Interaction of the 14-residue peptaibols, harzianins HC, with lipid bilayers: permeability modifications and conductance properties

Importance of isoleucine residue in ion channel formation ability of 11-residue peptaibols

Peptaibols are a class of short peptides, typically 7 to 20 amino acids long, characterized by noncanonical amino acid residues such as aminoisobutyric acid (Aib). Although the helix length is shorter than the membrane thickness, the 11-residue peptaibol trichorovin-XII (TV-XII) can form ion channels in membranes. Assuming that a higher proportion of isoleucine (Ile) relative to leucine (Leu) residues is crucial for maintaining the ion channel activity of TV-XII, peptide analogs of TV-XII with varying Ile content were designed, synthesized, and evaluated. The secondary structure of all derivatives under hydrophobic conditions was confirmed by CD measurement as an α-helix-like β-bend ribbon spiral structure. The most stable ion channel activity was found in compound 4a with maximum Ile. Furthermore, the C-terminal Ile analog showed greater ion channel activity compared to the Leu analog. This suggests that the choice between Leu and Ile can influence the expression of ion channel activity, which will be crucial for the de novo designed functional peptides.

Thirteen new peptaibols with antimicrobial activities from Trichoderma sp

From the fungus Trichoderma sp., we isolated seven novel 18-residue peptaibols, neoatroviridins E-K (1-7), and six new 14-residue peptaibols, harzianins NPDG J-O (8-13). Additionally, four previously characterized 18-residue peptaibols neoatroviridins A-D (14-17) were also identified. The structural configurations of the newly identified peptaibols (1-13) were determined by comprehensive nuclear magnetic resonance (NMR) and high-resolution electrospray ionization tandem mass spectrometry (HR-ESI-MS/MS) data. Their absolute configurations were further determined using Marfey's method. Notably, compounds 12 and 13 represent the first 14-residue peptaibols containing an acidic amino acid residue. In antimicrobial assessments, all 18-residue peptaibols (1-7, 14-17) exhibited moderate inhibitory activities against Staphylococcus aureus 209P, with minimum inhibitory concentration (MIC) values ranging from 8-32 μg·mL-1. Moreover, compound 9 exhibited moderate inhibitory effect on Candida albicans FIM709, with a MIC value of 16 μg·mL-1.

New carvacrol and thymol derivatives as potential insecticides: synthesis, biological activity, computational studies and nanoencapsulation

New compounds with potential insecticide activity were synthesized by structural modifications performed in the monoterpenoid phenolic moieties of carvacrol and thymol, resulting in a set of derivatives with the ether function containing the propyl, chloropropyl or hydroxypropyl chains, as well as a bicyclic ether with an unsaturated chain containing a carboxylic acid terminal. In addition, an analogue of carvacrol and thymol isomers bearing methoxyl, 1-hydroxyethyl and (3-chlorobenzoyl)oxy, instead of the three original methyl groups, was also synthesized. Several structural changes that resulted in diminished insecticide activity have been identified, but two significantly active molecules have been synthesized, one of them being less toxic to human cells than the naturally-derived starting materials. Structure-based inverted virtual screening and molecular dynamics simulations demonstrate that these active molecules likely target the insect odorant binding proteins and/or acetylcholinesterase and are able to form stable complexes. For the most promising compounds, nanoencapsulation assays were carried out in liposomes of egg phosphatidylcholine/cholesterol (7 : 3) prepared by both thin film hydration and ethanolic injection methods. The compound-loaded liposomes were generally monodisperse and with sizes smaller than or around 200 nm. The thin film hydration method allowed high encapsulation efficiencies (above 85%) for both compounds and a delayed release, while for the systems prepared by ethanolic injection the encapsulation efficiency is lower than 50%, but the release is almost complete in two days.

Diversity of Linear Non-Ribosomal Peptide in Biocontrol Fungi

Biocontrol fungi (BFs) play a key role in regulation of pest populations. BFs produce multiple non-ribosomal peptides (NRPs) and other secondary metabolites that interact with pests, plants and microorganisms. NRPs-including linear and cyclic peptides (L-NRPs and C-NRPs)-are small peptides frequently containing special amino acids and other organic acids. They are biosynthesized in fungi through non-ribosomal peptide synthases (NRPSs). Compared with C-NRPs, L-NRPs have simpler structures, with only a linear chain and biosynthesis without cyclization. BFs mainly include entomopathogenic and mycoparasitic fungi, that are used to control insect pests and phytopathogens in fields, respectively. NRPs play an important role of in the interactions of BFs with insects or phytopathogens. On the other hand, the residues of NRPs may contaminate food through BFs activities in the environment. In recent decades, C-NRPs in BFs have been thoroughly reviewed. However, L-NRPs are rarely investigated. In order to better understand the species and potential problems of L-NRPs in BFs, this review lists the L-NRPs from entomopathogenic and mycoparasitic fungi, summarizes their sources, structures, activities and biosynthesis, and details risks and utilization prospects.

14-Residue peptaibol velutibol A from Trichoderma velutinum: its structural and cytotoxic evaluation

Velutibol A (1), a new 14-residue peptaibol was isolated from the Himalayan cold habitat fungus Trichoderma velutinum. The structural characterization was carried out by 1D and 2D NMR studies, and tandem mass studies, and Marfey's method aided in determining the stereochemistry of the amino acids. The CD analysis revealed folding of the peptide in a 3₁₀-helical conformation. The intramolecular H-bonding was determined by an NMR-VT experiment. Cytotoxic evaluation was carried out against a panel of cancer cell lines. The cell cycle assay was carried out on human myeloid leukaemia (HL-60) cells and revealed the formation of apoptotic bodies and DNA damage in a dose-dependent manner. Three other peptaibols namely velutibol B (2), velutibol C (3), and velutibol D (4) were also isolated in trace amounts from the psychotropic fungus and characterized through tandem mass spectroscopy and Marfey's analysis.

Velutibol A (1), a new 14-residue peptaibol isolated from the Himalayan cold habitat fungus Trichoderma velutinum.

Novel dehydropeptide-based magnetogels containing manganese ferrite nanoparticles as antitumor drug nanocarriers

Novel peptide-based magnetogels, containing MnFe₂O₄ nanoparticles of 20 nm size, were developed and successfully tested as nanocarriers for antitumor drugs.

Orthogonal 19 F-Labeling for Solid-State NMR Spectroscopy Reveals the Conformation and Orientation of Short Peptaibols in Membranes

Peptaibols are promising drug candidates in view of their interference with cellular membranes. Knowledge of their lipid interactions and membrane-bound structure is needed to understand their activity and should be, in principle, accessible by solid-state NMR spectroscopy. However, their unusual amino acid composition and noncanonical conformations make it very challenging to find suitable labels for NMR spectroscopy. Particularly in the case of short sequences, new strategies are required to maximize the structural information that can be obtained from each label. Herein, l-3-(trifluoromethyl)bicyclopent[1.1.1]-1-ylglycine, (R)- and (S)-trifluoromethylalanine, and ¹⁵ N-backbone labels, each probing a different direction in the molecule, have been combined to elucidate the conformation and membrane alignment of harzianin HK-VI. For the short sequence of 11 amino acids, 12 orientational constraints have been obtained by using ¹⁹ F and ¹⁵ N NMR spectroscopy. This strategy revealed a β-bend ribbon structure, which becomes realigned in the membrane from a surface-parallel state towards a membrane-spanning state, with increasing positive spontaneous curvature of the lipids.

How a short pore forming peptide spans the lipid membrane

Many antimicrobial peptides function by forming pores in the plasma membrane of the target cells. Intriguingly, some of these peptides are very short, and thus, it is not known how they can span the membrane, or whether other mechanisms of cell disruption are dominant. Here, the conformation and orientation of the 14-residue peptaibol SPF-5506-A₄ (SPF) are investigated in lipid environments by atomistic and coarse grained molecular dynamics (MD) simulations, circular dichroism, and nuclear magnetic resonance (NMR) experiments. The MD simulations show that SPF is inserted spontaneously in a transmembrane orientation in both 1,2-dimyristoyl-sn-glycero-3-phosphocholine and 1-palmitoyl-2-oleoyl-sn-glycero-3-phosphocholine bilayers resulting in thinning of the bilayers near the peptides, which drives the peptide aggregation. Furthermore, the backbone conformation of the peptide in the bilayer bound state is different from that of the NMR model solved in small bicelles. These results demonstrate that mutual adaption between the peptides and the membrane is likely to be important for pore formation.

Magnetoliposomes as carriers for promising antitumor thieno[3,2-b]pyridin-7-arylamines: photophysical and biological studies

Magnetoliposomes containing MnFe₂O₄ nanoparticles were used as nanocarriers for new potent antitumor thieno[3,2-b]pyridin-7-arylamines, inhibiting the growth of human tumor cells.

Electrophysiology investigation of Trichogin GA IV activity in planar lipid membranes reveals ion channels of well-defined size

Trichogin GA IV, an antimicrobial peptaibol, exerts its function by augmenting membrane permeability, but the molecular aspects of its pore-forming mechanism are still debated. Several lines of evidence indicate a 'barrel-stave' channel structure, similar to that of alamethicin, but the length of a trichogin helix is too short to span a normal bilayer. Herein, we present electrophysiology measurements in planar bilayers, showing that trichogin does form channels of a well-defined size (R=4.2⋅10(9)  Ω; corresponding at least to a trimeric aggregate) that span the membrane and allow ion diffusion, but do not exhibit voltage-dependent rectification, unlike those of alamethicin.

Four complete turns of a curved 3₁₀-helix at atomic resolution: the crystal structure of the peptaibol trichovirin I-4A in a polar environment suggests a transition to α-helix for membrane function

The first crystal structure of a member of peptaibol antibiotic subfamily 4, trichovirin I-4A (14 residues), has been determined by direct methods and refined at atomic resolution. The monoclinic unit cell has two molecules in the asymmetric unit. Both molecules assume a 3₁₀ right-handed helical conformation and are significantly bent. The molecules pack loosely along the crystallographic twofold axis, forming two large tunnels between symmetry-related molecules in which no ordered solvent could be located. Carbonyl O atoms which are not involved in intramolecular hydrogen bonding participate in close van der Waals interactions with apolar groups. The necessary amphipathicity for biological activity of peptaibols is not realised in the crystal structure. Hence, a structural change of trichovirin to an α-helical conformation is proposed for membrane integration and efficient water/ion transportation across the lipid bilayer.

Formation of atroviridin by Hypocrea atroviridis is conidiation associated and positively regulated by blue light and the G protein GNA3

Species of the mycoparasitic fungal genus Hypocrea/Trichoderma are prominent producers of peptaibols, a class of small linear peptides of fungal origin. Some of these peptaibols have been shown to act synergistically with cell-wall-degrading enzymes in the inhibition of the growth of other fungi in vitro and in vivo. Here we present the structure of the Hypocrea atroviridis peptaibol synthetase gene (pbs1), deduced from the genome sequence of H. atroviridis. It consists of 19 typical peptide synthetase modules with the required additional modifying domains at the N and C termini. Phylogenetic and similarity analyses of the individual amino acid-activating modules is consistent with its ability to synthesize atroviridins. Matrix-assisted laser desorption ionization-time of flight mass spectrometry of surface-grown cultures of H. atroviridis showed that no peptaibols were formed during vegetative growth, but a microheterogenous mixture of atroviridins accumulated when the colonies started to sporulate. This correlation between sporulation and atroviridin formation was shown to be independent of the pathway inducing sporulation (i.e., light, mechanical injury and carbon starvation, respectively). Atroviridin formation was dependent on the function of the two blue light regulators, BLR1 and BLR2, under some but not all conditions of sporulation and was repressed in a pkr1 (regulatory subunit of protein kinase A) antisense strain with constitutively active protein kinase A. Conversely, however, loss of function of the Galpha-protein GNA3, which is a negative regulator of sporulation and leads to a hypersporulating phenotype, fully impairs atroviridin formation. Our data show that formation of atroviridin by H. atroviridis occurs in a sporulation-associated manner but is uncoupled from it at the stage of GNA3.

Toxicity assessment of peptaibols and contaminated sediments on Crassostrea gigas embryos

Peptaibols are known membrane-modifying peptides that were recently detected in marine sediments and mussels collected from a shellfish farming area (Fier d'Ars, Atlantic coast, France). In this investigation, embryotoxicity bioassays with oysters (Crassostrea gigas) were performed to assess acute toxicity of alamethicin and different groups of peptaibols produced by a Trichoderma longibrachiatum strain isolated from marine environment. C. gigas embryos appeared very sensitive to all the metabolites examined with higher toxic effects for long-sequence peptides (EC50 ranging from 10 to 64 nM). D-shaped larvae with mantle abnormality were particularly noticed when peptaibol concentrations increased. Disturbances of embryogenesis were also observed following exposure to organic and aqueous extract of sediments from Fier d'Ars (EC50=42.4 and 6.6 g L(-1) dry weight, respectively). Although peptaibol concentrations measured in these sediments could explain only a part of the toxic effects observed, this study suggests that these mycotoxins can induce larval abnormalities in a population of exposed animals at environmentally realistic concentrations. Their detection in coastal areas devoted to bivalve culture should be taken into account.

Peptaibiotics and Peptaibols: An Alternative to Classical Antibiotics?

The development and antimicrobial properties of peptaibiotics and peptaibols are discussed. Also, the role of emerging peptaibol analogues, of alamethicin, e.g., harzianins HC, trichotoxin, and antiamoebin, is outlined.

Peptaibols of trichoderma

The fungal genus Trichoderma has various applications in industry and in medicine, and several species have economic importance as sources of enzymes, antibiotics, plant growth promoters, decomposers of xenobiotics, and as commercial biofungicides. Peptaibiotics and peptaibols are a class of linear peptides synthesized by such fungi, and more than 300 have been described to date. Of this class, those compounds exhibiting antimicrobial activity are referred to as antibiotic peptides. In this review, the biosynthesis, fermentation, structure elucidation (by MS and NMR techniques in particular) and biological activity of antibiotic peptides from Trichoderma species are described.

Membrane association and activity of 15/16-membered peptide antibiotics: zervamicin IIB, ampullosporin A and antiamoebin I

Permeabilization of the phospholipid membrane, induced by the antibiotic peptides zervamicin IIB (ZER), ampullosporin A (AMP) and antiamoebin I (ANT) was investigated in a vesicular model system. Membrane-perturbing properties of these 15/16 residue peptides were examined by measuring the K(+) transport across phosphatidyl choline (PC) membrane and by dissipation of the transmembrane potential. The membrane activities are found to decrease in the order ZER>AMP>>ANT, which correlates with the sequence of their binding affinities. To follow the insertion of the N-terminal Trp residue of ZER and AMP, the environmental sensitivity of its fluorescence was explored as well as the fluorescence quenching by water-soluble (iodide) and membrane-bound (5- and 16-doxyl stearic acids) quenchers. In contrast to AMP, the binding affinity of ZER as well as the depth of its Trp penetration is strongly influenced by the thickness of the membrane (diC(16:1)PC, diC(18:1)PC, C(16:0)/C(18:1)PC, diC(20:1)PC). In thin membranes, ZER shows a higher tendency to transmembrane alignment. In thick membranes, the in-plane surface association of these peptaibols results in a deeper insertion of the Trp residue of AMP which is in agreement with model calculations on the localization of both peptide molecules at the hydrophilic-hydrophobic interface. The observed differences between the membrane affinities/activities of the studied peptaibols are discussed in relation to their hydrophobic and amphipathic properties.

Trichogin: a paradigm for lipopeptaibols

Lipopeptaibols are members of a novel family of naturally occurring, short peptides with antimicrobial activity, characterized by a lipophilic acyl chain at the N-terminus, a high content of turn/helix inducing alpha-aminoisobutyric acid and a 1,2-amino alcohol at the C-terminus. Using solution methods, the prototypical lipopeptaibol trichogin GA IV and a large series of appropriately designed analogues were synthesized, which allow: (i) determination of the minimal lipid chain and peptide main-chain lengths for the onset of membrane activity, and (ii) exploitation of a number of physico-chemical techniques aimed at assessing the trichogin preferred conformation under a variety of conditions and at investigating its mechanism of interaction with the phospholipid membranes.

Biological effects of Trichoderma harzianum peptaibols on mammalian cells

Trichoderma species isolated from water-damaged buildings were screened for toxicity by using boar sperm cells as indicator cells. The crude methanolic cell extract from Trichoderma harzianum strain ES39 inhibited the boar sperm cell motility at a low exposure concentration (50% effective concentration, 1 to 5 microg [dry weight] ml of extended boar semen(-1)). The same exposure concentration depleted the boar sperm cells of NADH(2). Inspection of the exposed boar sperm cells by transmission electron microscopy revealed damage to the plasma membrane. By using the black lipid membrane technique, it was shown that the semipurified metabolites (eluted from a SepPak C(18) cartridge) of T. harzianum strain ES39 induced voltage-dependent conductivity. The high-performance liquid chromatography-purified metabolites of T. harzianum strain ES39 dissipated the mitochondrial membrane potential (Deltapsi(m)) of human lung epithelial carcinoma cells (cell line A549). The semipurified metabolites (eluted from a SepPak C(18) cartridge) of T. harzianum strain ES39 were analyzed by mass spectrometry (MS). Matrix-assisted laser desorption ionization and nanoflow electrospray ionization MS revealed five major peptaibols, each of which contained 18 residues and had a mass ranging from 1,719 to 1,775 Da. Their partial amino acid sequences were determined by collision-induced dissociation tandem MS.

Detection of new sequences of peptaibol antibiotics trichotoxins A-40 by on-line liquid chromatography-electrospray ionization mass spectrometry

Using high-performance liquid chromatography (HPLC) coupled to electrospray ionization mass spectrometry (ESI-MS) the sequences of the microheterogeneous peptide mixture of the 18-residue "peptaibol" antibiotics trichotoxins A-40, isolated from the mold Trichoderma viride strain NRRL 5242, were reinvestigated. The structures of two major and one minor component [J. Chromatogr., 296 (1984) 236] could be confirmed and hitherto not known sequences of a further major and two minor peptides could be determined. It is demonstrated that ESI-MS in the positive ionization mode is advantageously completed by applying negative ionization. The methods used make possible the sequence determination of components of peptaibols without previous isolation and allow, in certain cases, sequencing of peptides which are incompletely or not resolved by HPLC.

Antiamoebin can function as a carrier or as a pore-forming peptaibol

Antiamoebin is a 16-residue polypeptide whose crystal structure and lytic activity in membrane vesicles have recently been reported. It is a bent helical molecule and a member of the peptaibol family of antibiotics. Under conditions which produce voltage-dependent conductance activity by other members of the family, no single-channel conductance was detected for antiamoebin, and a carrier-like mechanism was put forward to account for its mode of action. We now present evidence for pore formation that is largely voltage-insensitive, with large amplitude single-channel events on top of a background conductance that may account for the previously proposed carrier-like activity. Thus, antiamoebin may be the first instance of a peptide which can function both as an ion carrier and a pore former.

Alamethicin-like behaviour of new 18-residue peptaibols, trichorzins PA. Role of the C-terminal amino-alcohol in the ion channel forming activity

The influences of peptide length, absence of a Glx (Gln/Glu) residue and the C-terminal amino alcohol on liposome permeabilization and ion-channel characteristics in planar lipid bilayers were examined with two 18-residue peptaibols, PA V and PA IX. As compared to the 20-residue alamethicin, both peptides belonging to the newly isolated trichorzin family, lack a proline in the N-terminal part and one of the two Gln/Glu residues in the C-terminal part of the sequence. The two analogues studied here differ among themselves in their C-terminal amino alcohol (tryptophanol for PA V and phenylalaninol for PA IX). These alpha-helical peptaibols modify to a similar extent the permeability of liposomes, as measured by leakage of a previously entrapped fluorescent probe. Monitoring tryptophanol fluorescence, a greater embedment of the peptide PA V is observed in cholesterol-free bilayers. Macroscopic conductance studies for PA V and PA IX display alamethicin-like current-voltage curves, with a similar voltage dependence, but a smaller mean number of monomers per conducting aggregate is estimated for the tryptophanol analogue, PA V. Single-channel recordings indicate faster current fluctuations for PA IX, while amplitude histograms show lower conductance levels for PA V. Apart from underlining the role of the mismatch between helix length and bilayer hydrophobic thickness, these results stress that the C-terminal tryptophanol favours a stabilization of the conducting aggregates.