting with anionic lipids, and possess a dual behavior by either presenting their cationic or hydrophobic domains towards the phospholipid face, depending on the lipid nature (anionic vs zwitterionic, respectively). Surprisingly, the increase of electrostatic interactions at the water membrane interface prevents the insertion of RL16 hydrophobic region in the bilayer, but is essential for the interaction of penetratin. Modulation of amphipathic profiles and charge distribution of CPPs can alter the balance of hydrophobic and electrostatic membrane interaction leading to translocation or and membrane permeabilisation. Penetratin has a relative pure CPP behavior whereas RL16 presents mixed CPP/AMP properties. A better understanding of those processes is essential to unveil their cell translocation mechanism. [Copyright &y& Elsevier]

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]

Abstract: A polymer-grafted liposomal formulation that has the potential to be developed for aerosolic pulmonary delivery of vasoactive intestinal peptide (VIP), a potent vasodilatory neuropeptide, is described. As VIP is prone to rapid proteolytic degradation in the microenvironment of the lung a proper delivery system is required to increase the half-life and bioavailability of the peptide. Here we investigate structural parameters of unilamellar liposomes composed of palmitoyl-oleoyl-phosphatidylcholine, lyso-stearyl-phosphatidylglycerol and distearyl-phosphatidyl-ethanolamine covalently linked to polyethylene glycol 2000, and report on VIP–lipid interaction mechanisms. We found that the cationic VIP is efficiently entrapped by the negatively charged spherical liposomes and becomes converted to an amphipathic α-helix. By fluorescence spectroscopy using single Trp-modified VIP we could show that VIP is closely associated to the membrane. Our data suggest that the N-terminal random-coiled domain is embedded in the interfacial headgroup region of the phospholipid bilayer. By doing so, neither the bilayer thickness of the lipid membrane nor the mobility of the phospholipid acyl chains are affected as shown by small angle X-ray scattering and electron spin resonance spectroscopy. Finally, in an ex vivo lung arterial model system we found that liposomal-associated VIP is recognized by its receptors to induce vasodilatory effects with comparable high relaxation efficiency as free VIP but with a significantly retarded dilatation kinetics. In conclusion, we have designed and characterized a liposomal formulation that is qualified to entrap biologically active VIP and displays structural features to be considered for delivery of VIP to the lung. [Copyright &y& Elsevier]

Abstract: We have previously shown that self-association of human vasoactive intestinal peptide with sterically stabilized liposomes (VIP-α) alters peptide conformation from random coil in aqueous solution to α-helix. This, in turn, protects the peptide from hydrolysis and amplifies and prolongs its bioactivity. The purpose of this study was to determine whether a single, intravenous injection of low-dose human VIP-α normalizes systemic arterial pressure in anesthetized spontaneously hypertensive hamsters for a prolonged period of time in a selective fashion. We found that intravenous injection of human VIP-α, VIP alone (each, 1.0nmol) and empty liposomes had no significant effects on mean arterial pressure (MAP) in normotensive hamsters. By contrast, human VIP-α (0.01–1.0nmol) evoked a significant concentration-dependent decrease in MAP to the normative range in spontaneously hypertensive hamsters that lasted throughout the observation period (6h; p <0.05). VIP alone and empty liposomes had no significant effects on MAP in these animals. We conclude that a single, low-dose intravenous injection of human VIP-α normalizes systemic arterial pressure in spontaneously hypertensive hamsters for a prolonged period of time in a selective fashion. We suggest that human VIP-α should be further developed as a long-acting, biocompatible and biodegradable peptide nanomedicine for essential hypertension. [Copyright &y& Elsevier]

Abstract: The development of therapeutic peptides and proteins is limited by the poor permeability and the selectivity of the cell membrane. The discovery of protein transduction domains has given a new hope for administration of large proteins and peptides in vivo. We have developed a non-covalent strategy for protein transduction based on an amphipathic peptide, Pep-1, that consists of a hydrophobic domain and a hydrophilic lysine-rich domain. Pep-1 efficiently delivers a variety of fully biologically active peptides and proteins into cells, without the need for prior chemical cross-linking or chemical modifications. The mechanism through which Pep-1 delivers active macromolecules does not involve the endosomal pathway and the dissociation of the Pep-1/macromolecule particle occurs immediately after it crosses the cell membrane. Pep-1 has been successfully applied to the screening of therapeutic peptides in vivo and presents several advantages: stability in physiological buffer, lack of toxicity and of sensitivity to serum. In conclusion, Pep-1 technology could contribute significantly to the development of fundamental and therapeutic applications and be an alternative to covalent protein transduction domain-based technologies. [Copyright &y& Elsevier]

Abstract: Besides being a useful tool in research, gene transfer has a high potential as treatment for a variety of genetic and acquired diseases. However, in order to enable a gene to become a pharmaceutical, efficient and safe methods of delivery have to be developed. We recently found that cationic amphipathic histidine-rich peptide antibiotics can efficiently deliver DNA into mammalian cells. Our lead compound, LAH4 (KKALLALALHHLAHLALHLALALKKA), demonstrated in vitro transfection efficiencies comparable to those of commercially available reagents. Synthesis and evaluation of LAH mutants provided evidence that the transfection efficiency depends on the number and positioning of histidine residues in the peptide as well as on the pH at which the in-plane to transmembrane transition takes place. Moreover, recent results suggest that binding of the DNA complexes to the plasma membrane is mediated by heparan sulfate proteoglycans and that anionic phospholipids may be involved in the endosomal destabilization process. Finally, we also describe in this review the rationale that led to the development of LAH4 as a DNA carrier as well as the biophysical methods that have allowed us to propose a model which could explain the way this peptide destabilizes the endosomal bilayer. [Copyright &y& Elsevier]

Abstract: In recent years, cell-penetrating peptides have proven to be an efficient intracellular delivery system. The mechanism for CPP internalisation, which first involves interaction with the extracellular matrix, is followed in most cases by endocytosis and finally, depending on the type of endocytosis, an intracellular fate is reached. Delivery of cargo attached to a CPP requires endosomal release, for which different methods have recently been proposed. Positively charged amino acids, hydrophobicity and/or amphipathicity are common to CPPs. Moreover, some CPPs can self-assemble. Herein is discussed the role of self assembly in the cellular uptake of CPPs. Sweet Arrow Peptide (SAP) CPP has been shown to aggregate by CD and TEM (freeze-fixation/freeze-drying), although the internalised species have yet to be identified as either the monomer or an aggregate. [Copyright &y& Elsevier]

A synthetic peptide of 23 residues corresponding to the carboxyterminal 113 to 135 region of component-3 of proteose peptone (PP3) has been investigated with regard to its antibacterial properties. This cationic amphipathic peptide that we refer to as lactophoricin, displayed a growth-inhibitory activity against both gram-positive and gram-negative bacteria. For most of the strains tested, bacterial growth was observed in the presence of lactophoricin except for Streptococcus thermophilus. In that case, lactophoricin exhibited a minimum inhibitory concentration of 10 µM and a minimum lethal concentration of 20 µM. No hemolysis of human red blood cells was detected for peptide concentrations between 2 to 200 µM, indicating that lactophoricin would be noncytotoxic when used in this concentration range. [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]