Structure-activity relationship study of antimicrobial dermaseptin S4 showing the consequences of peptide oligomerization on selective cytotoxicity

Protective role of the neuropeptide urocortin II against experimental sepsis and leishmaniasis by direct killing of pathogens

We currently face an alarming resurgence in infectious diseases characterized by antimicrobial resistance and therapeutic failure. This has generated the urgent need of developing new therapeutic approaches that include agents with nontraditional modes of action. A recent interest focused on approaches based on our natural immune defenses, especially on peptides that combine innate antimicrobial activity against diverse pathogens and immunoregulatory functions. In this study, to our knowledge, we describe for the first time the antimicrobial activity of the neuropeptide urocortin II (UCNII) against a panel of Gram-positive and Gram-negative bacteria and tropical parasites of the genus Leishmania. Importantly, this cytotoxicity was selective for pathogens, because UCNII did not affect mammalian cell viability. Structurally, UCNII has a cationic and amphipathic design that resembles antimicrobial peptides. Using mutants and UCNII fragments, we determined the structural requirements for the interaction between the peptide and the surface of pathogen. Following its binding to pathogen, UCNII caused cell death through different membrane-disrupting mechanisms that involve aggregation and membrane depolarization in bacteria and pore formation in Leishmania. Noteworthily, UCNII killed the infective form of Leishmania major even inside the infected macrophages. Consequently, UCNII prevented mortality caused by polymicrobial sepsis and ameliorated pathological signs of cutaneous leishmaniasis. Besides its presence in body physical and mucosal barriers, we found that innate immune cells produce UCNII in response to infections. Therefore, UCNII could be considered as an ancient highly-conserved host peptide involved in the natural antimicrobial defense and emerge as an attractive alternative to current treatments for microbial disorders with associated drug resistances.

Induction of the Cpx envelope stress pathway contributes to Escherichia coli tolerance to antimicrobial peptides

Antimicrobial peptides produced by multicellular organisms as part of their innate system of defense against microorganisms are currently considered potential alternatives to conventional antibiotics in case of infection by multiresistant bacteria. However, while the mode of action of antimicrobial peptides is relatively well described, resistance mechanisms potentially induced or selected by these peptides are still poorly understood. In this work, we studied the mechanisms of action and resistance potentially induced by ApoEdpL-W, a new antimicrobial peptide derived from human apolipoprotein E. Investigation of the genetic response of Escherichia coli upon exposure to sublethal concentrations of ApoEdpL-W revealed that this antimicrobial peptide triggers activation of RcsCDB, CpxAR, and σ(E) envelope stress pathways. This genetic response is not restricted to ApoEdpL-W, since several other antimicrobial peptides, including polymyxin B, melittin, LL-37, and modified S4 dermaseptin, also activate several E. coli envelope stress pathways. Finally, we demonstrate that induction of the CpxAR two-component system directly contributes to E. coli tolerance toward ApoEdpL-W, polymyxin B, and melittin. These results therefore show that E. coli senses and responds to different antimicrobial peptides by activation of the CpxAR pathway. While this study further extends the understanding of the array of peptide-induced stress signaling systems, it also provides insight into the contribution of Cpx envelope stress pathway to E. coli tolerance to antimicrobial peptides.

Insight into the role of physicochemical parameters in a novel series of amphipathic peptides for efficient DNA delivery

Amphipathic peptides constitute a class of molecules with the potential to develop as efficient and safer alternatives to viral and other nonviral vectors for intracellular delivery of therapeutics. These peptides can be useful for nucleic acid delivery and hence promise to have pharmaceutical application, particularly in gene therapy. In order to design novel amphipathic peptides and improve their efficiency of therapeutic cargo delivery, one needs to understand the role of the physicochemical properties of the peptide. There are very few reports in the literature where the physicochemical properties of the peptide have been correlated with efficiency of plasmid DNA delivery. In the present work we hunted out a naturally occurring amphipathic peptide termed Mgpe-1 (derived from HUMAN Protein phosphatase 1E) as a possible novel DNA delivery agent. We systematically altered the physicochemical parameters of this peptide to further enhance its DNA delivery efficiency. We changed its amphipathicity (from secondary to primary), the total charge (from +6 to +9), hydrophobicity, and the amino acid composition (lysine and serines to arginine; substitution of tryptophan) and studied which of these alterations affect DNA delivery efficiency. Our results showed that although Mgpe-1 exhibited very strong cellular uptake, its plasmid DNA delivery efficiency was poor. The presence of nine arginines improved the DNA delivery efficiency, and the effect was observed in both the primary and the secondary amphipathic variants. We further observed that the presence of tryptophan was important but not essential and the effect of its removal was stronger in the case of the secondary amphipathic peptide. However, increase in total hydrophobicity of the peptide led to a fall in transfection efficiency in the primary amphipathic peptide whereas the secondary amphipathic peptide having the same chemical composition was almost unaffected by this change. The primary amphipathic peptides with high positive charge and low hydrophobicity formed colloidally stable polyplexes with DNA and avoided a major impediment in DNA delivery, namely, the aggregation of polyplexes and cytotoxicity. The secondary amphipathic variants by virtue of the positional arrangement of the amino acids led to formation of polyplexes with partly hydrophilic surfaces which prevented aggregation and controlled particle size irrespective of the hydrophobicity. Two variants in the series Mgpe-3 and Mgpe-4 having nine positive charges with less hydrophobicity showed high transfection efficiency in multiple cell lines along with serum stability and much less cytotoxicity and promise to be novel and efficient DNA delivery vectors.

Cationic antimicrobial polymers and their assemblies

Cationic compounds are promising candidates for development of antimicrobial agents. Positive charges attached to surfaces, particles, polymers, peptides or bilayers have been used as antimicrobial agents by themselves or in sophisticated formulations. The main positively charged moieties in these natural or synthetic structures are quaternary ammonium groups, resulting in quaternary ammonium compounds (QACs). The advantage of amphiphilic cationic polymers when compared to small amphiphilic molecules is their enhanced microbicidal activity. Besides, many of these polymeric structures also show low toxicity to human cells; a major requirement for biomedical applications. Determination of the specific elements in polymers, which affect their antimicrobial activity, has been previously difficult due to broad molecular weight distributions and random sequences characteristic of radical polymerization. With the advances in polymerization control, selection of well defined polymers and structures are allowing greater insight into their structure-antimicrobial activity relationship. On the other hand, antimicrobial polymers grafted or self-assembled to inert or non inert vehicles can yield hybrid antimicrobial nanostructures or films, which can act as antimicrobials by themselves or deliver bioactive molecules for a variety of applications, such as wound dressing, photodynamic antimicrobial therapy, food packing and preservation and antifouling applications.

Effect of repetitive lysine-tryptophan motifs on the eukaryotic membrane

In a previous study, we synthesized a series of peptides containing simple sequence repeats, (KW)_n–NH₂ (n = 2,3,4 and 5) and determined their antimicrobial and hemolytic activities, as well as their mechanism of antimicrobial action. However, (KW)₅ showed undesirable cytotoxicity against RBC cells. In order to identify the mechanisms behind the hemolytic and cytotoxic activities of (KW)₅, we measured the ability of these peptides to induce aggregation of liposomes. In addition, their binding and permeation activities were assessed by Trp fluorescence, calcein leakage and circular dichrorism using artificial phospholipids that mimic eukaryotic liposomes, including phosphatidylcholine (PC), PC/sphingomyelin (SM) (2:1, w/w) and PC/cholesterol (CH) (2:1, w/w). Experiments confirmed that only (KW)₅ induced aggregation of all liposomes; it formed much larger aggregates with PC:CH (2:1, w/w) than with PC or PC:SM (2:1, w/w). Longer peptide (KW)₅, but not (KW)₃ or (KW)₄, strongly bound and partially inserted into PC:CH compared to PC or PC:SM (2:1, w/w). Calcein release experiments showed that (KW)₅ induced calcein leakage from the eukaryotic membrane. Greater calcein leakage was induced by (KW)₅ from PC:CH than from PC:SM (2:1, w/w) or PC, whereas (KW)₄ did not induce calcein leakage from any of the liposomes. Circular dichroism measurements indicated that (KW)₅ showed higher conformational transition compared to (KW)₄ due to peptide-liposome interactions. Taken together, our results suggest that (KW)₅ reasonably mediates the aggregation and permeabilization of eukaryotic membranes, which could in turn explain why (KW)₅ displays efficient hemolytic activity.

Modes of action of Leishmanicidal antimicrobial peptides

Leishmaniasis is one of the major neglected tropical diseases of the world. It is present in 88 countries with an estimated number of 500,000 cases of visceral leishmaniasis and 1.5 million cases of cutaneous disease. No effective vaccinations are available against leishmaniasis and the efficacy of existing treatments is compromised due to the emergence of drug resistance. Thus, there is an urgent need to develop new compounds with antileishmanial activity. Antimicrobial peptides have potential as novel antileishmanial therapy, either for use alone or in combination with current drug regimens. The modes of action of these peptides against Leishmania includes: membrane disruption leading to necrotic cell death; induction of apoptosis; binding to intracellular target(s); and indirect effects via immunomodulation of host immune cells. This article reviews the mechanisms of action of antimicrobial peptides with leishmanicidal activity.

In vitro antiviral activity of dermaseptin S(4) and derivatives from amphibian skin against herpes simplex virus type 2

Herpes simplex virus (HSV) infections have become a public health problem worldwide. The emergence of acyclovir-resistant viral strains and the failure of vaccination to prevent herpetic infections have prompted the search for new antiviral drugs. Accordingly, the present study was undertaken to synthesize chemically and evaluate Dermaseptin S(4) (S(4)), an anti-microbial peptide derived from amphibian skin, and its derivatives in terms of anti-herpetic activity. The effects of biochemical modifications on their antimicrobial potential were also investigated. The peptides were incubated together with HSV-2 on target cells under various conditions, and the antiviral effects were examined via a cell metabolic labeling method. The findings revealed that DS(4) derivatives elicited concentration-dependent antiviral activity at micromole concentrations. The biochemical modifications of S(4) allowed for the reduction of peptide cytotoxicity without altering antiviral activity. Dermaseptins were added at different times during the viral cycle to investigate the mode of antiviral action. At the highest non-cytotoxic concentrations, most of the tested derivatives were noted to exhibit high antiviral activity particularly when pre-incubated with free herpes viruses prior to infection. Among these peptides, K(4)K(20)S(4) exhibited the highest antiviral activity against HSV-2 sensitive and resistant strains. Interestingly, the antiviral activity of K(4)K(20)S(4) was effective on both acyclovir-resistant and -sensitive viruses. The findings indicate that K(4)K(20)S(4) can be considered a promising candidate for future application as a therapeutic virucidal agent for the treatment of herpes viruses.

Effect of repetitive lysine-tryptophan motifs on the bactericidal activity of antimicrobial peptides

Previous studies identified lysine- and tryptophan-rich sequences within various cationic antimicrobial peptides. In the present study, we synthesized a series of peptides composed of lysine (K)-tryptophan (W) repeats (KW)_n (where n equals 2, 3, 4 or 5) with amidation of the C-terminal to increase cationicity. We found that increases in chain length up to (KW)₄ enhanced the peptides’ antibacterial activity; (KW)₅ exhibited somewhat less bactericidal activity than (KW)₄. Cytotoxicity, measured as lysis of human red blood cells, also increased with increasing chain length. With (KW)₅, reduced antibacterial activity and increased cytotoxicity correlated with greater hydrophobicity and self-aggregation in the aqueous environment. The peptides acted by inducing rapid collapse of the bacterial transmembrane potential and induction of membrane permeability. The mode of interaction of the peptides and the phosphate groups of lipopolysaccharide was dependent upon the peptides’ ability to permeate the membrane. Longer peptides [(KW)₄ and (KW)₅] but not shorter peptides [(KW)₂ and (KW)₃] strongly bound and partially inserted into negatively charged, anionic lipid bilayers. These longer peptides also induced membrane permeabilization and aggregation of lipid vesicles. The peptides had a disordered structure in aqueous solution, and only (KW)₄ and (KW)₅ displayed a folded conformation on lipid membranes. Moreover, (KW)₄ destroyed and agglutinated bacterial cells, demonstrating its potential as an antimicrobial agent. Collectively, the results show (KW)₄ to be the most efficacious peptide in the (KW)_n series, exhibiting strong antibacterial activity with little cytotoxicity.

Anti-plasmodial action of de novo-designed, cationic, lysine-branched, amphipathic, helical peptides

BACKGROUND

A lack of vaccine and rampant drug resistance demands new anti-malarials.

METHODS

In vitro blood stage anti-plasmodial properties of several de novo-designed, chemically synthesized, cationic, amphipathic, helical, antibiotic peptides were examined against Plasmodium falciparum using SYBR Green assay. Mechanistic details of anti-plasmodial action were examined by optical/fluorescence microscopy and FACS analysis.

RESULTS

Unlike the monomeric decapeptides {(Ac-GXRKXHKXWA-NH2) (X = F,ΔF) (Fm, ΔFm IC50 >100 μM)}, the lysine-branched,dimeric versions showed far greater potency {IC50 (μM) Fd 1.5 , ΔFd 1.39}. The more helical and proteolytically stable ΔFd was studied for mechanistic details. ΔFq, a K-K2 dendrimer of ΔFm and (ΔFm)2 a linear dimer of ΔFm showed IC50 (μM) of 0.25 and 2.4 respectively. The healthy/infected red cell selectivity indices were >35 (ΔFd), >20 (ΔFm)2 and 10 (ΔFq). FITC-ΔFd showed rapid and selective accumulation in parasitized red cells. Overlaying DAPI and FITC florescence suggested that ΔFd binds DNA. Trophozoites and schizonts incubated with ΔFd (2.5 μM) egressed anomalously and Band-3 immunostaining revealed them not to be associated with RBC membrane. Prematurely egressed merozoites from peptide-treated cultures were found to be invasion incompetent.

CONCLUSION

Good selectivity (>35), good resistance index (1.1) and low cytotoxicity indicate the promise of ΔFd against malaria.

Effects of cyclic lipodepsipeptide structural modulation on stability, antibacterial activity, and human cell toxicity

Bacterial infections are becoming increasingly difficult to treat due to the development and spread of antibiotic resistance. Therefore, identifying novel antibacterial targets and new antibacterial agents capable of treating infections by drug-resistant bacteria is of vital importance. The structurally simple yet potent fusaricidin or LI-F class of natural products represents a particularly attractive source of candidates for the development of new antibacterial agents. We synthesized 18 fusaricidin/LI-F analogues and investigated the effects of structure modification on their conformation, serum stability, antibacterial activity, and toxicity toward human cells. Our findings show that substitution of an ester bond in depsipeptides with an amide bond may afford equally potent analogues with improved stability and greatly decreased cytotoxicity. The lower overall hydrophobicity/amphiphilicity of amide analogues in comparison with their parent depsipeptides, as indicated by HPLC retention times, may explain the dissociation of antibacterial activity and human cell cytotoxicity. These results indicate that amide analogues may have significant advantages over fusaricidin/LI-F natural products and their depsipeptide analogues as lead structures for the development of new antibacterial agents.

Antiplasmodial properties of acyl-lysyl oligomers in culture and animal models of malaria

Our previous analysis of antiplasmodial properties exhibited by dodecanoyl-based oligo-acyl-lysyls (OAKs) has outlined basic attributes implicated in potent inhibition of parasite growth and underlined the critical role of excess hydrophobicity in hemotoxicity. To dissociate hemolysis from antiplasmodial effect, we screened >50 OAKs for in vitro growth inhibition of Plasmodium falciparum strains, thus revealing the minimal requirements for antiplasmodial potency in terms of sequence and composition, as confirmed by efficacy studies in vivo. The most active sequence, dodecanoyllysyl-bis(aminooctanoyllysyl)-amide (C(12)K-2α(8)), inhibited parasite growth at submicromolar concentrations (50% inhibitory concentration [IC(50)], 0.3 ± 0.1 μM) and was devoid of hemolytic activity (<0.4% hemolysis at 150 μM). Unlike the case of dodecanoyl-based analogs, which equally affect ring and trophozoite stages of the parasite developmental cycle, the ability of various octanoyl-based OAKs to distinctively affect these stages (rings were 4- to 5-fold more sensitive) suggests a distinct antiplasmodial mechanism, nonmembranolytic to host red blood cells (RBCs). Upon intraperitoneal administration to mice, C(12)K-2α(8) demonstrated sustainable high concentrations in blood (e.g., 0.1 mM at 25 mg/kg of body weight). In Plasmodium vinckei-infected mice, C(12)K-2α(8) significantly affected parasite growth (50% effective dose [ED(50)], 22 mg/kg) but also caused mortality in 2/3 mice at high doses (50 mg/kg/day × 4).

Connecting peptide physicochemical and antimicrobial properties by a rational prediction model

The increasing rate in antibiotic-resistant bacterial strains has become an imperative health issue. Thus, pharmaceutical industries have focussed their efforts to find new potent, non-toxic compounds to treat bacterial infections. Antimicrobial peptides (AMPs) are promising candidates in the fight against antibiotic-resistant pathogens due to their low toxicity, broad range of activity and unspecific mechanism of action. In this context, bioinformatics' strategies can inspire the design of new peptide leads with enhanced activity. Here, we describe an artificial neural network approach, based on the AMP's physicochemical characteristics, that is able not only to identify active peptides but also to assess its antimicrobial potency. The physicochemical properties considered are directly derived from the peptide sequence and comprise a complete set of parameters that accurately describe AMPs. Most interesting, the results obtained dovetail with a model for the AMP's mechanism of action that takes into account new concepts such as peptide aggregation. Moreover, this classification system displays high accuracy and is well correlated with the experimentally reported data. All together, these results suggest that the physicochemical properties of AMPs determine its action. In addition, we conclude that sequence derived parameters are enough to characterize antimicrobial peptides.

Underlying mechanism of in vivo and in vitro activity of C-terminal-amidated thanatin against clinical isolates of extended-spectrum beta-lactamase-producing Escherichia coli

BACKGROUND

Infections with extended-spectrum β-lactamase-producing Escherichia coli (ESBL-EC) have developed resistance to current therapies. Therefore, the underlying mechanisms of in vivo and in vitro activity of C-terminal-amidated thanatin (A-thanatin) against clinical isolates of ESBL-EC were studied in an attempt to resolve this problem.

METHODS

A-thanatin was synthesized to determine its minimum inhibitory concentration (MIC), minimum bactericidal concentration (MBC), and kill curve for ESBL-EC. The hemolytic toxicity, stability, and resistance induction of A-thanatin were determined. ESBL-EC-infected mice were used to determine the in vivo activity of A-thanatin. Scanning and transmission electron microscopy and fluorescence microscopy were used to study the underlying mechanism of A-thanatin.

RESULTS

A-thanatin is highly effective against ESBL-EC in vitro, with MIC values ≤4 μg/mL. It has been confirmed that A-thanatin has little hemolysis and relative high stability in plasma. Excellent in vivo therapeutic effects were also observed in a septicemic animal model, with survival rates of 50.0%, 66.7%, and 91.7% in the low-dose, middle-dose, and high-dose groups, respectively. Membrane permeabilization may be a major biological action of A-thanatin.

CONCLUSIONS

Because the development of multidrug resistance limits the available therapeutic options, A-thanatin may provide a novel strategy for treating ESBL-EC infection and other infections due to multidrug-resistant bacteria.

Antimicrobial peptides from Phyllomedusa frogs: from biomolecular diversity to potential nanotechnologic medical applications

Screening for new bioactive peptides in South American anurans has been pioneered in frogs of the genus Phyllomedusa. All frogs of this genus have venomous skin secretions, i.e., a complex mixture of bioactive peptides against potential predators and pathogens that presumably evolved in a scenario of predator-prey interaction and defense against microbial invasion. For every new anuran species studied new peptides are found, with homologies to hormones, neurotransmitters, antimicrobials, and several other peptides with unknown biological activity. From Vittorio Erspamer findings, this genus has been reported as a "treasure store" of bioactive peptides, and several groups focus their research on these species. From 1966 to 2009, more than 200 peptide sequences from different Phyllomedusa species were deposited in UniProt and other databases. During the last decade, the emergence of high-throughput molecular technologies involving de novo peptide sequencing via tandem mass spectrometry, cDNA cloning, pharmacological screening, and surface plasmon resonance applied to peptide discovery, led to fast structural data acquisition and the generation of peptide molecular libraries. Research groups on bioactive peptides in Brazil using these new technologies, accounted for the exponential increase of new molecules described in the last decade, much higher than in any previous decades. Recently, these secretions were also reported as a rich source of multiple antimicrobial peptides effective against multidrug resistant strains of bacteria, fungi, protozoa, and virus, providing instructive lessons for the development of new and more efficient nanotechnological-based therapies for infectious diseases treatment. Therefore, novel drugs arising from the identification and analysis of bioactive peptides from South American anuran biodiversity have a promising future role on nanobiotechnology.

Dermaseptins and magainins: antimicrobial peptides from frogs' skin-new sources for a promising spermicides microbicides-a mini review

Sexually transmitted infections (STIs) and human immunodeficiency virus (HIV), the causative agents of acquired immunodeficiency syndrome (AIDS), are two great concerns in the reproductive health of women. Thus, the challenge is to find products with a double activity, on the one hand having antimicrobial/antiviral properties with a role in the reduction of STI, and on the other hand having spermicidal action to be used as a contraceptive. In the absence of an effective microbicide along with the disadvantages of the most commonly used spermicidal contraceptive worldwide, nonoxynol-9, new emphasis has been focused on the development of more potential intravaginal microbicidal agents. Topical microbicides spermicides would ideally provide a female-controlled method of self-protection against HIV as well as preventing pregnancies. Nonoxynol-9, the only recommended microbicide spermicide, damages cervicovaginal epithelium because of its membrane-disruptive properties. Clearly, there is an urgent need to identify new compounds with dual potential microbicidal properties; antimicrobial peptides should be candidates for such investigations. Dermaseptins and magainins are two classes of cationic, amphipathic alpha-helical peptides that have been identified in the skin extracts of frogs Phyllomedusa sauvagei and Xenopus laevis. Regarding their contraceptive activities and their effect against various STI-causing pathogens, we believe that these two peptides are appropriate candidates in the evaluation of newer and safer microbicides spermicides in the future.

Structure-activity relationships among random nylon-3 copolymers that mimic antibacterial host-defense peptides

Host-defense peptides are natural antibiotics produced by multicellular organisms to ward off bacterial infection. Since the discovery of these molecules in the 1980s, a great deal of effort has been devoted to elucidating their mechanisms of action and to developing analogues with improved properties for possible therapeutic use. The vast majority of this effort has focused on materials composed of a single type of molecule, most commonly a peptide with a specific sequence of alpha-amino acid residues. We have recently shown that sequence-random nylon-3 copolymers can mimic favorable properties of host-defense peptides, and here we document structure-activity relationships in this polymer family. Although the polymers are heterogeneous in terms of subunit order and stereochemistry, these materials display structure-activity relationships comparable to those that have been documented among host-defense peptides and analogous synthetic peptides. Previously such relationships have been interpreted in terms of a specific and regular folding pattern (usually an alpha-helix), but our findings show that these correlations between covalent structure and biological activity do not require the adoption of a specific or regular conformation. In some cases our observations suggest alternative interpretations of results obtained with discrete peptides.

An orphan dermaseptin from frog skin reversibly assembles to amyloid-like aggregates in a pH-dependent fashion

Dermaseptin PD-3-7 (aDrs) from frog skin contains three aspartic acid residues resulting in a negative net charge at neutral pH, as opposed to numerous other dermaseptins which are cationic helical antimicrobial peptides. Still, this peptide can be fitted into an amphipathic alpha helix by an Edmundson wheel projection. However, folding to the proposed helix was induced to only a low extent by zwitterionic vesicles or even detergents. Furthermore, no evidence of antibacterial or cytotoxic activity from soluble aDrs could be obtained. The peptide has an inherent propensity to an extended conformation in aqueous solution and self-assembles into amyloid fibrils in a reversible pH-controlled fashion, which was studied in some detail; above pH 5, the amyloid fibrils disassemble in a cooperative manner. This is probably caused by deprotonation of both side chain and terminal carboxyl groups, which results in intermolecular electrostatic repulsion. At neutral pH, this process proceeds instantaneously to the soluble form. Within the transition interval (pH 5-6.5), however, 'backward' granular aggregates, 10-500 nm in size, are formed. Such metastable amorphous aggregates, which are quickly released from an amyloid depot by a shift in pH, can mediate a strong cytotoxic effect. This activity does not involve lysis or interference with the cellular redox status, but apparently acts via an as yet unidentified mechanism. In this study, we present a new member of an emerging class of self-assembling frog skin peptides with extraordinary self-aggregation properties, which may potentially be relevant for biological processes. Structured digital abstract: * MINT-7256467: Dermaseptin (uniprotkb:O93455) and Dermaseptin (uniprotkb:O93455) bind (MI:0407) by circular dichroism (MI:0016) * MINT-7255686: Dermaseptin (uniprotkb:O93455) and Dermaseptin (uniprotkb:O93455) bind (MI:0407) by biophysical (MI:0013) * MINT-7256439: Dermaseptin (uniprotkb:O93455) and Dermaseptin (uniprotkb:O93455) bind (MI:0407) by fluorescence microscopy (MI:0416) * MINT-7256449: Dermaseptin (uniprotkb:O93455) and Dermaseptin (uniprotkb:O93455) bind (MI:0407) by electron microscopy (MI:0040) * MINT-7256430: Dermaseptin (uniprotkb:O93455) and Dermaseptin (uniprotkb:O93455) bind (MI:0407) by fluorescence technologies (MI:0051).

Arabidopsis HARMLESS TO OZONE LAYER protein methylates a glucosinolate breakdown product and functions in resistance to Pseudomonas syringae pv. maculicola

Almost all of the chlorine-containing gas emitted from natural sources is methyl chloride (CH(3)Cl), which contributes to the destruction of the stratospheric ozone layer. Tropical and subtropical plants emit substantial amounts of CH(3)Cl. A gene involved in CH(3)Cl emission from Arabidopsis was previously identified and designated HARMLESS TO OZONE LAYER (hereafter AtHOL1) based on the mutant phenotype. Our previous studies demonstrated that AtHOL1 and its homologs, AtHOL2 and AtHOL3, have S-adenosyl-l-methionine-dependent methyltransferase activities. However, the physiological functions of AtHOLs have yet to be elucidated. In the present study, our comparative kinetic analyses with possible physiological substrates indicated that all of the AtHOLs have low activities toward chloride. AtHOL1 was highly reactive to thiocyanate (NCS(-)), a pseudohalide, synthesizing methylthiocyanate (CH(3)SCN) with a very high k(cat)/K(m) value. We demonstrated in vivo that substantial amounts of NCS(-) were synthesized upon tissue damage in Arabidopsis and that NCS(-) was largely derived from myrosinase-mediated hydrolysis of glucosinolates. Analyses with the T-DNA insertion Arabidopsis mutants (hol1, hol2, and hol3) revealed that only hol1 showed increased sensitivity to NCS(-) in medium and a concomitant lack of CH(3)SCN synthesis upon tissue damage. Bacterial growth assays indicated that the conversion of NCS(-) into CH(3)SCN dramatically increased antibacterial activities against Arabidopsis pathogens that normally invade the wound site. Furthermore, hol1 seedlings showed an increased susceptibility toward an Arabidopsis pathogen, Pseudomonas syringae pv. maculicola. Here we propose that AtHOL1 is involved in glucosinolate metabolism and defense against phytopathogens. Moreover, CH(3)Cl synthesized by AtHOL1 could be considered a byproduct of NCS(-) metabolism.

Mechanism of antibacterial action of dermaseptin B2: interplay between helix-hinge-helix structure and membrane curvature strain

Dermaseptin B2 (Drs B2) is a 33-residue-long cationic, alpha-helical antimicrobial peptide endowed with membrane-damaging activity against a broad spectrum of microorganisms, including bacteria, yeasts, fungi, and protozoa, but its precise mechanism of action remained ill-defined. A detailed characterization of peptide-membrane interactions of Drs B2 was undertaken in comparison with a C-terminal truncated analogue, [1-23]-Drs B2, that was virtually inactive on bacteria despite retaining the cationic charge of the full-length peptide. Both peptides were tested on living cells using membrane permeabilization assays and on large unilamellar and multilamellar phospholipid vesicles composed of binary lipid mixtures by dye leakage assay, fluorescence spectroscopy, circular dichroism, and differential scanning calorimetry and also on SDS micelles using NMR spectroscopy. The results indicate that Drs B2 induces a strong perturbation of anionic lipid bilayers, resides at the hydrocarbon core-water interface, parallel to the plane of the membrane, and interacts preferentially with the polar head groups and glycerol backbone region of the anionic phospholipids, as well as the region of the lipid acyl chain near the bilayer surface. The interfacial location of Drs B2 induces a positive curvature of the bilayer and clustering of anionic lipids, consistent with a carpet mechanism, that may lead to the formation of mixed peptide-phospholipid toroidal, transient pores and membrane permeation/disruption once a threshold peptide accumulation is reached. In constrast, the truncated [1-23]-Drs B2 analogue interacts at the head group level without penetrating and perturbing the hydrophobic core of the bilayer. NMR study in SDS micelles showed that [1-23]-Drs B2 adopts a well-defined helix encompassing residues 2-20, whereas Drs B2 was previously found to adopt helical structures interrupted around the Val(9)-Gly(10) segment. Thus the antibacterial activity of Drs B2 depends markedly on a threshold number of hydrophobic residues to be present on both extremities of the helix. In a membrane environment with a strong positive curvature strain, Drs B2 can adopt a flexible helix-hinge-helix structure that facilitates the concomitant insertion of the strongly hydrophobic N- and C-termini of the peptide into the acyl core of the membrane.

Leishmanicidal activity and immobilization of dermaseptin 01 antimicrobial peptides in ultrathin films for nanomedicine applications

Antimicrobial peptides (AMPs) are essential for the innate immune system of eukaryotes, imparting protection against pathogens and their proliferation in host organisms. The recent interest in AMPs as active materials in bionanostructures is due to the properties shown by these biological molecules, such as the presence of an alpha-helix structure and distribution of positive charges along the chain. In this study the antimicrobial peptide dermaseptin 01 (DS 01), from the skin secretion of Phyllomedusa hypochondrialis frogs was immobilized in nanostructured layered films in conjunction with nickel tetrasulfonated phthalocyanines. The leishmanicidal activity of DS 01 was confirmed using kinetic essays, in which DS 01 promoted death of all metacyclic promastigote cells in 45 minutes. Surprisingly, the immobilized DS 01 molecules displayed electroactivity, as revealed by electrochemical experiments, in which an oxidation peak at about 0.61 V was observed for a DS 01 monolayer deposited on top of a conductive electrode. Such electroactivity was used to investigate the sensing abilities of the nanostructured films toward Leishmania. We observed an increase in the oxidation current as a function of number of Leishmania cells in the electrolytic solution at concentrations down to 10(3) cells/mL. The latter is indicative that the use of AMPs immobilized in electroactive nanostructured films may be of interest for applications in the pharmaceutical industry and diagnosis.

FROM THE CLINICAL EDITOR

The recent interest in Antimicrobial peptides (AMPs) as active materials in bionanostructures is due to the properties shown by these biological molecules. Leishmanicidal activity of a particular AMP is demonstrated in this paper.

Antimicrobial peptide mimics for improved therapeutic properties

The relatively recent recognition of the major role played by antimicrobial peptides (AMPs) in sustaining an effective host response to immune challenges was greatly influenced by studies of amphibian peptides. AMPs are also widely regarded as a potential source of future antibiotics owing to a remarkable set of advantageous properties ranging from molecular simplicity to low-resistance swift-kill of a broad range of microbial cells. However, the peptide formula per se, represents less than ideal drug candidates, namely because of poor bioavailability issues, potential immunogenicity, optional toxicity and high production costs. To address these issues, synthetic peptides have been designed, reproducing the critical peptide biophysical characteristic in unnatural sequence-specific oligomers. Thus, the use of peptidomimetics to overcome the limitations inherent to peptides physical characteristics is becoming an important and promising approach for improving the therapeutic potential of AMPs. Here, we review most recent advances in the design strategies and the biophysical properties of the main classes of mimics to natural AMPs, emphasizing the importance of structure-activity relationship studies in fine-tuning of their physicochemical attributes for improved antimicrobial properties.

Impact of self-assembly properties on antibacterial activity of short acyl-lysine oligomers

We investigated both the structural and functional consequences of modifying the hydrophobic, lipopeptide-mimetic oligo-acyl-lysine (OAK) N(alpha)-hexadecanoyl-l-lysyl-l-lysyl-aminododecanoyl-l-lysyl-amide (c(16)KKc(12)K) to its unsaturated analog hexadecenoyl-KKc(12)K [c(16(omega7))KKc(12)K]. Despite similar tendencies for self-assembly in solution (critical aggregation concentrations, approximately 10 muM), the analogous OAKs displayed dissimilar antibacterial properties (e.g., bactericidal kinetics taking minutes versus hours). Diverse experimental evidence provided insight into these discrepancies: whereas c(16(omega7))KKc(12)K created wiry interconnected nanofiber networks, c(16)KKc(12)K formed both wider and stiffer fibers which displayed distinct binding properties to phospholipid membranes. Unsaturation also shifted their gel-to-liquid transition temperatures and altered their light-scattering properties, suggesting the disassembly of c(16(omega7))KKc(12)K in the presence of bacteria. Collectively, the data indicated that the higher efficiency in interfering with bacterial viability emanated from a wobbly packing imposed by a single double bond. This suggests that similar strategies might improve hydrophobic OAKs and related lipopeptide antibiotics.

Synthesis and antimicrobial activity of dermaseptin S1 analogues

Dermaseptins are peptides found in the skin secretions of Phyllomedusinae frogs. These peptides exert lytic action on some microorganisms without substantial haemolysis. In an attempt to understand the antimicrobial activity of these peptides we designed several dermaseptin S1 (ALWKTMLKKLGTMALHAGKAALGAAADTISQGTQ) (DS1) analogues. All peptides were tested on the growth of prokaryotic (Gram-positive and Gram-negative bacteria) and eukaryotic (the yeast Candida albicans and the protozoon Leishmania major) organisms. Our data showed a dose-dependent killing effect by most DS1 derivatives. Maximal antibacterial activity was displayed by a 16-mer peptide that was more active than native DS1.

Structure-activity relationships of antibacterial acyl-lysine oligomers

We describe structure-activity relationships that emerged from biophysical data obtained with a library of antimicrobial peptide mimetics composed of 103 oligoacyllysines (OAKs) designed to pin down the importance of hydrophobicity (H) and charge (Q). Based on results obtained with OAKs displaying minimal inhibitory concentration < or = 3 microM, the data indicate that potent inhibitory activity of the gram-negative Escherichia coli and the gram-positive Staphylococcus aureus required a relatively narrow yet distinct window of HQ values where the acyl length played multiple and critical roles, both in molecular organization and in selective activity. Thus, incorporation of long-but not short-acyl chains within a peptide backbone is shown to lead to rigid supramolecular organization responsible for poor antibacterial activity and enhanced hemolytic activity. However, sequence manipulations, including introduction of a tandem lysine motif into the oligomer backbone, enabled disassembly of aggregated OAKs and subsequently revealed tiny, nonhemolytic, yet potent antibacterial derivatives.

Peptoids that mimic the structure, function, and mechanism of helical antimicrobial peptides

Antimicrobial peptides (AMPs) and their mimics are emerging as promising antibiotic agents. We present a library of "ampetoids" (antimicrobial peptoid oligomers) with helical structures and biomimetic sequences, several members of which have low-micromolar antimicrobial activities, similar to cationic AMPs like pexiganan. Broad-spectrum activity against six clinically relevant BSL2 pathogens is also shown. This comprehensive structure-activity relationship study, including circular dichroism spectroscopy, minimum inhibitory concentration assays, hemolysis and mammalian cell toxicity studies, and specular x-ray reflectivity measurements shows that the in vitro activities of ampetoids are strikingly similar to those of AMPs themselves, suggesting a strong mechanistic analogy. The ampetoids' antibacterial activity, coupled with their low cytotoxicity against mammalian cells, make them a promising class of antimicrobials for biomedical applications. Peptoids are biostable, with a protease-resistant N-substituted glycine backbone, and their sequences are highly tunable, because an extensive diversity of side chains can be incorporated via facile solid-phase synthesis. Our findings add to the growing evidence that nonnatural foldamers will emerge as an important class of therapeutics.

Resistance of Porphyromonas gingivalis ATCC 33277 to direct killing by antimicrobial peptides is protease independent

Antimicrobial peptides are short, positively charged, amphipathic peptides that possess a wide spectrum of antimicrobial activity and have an important role in the host's innate immunity. Lack of, or dysfunctions in, antimicrobial peptides have been correlated with infectious diseases, including periodontitis. Porphyromonas gingivalis, a gram-negative anaerobe and a major pathogen associated with periodontal diseases, is resistant to antimicrobial peptides of human and nonhuman origin, a feature that likely contributes to its virulence. Expressing a robust proteolytic activity, P. gingivalis hydrolyzes antimicrobial peptides. In this study, P. gingivalis inactivated three antimicrobial peptides, while a d-enantiomer was resistant to degradation. P. gingivalis was resistant to the protease-resistant d-enantiomer peptide, and importantly, a protease-deficient P. gingivalis mutant was also resistant to the antimicrobial peptide. Finally, the binding of a fluorescently labeled antimicrobial peptide to protease-deficient P. gingivalis was much weaker than the binding of susceptible Escherichia coli. Our results suggest that the resistance of P. gingivalis ATCC 33277 to direct killing by antimicrobial peptides is protease independent and results (at least partially) from the low affinity of antimicrobial peptides to P. gingivalis.

Decoralin, a novel linear cationic alpha-helical peptide from the venom of the solitary eumenine wasp Oreumenes decoratus

A novel peptide, decoralin, was isolated from the venom of the solitary eumenine wasp Oreumenes decoratus. Its sequence, Ser-Leu-Leu-Ser-Leu-Ile-Arg-Lys-Leu-Ile-Thr, was determined by Edman degradation and corroborated by solid-phase synthesis. This sequence has the characteristic features of linear cationic alpha-helical peptides; rich in hydrophobic and basic amino acids with no disulfide bond, and accordingly, it can be predicted to adopt an amphipathic alpha-helix secondary structure. In fact, the CD spectra of decoralin in the presence of TFE or SDS showed a high alpha-helical conformation content. In a biological evaluation, decoralin exhibited a significant broad-spectrum antimicrobial activity, and moderate mast cell degranulation and leishmanicidal activities, but showed virtually no hemolytic activity. A synthetic analog with C-terminal amidation showed a much more potent activity in all the biological assays.

Synthetic lipopeptides: a novel class of anti-infectives

Lipopeptide daptomycin is one of the few recently approved antibiotics based on the novel mechanism of action. Recent advances in synthetic lipopeptides, driven by the biochemical and biophysical research, expanded their spectrum of antimicrobial activity and reduced their size to achieve economically viable production. Lipopeptides, consisting of a short peptide chain conjugated with an acyl chain, form a structurally defined conformation, which inserts into the bacterial membrane and dissipates its transmembrane potential. In addition to antimicrobial activity, synthetic lipopeptides also suppress inflammation through the neutralization of bacterial agonists of the innate immune response, synergize with conventional antibiotics and have improved proteolytic stability. Activities in animal models indicate that synthetic lipopeptides may surpass the natural lipopeptides as the perspective class of anti-infective agents.

Trypanocidal and leishmanicidal activities of different antimicrobial peptides (AMPs) isolated from aquatic animals

Most of the available animal antimicrobial peptides (AMPs) have been tested against bacteria and fungi, but very few against protozoan parasites. In the present study, we investigated the antiparasitic activity of different AMPs isolated from aquatic animals: tachyplesin (Tach, from Tachypleus tridentatus), magainin (Mag, from Xenopus laevis), clavanin (Clav, from Styela clava), penaeidin (Pen, from Litopenaeus vannamei), mytilin (Myt, from Mytilus edulis) and anti-lipopolysaccharide factor (ALF, from Penaeus monodon). The antiparasitic activity was evaluated against the promastigote form of Leishmania braziliensis and epi and trypomastigote forms of Trypanosoma cruzi, through the MTT method. Tach was the most potent peptide, killing completely L. braziliensis and trypomastigote T. cruzi from 12.5microM, whereas Pen and Clav were weakly active against trypomastigotes and Myt against L. braziliensis, only at a high concentration (100microM). Tach and Mag were markedly hemolytic at high concentrations, whereas the other peptides caused only a slight hemolysis (<10% up to 50microM). Our results point to Tach as the only potential candidate for further investigation and potential application as a therapeutic agent.

Improved antimicrobial peptides based on acyl-lysine oligomers

We describe peptidomimetic oligomers that show rapid, nonhemolytic, broad-spectrum bactericidal properties in mice and do not induce the emergence of resistance. The oligomers contain acyl chains, which prevent the formation of stable secondary structure. This design appears advantageous over conventional antimicrobial peptides with respect to in vivo efficacy and safety, and may provide a convenient platform for the development of peptide antibiotics.

Antiplasmodial activity of lauryl-lysine oligomers

The ever evolving resistance of the most virulent malaria parasite, Plasmodium falciparum, to antimalarials necessitates the continuous development of new drugs. Our previous analysis of the antimalarial activities of the hemolytic antimicrobial peptides dermaseptins and their acylated derivatives implicated the importance of hydrophobicity and charge for drug action. Following these findings, an oligoacyllysine (OAK) tetramer designed to mimic the characteristics of dermaseptin was synthesized and assessed for its antimalarial activity in cultures of P. falciparum. The tetramer inhibited the growth of different plasmodial strains at low micromolar concentrations (mean 50% inhibitory concentration [IC(50)], 1.8 microM). A structure-activity relationship study involving eight derivatives unraveled smaller, more potent OAK analogs (IC(50)s, 0.08 to 0.14 microM). The most potent analogs were the most selective, with selectivity ratios of 3 orders of magnitude. Selectivity was strongly influenced by the self-assembly properties resulting from interactions between hydrophobic OAKs, as has been observed with conventional antimicrobial peptides. Further investigations performed with a representative OAK revealed that the ring and trophozoite stages of the parasite developmental cycle were equally sensitive to the compound. A shortcoming of the tested compound was the need for long incubation times in order for it to exert its full effect. Nevertheless, the encouraging results obtained in this study regarding the efficiency and selectivity of some compounds establish them as leads for further development.

Susceptibility of Neisseria gonorrhoeae to antimicrobial peptides from amphibian skin, dermaseptin, and derivatives

We evaluated the antimicrobial effect of antimicrobial peptides from frog skin belonging to the dermaseptin family against reference and clinical Neisseria gonorrhoeae strains, including penicillin-resistant strains. Dermaseptin S4 exhibited anti-N. gonorrhoeae activity against all strains with MICs ranging between 10 and 100 microg/mL. We then used derivatives of DS4 and determined the anti-N. gonorrhoeae activity of each of analogs. All the derivatives showed antimicrobial activity. Among the different molecules tested, we found that dermaseptins K4S4 (1-16)a and K4S4 (1-28) were the more potent to inhibit N. gonorrhoeae growth with MIC of 10 microg/mL against all strains.

In Vitro Discriminative Antipseudomonal Properties Resulting from Acyl Substitution of N-Terminal Sequence of Dermaseptin S4 Derivatives

Truncation and acylation were combined to investigate the broad-spectrum bactericidal and hemolytic peptide S4(1-15). Substitution of up to seven residues with dodecanoic acid (C(12)) gradually led to specific antipseudomonal activity: out of 40 bacterial strains tested in vitro, C(12)-S4(8-15) displayed similar minimal inhibitory concentrations (MICs) as S4(1-15) against Pseudomonas aeruginosa sp. (identical MIC(90)) but was practically inactive against most other bacteria or erythrocytes. Surface plasmon resonance and isothermal titration calorimetry experiments revealed the binding properties of S4(1-15) to be consistent with its nonselective activities, while discriminative activities of C(12)-S4(8-15) correlated with high binding affinity to a membrane containing pseudomonal lipopolysaccharides and with lower affinities to membranes containing nonpseudomonal lipopolysaccharides or cholesterol. Various mechanistic studies failed to detect significant differences in secondary structure, bactericidal kinetics, or ability to perturb the cytoplasmic membrane, pointing to a similar mode of action.

Acyl-substituted dermaseptin S4 derivatives with improved bactericidal properties, including on oral microflora

The 15-mer dermaseptin S4 derivative S4(1-15) was recently shown to exhibit potent activity against oral pathogens associated with caries and periodontitis. Here, we investigated possible modes for improving the peptide's properties through systematic replacement of an N-terminal amino acid(s) with various fatty acids that modulate the peptide's hydrophobicity and/or charge. Deletion of 1 to 3 residues led to progressive loss of potency as assessed by MIC experiments performed on four test bacteria. Replacing the deleted amino acids with fatty acids most often resulted in potency recovery or improvement, as evidenced by lower MICs and faster bactericidal kinetics in culture media. Best results were obtained after replacement of the N-terminal dipeptide alanine-leucine with heptanoic (C7) or aminododecanoic (NC12) acid. Circular dichroism analysis correlated antibacterial properties to the peptide's secondary structure. MIC experiments and confocal laser scanning microscopy results indicated that C7-S4(3-15) and NC12-S4(3-15) were bactericidal to various oral pathogens, including those which are immobilized in a biofilm. C7-S4(3-15) performed similarly to or better than (depending on growth medium) IB-367, a peptide assessed in clinical trials for treatment of oral mucositis, reducing CFU counts by >3 log units within 2 min of incubation. Collectively, the data indicate that substitution of fatty acids for amino acids may be a useful strategy in revealing improved derivatives of known antimicrobial peptides and suggest the suitability of such compounds for controlling pathogens associated with oral diseases.

Composition effect on peptide interaction with lipids and bacteria: variants of C3a peptide CNY21

The effect of peptide hydrophobicity and charge on peptide interaction with model lipid bilayers was investigated for the C3a-derived peptide CNY21 by fluorescence spectroscopy, circular dichroism, ellipsometry, z-potential, and photon correlation spectroscopy measurements. For both zwitterionic and anionic liposomes, the membrane-disruptive potency for CNY21 variants increased with increasing net positive charge and mean hydrophobicity and was completely lost on elimination of all peptide positive charges. Analogous effects of elimination of the peptide positive net charge in particular were found regarding bacteria killing for both Pseudomonas aeruginosa and Bacillus subtilis. The peptides, characterized by moderate helix content both in buffer and when attached to the liposomes, displayed high adsorption for the net positively charged peptide variants, whereas adsorption was non-measurable for the uncharged peptide. That electrostatically driven adsorption represents the main driving force for membrane disruption in lipid systems was also demonstrated by a drastic reduction in both liposome leakage and peptide adsorption with increasing ionic strength, and this salt inactivation can be partly avoided by increasing the peptide hydrophobicity. This increased electrolyte resistance translates also to a higher antibacterial effect for the hydrophobically modified variant at high salt concentration. Overall, our findings demonstrate the importance of the peptide adsorption and resulting peptide interfacial density for membrane-disruptive effects of these peptides.

Physicochemical properties that enhance discriminative antibacterial activity of short dermaseptin derivatives

Antimicrobial peptides are widely believed to exert their effects by nonspecific mechanisms. We assessed the extent to which physicochemical properties can be exploited to promote discriminative activity by manipulating the N-terminal sequence of the 13-mer dermaseptin derivative K(4)-S4(1-13) (P). Inhibitory activity determined in culture media against 16 strains of bacteria showed that when its hydrophobicity and charge were changed, P became predominantly active against either gram-positive or gram-negative bacteria. Thus, conjugation of various aminoacyl-lysin moieties (e.g., aminohexyl-K-P) led to inactivity against gram-positive bacteria (MIC(50) > 50 microM) but potent activity against gram-negative bacteria (MIC(50), 6.2 microM). Conversely, conjugation of equivalent acyls to the substituted analog M(4)-S4(1-13) (e.g., hexyl-M(4)-P) led to inactivity against gram-negative bacteria (MIC(50) > 50 microM) but potent activity against gram-positive bacteria (MIC(50), 3.1 microM). Surface plasmon resonance experiments, used to investigate peptides' binding properties to lipopolysaccharide-containing idealized phospholipid membranes, suggest that although the acylated derivatives have increased lipophilic properties with parallel antibacterial behavior, hydrophobic derivatives are prevented from reaching the cytoplasmic membranes of gram-negative bacteria. Moreover, unlike modifications that enhanced the activity against gram-positive bacteria, which also enhanced hemolysis, we found that modifications that enhanced activity against gram-negative bacteria generally reduced hemolysis. Thus, compared with the clinically tested peptides MSI-78 and IB-367, the dermaseptin derivative aminohexyl-K-P performed similarly in terms of potency and bactericidal kinetics but was significantly more selective in terms of discrimination between bacteria and human erythrocytes. Overall, the data suggest that similar strategies maybe useful to derive potent and safe compounds from known antimicrobial peptides.

Dermaseptin S9, an alpha-helical antimicrobial peptide with a hydrophobic core and cationic termini

The dermaseptins S are closely related peptides with broad-spectrum antibacterial activity that are produced by the skin of the South American hylid frog, Phyllomedusa sauvagei. These peptides are polycationic (Lys-rich), alpha-helical, and amphipathic, with their polar/charged and apolar amino acids on opposing faces along the long axis of the helix cylinder. The amphipathic alpha-helical structure is believed to enable the peptides to interact with membrane bilayers, leading to permeation and disruption of the target cell. We have identified new members of the dermaseptin S family that do not resemble any of the naturally occurring antimicrobial peptides characterized to date. One of these peptides, designated dermaseptin S9, GLRSKIWLWVLLMIWQESNKFKKM, has a tripartite structure that includes a hydrophobic core sequence encompassing residues 6-15 (mean hydrophobicity, +4.40, determined by the Liu-Deber scale) flanked at both termini by cationic and polar residues. This structure is reminiscent of that of synthetic peptides originally designed as transmembrane mimetic models and that spontaneously become inserted into membranes [Liu, L., and Deber, C. M. (1998) Biopolymers 47, 41-62]. Dermaseptin S9 is a potent antibacterial, acting on gram-positive and gram-negative bacteria. The structure of dermaseptin S9 in aqueous solution and in TFE/water mixtures was analyzed by circular dichroism and two-dimensional NMR spectroscopy combined with molecular dynamics calculations. Dermaseptin S9 is aggregated in water, but a monomeric nonamphipathic alpha-helical conformation, mostly in residues 6-21, is stabilized by the addition of TFE. These results, combined with membrane permeabilization assays and surface plasmon resonance analysis of the peptide binding to zwitterionic and anionic phospholipid bilayers, demonstrate that spatial segregation of hydrophobic and hydrophilic/charged residues on opposing faces along the long axis of a helix is not essential for the antimicrobial activity of cationic alpha-helical peptides.

Effect of Natural l- to d-Amino Acid Conversion on the Organization, Membrane Binding, and Biological Function of the Antimicrobial Peptides Bombinins H

Antimicrobial peptides (AMPs) are evolutionarily old components of innate immunity found in all living pluricellular organisms. Interestingly, some organisms express families of AMPs with only a slight variation among their members, possibly to increase their spectrum of activity. Despite the growing body of knowledge about their biological activity and mode of action on bacteria, only a few of them have been tested on Leishmania, a worldwide spread protozoan pathogen, and the parameters contributing to this activity are yet to be determined. We report on the anti-Leishmania activity and mode of action of bombinins H2 and H4 isolated from the skin secretion of the frog Bombina variegata. H4, the most active, is the first natural AMP of animal origin with a single L- to D-amino acid isomerization. Membrane depolarization and membrane permeation assays, as well as electron microscopy, suggest that the lethal mechanism involves plasma membrane permeation and/or disruption. To better understand the enhanced activity of H4, we determined the peptide's structure in membranes mimicking those of mammals, bacteria, and Leishmania by using ATR-FTIR and CD spectroscopies and assessed their membrane binding by using surface plasmon resonance. The data reveal that (i) H2 but not H4 partially aggregates in membranes mimicking those of Leishmania, (ii) H2 is slightly more helical than H4 in all membranes, and (iii) H4 binds the Leishmania model membrane approximately 5-fold better than H2. This study highlights the importance of a single alpha-amino acid epimerization as a tool used by nature to modulate the activity of AMPs. In addition, our findings suggest bombinins H as potential templates for the development of new drugs with a new mode of action against Leishmania.

Antibacterial properties of dermaseptin S4 derivatives under extreme incubation conditions

Antibacterial properties of the frog-derived peptide dermaseptin S4 and a series of synthetic derivatives against the food pathogen Escherichia coli O157:H7 were investigated under extreme incubation conditions. The 28-mer analog K4K20S4 (P28) displayed an MIC of 8 microM and rapid bactericidal kinetics under standard culture conditions. Potent bactericidal properties were maintained at high salt concentrations, under acidic or basic conditions, and at extreme temperatures. The N-terminal 14-mer sequence (P14) displayed higher potency (MIC, 4 microM) but only within a narrow range of incubation conditions, pointing to the importance of the C-terminal domain of P28. The potency range was reextended upon conjugation of aminododecanoic acid to P14. The resulting lipopeptide was even more potent (MIC, 2 microM) and affected bacterial viability under most of the conditions tested, including in commercial apple juice. The mechanistic implications of peptides' hydrophobicity, charge, structure, and binding to an idealized membrane were probed and are discussed here. Collectively, the data indicate interest in simple peptide-based compounds for design of antimicrobials that affect pathogens under a variable range of incubation conditions.

Identification of antimicrobial peptide regions derived from genomic sequences of phage lysins

This study was designed to test the possibility that antimicrobial peptides could be derived from the genomic sequences of phage lysins. Using two lysins (D3 and PhiKZ) we selected and produced two putative peptides (X and Z, respectively) believed to possess antimicrobial properties based on their physicochemical characteristics. The data presented support this hypothesis in that the peptides and various analogs displayed antibacterial activity, bacteriostatic or bactericidal, either individually or upon combination. These putative peptides are believed to act by a mechanism of action resembling that of conventional antimicrobial peptides when judged by both structural and functional criteria. Thus, the peptides are shown to have the ability to form a helical structure, to bind to model bacterial membranes and permeabilize model liposomes. They also display rapid bactericidal kinetics and their antibacterial potency is increased upon amidation. The possible relevance of these results in contributing to potency of phage lysins is discussed. Such peptides may be used to design new potent antimicrobial compounds much needed in face of the ever threatening drug resistance problems.

Consequences of N-acylation on structure and membrane binding properties of dermaseptin derivative K4-S4-(1-13)

Acyl conjugation to antimicrobial peptides is known to enhance antimicrobial properties. Here, we investigated the consequences of aminolauryl (NC(12)) conjugation to the dermaseptin derivative K(4)-S4-(1-13) (P) on binding properties to bilayer models mimicking bacterial plasma membrane, which is often cited as the ultimate site of action. Isothermal titration calorimetry revealed that acylation was responsible for enhancing the binding affinity of NC(12)-P compared with P (K = 13 x 10(5) and 1.5 x 10(5) m(-1), respectively). Surface plasmon resonance measurements confirmed the isothermal titration calorimetry results (K(app) = 12.6 x 10(5) and 1.53 x 10(5) m(-1), respectively) and further indicated that enhanced adhesion affinity (K(adhesion) = 3 x 10(5) and 1 x 10(5) m(-1), respectively) was coupled to enhanced tendency to insert within the bilayer (K(insertion) = 4.5 and 1.5, respectively). To gain insight into the molecular basis for these observations, we investigated the three-dimensional structures in the presence of dodecylphosphocholine using NMR. The ensemble of NMR-calculated structures (backbone root mean square deviation <0.6 A) showed that the acyl moiety was responsible for a significant molecular reorganization, possibly affecting the electrostatic potential distribution in NC(12)-P relative to that of P. The combined data present compelling evidence in support of the hypothesis that N-acylation affects antimicrobial properties by modifying the secondary structure of the peptide in a manner that facilitates contact with the membrane and consequently increases its disruption.

Spermicidal activity of dermaseptins

OBJECTIVE

The present study was undertaken to elucidate the spermicidal efficacy of two synthetic antimicrobial peptides, dermaseptin (DS1 and DS4).

METHODS

Twenty samples of fresh semen were obtained from patients aged between 23 and 35 years. The ability of DS to kill sperm was evaluated by the Sander-Cramer test under in vitro conditions.

RESULTS

The data showed that sperm motility was inhibited with various concentrations of DS at different intervals ranging from 2 to 240 min. The effective 100% inhibitory concentration (EC(100)) of DS4 in 2 min during the sperm immobilization assay was 100 microg/mL whereas the sperm immobilization of EC(100) of DS1 was 200 microg/mL. The presence of 0.1% chelating agent ethylenediaminetetraacetic acid (EDTA) reduced the EC(100) of DS4 to 10 microg/mL whereas less than a two-time enhancement in DS1 activity was observed upon combination with EDTA. The action of DSs on sperm motility was observed to be dose dependent. Supplementation with pentoxifylline and that with calcium are known to enhance the motility of sperm but they did not prevent the spermicidal action of DSs.

CONCLUSION

This present study indicates that DS is an effective agent to kill sperm. In view of this fact, it is suggested that DS4 has antibacterial, antiviral, antifungal and potentially spermicidal activities and could be a potent vaginal contraceptive.