Designer assays for antimicrobial peptides. Disputing the "one-size-fits-all" theory

Turbidimetric bioassays: A solution to antimicrobial activity detection in asymptomatic bacteriuria isolates against uropathogenic Escherichia coli

Traditional bacteriocin screening methods often face limitations due to diffusion-related challenges in agar matrices, which can prevent the peptides from reaching their target organism. Turbidimetric techniques offer a solution to these issues, eliminating diffusion-related problems and providing an initial quantification of bacteriocin efficacy in producer organisms. This study involved screening the cell-free supernatant (CFS) from eight uncharacterized asymptomatic bacteriuria (ABU) isolates and Escherichia coli 83972 for antimicrobial activity against clinical uropathogenic E. coli (UPEC) strains using turbidimetric growth methods. ABU isolates exhibiting activity against five or more UPEC strains were further characterized (PUTS 37, PUTS 58, PUTS 59, S-07-4, and SK-106-1). The inhibition of the CFS by proteinase K suggested that the antimicrobial activity was proteinaceous in nature, potentially bacteriocins. The activity of E. coli PUTS 58 and SK-106-1 was enhanced in an artificial urine medium, with both inhibiting all eight UPECs. A putative microcin H47 operon was identified in E. coli SK-106-1, along with a previously identified microcin V and colicin E7 in E. coli PUTS 37 and PUTS 58, respectively. These findings indicate that ABU bacteriocin-producers could serve as viable prophylactics and therapeutics in the face of increasing antibiotic resistance among uropathogens.

Bacterial pneumonia-induced shedding of epithelial heparan sulfate inhibits the bactericidal activity of cathelicidin in a murine model

Bacterial pneumonia is a common clinical syndrome leading to significant morbidity and mortality worldwide. In the current study, we investigate a novel, multidirectional relationship between the pulmonary epithelial glycocalyx and antimicrobial peptides in the setting of methicillin-resistant Staphylococcus aureus (MRSA) pneumonia. Using an in vivo pneumonia model, we demonstrate that highly sulfated heparan sulfate (HS) oligosaccharides are shed into the airspaces in response to MRSA pneumonia. In vitro, these HS oligosaccharides do not directly alter MRSA growth or gene transcription. However, in the presence of an antimicrobial peptide (cathelicidin), increasing concentrations of HS inhibit the bactericidal activity of cathelicidin against MRSA as well as other nosocomial pneumonia pathogens (Klebsiella pneumoniae and Pseudomonas aeruginosa) in a dose-dependent manner. Surface plasmon resonance shows avid binding between HS and cathelicidin with a dissociation constant of 0.13 μM. These findings highlight a complex relationship in which shedding of airspace HS may hamper host defenses against nosocomial infection via neutralization of antimicrobial peptides. These findings may inform future investigation into novel therapeutic targets designed to restore local innate immune function in patients suffering from primary bacterial pneumonia.NEW & NOTEWORTHY Primary Staphylococcus aureus pneumonia causes pulmonary epithelial heparan sulfate (HS) shedding into the airspace. These highly sulfated HS fragments do not alter bacterial growth or transcription, but directly bind with host antimicrobial peptides and inhibit the bactericidal activity of these cationic polypeptides. These findings highlight a complex local interaction between the pulmonary epithelial glycocalyx and antimicrobial peptides in the setting of bacterial pneumonia.

Recipe for Success: Suggestions and Recommendations for the Isolation and Characterisation of Bacteriocins

Bacteriocins are bacterially produced antimicrobial peptides. Although only two peptides have been approved for use as natural preservatives foods, current research is focusing on expanding their application as potential therapeutics against clinical pathogens. Our laboratory group has been working on bacteriocins for over 25 years, and during that time, we have isolated bacteriocin-producing microorganisms from a variety of sources including human skin, human faeces, and various foods. These bacteriocins were purified and characterised, and their potential applications were examined. We have also identified bioengineered derivatives of the prototype lantibiotic nisin which possess more desirable properties than the wild-type, such as enhanced antimicrobial activity. In the current communication, we discuss the main methods that were employed to identify such peptides. Furthermore, we provide a step-by-step guide to carrying out these methods that include accompanying diagrams. We hope that our recommendations and advice will be of use to others in their search for, and subsequent analysis of, novel bacteriocins, and derivatives thereof.

Deciphering Novel Antimicrobial Peptides from the Transcriptome of Papilio xuthus

Simple Summary

Insects live in a pathogenic microorganism rich environment. Thus, insects develop a stronger defense in terms of innate immunity. Antimicrobial peptides (AMPs) are one of the key tools in the insect’s innate immune system, which kills the invading pathogens. In this study, we used Papilio xuthus, the Asian swallowtail butterfly, to identify the AMPs from their genomic product. We utilized next generation sequencing technology and in silico analysis tools to decipher the possible novel AMPs. The obtained novel AMPs were then tested for the antibacterial and antifungal activities. Seven novel peptides were identified as the antimicrobial agent, and these can be used as a lead candidate in the process of antibacterial therapy development against various infectious diseases.

Abstract

An insect’s innate immune system is the front line of defense against many invading microorganisms. One of the important components of this defense system is antimicrobial peptides (AMPs). Papiliocin is a well-studied antimicrobial peptide (AMP) isolated from the swallowtail butterfly, Papilio xuthus, and it was previously reported to be effective against Gram-positive bacteria, Gram-negative bacteria, and fungi, particularly in drug resistant Gram-negative bacteria. Hence, we aimed to identify novel AMPs from Papilio xuthus using its transcriptome. We immunized the swallowtail butterfly with Escherichia coli, Staphylococcus aureus, Candida albicans, and the total RNA was isolated. De novo transcriptome assembly and functional annotations were conducted, and AMPs were predicted using an in-silico pipeline. The obtained 344,804,442 raw reads were then pre-processed to retrieve 312,509,806 (90.6%) total clean reads. A total of 38,272 unigenes were assembled with the average length of 1010 bp. Differential gene expression analysis identified 584 and 1409 upregulated and downregulated genes, respectively. The physicochemical, aggregation, and allergen propensity were used as filtration criteria. A total of 248 peptides were predicted using our in-house pipeline and the known AMPs were removed, resulting in 193 novel peptides. Finally, seven peptides were tested in vitro and three peptides (Px 5, 6, and 7) showed stronger antimicrobial activity against Gram-negative bacteria and yeast. All the tested peptides were non-allergens. The identified novel AMPs may serve as potential candidates for future antimicrobial studies.

Transcriptome Analysis of Psacothea hilaris: De Novo Assembly and Antimicrobial Peptide Prediction

Antimicrobial peptides (AMPs) are the frontline innate defense system evolutionarily preserved in insects to combat invading pathogens. These AMPs could serve as an alternative to classical antibiotics to overcome the burden of treating multidrug resistant bacteria. Psacotheasin, a knottin type AMP was isolated from Psacothea hilaris and shown to exhibit antimicrobial activity, especially against fungi through apoptosis mediated cell death. In this study, we aimed to identify novel probable AMPs from Psacothea hilaris, the yellow spotted longicorn beetle. The beetle was immunized with the two bacterial strains (E. coli and S. aureus), and the yeast strain C. albicans. After immunization, total RNA was isolated and sequenced in Illumina platform. Then, beetle transcriptome was de novo assembled and searched for putative AMPs with the known physiochemical features of the AMPs. A selection of AMP candidates were synthesized and tested for antimicrobial activity. Four peptides showed stronger activity against E. coli than the control AMP, melittin while one peptide showed similar activity against S. aureus. Moreover, four peptides and two peptides showed antifungal activity stronger than and similar to melittin, respectively. Collectively one peptide showed both antibacterial and antifungal activity superior to melittin; thus, it provides a potent antimicrobial peptide. All the peptides showed no hemolysis in all the tested concentrations. These results suggest that in silico mining of insects' transcriptome could be a promising tool to obtain and optimize novel AMPs for human needs.

In silico identification and functional validation of linear cationic α-helical antimicrobial peptides in the ascidian Ciona intestinalis

We developed a computing method to identify linear cationic α-helical antimicrobial peptides (LCAMPs) in the genome of Ciona intestinalis based on its structural and physicochemical features. Using this method, 22 candidates of Ciona LCAMPs, including well-known antimicrobial peptides, were identified from 21,975 non-redundant amino acid sequences in Ciona genome database, Ghost database. We also experimentally confirmed the antimicrobial activities of five LCAMP candidates, and three of them were found to be active in the presence of 500 mM NaCl, nearly equivalent to the salt concentration of seawater. Membrane topology prediction suggested that salt resistance of Ciona LCAMPs might be influenced by hydrophobic interactions between the peptide and membrane. Further, we applied our method to Xenopus tropicalis genome and found 11 LCAMP candidates. Thus, our method may serve as an effective and powerful tool for searching LCAMPs that are difficult to find using conventional homology-based methods.

Design of a Helical-Stabilized, Cyclic, and Nontoxic Analogue of the Peptide Cm-p5 with Improved Antifungal Activity

Following the information obtained by a rational design study, a cyclic and helical-stabilized analogue of the peptide Cm-p5 was synthetized. The cyclic monomer showed an increased activity in vitro against Candida albicans and Candida parapsilosis, compared to Cm-p5. Initially, 14 mutants of Cm-p5 were synthesized following a rational design to improve the antifungal activity and pharmacological properties. Antimicrobial testing showed that the activity was lost in each of these 14 analogues, suggesting, as a main conclusion, that a Glu-His salt bridge could stabilize Cm-p5 helical conformation during the interaction with the plasma membrane. A derivative, obtained by substitution of Glu and His for Cys, was synthesized and oxidized with the generation of a cyclic monomer with improved antifungal activity. In addition, two dimers were generated during the oxidation procedure, a parallel and antiparallel one. The dimers showed a helical secondary structure in water, whereas the cyclic monomer only showed this conformation in SDS. Molecular dynamic simulations confirmed the helical stabilizations for all of them, therefore indicating the possible essential role of the Glu-His salt bridge. In addition, the antiparallel dimer showed a moderate activity against Pseudomonas aeruginosa and a significant activity against Listeria monocytogenes. Neither the cyclic monomer nor the dimers were toxic against macrophages or THP-1 human cells. Due to its increased capacity for fungal control compared to fluconazole, its low cytotoxicity, together with a stabilized α-helix and disulfide bridges, that may advance its metabolic stability, and in vivo activity, the new cyclic Cm-p5 monomer represents a potential systemic antifungal therapeutic candidate.

Cationic Intrinsically Disordered Antimicrobial Peptides (CIDAMPs) Represent a New Paradigm of Innate Defense with a Potential for Novel Anti-Infectives

In the search for potential mechanisms underlying the remarkable resistance of healthy skin against infection by soil bacteria like Pseudomonas (P.) aeruginosa we identified fragments of the intrinsically disordered protein hornerin as potent microbicidal agents in the stratum corneum. We found that, independent of the amino acid (AA)-sequence, any tested linear cationic peptide containing a high percentage of disorder-promoting AA and a low percentage of order-promoting AA is a potent microbicidal antimicrobial. We further show that the antimicrobial activity of these cationic intrinsically disordered antimicrobial peptides (CIDAMPs) depends on the peptide chain length, its net charge, lipidation and environmental conditions. The ubiquitous presence of latent CIDAMP sources in nature suggests a common and yet overlooked adapted innate disinfection system of body surfaces. The simple structure and virtually any imaginable sequence or composition of disorder-promoting AA allow the generation of a plethora of CIDAMPs. These are potential novel microbicidal anti-infectives for various bacterial pathogens, including P. aeruginosa, methicillin-resistant Staphylococcus aureus (MRSA) and fungal pathogens like Candida albicans and Cryptococcus neoformans.

Efficient Production of Recombinant Protegrin-1 From Pichia pastoris, and Its Antimicrobial and in vitro Cell Migration Activity

Protegrin (PG) belongs to the antimicrobial peptide cathelicidin family. To date, five protegrin sequences have been identified in pigs, PG-1 to PG-5. Of these, PG-1 exhibits potent antimicrobial activity against a broad range of antibiotic-resistant microorganisms as well as viruses. However, the other potential role(s) of PG beyond antimicrobial has largely been unexplored. The aim of this study was to use nonpathogenic yeast Pichia pastoris to express antimicrobially active recombinant protegrin (rPG-1). Additionally, the effect of PG-1 on cell migration and proliferation was also examined in vitro using pig intestinal epithelial cells as a model. Highest level of rPG-1 (104 ± 11 μg/mL) was detected at 24 h in fermentation culture medium. Similar to rPG-1, 0.8 ± 0.10 g/L of proform PG-1 (rProPG-1) and 0.2 ± 0.02 g/L of the PG-1 cathelin domain (rCath) was detected in fermentation culture medium. Resulting recombinant PG-1 and cleaved rProPG-1 exerted antimicrobial activity against Escherichia coli DH5α at the same level as chemically synthesized PG-1. Enhanced cell migration was observed (p < 0.05) in groups treated with rProPG-1, rCath, and rPG-1 compared to the control. Furthermore, rPG-1 was stable at temperatures ranging from 25°C to 80°C. In summary, biologically active recombinant protegrin in its pro-, cathelin-, and mature- forms were successfully expressed in P. pastoris suggesting potential feasibility for future therapeutic applications.

Bleogens: Cactus-Derived Anti-Candida Cysteine-Rich Peptides with Three Different Precursor Arrangements

Cysteine-rich peptides (CRPs) play important host-defense roles in plants. However, information concerning CRPs in the Cactaceae (cactus) family is limited, with only a single cactus-derived CRP described to date. Here, we report the identification of 15 novel CRPs with three different precursor architectures, bleogens pB1-15 from Pereskia bleo of the Cactaceae family. By combining proteomic and transcriptomic methods, we showed that the prototype, bleogen pB1, contained 36 amino acid residues, a six-cysteine motif typical of the six-cysteine-hevein-like peptide (6C-HLP) family, and a type I two-domain precursor consisting of an endoplasmic reticulum (ER) and a mature domain. In contrast, the precursors of the other 14 bleogens contained a type II three-domain architecture with a propeptide domain inserted between the ER and the mature bleogen domain. Four of these 14 bleogens display a third type of architecture with a tandemly repeating bleogen domain. A search of the Onekp database revealed that <1% plant species possess three different precursor architectures for the biosynthesis of 6C-HLPs, including Lophophora williamsii, Pereskia aculeate, Portulaca cryptopetala, Portulaca oleracea, Portulaca suffruticosa, and Talinum sp. NMR analysis confirmed that bleogen pB1 has cystine-knot disulfide connectivity as well as a two-beta-sheet and a four-loop structural fold that is similar to other 6C-HLPs. Sequence analysis, structural studies, and in silico modeling revealed that bleogen pB1 has a cation-polar-cation motif, a signature heparin-binding motif that was confirmed by heparin affinity chromatography. Cell-based assays showed that bleogen pB1 is non-toxic to mammalian cells but functions as an anti-Candida peptide. Taken together, our findings provide insight into the occurrence, functions and precursor architectures of CRPs in the cactus family.

Isolation of biologically active peptides from the venom of Japanese carpenter bee, Xylocopa appendiculata

Background

Mass spectrometry-guided venom peptide profiling is a powerful tool to explore novel substances from venomous animals in a highly sensitive manner. In this study, this peptide profiling approach is successfully applied to explore the venom peptides of a Japanese solitary carpenter bee, Xylocopa appendiculata (Hymenoptera: Apoidea: Apidae: Anthophila: Xylocopinae: Xylocopini). Although interesting biological effects of the crude venom of carpenter bees have been reported, the structure and biological function of the venom peptides have not been elucidated yet.

Methods

The venom peptide profiling of the crude venom of X. appendiculata was performed by matrix-assisted laser desorption/ionization-time of flight mass spectroscopy. The venom was purified by a reverse-phase HPLC. The purified peptides were subjected to the Edman degradation, MS/MS analysis, and/or molecular cloning methods for peptide sequencing. Biological and functional characterization was performed by circular dichroism analysis, liposome leakage assay, and antimicrobial, histamine releasing and hemolytic activity tests.

Results

Three novel peptides with m/z 16508, 1939.3, and 1900.3 were isolated from the venom of X. appendiculata. The peptide with m/z 16508 was characterized as a secretory phospholipase A₂ (PLA₂) homolog in which the characteristic cysteine residues as well as the active site residues found in bee PLA₂s are highly conserved. Two novel peptides with m/z 1939.3 and m/z 1900.3 were named as Xac-1 and Xac-2, respectively. These peptides are found to be amphiphilic and displayed antimicrobial and hemolytic activities. The potency was almost the same as that of mastoparan isolated from the wasp venom.

Conclusion

We found three novel biologically active peptides in the venom of X. appendiculata and analyzed their molecular functions, and compared their sequential homology to discuss their molecular diversity. Highly sensitive mass analysis plays an important role in this study.

Electronic supplementary material

The online version of this article (doi:10.1186/s40409-017-0119-6) contains supplementary material, which is available to authorized users.

Histones from Avian Erythrocytes Exhibit Antibiofilm activity against methicillin-sensitive and methicillin-resistant Staphylococcus aureus

Staphylococcus aureus, a human pathogen associated with many illnesses and post-surgical infections, can resist treatment due to the emergence of antibiotic-resistant strains and through biofilm formation. The current treatments for chronic biofilm infections are antibiotics and/or surgical removal of the contaminated medical device. Due to higher morbidity and mortality rates associated with overuse/misuse of antibiotics, alternate treatments are essential. This study reports the antibiofilm activity of avian erythrocyte histones against methicillin-sensitive Staphylococcus aureus (MSSA) and methicillin-resistant Staphylococcus aureus (MRSA). Fluorescence and scanning electron microscopy revealed membrane damage to bacteria in histone-treated biofilms. Histones and indolicidin (positive control) increased the expression of apsS and apsR, which are associated with the Antimicrobial Peptide (AMP) sensor/regulator system in S. aureus. The expression of dltB, and vraF, associated with AMP resistance mechanisms, were under histone inducible control in the biofilm-embedded bacterial cells. The time kill kinetics for histones against S. aureus revealed a rapid biocidal activity (<5 min). Purified erythrocyte-specific histone H5 possessed 3-4 fold enhanced antimicrobial activity against planktonic cells compared to the histone mixture (H1, H2A, H2B, H3, H4, H5). These results demonstrate the promise of histones and histone-like derivatives as novel antibiotics against pathogens in their planktonic and biofilm forms.

Diminished Antimicrobial Peptide and Antifungal Antibiotic Activities against Candida albicans in Denture Adhesive

The underlying causes of denture stomatitis may be related to the long-term use of adhesives, which may predispose individuals to oral candidiasis. In this study, we hypothesize that antimicrobial peptides and antifungal antibiotics have diminished anti-Candida activities in denture adhesive. To show this, nine antimicrobial peptides and five antifungal antibiotics with and without 1.0% denture adhesive were incubated with Candida albicans strains ATCC 64124 and HMV4C in radial diffusion assays. In gels with 1.0% adhesive, HNP-1, HBD2, HBD3, IP-10, LL37 (only one strain), histatin 5 (only one strain), lactoferricin B, and SMAP28 showed diminished activity against C. albicans. In gels with 1.0% adhesive, amphotericin B and chlorhexidine dihydrochloride were active against both strains of C. albicans. These results suggest that denture adhesive may inactivate innate immune mediators in the oral cavity increasing the risk of C. albicans infections, but inclusion of antifungal antibiotics to denture adhesive may aid in prevention or treatment of Candida infections and denture stomatitis.

Host Cell Interactions Are a Significant Barrier to the Clinical Utility of Peptide Antibiotics

Despite longstanding promise and many known examples, antimicrobial peptides (AMPs) have failed, thus far, to impact human medicine. On the basis of the physical chemistry and mechanism of action of AMPs, we hypothesized that host cell interactions could contribute to a loss of activity in vivo where host cells are highly concentrated. To test this idea, we characterized AMP activity in the presence of human red blood cells (RBC). Indeed, we show that most of a representative set of natural and synthetic AMPs tested are significantly inhibited by preincubation with host cells and would be effectively inactive at physiological cell density. We studied an example broad-spectrum AMP, ARVA (RRGWALRLVLAY), in a direct, label-free binding assay. We show that weak binding to host cells, coupled with their high concentration, is sufficient to account for a loss of useful activity, for at least some AMPs, because >1 × 10⁸ peptides must be bound to each bacterial cell to achieve sterilization. The effect of host cell preincubation on AMP activity is comparable to that of serum protein binding. Feasible changes in host cell binding could lead to AMPs that do not lose activity through interaction with host cells. We suggest that the intentional identification of AMPs that are active in the presence of concentrated host cells can be achieved with a paradigm shift in the way AMPs are discovered.

Activation of human mast cells by retrocyclin and protegrin highlight their immunomodulatory and antimicrobial properties

Preclinical evaluation of Retrocyclins (RC-100, RC-101) and Protegrin-1 (PG-1) antimicrobial peptides (AMPs) is important because of their therapeutic potential against bacterial, fungal and viral infections. Human mast cells (HMCs) play important roles in host defense and wound healing but the abilities of retrocyclins and protegrin-1 to harness these functions have not been investigated. Here, we report that chemically synthesized RC-100 and PG-1 caused calcium mobilization and degranulation in HMCs but these responses were not blocked by an inhibitor of formyl peptide receptor-like 1 (FPRL1), a known receptor for AMPs. However, RC-100 and PG-1 induced degranulation in rat basophilic leukemia (RBL-2H3) cells stably expressing Mas related G protein coupled receptor X2 (MrgX2). Chemical synthesis of these AMPs is prohibitively expensive and post-synthesis modifications (cyclization, disulfide bonds, folding) are inadequate for optimal antimicrobial activity. Indeed, we found that synthetic RC-100, which caused mast cell degranulation via MrgX2, did not display any antimicrobial activity. Green-fluorescent protein (GFP)-tagged RC-101 (analog of RC-100) and GFP-tagged PG-1 purified from transgenic plant chloroplasts killed bacteria and induced mast cell degranulation. Furthermore, GFP-PG1 bound specifically to RBL-2H3 cells expressing MrgX2. These findings suggest that retrocyclins and protegrins activate HMCs independently of FPRL1 but via MrgX2. Harnessing this novel feature of AMPs to activate mast cell's host defense/wound healing properties in addition to their antimicrobial activities expands their clinical potential. Low cost production of AMPs in plants should facilitate their advancement to the clinic overcoming major hurdles in current production systems.

A Requirement for Metamorphic Interconversion in the Antimicrobial Activity of Chemokine XCL1

Chemokines make up a superfamily of ∼50 small secreted proteins (8-12 kDa) involved in a host of physiological processes and disease states, with several previously shown to have direct antimicrobial activity comparable to that of defensins in efficacy. XCL1 is a unique metamorphic protein that interconverts between the canonical chemokine fold and a novel all-β-sheet dimer. Phylogenetic analysis suggests that, within the chemokine family, XCL1 is most closely related to CCL20, which exhibits antibacterial activity. The in vitro antimicrobial activity of WT-XCL1 and structural variants was quantified using a radial diffusion assay (RDA) and in solution bactericidal assays against Gram-positive and Gram-negative species of bacteria. Comparisons of WT-XCL1 with variants that limit metamorphic interconversion showed a loss of antimicrobial activity when restricted to the conserved chemokine fold. These results suggest that metamorphic folding of XCL1 is required for potent antimicrobial activity.

Anticancer activity of CopA3 dimer peptide in human gastric cancer cells

CopA3 is a homodimeric α-helical peptide derived from coprisin which is a defensin-like antimicrobial peptide that was identified from the dung beetle, Copris tripartitus. CopA3 has been reported to have anticancer activity against leukemia cancer cells. In the present study, we investigated the anticancer activity of CopA3 in human gastric cancer cells. CopA3 reduced cell viability and it was cytotoxic to gastric cancer cells in the MTS and LDH release assay, respectively. CopA3 was shown to induce necrotic cell death of the gastric cancer cells by flow cytometric analysis and acridine orange/ethidium bromide staining. CopA3-induced cell death was mediated by specific interactions with phosphatidylserine, a membrane component of cancer cells. Taken together, these data indicated that CopA3 mainly caused necrosis of gastric cancer cells, probably through interactions with phosphatidylserine, which suggests the potential utility of CopA3 as a cancer therapeutic. [BMB Reports 2015; 48(6): 324-329]

Antifungal Activity and Action Mechanism of Histatin 5-Halocidin Hybrid Peptides against Candida ssp

The candidacidal activity of histatin 5 is initiated through cell wall binding, followed by translocation and intracellular targeting, while the halocidin peptide exerts its activity by attacking the Candida cell membrane. To improve antimicrobial activities and to understand the killing mechanism of two peptides, six hybrid peptides were designed by conjugating histatin 5 and halocidin. A comparative approach was established to study the activity, salt tolerance, cell wall glucan binding assay, cytotoxicity, generation of ROS and killing kinetics. CD spectrometry was conducted to evaluate secondary structures of these hybrid peptides. Furthermore the cellular localization of hybrid peptides was investigated by confocal fluorescence microscopy. Of the six hybrid congeners, di-PH2, di-WP2 and HHP1 had stronger activities than other hybrid peptides against all tested Candida strains. The MIC values of these peptides were 1–2, 2–4 and 2–4 μg/ml, respectively. Moreover, none of the hybrid peptides was cytotoxic in the hemolytic assay and cell-based cytotoxicity assay. Confocal laser microscopy showed that di-PH2 and HHP1 were translocated into cytoplasm whereas di-WP2 was accumulated on surface of C. albicans to exert their candidacidal activity. All translocated peptides (Hst 5, P113, di-PH2) were capable of generating intracellular ROS except HHP1. Additionally, the KFH residues at C-terminal end of these peptides were assumed for core sequence for active translocation.

Physicochemical and biological characterizations of Pxt peptides from amphibian (Xenopus tropicalis) skin

Pxt peptides (Pxt-1 through Pxt-12) have been isolated from amphibian, Xenopus tropicalis Pxt-related peptides (Pxt-2, Pxt-5, Pxt-12, reverse Pxt-2, reverse Pxt-5 and reverse Pxt-12) with significant foaming properties were further characterized. In the physicochemical experiments, all Pxt-related peptides formed significant amphiphilic α-helices in 50% 2,2,2-trifluoroethanol by circular dichroism measurements. Among Pxt-related peptides, both Pxt-5 and reverse Pxt-5 were the most effective in reducing their surface tensions. Moreover, Pxt-2, Pxt-5 and reverse Pxt-5 produced constant surface tensions above their critical association concentrations, suggesting the micelle-like assemblies. In the biological experiments, Pxt-5 possessed the most potent hemolytic activity, while reverse Pxt-5 exhibited the most remarkable gene expression of interleukin 8 and heme oxygenase 1 and the most potent cytotoxicity in HaCaT cells. In contrast, Pxt-12 and reverse Pxt-12 were much weaker in antimicrobial assays for Gram-negative bacteria, Gram-positive bacteria and yeasts, as well as in hemolytic, cell viability and cytotoxicity assays in HaCaT cells. All Pxt-related peptides exhibited about 20-50% of the total cellular histamine release at 10(-5) M, as well as mastoparan and melittin in mast cells. Real-time polymerase chain reaction analysis confirmed the gene expressions of Pxt-5 in testis and Pxt-12 in muscle, in addition to skin, while Pxt-2 was only in skin.

Role of arginine and lysine in the antimicrobial mechanism of histone-derived antimicrobial peptides

Translocation of cell-penetrating peptides is often promoted by increased content of arginine or other guanidinium groups. However, relatively little research has considered the role of these functional groups on antimicrobial peptide activity. This study compared the activity of three histone-derived antimicrobial peptides-buforin II, DesHDAP1, and parasin-with variants that contain only lysine or arginine cationic residues. These peptides operate via different mechanisms as parasin causes membrane permeabilization while buforin II and DesHDAP1 translocate into bacteria. For all peptides, antibacterial activity increased with increased arginine content. Higher arginine content increased permeabilization for parasin while it improved translocation for buforin II and DesHDAP1. These observations provide insight into the relative importance of arginine and lysine in these antimicrobial peptides.

Skin-Derived C-Terminal Filaggrin-2 Fragments Are Pseudomonas aeruginosa-Directed Antimicrobials Targeting Bacterial Replication

Soil- and waterborne bacteria such as Pseudomonas aeruginosa are constantly challenging body surfaces. Since infections of healthy skin are unexpectedly rare, we hypothesized that the outermost epidermis, the stratum corneum, and sweat glands directly control the growth of P. aeruginosa by surface-provided antimicrobials. Due to its high abundance in the upper epidermis and eccrine sweat glands, filaggrin-2 (FLG2), a water-insoluble 248 kDa S100 fused-type protein, might possess these innate effector functions. Indeed, recombinant FLG2 C-terminal protein fragments display potent antimicrobial activity against P. aeruginosa and other Pseudomonads. Moreover, upon cultivation on stratum corneum, P. aeruginosa release FLG2 C-terminus-containing FLG2 fragments from insoluble material, indicating liberation of antimicrobially active FLG2 fragments by the bacteria themselves. Analyses of the underlying antimicrobial mechanism reveal that FLG2 C-terminal fragments do not induce pore formation, as known for many other antimicrobial peptides, but membrane blebbing, suggesting an alternative mode of action. The association of the FLG2 fragment with the inner membrane of treated bacteria and its DNA-binding implicated an interference with the bacterial replication that was confirmed by in vitro and in vivo replication assays. Probably through in situ-activation by soil- and waterborne bacteria such as Pseudomonads, FLG2 interferes with the bacterial replication, terminates their growth on skin surface and thus may contributes to the skin's antimicrobial defense shield. The apparent absence of FLG2 at certain body surfaces, as in the lung or of burned skin, would explain their higher susceptibility towards Pseudomonas infections and make FLG2 C-terminal fragments and their derivatives candidates for new Pseudomonas-targeting antimicrobials.

Modification of β-Defensin-2 by Dicarbonyls Methylglyoxal and Glyoxal Inhibits Antibacterial and Chemotactic Function In Vitro

Background

Beta-defensins (hBDs) provide antimicrobial and chemotactic defense against bacterial, viral and fungal infections. Human β-defensin-2 (hBD-2) acts against gram-negative bacteria and chemoattracts immature dendritic cells, thus regulating innate and adaptive immunity. Immunosuppression due to hyperglycemia underlies chronic infection in Type 2 diabetes. Hyperglycemia also elevates production of dicarbonyls methylgloxal (MGO) and glyoxal (GO).

Methods

The effect of dicarbonyl on defensin peptide structure was tested by exposing recombinant hBD-2 (rhBD-2) to MGO or GO with subsequent analysis by MALDI-TOF MS and LC/MS/MS. Antimicrobial function of untreated rhBD-2 vs. rhBD-2 exposed to dicarbonyl against strains of both gram-negative and gram-positive bacteria in culture was determined by radial diffusion assay. The effect of dicarbonyl on rhBD-2 chemotactic function was determined by chemotaxis assay in CEM-SS cells.

Results

MGO or GO in vitro irreversibly adducts to the rhBD-2 peptide, and significantly reduces antimicrobial and chemotactic functions. Adducts derive from two arginine residues, Arg²² and Arg²³ near the C-terminus, and the N-terminal glycine (Gly¹). We show by radial diffusion testing on gram-negative E. coli and P. aeruginosa, and gram-positive S. aureus, and a chemotaxis assay for CEM-SS cells, that antimicrobial activity and chemotactic function of rhBD-2 are significantly reduced by MGO.

Conclusions

Dicarbonyl modification of cationic antimicrobial peptides represents a potential link between hyperglycemia and the clinical manifestation of increased susceptibility to infection, protracted wound healing, and chronic inflammation in undiagnosed and uncontrolled Type 2 diabetes.

Characterization and expression of attacin, an antibacterial protein-encoding gene, from the beet armyworm, Spodoptera exigua (Hübner) (Insecta: Lepidoptera: Noctuidae)

To isolate antimicrobial-related genes from the beet armyworm, Spodoptera exigua, we performed GeneFishing, a polymerase chain reaction (PCR)-based differential display technique. An attacin-like complementary DNA (cDNA) including a 3'-untranslated region was identified from among 18 over-expressed genes in microbial-infected larvae. The full-length attacin cDNA from S. exigua cDNA (Seattacin) was cloned using rapid amplification of cDNA ends PCR. The attacin-like cDNA transcript was 765 nucleotides in length, and the predicted polypeptide was 254 amino acids in length with a calculated molecular mass of 27.6 kDa and an isoelectric point of 6.44. The protein sequence of the attacin-like cDNA showed high identity to that of Trichoplusia ni (61.2%). The amino acid sequence identity of Seattacin to the orthologous proteins in Bombyx mori, Manduca sexta, Heliothis virescens, Hlicoverpa armigera, Hyphantria cunea, Hyalophora cecropia, and Drosophila melanogaster was 61.2, 46.1, 44.5, 42.2, 39.5, 45.1, and 24.0%, respectively. To examine possible immune functions of the attacin-like cDNA, its expression was investigated by reverse transcriptase PCR analysis after challenging S. exigua with microorganisms. The attacin-like cDNA was expressed at high levels 12 h post-infection, and its expression was slightly induced 4-8 h post-infection compared to control larvae inoculated with sterile water. Furthermore, induced Seattacin showed biological activity against several bacteria including Escherichia coli DH5α, Pseudomonas cichorii, Bacillus subtilis, and Listeria monocytogenes. These results suggest that the attacin-like cDNA of S. exigua codes for antimicrobial peptides.

Humanized theta-defensins (retrocyclins) enhance macrophage performance and protect mice from experimental anthrax infections

Retrocyclins are humanized versions of the -defensin peptides expressed by the leukocytes of several nonhuman primates. Previous studies, performed in serum-free media, determined that retrocyclins 1 (RC1) and RC2 could prevent successful germination of Bacillus anthracis spores, kill vegetative B. anthracis cells, and inactivate anthrax lethal factor. We now report that retrocyclins are extensively bound by components of native mouse, human, and fetal calf sera, that heat-inactivated sera show greatly enhanced retrocyclin binding, and that native and (especially) heat-inactivated sera greatly reduce the direct activities of retrocyclins against spores and vegetative cells of B. anthracis. Nevertheless, we also found that retrocyclins protected mice challenged in vivo by subcutaneous, intraperitoneal, or intranasal instillation of B. anthracis spores. Retrocyclin 1 bound extensively to B. anthracis spores and enhanced their phagocytosis and killing by murine RAW264.7 cells. Based on the assumption that spore-bound RC1 enters phagosomes by "piggyback phagocytosis," model calculations showed that the intraphagosomal concentration of RC1 would greatly exceed its extracellular concentration. Murine alveolar macrophages took up fluorescently labeled retrocyclin, suggesting that macrophages may also acquire extracellular RC1 directly. Overall, these data demonstrate that retrocyclins are effective in vivo against experimental murine anthrax infections and suggest that enhanced macrophage function contributes to this property.

Ancient antimicrobial peptides kill antibiotic-resistant pathogens: Australian mammals provide new options

Background

To overcome the increasing resistance of pathogens to existing antibiotics the 10×^'20 Initiative declared the urgent need for a global commitment to develop 10 new antimicrobial drugs by the year 2020. Naturally occurring animal antibiotics are an obvious place to start. The recently sequenced genomes of mammals that are divergent from human and mouse, including the tammar wallaby and the platypus, provide an opportunity to discover novel antimicrobials. Marsupials and monotremes are ideal potential sources of new antimicrobials because they give birth to underdeveloped immunologically naïve young that develop outside the sterile confines of a uterus in harsh pathogen-laden environments. While their adaptive immune system develops innate immune factors produced either by the mother or by the young must play a key role in protecting the immune-compromised young. In this study we focus on the cathelicidins, a key family of antimicrobial peptide genes.

Principal Finding

We identified 14 cathelicidin genes in the tammar wallaby genome and 8 in the platypus genome. The tammar genes were expressed in the mammary gland during early lactation before the adaptive immune system of the young develops, as well as in the skin of the pouch young. Both platypus and tammar peptides were effective in killing a broad range of bacterial pathogens. One potent peptide, expressed in the early stages of tammar lactation, effectively killed multidrug-resistant clinical isolates of Pseudomonas aeruginosa, Klebsiella pneumoniae and Acinetobacter baumannii.

Conclusions and Significance

Marsupial and monotreme young are protected by antimicrobial peptides that are potent, broad spectrum and salt resistant. The genomes of our distant relatives may hold the key for the development of novel drugs to combat multidrug-resistant pathogens.

Effect of proline position on the antimicrobial mechanism of buforin II

Buforin II (BF2) is a histone-derived antimicrobial peptide that causes cell death by translocating across membranes and interacting with nucleic acids. It contains one proline residue critical for its function. Previous research found that mutations replacing proline lead to decreased membrane translocation and antimicrobial activity as well as increased membrane permeabilization. This study further investigates the role of proline in BF2's antimicrobial mechanism by considering the effect of changing proline position on membrane translocation, membrane permeabilization, and antimicrobial activity. For this purpose, four mutants were made with proline substitution (P11A) or relocation (P11A/G7P, P11A/V12P, P11A/V15P). These mutations altered the amount of helical content. Although antimicrobial activity correlated with the α-helical content for the peptides containing proline, membrane translocation did not. This observation suggests that factors in BF2's bactericidal mechanism other than translocation must be altered by these mutations. To better explain these trends we also measured the nucleic acid binding and membrane permeabilization of the mutant peptides. A comparison of mutant and wild type BF2 activity revealed that BF2 relies principally on membrane translocation and nucleic acid binding for antimicrobial activity, although membrane permeabilization may play a secondary role for some BF2 variants. A better understanding of the role of proline in the BF2 antimicrobial mechanism will contribute to the further design and development of BF2 analogs. Moreover, since proline residues are prevalent among other antimicrobial peptides, this systematic characterization of BF2 provides general insights that can promote our understanding of other systems.

Antimicrobial activity of a halocidin-derived peptide resistant to attacks by proteases

Cationic antimicrobial peptides (AMPs) have attracted a great deal of interest as a promising candidate for a novel class of antibiotics that might effectively treat recalcitrant infections caused by a variety of microbes that are resistant to currently available drugs. However, the AMPs are inherently limited in that they are inevitably susceptible to attacks by proteases generated by human and pathogenic microbes; this vulnerability severely hinders their pharmaceutical use in human therapeutic protocols. In this study, we report that a halocidin-derived AMP, designated HG1, was found to be resistant to proteolytic degradation. As a result of its unique structural features, HG1 proved capable of preserving its antimicrobial activity after incubation with trypsin, chymotrypsin, and human matrix metalloprotease 7 (MMP-7). Additionally, HG1 was observed to exhibit profound antimicrobial activity in the presence of fluid from human skin wounds or proteins extracted from the culture supernatants of Staphylococcus aureus and Pseudomonas aeruginosa. Greater understanding of the structural motifs of HG1 required for its protease resistance might provide feasible ways to solve the problems intrinsic to the development of an AMP-based antibiotic.

Primary structure and antibacterial activity of chicken bone marrow-derived beta-defensins

Three biologically active beta-defensins were purified by chromatography from chicken bone marrow extract: avian beta-defensin 1 (AvBD1), AvBD2, and the newly isolated beta-defensin AvBD7. Mass spectrometry analyses showed that bone marrow-derived AvBD1, -2, and -7 peptides were present as mature peptides and revealed posttranslational modifications for AvBD1 and AvBD7 in comparison to their in silico-predicted amino acid sequences. Tandem mass spectrometry analysis using the nanoelectrospray-quadrupole time of flight method showed N-terminal glutaminyl cyclization of mature AvBD7 and C-terminal amidation of mature AvBD1 peptide, while posttranslational modifications were absent in bone marrow-derived mature AvBD2 peptide. Furthermore, mass spectrometry analysis performed on intact cells confirmed the presence of these three peptides in mature heterophils. In addition, the antibacterial activities of the three beta-defensins against a large panel of gram-positive and -negative bacteria were assessed. While the three defensins displayed similar antibacterial spectra of activity against gram-positive strains, AvBD1 and AvBD7 exhibited the strongest activity against gram-negative strains in comparison to AvBD2.

Cathelicidin administration protects mice from Bacillus anthracis spore challenge

Cathelicidins are a family of cationic peptides expressed in mammals that possess numerous bactericidal and immunomodulatory properties. In vitro analyses showed that human, mouse, and pig cathelicidins inhibited Bacillus anthracis bacterial growth at micromolar concentrations in the presence or absence of capsule. Combined in vitro analyses of the effects of each peptide on spore germination and vegetative outgrowth by time lapse phase contrast microscopy, transmission electron microscopy, and flow cytometric analysis showed that only the pig cathelicidin was capable of directly arresting vegetative outgrowth and killing the developing bacilli within the confines of the exosporium. C57BL/6 mice were protected from spore-induced death by each cathelicidin in a time- and dose-dependent manner. Protection afforded by the porcine cathelicidin was due to its bactericidal effects, whereas the human and mouse cathelicidins appeared to mediate protection through increased recruitment of neutrophils to the site of infection. These findings suggest that cathelicidins might be utilized to augment the initial innate immune response to B. anthracis spore exposure and prevent the development of anthrax.

The central kink region of fowlicidin-2, an alpha-helical host defense peptide, is critically involved in bacterial killing and endotoxin neutralization

Fowlicidins are a group of newly identified chicken cathelicidin host defense peptides. We have shown that the putatively mature fowlicidin-2 of 31 amino acid residues possesses potent antibacterial and lipopolysaccharide (LPS)- neutralizing activities, but with a noticeable toxicity to mammalian cells. As a first step in exploring the structure-activity relationships of fowlicidin-2, in this study we determined its tertiary structure by nuclear magnetic resonance spectroscopy. Unlike the majority of cathelicidins, which are composed of a predominant alpha-helix with a short hinge sequence near the center, fowlicidin-2 consists of 2 well-defined alpha-helical segments (residues 6-12 and 23-27) connected by a long extensive kink (residues 13-20) induced by proline. To further investigate the functional significance of each of these structural components, several N- and C-terminal deletion analogs of fowlicidin-2 were synthesized and analyzed for their antibacterial, cytotoxic and LPS-neutralizing activities. Our results indicated that neither the N- nor C-terminal alpha-helix alone is sufficient to confer any function. Rather, fowlicidin-2(1-18) and fowlicidin-2(15-31), 2 alpha-helical segments with inclusion of the central cationic kink region, retained substantial capacities to kill bacteria and neutralize the LPS-induced proinflammatory response, relative to the parent peptide. More desirably, these 2 peptide analogs showed substantially reduced toxicity to human erythrocytes and epithelial cells, indicative of improved potential as antibacterial and antisepsis agents. To our knowledge, fowlicidin-2 is the first alpha-helical cathelicidin, with the central kink region shown to be critically important in killing bacteria and neutralizing LPS.

The plasmid-encoded regulator activates factors conferring lysozyme resistance on enteropathogenic Escherichia coli strains

We demonstrate that enhanced lysozyme resistance of enteropathogenic Escherichia coli requires the plasmid-encoded regulator, Per, and is mediated by factors outside the locus for enterocyte effacement. EspC, a Per-activated serine protease autotransporter protein, conferred enhanced resistance on nonpathogenic E. coli, and a second Per-regulated, espC-independent lysozyme resistance mechanism was identified.

Targeted antimicrobial activity of a specific IgG-SMAP28 conjugate against Porphyromonas gingivalis in a mixed culture

Antimicrobial peptides coupled to a ligand, receptor or antibody for a specific pathogenic bacteria could be used to develop narrow-spectrum pharmaceuticals with 'targeted' antimicrobial activity void of adverse reactions often associated with the use of broad-spectrum antibiotics. To assess the feasibility of this approach, in this study sheep myeloid antimicrobial peptide (SMAP) 28 was linked to affinity- and protein G-purified rabbit immunoglobulin G (IgG) antibodies specific to the outer surface of Porphyromonas gingivalis strain 381. The selective activity of the P. gingivalis IgG-SMAP28 conjugate was then assessed by adding it to an artificially generated microbial community containing P. gingivalis, Aggregatibacter actinomycetemcomitans and Peptostreptococcus micros. The specificity of the P. gingivalis IgG-SMAP28 conjugate in this mixed culture was concentration-dependent. The conjugate at 50 microg protein/mL lacked specificity and killed P. gingivalis, A. actinomycetemcomitans and P. micros. The conjugate at 20 microg protein/mL was more specific and killed P. gingivalis. This is an initial step to develop a selective antimicrobial agent that can eliminate a specific periodontal pathogen, such as P. gingivalis, from patients with periodontal disease without harming the normal commensal flora.

Activity of an antimicrobial peptide mimetic against planktonic and biofilm cultures of oral pathogens

Antimicrobial peptides (AMPs) are naturally occurring, broad-spectrum antimicrobial agents that have recently been examined for their utility as therapeutic antibiotics. Unfortunately, they are expensive to produce and are often sensitive to protease digestion. To address this problem, we have examined the activity of a peptide mimetic whose design was based on the structure of magainin, exhibiting its amphiphilic structure. We demonstrate that this compound, meta-phenylene ethynylene (mPE), exhibits antimicrobial activity at nanomolar concentrations against a variety of bacterial and Candida species found in oral infections. Since Streptococcus mutans, an etiological agent of dental caries, colonizes the tooth surface and forms a biofilm, we quantified the activity of this compound against S. mutans growing under conditions that favor biofilm formation. Our results indicate that mPE can prevent the formation of a biofilm at nanomolar concentrations. Incubation with 5 nM mPE prevents further growth of the biofilm, and 100 nM mPE reduces viable bacteria in the biofilm by 3 logs. Structure-function analyses suggest that mPE inhibits the bioactivity of lipopolysaccharide and binds DNA at equimolar ratios, suggesting that it may act both as a membrane-active molecule, similar to magainin, and as an intracellular antibiotic, similar to other AMPs. We conclude that mPE and similar molecules display great potential for development as therapeutic antimicrobials.

Antimicrobial effect of halocidin-derived peptide in a mouse model of Listeria infection

Halocidin is an antimicrobial peptide found in the tunicate. A series of experiments were previously conducted in an attempt to develop a novel antibiotic derived from halocidin, as the peptide was determined to evidence profound antimicrobial activity against a variety of antibiotic-resistant microbes, with significantly less toxicity to human blood cells. In this study, we assessed the validity of one of the halocidin congeners, called Khal, as a new antibiotic for the treatment of systemic bacterial infections. Our in vitro antimicrobial tests showed that the MICs of Khal against several gram-positive bacteria were below 16 microg/ml in the presence of salt. We also determined that Khal retained sufficient target selectivity to discern microbial and human blood cells and was therefore capable of efficiently killing invading pathogens. Furthermore, Khal caused no aggregation problems upon incubation with human serum and also proved to be resistant to proteolysis by enzymes occurring in human serum. In the following experiments conducted with a mouse model of Listeria monocytogenes infection, we demonstrated that a single intravenous inoculation with Khal resulted in significant therapeutic effects on the survival of mice. In addition, our bacterial-enumeration analysis showed that after Listeria infection, livers and spleens from Khal-treated mice generated a great deal fewer recoverable CFU. Finally, the antibiotic effects of Khal were evaluated under confocal microscopy after we immunostained the liver sections with anti-Khal antibody. It was concluded that Khal bound specifically to the surfaces of bacteria colonized in the mouse liver and killed the bacteria rapidly.

[A mixture of antimicrobial peptides and fibrin glue in treatment of partial-thickness burn wounds]

BACKGROUND

Antimicrobial peptides are naturally occurring cationic peptides. The first-line of defense in infected burns is the innate immune system, of which antimicrobial peptides are essential parts. To facilitate their topical use in infected partial-thickness burns, the efficacy of a mixture with fibrin glue in vitro and in vivo was tested.

METHODS

After in vitro tests, 15 male Sprague-Dawley rats received partial-thickness burns. Afterwards, the wounds were infected with multiresistant Pseudomonas aeruginosa. The animals received PG-1 (100 microg/ml, n=5), fibrin glue (n=5), or a mixture of both (n=5) topically. The efficacy of the materials was previously proven by radial diffusion assay. After 24 h, the infected and burned skin was harvested and quantitative bacterial counts per gram of skin performed.

RESULTS

The biologic effect of the peptides was confirmed in vitro. The PG-1 and fibrin glue groups did not show significant differences in bacterial numbers, whereas the mixture group showed significant reduction in Pseudomonas in vivo (P<0.04 and P<0.01).

CONCLUSION

A mixture of an antimicrobial peptide and commercially available fibrin glue is capable of significantly reducing bacteria in infected partial thickness burns in vivo compared to controls.

Synthetic histidine-rich peptides inhibit Candida species and other fungi in vitro: role of endocytosis and treatment implications

A family of histidine-rich peptides, histatins, is secreted by the parotid gland in mammals and exhibits marked inhibitory activity against a number of Candida species. We were particularly interested in the mechanism by which histidine-rich peptides inhibit fungal growth, because our laboratory has synthesized a variety of such peptides for drug and nucleic acid delivery. In contrast to naturally occurring peptides that are linear, peptides made on synthesizers can be varied with respect to their degrees of branching. Using this technology, we explored whether histidine-lysine (HK) polymers of different complexities and degrees of branching affect the growth of several species of Candida. Polymers with higher degrees of branching were progressively more effective against Candida albicans, with the four-branched polymer, H2K4b, most effective. Furthermore, H2K4b accumulated efficiently in C. albicans, which may indicate its ability to transport other antifungal agents intracellularly. Although H2K4b had greater antifungal activity than histatin 5, their mechanisms were similar. Toxicity in C. albicans induced by histatin 5 or branched HK peptides was markedly reduced by 4,4'-diisothiocyanato-stilbene-2,2'-disulfonate, an inhibitor of anion channels. We also determined that bafilomycin A1, an inhibitor of endosomal acidification, significantly decreased the antifungal activity of H2K4b. This suggests that the pH-buffering and subsequent endosomal-disrupting properties of histidine-rich peptides have a role in their antifungal activity. Moreover, the ability of the histidine component of these peptides to disrupt endosomes, which allows their escape from the lysosomal pathway, may explain why these peptides are both effective antifungal agents and nucleic acid delivery carriers.

Total Chemical Synthesis of Human Psoriasin by Native Chemical Ligation†

Human psoriasin (S100A7), a member of the S100 family of calcium-binding proteins, is richly expressed in keratinocytes of patients suffering from psoriasis. To date, the exact physiological function of psoriasin abundant in many human cell types remains unclear. A recent report by Schröder and colleagues suggests that psoriasin, purified from human stratum corneum extracts, selectively kills Escherichia coli by sequestering Zn(2+) ions essential for bacterial growth, indicative of an important role in innate immune defense against microbial infection. We chemically synthesized the N-terminally acetylated psoriasin of 100 amino acid residues using solid phase peptide synthesis in combination with native chemical ligation. More than 140 mg of highly pure and correctly folded synthetic psoriasin was obtained from a single synthesis on a 0.25 mmol scale. Analysis of synthetic psoriasin by size exclusion chromatography showed that the protein forms a homodimer in solution. Circular dichroism analysis indicated that the alpha-helicity of psoriasin increases by more than 20% in the presence of CaCl(2) or ZnCl(2), suggesting a metal ion binding induced conformational change. Circular dichroism based titration further established that the synthetic protein binds two Ca(2+) and two Zn(2+) ions per dimer, in agreement with the published structural findings. Importantly, the ability of the synthetic protein to kill E. coli and the inhibition of the killing by ZnCl(2) is comparable to that of psoriasin isolated from its natural source. The robust synthetic access to large quantities of human psoriasin should facilitate studies of its biological functions as well as its mode of action.

Activity of histone H1.2 in infected burn wounds

OBJECTIVES

Infections with multidrug-resistant microorganisms (e.g. Pseudomonas aeruginosa and Staphylococcus aureus) cause immense complications in wound care and in the treatment of immunosuppressed patients. Like most antimicrobial peptides, histones are relatively small polycationic proteins located in each eukaryotic nucleus, which naturally supercoil DNA. The aim of this study was to investigate the in vitro and in vivo activity of histone H1.2 in infected burn wounds and its potential toxicity.

METHODS

To characterize the antimicrobial properties of histone H1.2 against potential causative organisms of burn wound infections, the in vitro radial diffusion assay and modified NCCLS microbroth dilution MIC assay were carried out. Haemolytic and cytotoxic properties were determined in human red blood cells and primary human keratinocytes. In vivo antimicrobial activity was tested in an infected rat burn model with P. aeruginosa (ATCC 27853). All results were compared with the naturally occurring broad-spectrum antimicrobial peptide protegrin-1 and with antibiotics clinically used against the corresponding bacteria.

RESULTS

Human histone H1.2 exerted good antimicrobial activity against all tested microorganisms without significant haemolytic activity. Surprisingly, histone H1.2 showed cytotoxicity with an LD50 of 7.91 mg/L in primary human keratinocytes. The in vivo burn model data revealed a significant three-fold higher reduction in bacterial counts within 4 h compared with carrier control.

CONCLUSIONS

These findings indicate that histone H1.2 is a potential candidate for use as a local and, because of its low haemolytic activity, systemic antimicrobial agent. However, further investigations are needed to specify the cytotoxicity and the dose-response relationship for histone H1.2.

Lysozyme secretion by submucosal glands protects the airway from bacterial infection

Submucosal glands are abundant (approximately 1 gland/mm2) secretory structures in the tracheobronchial airways of the human lung. Because submucosal glands express antibacterial proteins, it has been proposed that they contribute to lung defense. However, this concept is challenged by the fact that mice do not have submucosal glands in their bronchial airways, yet are quite resistant to bacterial lung infection. The contribution of airway submucosal glands to host defense is also debated as a pathophysiologic component of cystic fibrosis lung disease. Here, we asked whether submucosal glands protect airways against bacterial infection. By comparing tracheal xenograft airways with and without glands, we found that the presence of glands enhanced bacterial killing in vivo and by airway secretions in vitro. Moreover, immunodepletion studies suggested that lysozyme is a major antibacterial component secreted by submucosal glands. These studies provide evidence that submucosal glands are a major source of antibacterials critical for maintaining sterile airways.

Inhibition of early steps in the lentiviral replication cycle by cathelicidin host defense peptides

Background

The antibacterial activity of host defense peptides (HDP) is largely mediated by permeabilization of bacterial membranes. The lipid membrane of enveloped viruses might also be a target of antimicrobial peptides. Therefore, we screened a panel of naturally occurring HDPs representing different classes for inhibition of early, Env-independent steps in the HIV replication cycle. A lentiviral vector-based screening assay was used to determine the inhibitory effect of HDPs on early steps in the replication cycle and on cell metabolism.

Results

Human LL37 and porcine Protegrin-1 specifically reduced lentiviral vector infectivity, whereas the reduction of luciferase activities observed at high concentrations of the other HDPs is primarily due to modulation of cellular activity and/ or cytotoxicity rather than antiviral activity. A retroviral vector was inhibited by LL37 and Protegrin-1 to similar extent, while no specific inhibition of adenoviral vector mediated gene transfer was observed. Specific inhibitory effects of Protegrin-1 were confirmed for wild type HIV-1.

Conclusion

Although Protegrin-1 apparently inhibits an early step in the HIV-replication cycle, cytotoxic effects might limit its use as an antiviral agent unless the specificity for the virus can be improved.

Isolation and characterisation of proline/arginine-rich cathelicidin peptides from ovine neutrophils

Cathelicidins are a family of gene-encoded antimicrobial peptides found in mammals. Seven cathelicidin genes have been identified in sheep, but up to now only two variants of one of these predicted peptides (OaBac5) have been purified from ovine neutrophils. In this work numerous proline/arginine-rich cathelicidin peptides were purified, including the originally predicted OaBac5 and another OaBac5 variant. As well as this, the C-terminus of the predicted OaBac7.5 and various truncated forms of OaBac11 were purified. Even though these peptides were much smaller than those predicted, they still displayed antimicrobial activity.

Novispirin G10-induced lung toxicity in a Klebsiella pneumoniae infection model

Mammalian cathelicidins are a class of innate antimicrobial peptides isolated from leukocytes and epithelial cells that aid host defense against bacterial infections. Synthetic analogs of cathelicidins offer the promise of potent broad-spectrum antimicrobial efficacy. We developed a combined lung infection and ex vivo whole-blood assay model to characterize the toxicity and efficacy of synthetic cathelicidin-derived peptides. Male C57BL/6 mice were administered saline or Klebsiella pneumoniae by intratracheal instillation. Five hours later, the Klebsiella-infected mice were instilled with saline, tobramycin (1 mg/kg of body weight or 10 mg/kg), novispirin G10 (0.4 mg/kg), or a combination of tobramycin (1 mg/kg) and G10 (0.4 mg/kg). At 24 h, bronchoalveolar lavage fluid (BAL) was collected for analysis of culturable bacteria and for markers of inflammation and lung toxicity. Blood samples were analyzed for circulating cytokines. Recovery of Klebsiella from the lung, recruitment of neutrophils, and production of interleukin-6 (IL-6) in BAL samples were highly correlated (r=0.68 and 0.84, respectively; P<0.01). Animals treated with G10 or G10 plus tobramycin had increased hemoglobin (P<0.001) and protein (P<0.001) levels compared to those for Klebsiella-infected or tobramycin-alone-treated animals. The levels of circulating IL-6 in mice infected with Klebsiella were 1000- to 10,000-fold higher than in the noninfected controls. The highest levels of IL-6 were measured in mice given G10 alone or in combination with tobramycin. These studies demonstrated that G10 was relatively nontoxic in saline-treated mice but was highly toxic in mice infected with Klebsiella. This finding establishes the importance of investigating candidate antimicrobial agents in an in vivo infection model.

Antimicrobial peptides: current status and therapeutic potential

Antimicrobial peptides (AMPs) are effector molecules of the innate immune system. A variety of AMPs have been isolated from species of all kingdoms and are classified based on their structure and amino acid motifs. AMPs have a broad antimicrobial spectrum and lyse microbial cells by interaction with biomembranes. Besides their direct antimicrobial function, they have multiple roles as mediators of inflammation with impact on epithelial and inflammatory cells influencing diverse processes such as cell proliferation, immune induction, wound healing, cytokine release, chemotaxis and protease-antiprotease balance. AMPs qualify as prototypes of innovative drugs that may be used as antimicrobials, anti-lipopolysaccharide drugs or modifiers of inflammation. Several strategies have been followed to identify lead candidates for drug development, to modify the peptides' structures, and to produce sufficient amounts for pre-clinical and clinical studies. This review summarises the current knowledge about the basic and applied biology of AMPs.

Role for phosphoglucomutase in Vibrio fischeri-Euprymna scolopes symbiosis

Vibrio fischeri, a luminescent marine bacterium, specifically colonizes the light organ of its symbiotic partner, the Hawaiian squid Euprymna scolopes. In a screen for V. fischeri colonization mutants, we identified a strain that exhibited on average a 10-fold decrease in colonization levels relative to that achieved by wild-type V. fischeri. Further characterization revealed that this defect did not result from reduced luminescence or motility, two processes required for normal colonization. We determined that the transposon in this mutant disrupted a gene with high sequence identity to the pgm (phosphoglucomutase) gene of Escherichia coli, which encodes an enzyme that functions in both galactose metabolism and the synthesis of UDP-glucose. The V. fischeri mutant grew poorly with galactose as a sole carbon source and was defective for phosphoglucomutase activity, suggesting functional identity between E. coli Pgm and the product of the V. fischeri gene, which was therefore designated pgm. In addition, lipopolysaccharide profiles of the mutant were distinct from that of the parent strain and the mutant exhibited increased sensitivity to various cationic agents and detergents. Chromosomal complementation with the wild-type pgm allele restored the colonization ability to the mutant and also complemented the other noted defects. Unlike the pgm mutant, a galactose-utilization mutant (galK) of V. fischeri colonized juvenile squid to wild-type levels, indicating that the symbiotic defect of the pgm mutant is not due to an inability to catabolize galactose. Thus, pgm represents a new gene required for promoting colonization of E. scolopes by V. fischeri.

Activity of novispirin G10 against Pseudomonas aeruginosa in vitro and in infected burns

The emergence of multidrug-resistant microbes has serious implications for managing infection and sepsis and has stimulated efforts to develop alternative treatments, such as antimicrobial peptides. The objective of this study was to test a designer peptide, novispirin G10, against multidrug-resistant microorganisms. By two-stage radial diffusion assays, its activity against such organisms compared favorably with that of standard antibiotics and other antimicrobial peptides. It killed bacteria very rapidly, was nonhemolytic, and was relatively noncytotoxic. The peptide induced an immediate, massive efflux of potassium from Pseudomonas aeruginosa, suggesting that it altered the permeability of its inner membrane. The presence of human serum reduced but did not eliminate its activity. We tested the in vivo activity of novispirin G10 in rats with an infected, partial-thickness burn that covered 20% of their total body surface area. The burned area was seeded with 10(6) CFU of a Silvadene-resistant P. aeruginosa strain, and 24 h later a single treatment with 0, 1, 3, or 6 mg of synthetic novispirin G10 (n = 16 at each concentration) per kg was given intradermally. Significant bacterial killing (P < 0.0001) was evident within 4 h in each peptide group compared to controls receiving vehicle. Antimicrobial peptides such as novispirin G10 may provide a useful alternative or adjunct to standard antibiotic agents in treating burns or other wound infections.

Retrocyclin: a primate peptide that protects cells from infection by T- and M-tropic strains of HIV-1

Human bone marrow expresses a pseudogene that encodes an antimicrobial peptide homologous to rhesus monkey circular minidefensins (delta-defensins). We prepared the putative ancestral human peptide by solid-phase synthesis and named it "retrocyclin." Retrocyclin did not cause direct inactivation of HIV-1, and its modest antibacterial properties resembled those of its rhesus homologs. Nevertheless, retrocyclin had a remarkable ability to inhibit proviral DNA formation and to protect immortalized and primary human CD4(+) lymphocytes from in vitro infection by both T-tropic and M-tropic strains of HIV-1. Confocal fluorescent microscopy studies performed with BODIPY-FL-labeled RC-101, a close analog of retrocyclin, showed that the peptide formed patch-like aggregates on the surface of CD4(+) cells. These findings suggest that retrocyclin interferes with an early stage of HIV-1 infection and that retrocyclin-like agents might be useful topical agents to prevent sexually acquired HIV-1 infections.

Binding of protegrin-1 to Pseudomonas aeruginosa and Burkholderia cepacia

BACKGROUND

Pseudomonas aeruginosa and Burkholderia cepacia infections of cystic fibrosis patients' lungs are often resistant to conventional antibiotic therapy. Protegrins are antimicrobial peptides with potent activity against many bacteria, including P. aeruginosa. The present study evaluates the correlation between protegrin-1 (PG-1) sensitivity/resistance and protegrin binding in P. aeruginosa and B. cepacia.

METHODS

The PG-1 sensitivity/resistance and PG-1 binding properties of P. aeruginosa and B. cepacia were assessed using radial diffusion assays, radioiodinated PG-1, and surface plasmon resonance (BiaCore).

RESULTS

The six P. aeruginosa strains examined were very sensitive to PG-1, exhibiting minimal active concentrations from 0.0625-0.5 microg/ml in radial diffusion assays. In contrast, all five B. cepacia strains examined were greater than 10-fold to 100-fold more resistant, with minimal active concentrations ranging from 6-10 microg/ml. When incubated with a radioiodinated variant of PG-1, a sensitive P. aeruginosa strain bound considerably more protegrin molecules per cell than a resistant B. cepacia strain. Binding/diffusion and surface plasmon resonance assays revealed that isolated lipopolysaccharide (LPS) and lipid A from the sensitive P. aeruginosa strains bound PG-1 more effectively than LPS and lipid A from resistant B. cepacia strains.

CONCLUSION

These findings support the hypothesis that the relative resistance of B. cepacia to protegrin is due to a reduced number of PG-1 binding sites on the lipid A moiety of its LPS.

RL-37, an alpha-helical antimicrobial peptide of the rhesus monkey

Rhesus monkey bone marrow expresses a cathelicidin whose C-terminal domain comprises a 37-residue alpha-helical peptide (RL-37) that resembles human LL-37. Like its human counterpart, RL-37 rapidly permeabilized the membranes of Escherichia coli ML-35p and lysed liposomes that simulated bacterial membranes. When tested in media whose NaCl concentrations approximated those of extracellular fluids, RL-37 was considerably more active than LL-37 against staphylococci. Whereas human LL-37 contains five acidic residues and has a net charge of +6, rhesus RL-37 has only two acidic residues and a net charge of +8. Speculating that the multiple acidic residues of human LL-37 reduced its efficacy against staphylococci, we made a peptide (LL-37 pentamide) in which each aspartic acid of LL-37 was replaced by an asparagine and each glutamic acid was replaced by a glutamine. LL-37 pentamide's antistaphylococcal activity was substantially greater than that of LL-37. Thus, although the precursor of LL-37 is induced in human skin keratinocytes by injury or inflammation, its insufficiently cationic antimicrobial domain may contribute to the success of staphylococci in colonizing and infecting human skin.