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

Structural characterization and bioactivity profiling of the fungal peptaibiotic tolypin reveal protective effects against influenza viruses

In a bioprospection for new antivirals, we tested nonribosomally biosynthesized polypeptide antibiotics in MDCK II cells for their actions on influenza A and B viruses (IAV/IBV). Only tolypin, a mixture of closely related 16-residue peptaibiotics from the fungus Tolypocladium inflatum IE 1897, showed promising activity. It was selected for further investigation and structural characterization by ultrahigh performance liquid chromatography coupled to high-resolution mass spectrometry (UHPLC-HR-MS/MS) and ultrahigh performance liquid chromatography coupled to in-source collision-induced dissociation tandem mass spectrometry (UHPLC-isCID-HR-MS/MS), revealing 12 partially co-eluting individual peptides that were fully sequenced. Since tolypin-related efrapeptins are potent inhibitors of F1/Fo-ATPase, we screened tolypin for its toxicity against MDCK II cells and larvae of the greater wax moth Galleria mellonella. We found that a nontoxic concentration of tolypin (1 µg/mL) reduced the titer of two IBV strains by 4-5 log values, and that of an H3N2 strain by 1-2 log values, but the H1N1pdm strain was not affected. The higher concentrations of tolypin were cytostatic to MDCK II cells, shifted their metabolism from oxidative phosphorylation to glycolysis, and induced paralysis in G. mellonella, supporting the inhibition of F1/Fo-ATPase as the mode of action. Our results lay the foundations for future work to investigate the interplay between viral replication and cellular energy metabolism, as well as the development of drugs that target host factors.

Multi-oligomeric states of alamethicin ion channel: Assemblies and conductance

Transmembrane assemblies of the peptaibol alamethicin (ALM) are among the most extensively studied ion channels not only because of their antimicrobial activity but also as models for channel structure and aggregation. In this study, several oligomeric states of ALM are investigated with molecular dynamics simulations to establish properties of the channel and obtain free energy profiles for ion transport and the corresponding values of conductance. The hexamer, heptamer, and octamer of ALM in phospholipid membrane are found to be stable but highly dynamic in barrel-stave structures, with calculated conductance equal to 18, 195, and 1270 pS, respectively, in 1 M KCl ion solution. The corresponding free energy profiles, reported for the first time, are reconstructed from simulations at applied voltage of 200 mV with the aid of the electrodiffusion model both with and without the knowledge of diffusivity. The calculated free energy barriers are equal to 2.5, 1.5, and 0.5 kcal/mol for K+ and 4.0, 2.2, and 1.5 kcal/mol for Cl-, for hexamer, heptamer, and octamer, respectively. The calculated conductance and the ratio between conductance in consecutive states are in good agreement with those measured experimentally. This suggests that the hexamer is the lowest conducting state, with measured conductance equal to 19 pS. The selectivity of K+ over Cl- is calculated as 1.5 and 2.3 for the octameric and heptameric channels, close to the selectivity measured for high-conductance states. Selectivity increases to 13 in the hexameric channel in which the narrowest Gln7 site has a pore radius of only ∼1.6 Å, again in accord with experiment. A good agreement found between calculated and measured conductance through a hexamer templated on cyclodextrin lands additional support for the results of our simulations, and the comparison with ALM reveals the dependence of conductance on the nature of phospholipid membrane.

Switchable foldamer ion channels with antibacterial activity

Synthetic ion channels may have applications in treating channelopathies and as new classes of antibiotics, particularly if ion flow through the channels can be controlled. Here we describe triazole-capped octameric α-aminoisobutyric acid (Aib) foldamers that "switch on" ion channel activity in phospholipid bilayers upon copper(ii) chloride addition; activity is "switched off" upon copper(ii) extraction. X-ray crystallography showed that CuCl2 complexation gave chloro-bridged foldamer dimers, with hydrogen bonds between dimers producing channels within the crystal structure. These interactions suggest a pathway for foldamer self-assembly into membrane ion channels. The copper(ii)-foldamer complexes showed antibacterial activity against B. megaterium strain DSM319 that was similar to the peptaibol antibiotic alamethicin, but with 90% lower hemolytic activity.

Flexible Proteins at the Origin of Life

Almost all modern proteins possess well-defined, relatively rigid scaffolds that provide structural preorganization for desired functions. Such scaffolds require the sufficient length of a polypeptide chain and extensive evolutionary optimization. How ancestral proteins attained functionality, even though they were most likely markedly smaller than their contemporary descendants, remains a major, unresolved question in the origin of life. On the basis of evidence from experiments and computer simulations, we argue that at least some of the earliest water-soluble and membrane proteins were markedly more flexible than their modern counterparts. As an example, we consider a small, evolved in vitro ligase, based on a novel architecture that may be the archetype of primordial enzymes. The protein does not contain a hydrophobic core or conventional elements of the secondary structure characteristic of modern water-soluble proteins, but instead is built of a flexible, catalytic loop supported by a small hydrophilic core containing zinc atoms. It appears that disorder in the polypeptide chain imparts robustness to mutations in the protein core. Simple ion channels, likely the earliest membrane protein assemblies, could also be quite flexible, but still retain their functionality, again in contrast to their modern descendants. This is demonstrated in the example of antiamoebin, which can serve as a useful model of small peptides forming ancestral ion channels. Common features of the earliest, functional protein architectures discussed here include not only their flexibility, but also a low level of evolutionary optimization and heterogeneity in amino acid composition and, possibly, the type of peptide bonds in the protein backbone.

Length-Dependent Formation of Transmembrane Pores by 310-Helical α-Aminoisobutyric Acid Foldamers

The synthetic biology toolbox lacks extendable and conformationally controllable yet easy-to-synthesize building blocks that are long enough to span membranes. To meet this need, an iterative synthesis of α-aminoisobutyric acid (Aib) oligomers was used to create a library of homologous rigid-rod 3₁₀-helical foldamers, which have incrementally increasing lengths and functionalizable N- and C-termini. This library was used to probe the inter-relationship of foldamer length, self-association strength, and ionophoric ability, which is poorly understood. Although foldamer self-association in nonpolar chloroform increased with length, with a ∼14-fold increase in dimerization constant from Aib₆ to Aib₁₁, ionophoric activity in bilayers showed a stronger length dependence, with the observed rate constant for Aib₁₁ ∼70-fold greater than that of Aib₆. The strongest ionophoric activity was observed for foldamers with >10 Aib residues, which have end-to-end distances greater than the hydrophobic width of the bilayers used (∼2.8 nm); X-ray crystallography showed that Aib₁₁ is 2.93 nm long. These studies suggest that being long enough to span the membrane is more important for good ionophoric activity than strong self-association in the bilayer. Planar bilayer conductance measurements showed that Aib₁₁ and Aib₁₃, but not Aib₇, could form pores. This pore-forming behavior is strong evidence that Aib_m (m ≥ 10) building blocks can span bilayers.

The SMART model: Soft Membranes Adapt and Respond, also Transiently, in the presence of antimicrobial peptides

Biophysical and structural studies of peptide-lipid interactions, peptide topology and dynamics have changed our view on how antimicrobial peptides insert and interact with membranes. Clearly, both the peptides and the lipids are highly dynamic, change and mutually adapt their conformation, membrane penetration and detailed morphology on a local and a global level. As a consequence, the peptides and lipids can form a wide variety of supramolecular assemblies in which the more hydrophobic sequences preferentially, but not exclusively, adopt transmembrane alignments and have the potential to form oligomeric structures similar to those suggested by the transmembrane helical bundle model. In contrast, charged amphipathic sequences tend to stay intercalated at the membrane interface where they cause pronounced disruptions of the phospholipid fatty acyl packing. At increasing local or global concentrations, the peptides result in transient membrane openings, rupture and ultimately lysis. Depending on peptide-to-lipid ratio, lipid composition and environmental factors (temperature, buffer composition, ionic strength, etc.), the same peptide sequence can result in a variety of those responses. Therefore, the SMART model has been introduced to cover the full range of possibilities. With such a view in mind, novel antimicrobial compounds have been designed from amphipathic polymers, peptide mimetics, combinations of ultra-short polypeptides with hydrophobic anchors or small designer molecules.

Towards co-evolution of membrane proteins and metabolism

Primordial metabolism co-evolved with the earliest membrane peptides to produce more environmentally fit progeny. Here, we map a continuous, evolutionary path that connects nascent biochemistry with simple, membrane-bound oligopeptides, ion channels and, further, membrane proteins capable of energy transduction and utilization of energy for active transport.

Membrane thickness and the mechanism of action of the short peptaibol trichogin GA IV

Trichogin GA IV (GAIV) is an antimicrobial peptide of the peptaibol family, like the extensively studied alamethicin (Alm). GAIV acts by perturbing membrane permeability. Previous data have shown that pore formation is related to GAIV aggregation and insertion in the hydrophobic core of the membrane. This behavior is similar to that of Alm and in agreement with a barrel-stave mechanism, in which transmembrane oriented peptides aggregate to form a channel. However, while the 19-amino acid long Alm has a length comparable to the membrane thickness, GAIV comprises only 10 amino acids, and its helix is about half the normal bilayer thickness. Here, we report the results of neutron reflectivity measurements, showing that GAIV inserts in the hydrophobic region of the membrane, causing a significant thinning of the bilayer. Molecular dynamics simulations of GAIV/membrane systems were also performed. For these studies we developed a novel approach for constructing the initial configuration, by embedding the short peptide in the hydrophobic core of the bilayer. These calculations indicated that in the transmembrane orientation GAIV interacts strongly with the polar phospholipid headgroups, drawing them towards its N- and C-termini, inducing membrane thinning and becoming able to span the bilayer. Finally, vesicle leakage experiments demonstrated that GAIV activity is significantly higher with thinner membranes, becoming similar to that of Alm when the bilayer thickness is comparable to its size. Overall, these data indicate that a barrel-stave mechanism of pore formation might be possible for GAIV and for similarly short peptaibols despite their relatively small size.

The crystal structure of samarosporin I at atomic resolution

The atomic resolution structures of samarosporin I have been determined at 100 and 293 K. This is the first crystal structure of a natural 15-residue peptaibol. The amino acid sequence in samarosporin I is identical to emerimicin IV and stilbellin I. Samarosporin is a peptide antibiotic produced by the ascomycetous fungus Samarospora rostrup and belongs to peptaibol subfamily 2. The structures at both temperatures are very similar to each other adopting mainly a 3₁₀-helical and a minor fraction of α-helical conformation. The helices are significantly bent and packed in an antiparallel fashion in the centered monoclinic lattice leaving among them an approximately 10-Å channel extending along the crystallographic twofold axis. Only two ordered water molecules per peptide molecule were located in the channel. Comparisons have been carried out with crystal structures of subfamily 2 16-residue peptaibols antiamoebin and cephaibols. The repercussion of the structural analysis of samarosporin on membrane function is discussed.

Molecular dynamics simulation of the antiamoebin ion channel: linking structure and conductance

Molecular-dynamics simulations were carried out to ascertain which of the potential multimeric forms of the transmembrane peptaibol channel, antiamoebin, is consistent with its measured conductance. Estimates of the conductance obtained through counting ions that cross the channel and by solving the Nernst-Planck equation yield consistent results, indicating that the motion of ions inside the channel can be satisfactorily described as diffusive. The calculated conductance of octameric channels is markedly higher than the conductance measured in single channel recordings, whereas the tetramer appears to be nonconducting. The conductance of the hexamer was estimated to be 115 ± 34 pS and 74 ± 20 pS, at 150 mV and 75 mV, respectively, in satisfactory agreement with the value of 90 pS measured at 75 mV. On this basis, we propose that the antiamoebin channel consists of six monomers. Its pore is large enough to accommodate K⁺ and Cl⁻ with their first solvation shells intact. The free energy barrier encountered by K⁺ is only 2.2 kcal/mol whereas Cl⁻ encounters a substantially higher barrier of nearly 5 kcal/mol. This difference makes the channel selective for cations. Ion crossing events are shown to be uncorrelated and follow Poisson statistics.

Self-assembly and function of primitive cell membranes

We describe possible pathways for separating amphiphilic molecules from organic material on the early earth to form membrane-bound structures required for the start of cellular life. We review properties of the first membranes and their function as permeability barriers. Finally, we discuss the emergence of protein-mediated ion transport across membranes, which facilitated many other cellular functions.

Antiamoebin I in Methanol Solution: Rapid Exchange between Right-Handed and Left-Handed310-Helical Conformations

Antiamoebin I (Aam-I) is a membrane-active peptaibol antibiotic isolated from fungal species belonging to the genera Cephalosporium, Emericellopsis, Gliocladium, and Stilbella. Antiamoebin I has the amino acid sequence: Ac-Phe(1)-Aib-Aib-Aib-Iva-Gly-Leu-Aib(8)-Aib-Hyp-Gln-Iva-Hyp-Aib-Pro-Phl(16). By using the uniformly (13)C,(15)N-labeled sample of Aam-I, the set of conformationally dependent J couplings and (3h)J(NC) couplings through H-bonds were measured. Analysis of these data along with the data on magnetic nonequivalence of the (13)C(beta) nuclei (Deltadelta((13)C(beta))) in Aib and Iva residues allowed us to draw the univocal conclusion that the N-terminal part (Phe(1)-Gly(6)) of Aam-I in MeOH solution is in fast exchange between the right-handed and left-handed 3(10)-helical conformations, with an approximately equal population of both states. An additional conformational exchange process was found at the Aib(8) residue. The (15)N-NMR-relaxation and CD-spectroscopy measurements confirmed these findings. Molecular modeling and Monte Carlo simulations revealed that both exchange processes are correlated and coupled with significant hinge-bending motions around the Aib(8) residue. Our results explain relatively low activity of Aam-I with respect to other 15-amino acid residue peptaibols (for example, zervamicin) in functional and biological tests. The high dynamic 'propensity' possibly prevents both initial binding of the antiamoebin to the membrane and subsequent formation of stable ionic channels according to the barrel-stave mechanism.

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.

Antiamoebins, myrocin B and the basis of antifungal antibiosis in the coprophilous fungus Stilbella erythrocephala (syn. S. fimetaria)

Antiamoebins I, III and XVI as well as several others in minor amounts were produced by four strains of the coprophilous fungus Stilbella erythrocephala (syn. S. fimetaria) in its natural substrate and in liquid culture. The total antiamoebin concentration in dung was 126-624 microg g(-1) fresh weight, with minimum inhibitory concentrations against most other coprophilous fungi being at or below 100 microg mL(-1). Myrocin B, not previously described from S. erythrocephala, was also produced, but only at low, nonfungicidal levels (< 5.3 microg g(-1)). No other antifungal substances were detected. It is concluded that antiamoebins are responsible for antibiosis in dung colonized by S. erythrocephala.

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.

High stability of the hinge region in the membrane-active peptide helix of zervamicin: paramagnetic relaxation enhancement studies

Zervamicin IIB is a 16 amino acid peptaibol that forms voltage dependent ion channels with multilevel conductance states in planar lipid bilayers and vesicular systems. Stability of the hinge region and intermolecular interactions were investigated in the N- and C-terminally spin-labelled peptide analogues. Intermolecular and intramolecular paramagnetic enhancement indicates that zervamicin behaves as a rigid helical rod in methanol solution. There are no high amplitude hinge-bending motions, and the peptaibol is monomeric up to concentration 1.5 mM. Stability of the hinge region illustrates the helix stabilising propensity of the Pro residue in membrane mimic environments and implies absence of significant conformational rearrangement due to voltage peptaibol activation.

Crystal structures of cephaibols

The crystal structures of the peptaibol antibiotics cephaibol A, cephaibol B and cephaibol C have been determined at ca. 0.9 A resolution. All three adopt a helical conformation with a sharp bend (of about 55 degrees) at the central hydroxyproline. All isovalines were found to possess the D configuration, superposition of all four models (there are two independent molecules in the cephaibol B structure) shows that the N-terminal helix is rigid and the C-terminus is flexible. There are differences in the hydrogen bonding patterns for the three structures that crystallize in different space groups despite relatively similar unit cell dimensions, but only in the case of cephaibol C does the packing emulate the formation of a membrane channel believed to be important for their biological function.

Helical kink and channel behaviour: a comparative study with the peptaibols alamethicin, trichotoxin and antiamoebin

Kinks or bends introduced in peptides and proteins by "helical distorter" residues such as proline, other imino acids and glycine, especially when these are in close proximity in the sequence, are increasingly recognized as playing an essential role in the gating of channel-forming peptides as well as of physiological ion channels. Peptaibols are useful simple models for the much more complex biological ion channels, especially voltage-gated ones. In this short review, we compare the monomeric structures of three selected peptaibols (alamethicin, trichotoxin and antiamoebin) that widely differ with regards their near-central kink angles and dipolar moment orientations. These structural features are then shown to be correlated to the different patterns of channel activity, both at the macroscopic and single-channel levels of investigation.

Solution NMR studies of antiamoebin, a membrane channel-forming polypeptide

Antiamoebin I is a membrane-active peptaibol produced by fungi of the species Emericellopsis which is capable of forming ion channels in membranes. Previous structure determinations by x-ray crystallography have shown the molecule is mostly helical, with a deep bend in the center of the polypeptide, and that the backbone structure is independent of the solvent used for crystallization. In this study, the solution structure of antiamoebin was determined by NMR spectroscopy in methanol, a solvent from which one of the crystal structures was determined. The ensemble of structures produced exhibit a right-handed helical C terminus and a left-handed helical conformation toward the N-terminus, in contrast to the completely right-handed helices found in the crystal structures. The NMR results also suggest that a "hinge" region exists, which gives flexibility to the polypeptide in the central region, and which could have functional implications for the membrane insertion process. A model for the membrane insertion and assembly process is proposed based on the antiamoebin solution and crystal structures, and is contrasted with the assembly and insertion mechanism proposed for other ion channel-forming polypeptides.

The peptaibol antiamoebin as a model ion channel: similarities to bacterial potassium channels

Antiamoebin (AAM) is a polypeptide antibiotic that is capable of forming ion channels in phospholipid membranes: planar bilayer studies have suggested the channels are octamers. The crystal structure of a monomeric form of AAM has provided the basis for molecular modelling of an octameric helical bundle channel. The channel model is funnel-shaped due to a substantial bend in the middle of the polypeptide chain caused by the presence of several imino acids. Inter-monomer hydrogen bonds orientate a ring of glutamine side chains to form a constriction in the pore lumen. The channel lumen is lined both by side chains of Gln11 and by polypeptide backbone carbonyl groups. Electrostatic calculations on the model are compatible with a channel that transports cations across membranes. The AAM channel model is compared with the crystal structures of two bacterial (KcsA andMthK) potassium channels. AAM and the potassium channels exhibit common functional features, such as cation-selectivity and similar single channel conductances. Common structural features include being multimers, each formed from a bundle of eight transmembrane helices, with lengths roughly comparable to the thickness of lipid bilayers. In addition, they all have aromatic amino acids that lie at the bilayer interfaces and which may aid in the stabilization of the transmembrane helices, as well as narrower constrictions that define the ion binding sites or selectivity filters in the pore lumen. The commonality of structural and functional features in these channels thus suggests that antiamoebin is a good, simple model for more complex bacterial and eukaryotic ion channels, capable of providing insight into details of the mechanisms of ion transport and multimeric channel stability.

New sequences and new fungal producers of peptaibol antibiotics antiamoebins

Mixtures of the microheterogeneous 16-mer peptaibol antibiotics called antiamoebins (AAM) have been isolated from the culture broths of strains of the filamentous fungi Stilbella erythrocephala ATCC 28144, Stilbella fimetaria CBS 548.84 and Gliocladium catenulatum CBS 511.66. Sequences were determined using on-line HPLC together with positive- and negative-ion electrospray ionization mass spectrometry. Some characteristic features are recognized in the mass spectrometric fragmentation pattern of AAM. From a sample originally used for sequencing AAM (from Hindustan Antibiotics, Ltd., Pimpri, Poona-411018, India), and a sample of AAM commercially available (from Sigma Chemicals, St. Louis, MO, USA) HPLC elution profiles and sequences were assigned. Further, sequences of AAM previously isolated from Emericellopsis synnematicola CBS 176.60 and Emericellopsis salmosynnemata CBS 382.62 were determined. The peptide designated AAM I was the most abundant in all isolates and its structure could be confirmed. AAM II was detectable as a minor component (1.9%) only in the original sample of AAM, but not in the other isolates. The structures of AAM III, IV and V, which had previously been partly assigned, were definitely established, and the new sequences AAM VI-XVI were elucidated. AAM showing Phe1/Leu1 or Phe1/Val1 exchange, respectively, are produced in amounts only by S. erythrocephala. Sequences, HPLC elution profiles ('fingerprints') and relative amounts of peptides of all isolates were correlated.

Common structural features in gramicidin and other ion channels

This review compares and contrasts the structures of several different types of ion channels with known three-dimensional structures, including gramicidin and the family of peptaibol channels, as well as the Streptomyces lividans potassium channel, to reveal common features in their structures that relate to their functional roles in ion binding and transport across membranes. Specifically, the locations of aromatic amino acids, the dimensions of the molecules, the multimeric nature of the channels and the roles of hydrogen bonds in stabilising such structures, the means by which the channels open and close, and the chemical nature of the groups which make up the channel lumen are discussed. The emphasis is on the commonality of features found in model channels, which may ultimately be found in other biological channel structures.

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.

Structures of trichovirins II, peptaibol antibiotics from the mold Trichoderma viride NRRL 5243

From the culture broth of the mold Trichoderma viride NRRL 5243 a mixture of polypeptides, named trichovirins (TV), could be isolated and purified by chromatography on XAD-2 adsorber resin and Sephadex LH-20 gel. Chromatography on silica gel using chloroform/methanol 8:2 as eluent provided a mixture of peptides named TV I. Subsequent elution with chloroform/methanol 1:1 yielded a second group of peptides named TV II. That group could be separated into individual components by repetitive HPLC on an octadecylsilyl and a fluorocarbon stationary phase. The sequences of 12 peptides of TV II could be determined by electrospray ionization tandem mass spectrometry of isolated peptides and gas chromatography-mass spectrometry of methanolysates. The N-termini of the 18-mer peptides are acetylated and the C-termini consist of leucinol. Owing to the presence of alpha-aminoisobutyric acid (Aib) residues and the bactericidal and hemolytic activity, the peptides belong to the family of peptaibol antibiotics.