Buforins: histone H2A-derived antimicrobial peptides from toad stomach

Design, Engineering and Discovery of Novel α-Helical and β-Boomerang Antimicrobial Peptides against Drug Resistant Bacteria

In an era where the pipeline of new antibiotic development is drying up, the continuous rise of multi-drug resistant (MDR) and extensively drug resistant (XDR) bacteria are genuine threats to human health. Although antimicrobial peptides (AMPs) may serve as promising leads against drug resistant bacteria, only a few AMPs are in advanced clinical trials. The limitations of AMPs, namely their low in vivo activity, toxicity, and poor bioavailability, need to be addressed. Here, we review engineering of frog derived short α-helical AMPs (aurein, temporins) and lipopolysaccharide (LPS) binding designed β-boomerang AMPs for further development. The discovery of novel cell selective AMPs from the human proprotein convertase furin is also discussed.

Transcriptome profiling and in silico detection of the antimicrobial peptides of red king crab Paralithodes camtschaticus

Endogenous antimicrobial peptides (AMPs) are evolutionarily ancient factors of innate immunity, which are produced by all multicellular organisms and play a key role in their protection against infection. Red king crab (Paralithodes camtschaticus), also called Kamchatka crab, is widely distributed and the best known species of all king crabs belonging to the family Lithodidae. Despite their economic importance, the genetic resources of king crabs are scarcely known and no full-genome sequences are available to date. Therefore, analysis of the red king crab transcriptome and identification and characterization of its AMPs could potentially contribute to the development of novel antimicrobial drug candidates when antibiotic resistance has become a global health threat. In this study, we sequenced the P. camtschaticus transcriptomes from carapace, tail flap and leg tissues using an Illumina NGS platform. Libraries were systematically analyzed for gene expression profiles along with AMP prediction. By an in silico approach using public databases we defined 49 cDNAs encoding for AMP candidates belonging to diverse families and functional classes, including buforins, crustins, paralithocins, and ALFs (anti-lipopolysaccharide factors). We analyzed expression patterns of 27 AMP genes. The highest expression was found for Paralithocin 1 and Crustin 3, with more than 8,000 reads. Other paralithocins, ALFs, crustins and ubiquicidins were among medium expressed genes. This transcriptome data set and AMPs provide a solid baseline for further functional analysis in P. camtschaticus. Results from the current study contribute also to the future application of red king crab as a bio-resource in addition to its being a known seafood delicacy.

Cathelicidin-DM is an Antimicrobial Peptide from Duttaphrynus melanostictus and Has Wound-Healing Therapeutic Potential

Antimicrobial peptides (AMPs) are a class of templates with application potential for drug development. Amphibians are important sources of AMPs. Duttaphrynus melanostictus is the main source of traditional Chinese medicine "Chansu", which has anti-infection effect while without a clear mechanism. This study aimed to find the cathelicidin peptide in D. melanostictus and then investigate the activity in vivo and in vitro, and an AMP-encoding gene (cathelicidin-DM, GenBank: KJ820824.1) was obtained from the constructed cDNA library of D. melanostictus. The MIC test and SYTOX Green uptake were used for the evaluation of the bactericidal capacity and mechanisms. The serum stability tests were used for the evaluation of the application potential. The skin wound infection model and in vivo imaging were used for in vitro application of possibility evaluation. The results showed that cathelicidin-DM was a 37 amino acid AMP with good bactericidal ability, which was similar to melittin: both can kill bacteria within 15 min. Moreover, cathelicidin-DM exhibits good therapeutic potential in the mouse wound infection model, and it can be enriched to the site of infection for treatment. Thus, cathelicidin-DM could be a new template for antimicrobial drug development given its good antibacterial activity in vivo and in vitro.

The effect of lipidation and glycosylation on short cationic antimicrobial peptides

The global health threat surrounding bacterial resistance has resulted in antibiotic researchers shifting their focus away from 'traditional' antibiotics and concentrating on other antimicrobial agents, including antimicrobial peptides. These low molecular weight "mini-proteins" exhibit broad-spectrum activity against bacteria, including multi-drug resistant strains, viruses, fungi and protozoa and constitute a major element of the innate-immune system of many multicellular organisms. Some naturally occurring antimicrobial peptides are lipidated and/or glycosylated and almost all antimicrobial peptides in clinical use are either lipopeptides (Daptomycin and Polymyxin E and B) or glycopeptides (Vancomycin). Lipidation, glycosylation and PEGylation are an option for improving stability and activity in serum and for reducing the rapid clearing via the kidneys and liver. Two broad-spectrum antimicrobial peptides NH₂-RIRIRWIIR-CONH₂ (A1) and NH₂-KRRVRWIIW-CONH₂ (B1) were conjugated via a linker, producing A2 and B2, to individual fatty acids of C₈, C₁₀, C₁₂ and C₁₄ and in addition, A2 was conjugated to either glucose, N-acetyl glucosamine, galactose, mannose, lactose or polyethylene glycol (PEG). Antimicrobial activity against two Gram-positive strains (methicillin resistant Staphylococcus aureus (MRSA) and vancomycin resistant Enterococcus faecalis (VRE)) and three Gram-negative strains (Salmonella typhimurium, E. coli and Pseudomonas aeruginosa) were determined. Activity patterns for the lipidated versions are very complex, dependent on sequence, bacteria and fatty acid. Two reciprocal effects were measured; compared to the parental peptides, some combinations led to a 16-fold improvement whereas other combinations let to a 32-fold reduction in antimicrobial activity. Glycosylation decreased antimicrobial activity by 2 to 16-fold in comparison to A1, respectively on the sugar-peptide combination. PEGylation rendered the peptide inactive. Antimicrobial activity in the presence of 25% human serum of A1 and B1 was reduced 32-fold and 8-fold, respectively. The longer chain fatty acids almost completely restored this activity; however, these fatty acids increased hemolytic activity. B1 modified with C8 increased the therapeutic index by 2-fold for four bacterial strains. Our results suggest that finding the right lipid-peptide combination can lead to improved activity in the presence of serum and potentially more effective drug candidates for animal studies. Glycosylation with the optimal sugar and numbers of sugars at the right peptide position could be an alternative route or could be used in addition to lipidation to counteract solubility and toxicity issues.

Physical Mechanisms of Bacterial Killing by Histones

Antibiotic resistance is a global epidemic, becoming increasingly pressing due to its rapid spread. There is thus a critical need to develop new therapeutic approaches. In addition to searching for new antibiotics, looking into existing mechanisms of natural host defense may enable researchers to improve existing defense mechanisms, and to develop effective, synthetic drugs guided by natural principles. Histones, primarily known for their role in condensing mammalian DNA, are antimicrobial and share biochemical similarities with antimicrobial peptides (AMPs); however, the mechanism by which histones kill bacteria is largely unknown. Both AMPs and histones are similar in size, cationic, contain a high proportion of hydrophobic amino acids, and possess the ability to form alpha helices. AMPs, which mostly kill bacteria through permeabilization or disruption of the biological membrane, have recently garnered significant attention for playing a key role in host defenses. This chapter outlines the structure and function of histone proteins as they compare to AMPs and provides an overview of their role in innate immune responses, especially regarding the action of specific histones against microorganisms and their potential mechanism of action against microbial pathogens.

Short peptides conjugated to non-peptidic motifs exhibit antibacterial activity

Short peptides derived from buforin and lactoferricin B were conjugated with other antimicrobial molecules of different chemical natures.

Host-Microbe Interactions in the Chemosynthetic Riftia pachyptila Symbiosis

All animals are associated with microorganisms; hence, host-microbe interactions are of fundamental importance for life on earth. However, we know little about the molecular basis of these interactions. Therefore, we studied the deep-sea Riftia pachyptila symbiosis, a model association in which the tubeworm host is associated with only one phylotype of endosymbiotic bacteria and completely depends on this sulfur-oxidizing symbiont for nutrition. Using a metaproteomics approach, we identified both metabolic interaction processes, such as substrate transfer between the two partners, and interactions that serve to maintain the symbiotic balance, e.g., host efforts to control the symbiont population or symbiont strategies to modulate these host efforts. We suggest that these interactions are essential principles of mutualistic animal-microbe associations.

The deep-sea tubeworm Riftia pachyptila lacks a digestive system but completely relies on bacterial endosymbionts for nutrition. Although the symbiont has been studied in detail on the molecular level, such analyses were unavailable for the animal host, because sequence information was lacking. To identify host-symbiont interaction mechanisms, we therefore sequenced the Riftia transcriptome, which served as a basis for comparative metaproteomic analyses of symbiont-containing versus symbiont-free tissues, both under energy-rich and energy-limited conditions. Our results suggest that metabolic interactions include nutrient allocation from symbiont to host by symbiont digestion and substrate transfer to the symbiont by abundant host proteins. We furthermore propose that Riftia maintains its symbiont by protecting the bacteria from oxidative damage while also exerting symbiont population control. Eukaryote-like symbiont proteins might facilitate intracellular symbiont persistence. Energy limitation apparently leads to reduced symbiont biomass and increased symbiont digestion. Our study provides unprecedented insights into host-microbe interactions that shape this highly efficient symbiosis.

Synergy Pattern of Short Cationic Antimicrobial Peptides Against Multidrug-Resistant Pseudomonas aeruginosa

With the rise of various multidrug-resistant (MDR) pathogenic bacteria, worldwide health care is under pressure to respond. Conventional antibiotics are failing and the development of novel classes and alternative strategies is a major priority. Antimicrobial peptides (AMPs) cannot only kill MDR bacteria, but also can be used synergistically with conventional antibiotics. We selected 30 short AMPs from different origins and measured their synergy in combination with polymyxin B, piperacillin, ceftazidime, cefepime, meropenem, imipenem, tetracycline, erythromycin, kanamycin, tobramycin, amikacin, gentamycin, and ciprofloxacin. In total, 403 unique combinations were tested against an MDR Pseudomonas aeruginosa isolate (PA910). As a measure of the synergistic effects, fractional inhibitory concentrations (FICs) were determined using microdilution assays with FICs ranges between 0.25 and 2. A high number of combinations between peptides and polymyxin B, erythromycin, and tetracycline were found to be synergistic. Novel variants of indolicidin also showed a high frequency in synergist interaction. Single amino acid substitutions within the peptides can have a very strong effect on the ability to synergize, making it possible to optimize future drugs toward synergistic interaction.

Cell-Penetrating And Antibacterial BUF-II Nanobioconjugates: Enhanced Potency Via Immobilization On Polyetheramine-Modified Magnetite Nanoparticles

Introduction

Controlled delivery of therapeutic molecules in a localized manner has become an area of interest due to its potential to reduce drug exposure to healthy tissues and consequently to minimize undesirable side effects. We have recently introduced novel cell-penetrating vehicles by immobilizing the antimicrobial peptide Buforin II (BUF-II) on magnetite nanoparticles (MPNPs). Despite the potent translocating abilities of such nanobioconjugates, they failed to preserve the antimicrobial activity of native BUF-II. In this work, we explored immobilization on MNPs with the aid of polymer surface spacers, which has been considered as an attractive alternative for the highly efficient conjugation of various biomolecules.

Methods

Here, we immobilized BUF-II on polyetheramine-modified magnetite nanoparticles to preserve its structural integrity. As a result, for the obtained nanobioconjugates the lost antimicrobial activity against gram-positive and gram-negative bacteria was only 50% with respect to the native BUF-II. The nanobioconjugates were also characterized via FTIR, DLS, TEM, and TGA. Delivery on THP-1, HaCaT, HFF, and Escherichia coli cells was conducted to confirm capability for cell membrane translocation.

Results

Colocalization with Lysotracker showed an endosomal escape efficiency of about 73∓12% in THP-1 cells. Avoidance of endocytic pathways of internalization was qualitatively confirmed by a delivery assay at low temperature. Nuclear penetration of the nanobioconjugates was corroborated via confocal microscopy and showed high biocompatibility as demonstrated by hemolysis levels below 5% and acute cytotoxicity of around 15%.

Conclusion

The obtained nanobioconjugates were capable of translocating the cell membrane and nuclei of different normal and cancerous cell lines without significantly decreasing viability. This makes the vehicle addressable for a number of applications ranging from antimicrobial topical treatments to the delivery of nucleotides and therapeutic molecules with difficulties to bypass cell membranes.

Targeted Diphtheria Toxin-Based Therapy: A Review Article

Cancer remains one of the leading causes of death worldwide. Conventional therapeutic strategies usually offer limited specificity, resulting in severe side effects and toxicity to normal tissues. Targeted cancer therapy, on the other hand, can improve the therapeutic potential of anti-cancer agents and decrease unwanted side effects. Targeted applications of cytolethal bacterial toxins have been found to be especially useful for the specific eradication of cancer cells. Targeting is either mediated by peptides or by protein-targeting moieties, such as antibodies, antibody fragments, cell-penetrating peptides (CPPs), growth factors, or cytokines. Together with a toxin domain, these molecules are more commonly referred to as immunotoxins. Targeting can also be achieved through gene delivery and cell-specific expression of a toxin. Of the available cytolethal toxins, diphtheria toxin (DT) is one of the most frequently used for these strategies. Of the many DT-based therapeutic strategies investigated to date, two immunotoxins, Ontak^TM and Tagraxofusp^TM, have gained FDA approval for clinical application. Despite some success with immunotoxins, suicide-gene therapy strategies, whereby controlled tumor-specific expression of DT is used for the eradication of malignant cells, are gaining prominence. The first part of this review focuses on DT-based immunotoxins, and it then discusses recent developments in tumor-specific expression of DT.

Cell penetrating peptides: the potent multi-cargo intracellular carriers

Introduction: Cell penetrating peptides (CPPs) known as protein translocation domains (PTD), membrane translocating sequences (MTS), or Trojan peptides (TP) are able to cross biological membranes without clear toxicity using different mechanisms, and facilitate the intracellular delivery of a variety of bioactive cargos. CPPs could overcome some limitations of drug delivery and combat resistant strains against a broad range of diseases. Despite delivery of different therapeutic molecules by CPPs, they lack cell specificity and have a short duration of action. These limitations led to design of combined cargo delivery systems and subsequently improvement of their clinical applications. Areas covered: This review covers all our studies and other researchers in different aspects of CPPs such as classification, uptake mechanisms, and biomedical applications. Expert opinion: Due to low cytotoxicity of CPPs as compared to other carriers and final degradation to amino acids, they are suitable for preclinical and clinical studies. Generally, the efficiency of CPPs was suitable to penetrate the cell membrane and deliver different cargos to specific intracellular sites. However, no CPP-based therapeutic approach has approved by FDA, yet; because there are some disadvantages for CPPs including short half-life in blood, and nonspecific CPP-mediated delivery to normal tissue. Thus, some methods were used to develop the functions of CPPs in vitro and in vivo including the augmentation of cell specificity by activatable CPPs, specific transport into cell organelles by insertion of corresponding localization sequences, incorporation of CPPs into multifunctional dendrimeric or liposomal nanocarriers to improve selectivity and efficiency especially in tumor cells.

Non-Lytic Antibacterial Peptides That Translocate Through Bacterial Membranes to Act on Intracellular Targets

The advent of multidrug resistance among pathogenic bacteria has attracted great attention worldwide. As a response to this growing challenge, diverse studies have focused on the development of novel anti-infective therapies, including antimicrobial peptides (AMPs). The biological properties of this class of antimicrobials have been thoroughly investigated, and membranolytic activities are the most reported mechanisms by which AMPs kill bacteria. Nevertheless, an increasing number of works have pointed to a different direction, in which AMPs are seen to be capable of displaying non-lytic modes of action by internalizing bacterial cells. In this context, this review focused on the description of the in vitro and in vivo antibacterial and antibiofilm activities of non-lytic AMPs, including indolicidin, buforin II PR-39, bactenecins, apidaecin, and drosocin, also shedding light on how AMPs interact with and further translocate through bacterial membranes to act on intracellular targets, including DNA, RNA, cell wall and protein synthesis.

Using fluorescence microscopy to shed light on the mechanisms of antimicrobial peptides

Antimicrobial peptides (AMPs) are promising in the fight against increasing bacterial resistance, but the development of AMPs with enhanced activity requires a thorough understanding of their mechanisms of action. Fluorescence microscopy is one of the most flexible and effective tools to characterize AMPs, particularly in its ability to measure the membrane interactions and cellular localization of peptides. Recent advances have increased the scope of research questions that can be addressed via microscopy through improving spatial and temporal resolution. Unique combinations of fluorescent labels and dyes can simultaneously consider different aspects of peptide-membrane interaction mechanisms. This review emphasizes the central role that fluorescence microscopy will continue to play in the interrogation of AMP structure-function relationships and the engineering of more potent peptides.

A histone H2A derived antimicrobial peptide, Fi-Histin from the Indian White shrimp, Fenneropenaeus indicus: Molecular and functional characterization

Antimicrobial peptides (AMPs) derived from histone proteins form an important category of peptide antibiotics. Present study deals with the molecular and functional characterization of a 27-amino acid histone H2A derived AMP from the Indian White shrimp, Fenneropenaeus indicus designated as Fi-Histin. This peptide displayed distinctive features of AMPs such as amphiphilic alpha helical structure and a net charge of +6. The synthetic peptide exhibited significant antimicrobial activity against Gram-negative and Gram-positive bacteria especially against V. vulnificus, P. aeruginosa, V. parahaemolyticus, V. cholera and S. aureus. Disruption of cell membrane and cell content leakage were observed in peptide treated V. vulnificus using scanning electron microscopy. The synthetic peptide Fi-His_1-21 exhibited DNA binding activity and found to be non-haemolytic at the tested concentrations. Peptide was also found to possess anticancer activity against NCI-H460 and HEp-2 cell lines with an IC₅₀ of 22.670 ± 13.939 μM and 31.274 ± 24.531 μM respectively. This is the first report of a histone H2A derived peptide from F. indicus with a specific antimicrobial activity and anticancer activity, which could be a new candidate for future applications in aquaculture and medicine.

Novel therapeutic interventions in cancer treatment using protein and peptide-based targeted smart systems

Cancer, being the most prevalent and resistant disease afflicting any gender, age or social status, is the ultimate challenge for the scientific community. The new generation therapeutics for cancer management has shifted the approach to personalized/precision medicine, making use of patient- and tumor-specific markers for specifying the targeted therapies for each patient. Peptides targeting these cancer-specific signatures hold enormous potential for cancer therapy and diagnosis. The rapid advancements in the combinatorial peptide libraries served as an impetus to the development of multifunctional peptide-based materials for targeted cancer therapy. The present review outlines benefits and shortcomings of peptides as cancer therapeutics and the potential of peptide modified nanomedicines for targeted delivery of anticancer agents.

Buforin-1 blocks neuronal SNARE-mediated membrane fusion by inhibiting SNARE complex assembly

Assembly of neuronal SNARE protein complexes is essential for fusion of synaptic vesicles with the presynaptic plasma membrane, which releases neurotransmitters into the synaptic cleft and mediates neurotransmission. However, despite the potential of pharmacological regulation of this process for the treatment of various neurological disorders, only a few reagents, including botulinum neurotoxins, are currently available. Here, we report that buforin-1, an antimicrobial peptide from the Asian toad Bufo gargarizans, inhibits neuronal SNARE complex assembly, resulting in neuronal SNARE-mediated membrane fusion in vitro via its direct association with neuronal t-SNAREs syntaxin-1 and SNAP-25. Consistently, buforin-1 significantly inhibited neuronal-SNARE-mediated exocytosis in PC-12 cells. Thus, buforin-1 has potential for the treatment of neurological disorders caused by dysregulated neurotransmission.

Root extracellular traps versus neutrophil extracellular traps in host defence, a case of functional convergence?

The root cap releases cells that produce massive amounts of mucilage containing polysaccharides, proteoglycans, extracellular DNA (exDNA) and a variety of antimicrobial compounds. The released cells - known as border cells or border-like cells - and mucilage secretions form networks that are defined as root extracellular traps (RETs). RETs are important players in root immunity. In animals, phagocytes are some of the most abundant white blood cells in circulation and are very important for immunity. These cells combat pathogens through multiple defence mechanisms, including the release of exDNA-containing extracellular traps (ETs). Traps of neutrophil origin are abbreviated herein as NETs. Similar to phagocytes, plant root cap-originating cells actively contribute to frontline defence against pathogens. RETs and NETs are thus components of the plant and animal immune systems, respectively, that exhibit similar compositional and functional properties. Herein, we describe and discuss the formation, molecular composition and functional similarities of these similar but different extracellular traps.

Biochemical and Biological Profile of Parotoid Secretion of the Amazonian Rhinella marina (Anura: Bufonidae)

Skin secretions of frogs have a high chemical complexity. They have diverse types of biomolecules, such as proteins, peptides, biogenic amines, and alkaloids. These compounds protect amphibians' skin against growth of bacteria, fungi, and protozoa and participate in defense system against attack from predators. Therewith, this work performed biochemical and biological profile of macroglands parotoid secretion from cane toad. For poison analysis, we performed molecular exclusion and reverse phase chromatography, electrophoresis, and mass spectrometry. Antimicrobial, antiplasmodial, leishmanicidal, cytotoxicity, genotoxicity, and inflammatory activity of crude and/or fractions of R. marina secretion were also evaluated. Fractionation prior to filtration from poison showed separation of low mass content (steroids and alkaloids) and high molecular mass (protein). Material below 10 kDa two steroids, marinobufagin and desacetylcinobufagin, was detected. Crude extract and fractions were active against Staphylococcus aureus, Pseudomonas aeruginosa, Escherichia coli, Plasmodium falciparum, Leishmania guyanensis, and Leishmania braziliensis. Crude extract was also active against cancer cells although it was not cytotoxic for normal cells. This extract did not show significant DNA damage but it showed an important inflammatory effect in vivo. The information obtained in this work contributes to the understanding of the constituents of R. marina secretion as well as the bioactive potential of these molecules.

Deep sequencing analysis of toad Rhinella schneideri skin glands and partial biochemical characterization of its cutaneous secretion

Background

Animal poisons and venoms are sources of biomolecules naturally selected. Rhinella schneideri toads are widespread in the whole Brazilian territory and they have poison glands and mucous gland. Recently, protein from toads’ secretion has gaining attention. Frog skin is widely known to present great number of host defense peptides and we hypothesize toads present them as well. In this study, we used a RNA-seq analysis from R. schneideri skin and biochemical tests with the gland secretion to unravel its protein molecules.

Methods

Total RNA from the toad skin was extracted using TRizol reagent, sequenced in duplicate using Illumina Hiseq2500 in paired end analysis. The raw reads were trimmed and de novo assembled using Trinity. The resulting sequences were submitted to functional annotation against non-redundant NCBI database and Database of Anuran Defense Peptide. Furthermore, we performed caseinolytic activity test to assess the presence of serine and metalloproteases in skin secretion and it was fractionated by fast liquid protein chromatography using a reverse-phase column. The fractions were partially sequenced by Edman’s degradation.

Results

We were able to identify several classes of antimicrobial peptides, such as buforins, peroniins and brevinins, as well as PLA₂, lectins and galectins, combining protein sequencing and RNA-seq analysis for the first time. In addition, we could isolate a PLA₂ from the skin secretion and infer the presence of serine proteases in cutaneous secretion.

Conclusions

We identified novel toxins and proteins from R. schneideri mucous glands. Besides, this is a pioneer study that presented the in depth characterization of protein molecules richness from this toad secretion. The results obtained herein showed evidence of novel AMP and enzymes that need to be further explored.

Electronic supplementary material

The online version of this article (10.1186/s40409-018-0173-8) contains supplementary material, which is available to authorized users.

Novel BUF2-magnetite nanobioconjugates with cell-penetrating abilities

Introduction

One of the major challenges of modern pharmacology is the development of systems for the delivery of therapeutic molecules in a controlled and localized manner. One strategy is to use nanostructured supports, which are well suited to carry a large number of molecules on a per mass basis. A major challenge for these supports is, however, their limited ability to bypass the cell membrane. Recent studies propose that to overcome this issue, potent translocating cell-penetrating peptides (CPPs) can be conjugated to their surfaces.

Methods

Here, we conjugated the antimicrobial CPP buforin II (BUF2) to the surface of magnetite nanoparticles to enhance their cell penetration. Conjugates were characterized via Fourier transform infrared spectroscopy, dynamic light scattering, and thermogravimetric analysis, and their biocompatibility was corroborated. The conjugates were delivered in both bacterial and mammalian cells demonstrating the intracellular inclusion in THP-1 cells for the first time.

Results

Despite the promising outcome, our studies showed that the obtained conjugates failed to maintain the native antimicrobial activity of BUF2. We hypothesize that to overcome this issue, a flexible linker can be inserted prior to conjugation.

Conclusion

Our study highlights the potential of BUF2-magnetite conjugates as cell-penetrating vehicles for the targeted delivery of pharmacological agents. This provides support for the idea of a promising combined drug delivery and antimicrobial peptide therapy.

Antibiotics, Resistome and Resistance Mechanisms: A Bacterial Perspective

History of mankind is regarded as struggle against infectious diseases. Rather than observing the withering away of bacterial diseases, antibiotic resistance has emerged as a serious global health concern. Medium of antibiotic resistance in bacteria varies greatly and comprises of target protection, target substitution, antibiotic detoxification and block of intracellular antibiotic accumulation. Further aggravation to prevailing situation arose on observing bacteria gradually becoming resistant to different classes of antibiotics through acquisition of resistance genes from same and different genera of bacteria. Attributing bacteria with feature of better adaptability, dispersal of antibiotic resistance genes to minimize effects of antibiotics by various means including horizontal gene transfer (conjugation, transformation, and transduction), Mobile genetic elements (plasmids, transposons, insertion sequences, integrons, and integrative-conjugative elements) and bacterial toxin-antitoxin system led to speedy bloom of antibiotic resistance amongst bacteria. Proficiency of bacteria to obtain resistance genes generated an unpleasant situation; a grave, but a lot unacknowledged, feature of resistance gene transfer.

Strategies for combating bacterial biofilms: A focus on anti-biofilm agents and their mechanisms of action

Biofilm refers to the complex, sessile communities of microbes found either attached to a surface or buried firmly in an extracellular matrix as aggregates. The biofilm matrix surrounding bacteria makes them tolerant to harsh conditions and resistant to antibacterial treatments. Moreover, the biofilms are responsible for causing a broad range of chronic diseases and due to the emergence of antibiotic resistance in bacteria it has really become difficult to treat them with efficacy. Furthermore, the antibiotics available till date are ineffective for treating these biofilm related infections due to their higher values of minimum inhibitory concentration (MIC) and minimum bactericidal concentration (MBC), which may result in in-vivo toxicity. Hence, it is critically important to design or screen anti-biofilm molecules that can effectively minimize and eradicate biofilm related infections. In the present article, we have highlighted the mechanism of biofilm formation with reference to different models and various methods used for biofilm detection. A major focus has been put on various anti-biofilm molecules discovered or tested till date which may include herbal active compounds, chelating agents, peptide antibiotics, lantibiotics and synthetic chemical compounds along with their structures, mechanism of action and their respective MICs, MBCs, minimum biofilm inhibitory concentrations (MBICs) as well as the half maximal inhibitory concentration (IC₅₀) values available in the literature so far. Different mode of action of anti biofilm molecules addressed here are inhibition via interference in the quorum sensing pathways, adhesion mechanism, disruption of extracellular DNA, protein, lipopolysaccharides, exopolysaccharides and secondary messengers involved in various signaling pathways. From this study, we conclude that the molecules considered here might be used to treat biofilm-associated infections after significant structural modifications, thereby investigating its effective delivery in the host. It should also be ensured that minimum effective concentration of these molecules must be capable of eradicating biofilm infections with maximum potency without posing any adverse side effects on the host.

Design of antimicrobial peptides from a cuttlefish database

No antimicrobial peptide has been identified in cephalopods to date. Annotation of transcriptomes or genomes using basic local alignment Search Tool failed to yield any from sequence identities. Therefore, we searched for antimicrobial sequences in the cuttlefish (Sepia officinalis) database by in silico analysis of a transcriptomic database. Using an original approach based on the analysis of cysteine-free antimicrobial peptides selected from our Antimicrobial Peptide Database (APD3), the online prediction tool of the Collection of Anti-Microbial Peptides (CAMP_R3), and a homemade software program, we identified potential antibacterial sequences. Nine peptides less than 25 amino acids long were synthesized. The hydrophobic content of all nine of them ranged from 30 to 70%, and they could form alpha-helices. Three peptides possessed similarities with piscidins, one with BMAP-27, and five were totally new. Their antibacterial activity was evaluated on eight bacteria including the aquatic pathogens Vibrio alginolyticus, Aeromonas salmonicida, or human pathogens such as Salmonella typhimurium, Listeria monocytogenes, or Staphylococcus aureus. Despite the prediction of an antimicrobial potential for eight of the peptides, only two-GR₂₁ and KT₁₉-inhibited more than one bacterial strain with minimal inhibitory concentrations below 25 µM. Some sequences like VA₂₀ and FK₁₉ were hemolytic, while GR₂₁ induced less than 10% of hemolysis on human blood cells at a concentration of 200 µM. GR₂₁ was the only peptide derived from a precursor with a signal peptide, suggesting a real role in cuttlefish immune defense.

Biology, role and therapeutic potential of circulating histones in acute inflammatory disorders

Histones are positively charged nuclear proteins that facilitate packaging of DNA into nucleosomes common to all eukaryotic cells. Upon cell injury or cell signalling processes, histones are released passively through cell necrosis or actively from immune cells as part of extracellular traps. Extracellular histones function as microbicidal proteins and are pro‐thrombotic, limiting spread of infection or isolating areas of injury to allow for immune cell infiltration, clearance of infection and initiation of tissue regeneration and repair. Histone toxicity, however, is not specific to microbes and contributes to tissue and end‐organ injury, which in cases of systemic inflammation may lead to organ failure and death. This review details the processes of histones release in acute inflammation, the mechanisms of histone‐related tissue toxicity and current and future strategies for therapy targeting histones in acute inflammatory diseases.

Antimicrobial Peptides: Features, Action, and Their Resistance Mechanisms in Bacteria

In recent years, because of increased resistance to conventional antimicrobials, many researchers have started to study the synthesis of new antibiotics to control the disease-causing effects of infectious pathogens. Antimicrobial peptides (AMPs) are among the newest antibiotics; these peptides are integral compounds in all kinds of organisms and play a significant role in microbial ecology, and critically contribute to the innate immunity of organisms by destroying invading microorganisms. Moreover, AMPs may encourage cells to produce chemokines, stimulate angiogenesis, accelerate wound healing, and influence programmed cell death in multicellular organisms. Bacteria differ in their inherent susceptibility and resistance mechanisms to these peptides when responding to the antimicrobial effects of AMPs. Generally, the development of AMP resistance mechanisms is driven by direct competition between bacterial species, and host and pathogen interactions. Several studies have shown diverse mechanisms of bacterial resistance to AMPs, for example, some bacteria produce proteases and trapping proteins; some modify cell surface charge, change membrane fluidity, and activate efflux pumps; and some species make use of biofilms and exopolymers, and develop sensing systems by selective gene expression. A closer understanding of bacterial resistance mechanisms may help in developing novel therapeutic approaches for the treatment of infections caused by pathogenic organisms that are successful in developing extensive resistance to AMPs. Based on these observations, this review discusses the properties of AMPs, their targeting mechanisms, and bacterial resistance mechanisms against AMPs.

Novel bioactive peptides from PD-L1/2, a type 1 ribosome inactivating protein from Phytolacca dioica L. Evaluation of their antimicrobial properties and anti-biofilm activities

Antimicrobial peptides, also called Host Defence Peptides (HDPs), are effectors of innate immune response found in all living organisms. In a previous report, we have identified by chemical fragmentation, and characterized the first cryptic antimicrobial peptide in PD-L4, a type 1 ribosome inactivating protein (RIP) from leaves of Phytolacca dioica L. We applied a recently developed bioinformatic approach to a further member of the differently expressed pool of type 1 RIPs from P. dioica (PD-L1/2), and identified two novel putative cryptic HDPs in its N-terminal domain. These two peptides, here named IKY31 and IKY23, exhibit antibacterial activities against planktonic bacterial cells and, interestingly, significant anti-biofilm properties against two Gram-negative strains. Here, we describe that PD-L1/2 derived peptides are able to induce a strong dose-dependent reduction in biofilm biomass, affect biofilm thickness and, in the case of IKY31, interfere with cell-to-cell adhesion, likely by affecting biofilm structural components. In addition to these findings, we found that both PD-L1/2 derived peptides are able to assume stable helical conformations in the presence of membrane mimicking agents (SDS and TFE) and intriguingly beta structures when incubated with extracellular bacterial wall components (LPS and alginate). Overall, the data collected in this work provide further evidence of the importance of cryptic peptides derived from type 1 RIPs in host/pathogen interactions, especially under pathophysiological conditions induced by biofilm forming bacteria. This suggests a new possible role of RIPs as precursors of antimicrobial and anti-biofilm agents, likely released upon defensive proteolytic processes, which may be involved in plant homeostasis.

Histone H5 is a potent Antimicrobial Agent and a template for novel Antimicrobial Peptides

Modern medicine is challenged continuously by the increasing prevalence of antibiotic resistant bacteria. Cationic antimicrobial peptides and their derivatives are interesting potential alternatives to antibiotics due to their rapid action, broad-spectrum of antimicrobial activity and limited emergence of bacterial resistance. This study reports the novel antimicrobial properties of histone H5, purified from chicken erythrocytes, and histone H5-derived synthetic peptides. Broth microdilution assays revealed that histone H5 has potent broad-spectrum antimicrobial activity against Gram-positive and Gram-negative planktonic bacteria (MIC range: 1.9 ± 1.8 to 4.9 ± 1.5 µg/mL), including vancomycin-resistant Enterococcus (VRE) and methicillin-resistant Staphylococcus aureus (MRSA). Moreover, histone H5 displayed anti-biofilm activity against established Listeria monocytogenes and Pseudomonas aeruginosa biofilms. Scanning electron microscopy demonstrated bacterial membrane damage after histone H5 treatment, while a hemolytic assay revealed that histone H5 is non-toxic towards mammalian erythrocytes, even at a concentration of 1 mg/mL. Although the predicted H5-derived antimicrobial peptides tested in this study were located within the antimicrobial domain of histone H5, their synthetic versions did not possess more potent antimicrobial activity than the full length protein. Overall, this study demonstrates that histone H5 is a potent antimicrobial and therefore a promising template for the development of novel histone H5-derived antimicrobial peptides.

Individual Impact of Distinct Polysialic Acid Chain Lengths on the Cytotoxicity of Histone H1, H2A, H2B, H3 and H4

Neutrophils are able to neutralize pathogens by phagocytosis, by the release of antimicrobial components, as well as by the formation of neutrophil extracellular traps (NETs). The latter possibility is a DNA-meshwork mainly consisting of highly concentrated extracellular histones, which are not only toxic for pathogens, but also for endogenous cells triggering several diseases. To reduce the negative outcomes initiated by extracellular histones, different approaches like antibodies against histones, proteases, and the polysaccharide polysialic acid (polySia) were discussed. We examined whether each of the individual histones is a binding partner of polySia, and analyzed their respective cytotoxicity in the presence of this linear homopolymer. Interestingly, all of the histones (H1, H2A, H2B, H3, and H4) seem to interact with α2,8-linked sialic acids. However, we observed strong differences regarding the required chain length of polySia to bind histone H1, H2A, H2B, H3, and H4. Moreover, distinct degrees of polymerization were necessary to act as a cytoprotective agent in the presence of the individual histones. In sum, the outlined results described polySia-based strategies to bind and/or to reduce the cytotoxicity of individual histones using distinct polySia chain length settings.

Fungicidal activity of peptides encoded by immunoglobulin genes

Evidence from previous works disclosed the antimicrobial, antiviral, anti-tumour and/or immunomodulatory activity exerted, through different mechanisms of action, by peptides expressed in the complementarity-determining regions or even in the constant region of antibodies, independently from their specificity and isotype. Presently, we report the selection, from available databases, of peptide sequences encoded by immunoglobulin genes for the evaluation of their potential biological activities. Synthetic peptides representing the translated products of J lambda and J heavy genes proved to act in vitro against pathogenic fungi, entering yeast cells and causing their death, and exerted a therapeutic effect in a Galleria mellonella model of infection by Candida albicans. No haemolytic, cytotoxic and genotoxic effects were observed on mammalian cells. These findings raise the hypothesis that antibodies could be the evolutionary result of the adaptive combination of gene products ancestrally devoted to innate antimicrobial immunity.

Impacts of environmental and biological stressors on immune system of Macrobrachium rosenbergii

Macrobrachium rosenbergii commonly called giant freshwater prawn is a widely farmed crustacean in freshwater. Similar to other aquatic organisms, their growth and well‐being is influenced by various physical, chemical and biological factors. We discuss about the critical growth limiting factors as well as disease causing agents and the potential immune molecules of M. rosenbergii that are proved to involve in preventing and/or responding to those limiting factors.

Antimicrobial effect of the 60S ribosomal protein L29 (cgRPL29), purified from the gill of pacific oyster, Crassostrea gigas

We purified an ∼6.4-kDa antimicrobial peptide from an acidified gill extract of the Pacific oyster, Crassostrea gigas, by cation-exchange and C₁₈ reversed-phase high performance liquid chromatography (HPLC). The identified peptide was composed of 54 amino acids and had a molecular weight of 6484.6 Da. Comparison of the amino acid sequence and molecular weight with those of other known proteins or peptides revealed that the peptide had high identity with the 60S ribosomal protein L29, and so was named cgRPL29. The full-length cgRPL29 cDNA of the Pacific oyster comprised 325-bp, including a 5'-untranslated region (UTR) of 100-bp, a 3'-UTR of 57-bp, and an open reading frame of 168-bp encoding 55 amino acids, with a Met residue at the N-terminus. The cgRPL29 mRNA tissue distribution suggested that it is constitutively expressed in a non-tissue-specific manner. Secondary structural prediction and homology modeling indicated cgRPL29 have an unordered structure containing two partial α-helical regions. This is to our knowledge the first report of the antimicrobial effect of the 60S ribosomal protein L29 from marine invertebrates.

A truncated Sph12-38 with potent antimicrobial activity showing resistance against bacterial challenge in Oryzias melastigma

Antimicrobial peptides (AMPs) represent an efficient part of innate immunity and are found in a variety of life. Among them Histone 2A (H2A), as a promising class of AMPs, attracts great attention, but the in vivo mechanism of H2A derived AMP is still less known. Based on the acquisition of Sphistin, a synthetic 38-amino acid H2A derived peptide from Scylla paramamosain, as reported in our previous study, was truncated into three short fragments (Sph_12-38, Sph_20-38 and Sph_30-38) and further investigated for its possible functional domains. The antimicrobial activities of these analogs against different Gram-positive bacteria, Gram-negative bacteria and fungi were illustrated. Among the analogs, Sph_12-38 showed a stronger activity with a much lower minimum inhibitory concentration (3 μM) against Staphylococcus aureus, Corynebacterium glutamicum, Micrococcus lysodeikticus Fleming, Bacillus subtilis, Pseudomonas fluorescens, Aeromonas hydrophila and A. sobria in comparison with the reported Sphistin. A leakage of intracellular content was described in E. coli treated with Sph_12-38. Unlike Sphistin which mainly disrupts the membrane integrity, Sph_12-38 could also combine the A. sobria genomic DNA with a minimum concentration of 6 μM and was located intracellularly in cells observed under confocal laser scanning microscope imaging. In comparison with the control group of Oryzias melastigma injected with A. sobria alone, the group treated with a mixture of Sph_12-38 and A. sobria showed a higher survival rate 7 days post-injection. Furthermore, in a pretreatment assay at 6 h, a higher survival rate was observed in the group injected with the mixture of Sph_12-38 and A. sobria. Taken together, the synthetic peptide of Sph_12-38 had a potent antimicrobial activity against bacteria. However, Sph_12-38 had no cytotoxicity towards the hemolymph of S. paramamosain. Our study suggested that, as with Sph_12-38, the H2A derived peptides were more likely prone to exert their activities in vivo through the truncated fragments while defending against different species of pathogens.

Screening and Optimizing Antimicrobial Peptides by Using SPOT-Synthesis

Peptide arrays on cellulose are a powerful tool to investigate peptide interactions with a number of different molecules, for examples antibodies, receptors or enzymes. Such peptide arrays can also be used to study interactions with whole cells. In this review, we focus on the interaction of small antimicrobial peptides with bacteria. Antimicrobial peptides (AMPs) can kill multidrug-resistant (MDR) human pathogenic bacteria and therefore could be next generation antibiotics targeting MDR bacteria. We describe the screen and the result of different optimization strategies of peptides cleaved from the membrane. In addition, screening of antibacterial activity of peptides that are tethered to the surface is discussed. Surface-active peptides can be used to protect surfaces from bacterial infections, for example implants.

H2A and Ca-L-hipposin gene: Characteristic analysis and expression responses to Aeromonas hydrophila infection in Carassius aurutus

Antimicrobial peptide is an important component of the host innate immune system and thus serves a crucial function in host defense against microbial invasion. In this study, H2A and derived antimicrobial peptide Ca-L-hipposin were cloned and characterized in Carassius aurutus. The gene H2A full-length cDNA is 908 bp and includes a 5'-terminal untranslated region (UTR) of 55 bp and a 3'-terminal UTR of 466 bp with a canonical polyadenylation signal sequence AATAA, as well as an open reading frame (ORF) of 387 bp encoding a polypeptide of 128 amino acids, with a molecular weight of 13.7 kDa, an isoelectric point of 10.7, and 94% homology with Danio rerio H2A. The secondary structure of H2A includes the α-spiral with 51 amino acids with a composition ratio of 39.8%, as well as a β-corner with 15 amino acids in a composition ratio of 11.7%. The online software ExPaSy predicted that a peptide sequence with 51 amino acids from the 2nd to 52nd amino acids in histone H2A can be produced through hydrolization by protease chymotrypsin, which indicates a difference of only three amino acids, compared with the antimicrobial peptide hipposin in Hippoglossus hippoglossus with a homology of 94%. Ca-L-hipposin includes 51 amino acids with a molecular weight of 5.4 kDa and an isoelectric point of 12.0, the secondary structure of which contains an α-helix of 17 amino acids accounting for 33.3% and a β-corner of 8 amino acids accounting for 15.7%. H2A was extensively expressed in the mRNA levels of various tissues, with higher expression levels in kidney and spleen. After C. aurutus was challenged with Aeromonas hydrophila, the mRNA expression levels of H2A were upregulated in the kidney, spleen, and liver. H2A serves an important function in the defense against the invasion of A. hydrophila. In addition, sequence characteristics reveal that Ca-L-hipposin could be a potential antimicrobial peptide for use in killing pathogenic bacteria in aquaculture.

Therapeutic potential of abalone and status of bioactive molecules: A comprehensive review

Marine organisms are increasingly being investigated as sources of bioactive molecules with therapeutic applications as nutraceuticals and pharmaceuticals. In particular, nutraceuticals are gaining popularity worldwide owing to their therapeutic potential and incorporation in functional foods and dietary supplements. Abalone, a marine gastropod, contains a variety of bioactive compounds with anti-oxidant, anti-thrombotic, anti-inflammatory, anti-microbial, and anti-cancer activities. For thousands of years different cultures have used abalone as a traditional functional food believing consumption provides health benefits. Abalone meat is one of the most precious commodities in Asian markets where it is considered a culinary delicacy. Recent research has revealed that abalone is composed of many vital moieties like polysaccharides, proteins, and fatty acids that provide health benefits beyond basic nutrition. A review of past and present research is presented with relevance to the therapeutic potential of bioactive molecules from abalone.

Evaluation of the use of therapeutic peptides for cancer treatment

Cancer along with cardiovascular disease are the main causes of death in the industrialised countries around the World. Conventional cancer treatments are losing their therapeutic uses due to drug resistance, lack of tumour selectivity and solubility and as such there is a need to develop new therapeutic agents. Therapeutic peptides are a promising and a novel approach to treat many diseases including cancer. They have several advantages over proteins or antibodies: as they are (a) easy to synthesise, (b) have a high target specificity and selectivity and (c) have low toxicity. Therapeutic peptides do have some significant drawbacks related to their stability and short half-life. In this review, strategies used to overcome peptide limitations and to enhance their therapeutic effect will be compared. The use of short cell permeable peptides that interfere and inhibit protein-protein interactions will also be evaluated.

Production of low-expressing recombinant cationic biopolymers with high purity

The growing complexity of recombinant biopolymers for delivery of bioactive agents requires the ability to control the biomaterial structure with high degree of precision. Genetic engineering techniques have provided this opportunity to synthesize biomaterials in an organism such as E. coli with full control over their lengths and sequences. One class of such biopolymers is recombinant cationic biopolymers with applications in gene delivery, regenerative medicine and variety of other biomedical applications. Unfortunately, due to their highly cationic nature and complex structure, their production in E. coli expression system is marred by low expression yield which in turn complicates the possibility of obtaining pure biopolymer. SlyD and ArnA endogenous E. coli proteins are considered the major culprits that copurify with the low-expressing biopolymers during the metal affinity chromatography. Here, we compared the impact of different parameters such as the choice of expression hosts as well as metal affinity columns in order to identify the most effective approach in obtaining highly pure recombinant cationic biopolymers with acceptable yield. The results of this study showed that by using E. coli BL21(DE3) LOBSTR strain and in combination with our developed stringent expression and Ni-NTA purification protocols highly pure products in one purification step (>99% purity) can be obtained. This approach could be applied to the production of other complex and potentially toxic biopolymers with wide range of applications in biomedicine.

Investigating the nucleic acid interactions of histone-derived antimicrobial peptides

While many antimicrobial peptides (AMPs) disrupt bacterial membranes, some translocate into bacteria and interfere with intracellular processes. Buforin II and DesHDAP1 are thought to kill bacteria by interacting with nucleic acids. Here, molecular modeling and experimental measurements are used to show that neither nucleic acid binding peptide selectively binds DNA sequences. Simulations and experiments also show that changing lysines to arginines enhances DNA binding, suggesting that including additional guanidinium groups is a potential strategy to engineer more potent AMPs. Moreover, the lack of binding specificity may make it more difficult for bacteria to evolve resistance to these and other similar AMPs.

Evidence of an Antimicrobial Peptide Signature Encrypted in HECT E3 Ubiquitin Ligases

The ubiquitin-proteasome pathway (UPP) is a hallmark of the eukaryotic cell. In jawed vertebrates, it has been co-opted by the adaptive immune system, where proteasomal degradation produces endogenous peptides for major histocompatibility complex class I antigen presentation. However, proteolytic products are also necessary for the phylogenetically widespread innate immune system, as they often play a role as host defense peptides (HDPs), pivotal effectors against pathogens. Here, we report the identification of the arachnid HDP oligoventin, which shares homology to a core member of the UPP, E3 ubiquitin ligases. Oligoventin has broad antimicrobial activity and shows strong synergy with lysozymes. Using computational and phylogenetic approaches, we show high conservation of the oligoventin signature in HECT E3s. In silico simulation of HECT E3s self-proteolysis provides evidence that HDPs can be generated by fine-tuned 26S proteasomal degradation, and therefore are consistent with the hypothesis that oligoventin is a cryptic peptide released by the proteolytic processing of an Nedd4 E3 precursor protein. Finally, we compare the production of HDPs and endogenous antigens from orthologous HECT E3s by proteasomal degradation as a means of analyzing the UPP coupling to metazoan immunity. Our results highlight the functional plasticity of the UPP in innate and adaptive immune systems as a possibly recurrent mechanism to generate functionally diverse peptides.

Bacterial Evasion of Host Antimicrobial Peptide Defenses

Antimicrobial peptides (AMPs), also known as host defense peptides, are small naturally occurring microbicidal molecules produced by the host innate immune response that function as a first line of defense to kill pathogenic microorganisms by inducing deleterious cell membrane damage. AMPs also possess signaling and chemoattractant activities and can modulate the innate immune response to enhance protective immunity or suppress inflammation. Human pathogens have evolved defense molecules and strategies to counter and survive the AMPs released by host immune cells such as neutrophils and macrophages. Here, we review the various mechanisms used by human bacterial pathogens to resist AMP-mediated killing, including surface charge modification, active efflux, alteration of membrane fluidity, inactivation by proteolytic digestion, and entrapment by surface proteins and polysaccharides. Enhanced understanding of AMP resistance at the molecular level may offer insight into the mechanisms of bacterial pathogenesis and augment the discovery of novel therapeutic targets and drug design for the treatment of recalcitrant multidrug-resistant bacterial infections.

[Amphibian skin as a source of therapeutic peptides]

The search for new bioactive molecules that could be used in therapeutics is a major public health issue, particularly in the treatment of certain diseases such as cancer. In this context the exploration of the venom of animals (snakes, amphibians, cones, scorpions, insects...) that produce molecules of various structures and biological activities, is a very promising direction. Research in this area led to the discovery of neuropeptides, hormones, toxins, antimicrobial peptides and other extremely potent mediators. These are now used in many areas both in fundamental research and in translational research, respectively, to understand biochemical and physiological mechanisms, or to use as medical diagnostic tools and for therapeutic purposes. Pr. V. Erspamer is the first researcher to have shown, in the 1930s, that in addition to biogenic amines and alkaloids, granular glands from the skin of amphibians also produced huge amounts of peptides with various structures and biological activities. He also showed that these peptides had their counterparts, most often in the form of identical or similar peptides, in the central nervous system and the gastrointestinal tract of mammals. These observations are summarized in the form of a triangle concept of "brain-gut-skin" that states that any peptide found in a compartment should be present in the other two. In addition, abundance, ease of extraction and identification of peptides from amphibian skin make this model a means to search for their counterparts in mammals where they are present in minute quantities. This approach has two advantages: (i) at the fundamental level, the large peptide diversity, ubiquity and multiplicity of functions to which they participate, constitute a true chemical library to understand the mechanisms of recognition and signal transduction and study the physicochemical basic of the specificity; and (ii) in terms of applications, the relative simplicity of these peptides and the rise of the production techniques by chemical or recombinant synthesis offer an innovative potential for the development of molecules with pharmacological or therapeutic purposes.

Identifying anticancer peptides by using improved hybrid compositions

Cancer is one of the main causes of threats to human life. Identification of anticancer peptides is important for developing effective anticancer drugs. In this paper, we developed an improved predictor to identify the anticancer peptides. The amino acid composition (AAC), the average chemical shifts (acACS) and the reduced amino acid composition (RAAC) were selected to predict the anticancer peptides by using the support vector machine (SVM). The overall prediction accuracy reaches to 93.61% in jackknife test. The results indicated that the combined parameter was helpful to the prediction for anticancer peptides.

Bacterial Spheroplasts as a Model for Visualizing Membrane Translocation of Antimicrobial Peptides

Studies attempting to characterize the membrane translocation of antimicrobial and cell-penetrating peptides are frequently limited by the resolution of conventional light microscopy. This study shows that spheroplasts provide a valuable approach to overcome these limits. Spheroplasts produce less ambiguous images and allow for more systematic analyses of localization. Data collected with spheroplasts are consistent with studies using normal bacterial cells and imply that a particular peptide may not always follow the same mechanism of action.

Actin and DNA Protect Histones from Degradation by Bacterial Proteases but Inhibit Their Antimicrobial Activity

Histones are small polycationic proteins located in the cell nucleus. Together, DNA and histones are integral constituents of the nucleosomes. Upon apoptosis, necrosis, and infection – induced cell death, histones are released from the cell. The extracellular histones have strong antimicrobial activity but are also cytotoxic and thought as mediators of cell death in sepsis. The antimicrobial activity of the cationic extracellular histones is inhibited by the polyanionic DNA and F-actin, which also become extracellular upon cell death. DNA and F-actin protect histones from degradation by the proteases of Pseudomonas aeruginosa and Porphyromonas gingivalis. However, though the integrity of the histones is protected, the activity of histones as antibacterial agents is lost. The inhibition of the histone’s antibacterial activity and their protection from proteolysis by DNA and F-actin indicate a tight electrostatic interaction between the positively charged histones and negatively charged DNA and F-actin, which may have physiological significance in maintaining the equilibrium between the beneficial antimicrobial activity of extracellular histones and their cytotoxic effects.