Natural Antimicrobial Peptides Research Articles

Self-Assembled Peptide Nanofibers Display Natural Antimicrobial Peptides to Selectively Kill Bacteria without Compromising Cytocompatibility

One of the major hurdles in the development of antimicrobial peptide (AMP)-based materials is their poor capacity in selectively killing bacteria without harming nearby mammalian cells. Namely, they are antimicrobial but cytotoxic. Current methods of nanoparticle-encapsulated AMPs to target bacteria selectively still have not yet overcome this hurdle. Here, we demonstrate a simple yet effective method to address this daunting challenge by associating a natural AMP with a β-sheet-forming synthetic peptide. The integrated peptides self-assembled to form a supramolecular nanofiber, resulting in the presentation of the AMP at the nanofiber-solvent interface in a precisely controlled manner. Using melittin as a model natural AMP, we found that the conformation of melittin changed dramatically when presented on the nanofiber surface, which, in turn, modulated the induced membrane permeability of the bacterial and mammalian cell membranes. Specifically, the presentation of melittin on the nanofiber restricted its hydrophobic residues, leading to a reduction of the hydrophobic interaction with lipids in the cell membranes. Compellingly, the reduced hydrophobic interaction led to a considerable decrease of melittin's induced permeability of the mammalian cell membrane than that of the bacterial cell membrane. As a result, the AMP-displaying nanofiber preferentially permeabilized and disrupted the membrane of the bacteria without compromising the mammalian cells. Such improved membrane selectivity and cytocompatibility were confirmed in a cell-based membrane localization and live-dead assay. Our new strategy holds great promise for fabricating cytocompatible antimicrobial assemblies that offer safer and more effective administration of therapeutic AMPs. These assemblies, with intrinsic antimicrobial activity and cytocompatibility, can also serve as building blocks for the construction of higher-ordered scaffolds for other biomedical applications such as tissue engineering and regenerative medicine.

Short self‐assembling cationic antimicrobial peptide mimetics based on a 3,5‐diaminobenzoic acid scaffold

AbstractInfections caused by Staphylococcal and Micrococcal species represent a major public health burden. Although treatments do exist, these tend to be associated with cytotoxic effects; furthermore, the emergence of antimicrobial resistance presents an immediate challenge. New classes of active compounds are required to address these threats to human health. Here we present a de novo peptidomimetic strategy that produces self‐assembling cationic antimicrobials. To identify a candidate compound with bactericidal activity, a small library of 8 peptidomimetics comprising ultrashort peptide sequences attached to a 3,5‐diaminobenzoic acid scaffold was generated and tested against Micrococcus luteus and Staphylococcus aureus. Self‐assembly appears to be the driving force for increased potency, likely by contributing to increased local surface charge density and peptide mass and producing a multivalent effect that enhances electrostatic interactions with negatively charged bacterial membranes, causing membrane disruption. The most active library member C7 forms patched micellar nanoparticles and has an activity higher than that of known natural antimicrobial peptides against M luteus. C7 also shows activity comparable to that of gramicidin S and the standard antibiotic vancomycin used in antibacterial therapy, but with a greater selectivity index. Importantly, C7 is also nontoxic and nonhemolytic, unlike the currently administered vancomycin, which can cause acute renal failure, and gramicidin S, which is highly hemolytic in nature. The short sequence length, ease of design, convenient synthesis strategy, and presence of a substitutable hydrophobic residue that enables self‐assembly into different nanostructures make this model compound highly attractive for generating cost‐effective, rapid‐acting peptide‐based antimicrobials.

A Short Peptide Derived from the ZorO Toxin Functions as an Effective Antimicrobial.

Antimicrobial peptides are potential molecules for the development of novel antibiotic agents. The ZorO toxin of a type I toxin–antitoxin system in Escherichia coli O157:H7 is composed of 29 amino acids and its endogenous expression inhibits E. coli growth. However, little is known about its inhibitory mechanism. In this study, we demonstrate that the ZorO localized in the inner membrane affects the plasma membrane integrity and potential when expressed in E. coli cells, which triggers the production of cytotoxic hydroxyl radicals. We further show that five internal amino acids (Ala–Leu–Leu–Arg–Leu; ALLRL) of ZorO are necessary for its toxicity. This result prompted us to address the potential of the synthetic ALLRL peptide as an antimicrobial. Exogenously-added ALLRL peptide to Gram-positive bacteria, Staphylococcus aureus and Bacillus subtilis, and a fungus, Candida albicans, trigger cell membrane damage and exhibit growth defect, while having no effect on Gram-negative bacterium, E. coli. The ALLRL peptide retains its activity under the physiological salt concentrations, which is in contrast to natural antimicrobial peptides. Importantly, this peptide has no toxicity against mammalian cells. Taken together, an effective and short peptide, ALLRL, would be an attractive antimicrobial to Gram-positive bacteria and C. albicans.

Antimicrobial peptides and their therapeutic potential as anti-infective drugs: A review

Antimicrobial peptides (AMPs), also referred to as host defense peptides, are small molecular weight proteins with broad spectrum antimicrobial activity against bacteria viruses, fungi, and parasites. The AMPs are important components of innate immune systems. They are believed to be existed more than 2.6 billion years ago as part of the innate immunity in primitive organisms. The antimicrobial activity of these natural peptides makes them possible candidates in the development of new drugs against the multidrug resistant bacterial strains that have emerged recently. However, development of new therapeutics from the natural source Anti-infective drugs (AMPs) seems to be faced with many problems, such as toxicity, rapid, degradation and inability to maintain required concentrations in the target tissues. This review focuses on the therapeutic possibility of the natural antimicrobial peptides, the advantages and disadvantages of these compounds when used for topical and systemic applications, as well as their possible utilization in the development of new anti-infective drugs.

Positive Charge Patterning and Hydrophobicity of Membrane-Active Antimicrobial Peptides as Determinants of Activity, Toxicity, and Pharmacokinetic Stability.

Natural α-helical cationic antimicrobial peptide (CAP) sequences are predominantly amphipathic, with only ca. 2% containing four or more consecutive positively charged amino acids (Lys/Arg). We have designed synthetic CAPs that deviate from these natural sequences, as typified by the charge-clustered peptide KKKKKKAAFAAWAAFAA-NH2, (termed 6K-F17), which displays high antimicrobial activity with no toxicity to mammalian cells. We created a series of peptides varying in charge patterning, increasing the amphipathic character of 6K-F17 to mimic the design of natural CAPs (e.g., KAAKKFAKAWAKAFAA-NH2). Amphipathic sequences displayed increased antimicrobial activity against bacteria but were significantly more toxic to mammalian cells and more susceptible to protease degradation than their corresponding charge-clustered variants, suggesting that amphipathic sequences may be desirable in nature to allow for more versatile functions (i.e., antibacterial, antifungal, antipredator) and rapid clearance from vulnerable host cells. Our approach to clustering of charges may therefore allow for specialization against bacteria, in concert with prolonged peptide half-life.

Isolation and purification of a novel antimicrobial peptide from Porphyra yezoensis.

We aimed to isolate antimicrobial peptides from Porphyra yezoensis. Enzymatic hydrolysate of P. yezoensis was purified by ultrafiltration, molecular sieve chromatography, and ion exchange chromatography sequentially. A novel peptide with strong antimicrobial activity against Staphylococcus aureus was isolated and the amino acid sequence was identified to be Thr-Pro-Asp-Ser-Glu-Ala-Leu (TPDSEAL). Physical and chemical properties and antimicrobial activity of the peptide were determined. The antimicrobial mechanism was studied. The antimicrobial activity of TPDSEAL kept stable under acidic or basic conditions, high temperature, and ultraviolet radiation. The antimicrobial mechanism of antimicrobial peptides may damage the cell wall and membrane, and enhance the permeability of cells, which leads to the outflow of intracellular substances and death of bacteria. This study provides novel insight into the preparation of marine-derived antimicrobial peptides. PRACTICAL APPLICATIONS: Antimicrobial peptides, which act as defensive weapons against microbes, have been broadly used as food additives in food industry. Due to the limited amount of natural antimicrobial peptides in organisms and the high cost of chemical synthesis, producing novel natural antimicrobial peptides with bioengineering methods has become an urgent task. In the present study, we prepared a novel antimicrobial peptide from pepsin-digested hydrolysate of Porphyra yezoensis using ultrafiltration, molecular sieve chromatography, ion exchange chromatography, and mass spectrometry analysis. A novel peptide with strong antimicrobial activity against Staphylococcus aureus was isolated and the amino acid sequence was identified to be Thr-Pro-Asp-Ser-Glu-Ala-Leu (TPDSEAL). The identified peptide exhibits great stability under acidic or basic conditions, high temperature, and ultraviolet radiation. Mechanism revealed that TPDSEAL treatment may damage the cell wall and membrane, enhance the permeability of cells, and lead to the death of bacteria. Our study provides the novel insight into the preparation of marine-derived antimicrobial peptides.

Plant defensins: types, mechanism of action and prospects of genetic engineering for enhanced disease resistance in plants.

Natural antimicrobial peptides have been shown as one of the important tools to combat certain pathogens and play important role as a part of innate immune system in plants and, also adaptive immunity in animals. Defensin is one of the antimicrobial peptides with a diverse nature of mechanism against different pathogens like viruses, bacteria and fungi. They have a broad function in humans, vertebrates, invertebrates, insects, and plants. Plant defensins primarily interact with membrane lipids for their biological activity. Several antimicrobial peptides (AMPs) have been overexpressed in plants for enhanced disease protection. The plants defensin peptides have been efficiently employed as an effective strategy for control of diseases in plants. They can be successfully integrated in plants genome along with some other peptide genes in order to produce transgenic crops for enhanced disease resistance. This review summarizes plant defensins, their expression in plants and enhanced disease resistance potential against phytopathogens.

Graphene oxide as antibacterial sensitizer: Mechanically disturbed cell membrane for enhanced poration efficiency of melittin

Natural antimicrobial peptides (AMPs) promise a fundamental solution to the devastating threat of multidrug-resistant bacteria, while drawbacks such as limited antibacterial efficiency block their clinical use. A key for solution is to enhance the bacterial membrane disruption ability of AMPs at low concentrations. Here, it was found that a small amount of graphene oxide (GO) nanosheets could have a strong effect on sensitizing lipid membranes to the peptide melittin and extremely decrease the required threshold concentration of melittin for killing of bacteria. Molecular leakage tests from model vesicles showed that pretreatment of membrane with GO, even at a low concentration of 0.1 μg mL−1, decreased the threshold working concentration of melittin to less than half of the initial value, while in the living bacteria tests, such sensitizing effect of GO reduced the MIC value of melittin by almost 10 times. By combining experiments and simulations, we found that the sensitizing effect of GO was derived from its similar mechanical disturbance to cell membranes as that of melittin at high concentrations in membrane structures including lipid diffusion, packing state, and pressure distribution. Our results provide a cost-effective strategy to enhance the antibacterial efficiency of AMPs for clinical use.

Systemic Administration of Avian Defensin 7: Distribution, Cellular Target, and Antibacterial Potential in Mice.

Defensins are natural antimicrobial peptides. The avian beta-defensin AvBD7 isolated from the chicken bone marrow possess broad antibacterial spectrum and strong resistance to proteolysis. However, its ability to fight systemic infections of major concern for public health, such as salmonellosis, is unknown. As a first approach, fluorescence labeling of AvBD7 allowed to track its systemic distribution after intraperitoneal injection in mice using whole body live imaging. It was associated to peritoneal cells and to deeper organs such as the liver. In the next step, the use of labeled AvBD7 allowed to observe its interaction with murine macrophages in culture. After incubation, it was able to penetrate inside the cells through an endocytosis-like mechanism. Furthermore, natural AvBD7 contributed to the control of intracellular multiplication of a multidrug resistant Salmonella strain, after incubation with infected macrophages. Finally, administration in a model of systemic lethal Salmonella infection in mice led to significant improvement of mouse survival, consistently with significant reduction of the liver bacterial load. In conclusion, the results reveal a hitherto unknown intracellular antibacterial effect of AvBD7 in Salmonella target cells and support AvBD7 as a candidate of interest for the treatment of infectious diseases caused by multidrug-resistant pathogenic Enterobacteriaceae.

The transcriptome analysis of Protaetia brevitarsis Lewis larvae.

Larvae of the pest Protaetia brevitarsis are used to treat infections in traditional Chinese medicine. However, genomic information about this non-model species is currently lacking. To better understand the fundamental biology of this non-model species, its transcriptome was obtained using next generation sequencing and then analyzed. A total of 7.62 Gb of clean reads were obtained, which were assembled into 169,087 transcripts corresponding to 142,000 annotated unigenes. These unigenes were functionally classified according to Gene Ontology (GO), euKaryotic Ortholog Groups of proteins (KOG), and Kyoto Encyclopedia of Genes and Genomes (KEGG) annotations. A total of 41,921 unigenes were assigned to 56 GO terms, 21,454 unigenes were divided among 26 KOG categories, and 16,368 unigenes were assigned to 32 KEGG pathways. In addition, 19,144 simple sequence repeats (SSRs) were identified. Furthermore, several kinds of natural antimicrobial peptides and proteins, 4 histones with potential antimicrobial activity, and 41 potential antimicrobial peptide sequences were identified. These data are the first reported whole transcriptome sequence of P. brevitarsis larvae, which represents a valuable genomic resource for studying this species, thus promoting the utilization of its medical potential.

Anti-leishmanial activity of Brevinin 2R and its Lauric acid conjugate type against L. major: In vitro mechanism of actions and in vivo treatment potentials.

Leishmaniasis, as a major health problem in tropical and sub-tropical areas in the world, needs novel, safe, nontoxic and plausible therapeutic solutions for its control. As a part of innate immune system, natural antimicrobial peptides have a potential to be used as new generation of antibiotics especially after persistent resistance of conventional antimicrobial agents. Brevinin 2R, a member of Defensin families of host defense peptides, showed promising effects against bacterial and fungal infections as well as cancerous cell lines. In the current research, the anti-leishmanial effect of Brevinin 2R and its lauric acid conjugate was investigated against Leishmania major (L. major) parasite. The data revealed that, conjugation of fatty acid to Brevinin 2R, strengthen its effect on L. major promastigotes as well as toxicity and hemolytic effect. These peptides showed anitleishmanial activity through cell membrane disruption and changes in the electrical and mitochondrial membrane potential. No signs of apoptosis induction or caspase activation were detected. Despite its hemolytic and cytotoxic effect in in vitro conditions, lauric acid- Brevinin 2R (L- Brevinin 2R) did not show site specific adverse reactions in animal model. Treatment course with L- Brevinin 2R in the L. major infected mice exhibited decreased parasite load in the lymph nodes adjacent to the infected site despite cytokine production profile and footpad swelling data.

Gramicidin Peptide to Combat Antibiotic Resistance: A Review

Emerging issues of Antibiotic drug resistance have increased the mortality cases all around the world. To deal with the situation natural antimicrobial peptide (AMP) replaces the classic antibiotics. Antimicrobial peptides are short, natural peptides that are active against most bacteria’s, viruses, and fungi etc., The AMP acts as a potent therapeutic agent and finds a new way in the field of drug discovery and pharmaceuticals. One such antimicrobial peptide is gramicidin (gramicidin D and gramicidin S) has high potential of almost 100% killing mechanisms against most of the gram-positive and few gram-negative bacteria’s and fungi which can be used as an alternative antibiotic in the near future. There are reviews focusing only on individual types of gramicidin or particular about their function. Hence, this review focus on providing an overview of antimicrobial peptide gramicidin and its types, structures, its interaction with the membranes/lipid bilayers, functions, stability, and uses. This review also focuses on the challenges to enhance the gramicidin peptide for further use as an efficient effective therapeutic peptide in the pharmaceutical industries.

Cathelicidin-related antimicrobial peptide protects against myocardial ischemia/reperfusion injury

BackgroundCathelicidins are a major group of natural antimicrobial peptides which play essential roles in regulating host defense and immunity. In addition to the antimicrobial and immunomodulatory activities, recent studies have reported the involvement of cathelicidins in cardiovascular diseases by regulating inflammatory response and microvascular dysfunction. However, the role of cathelicidins in myocardial apoptosis upon cardiac ischemia/reperfusion (I/R) injury remains largely unknown.MethodsCRAMP (cathelicidin-related antimicrobial peptide) levels were measured in the heart and serum from I/R mice and in neonatal mouse cardiomyocytes treated with oxygen glucose deprivation/reperfusion (OGDR). Human serum cathelicidin antimicrobial peptide (LL-37) levels were measured in myocardial infarction (MI) patients. The role of CRAMP in myocardial apoptosis upon I/R injury was investigated in mice injected with the CRAMP peptide and in CRAMP knockout (KO) mice, as well as in OGDR-treated cardiomyocytes.ResultsWe observed reduced CRAMP level in both heart and serum samples from I/R mice and in OGDR-treated cardiomyocytes, as well as reduced LL-37 level in MI patients. Knockdown of CRAMP enhanced cardiomyocyte apoptosis, and CRAMP KO mice displayed increased infarct size and myocardial apoptosis. In contrast, the CRAMP peptide reduced cardiomyocyte apoptosis and I/R injury. The CRAMP peptide inhibited cardiomyocyte apoptosis by activation of Akt and ERK1/2 and phosphorylation and nuclear export of FoxO3a. c-Jun was identified as a negative regulator of the CRAMP gene. Moreover, lower level of serum LL-37/neutrophil ratio was associated with readmission and/or death in MI patients during 1-year follow-up.ConclusionsCRAMP protects against cardiomyocyte apoptosis and cardiac I/R injury via activation of Akt and ERK and phosphorylation and nuclear export of FoxO3a. Increasing LL-37 might be a novel therapy for cardiac ischemic injury.

Membrane-targeting antibiotics: recent developments outside the peptide space.

The rise of antibiotic resistant bacteria requires unconventional strategies toward efficient chemotherapeutic agents, preferably with alternative mechanisms of action. The bacterial cell membrane has become an appealing target since its essential and highly conservative structure are key challenges to resistance mechanisms. Inspired by natural antimicrobial peptides, research on membrane-targeting antimicrobials has been growing out of the peptide space. The pursuit of more druggable molecules led to the discovery that the pharmacophore of antimicrobial peptides is smaller than anticipated. Several promising classes of membrane-targeting antimicrobials have been discovered, such as ceragenins, reutericyclines, carbohydrate amphiphiles - among others. This review will discuss the most recent findings on membrane-targeting antibiotics, focusing on small molecules outside the antimicrobial peptide molecular space.

Epsilon-poly-l-lysine decorated ordered mesoporous silica contributes to the synergistic antifungal effect and enhanced solubility of a lipophilic drug

The emergence of drug-resistant fungal strains remains a severe threat for the public health, which prompts strict restrictions on the uses of antifungal drugs. However, the majority of lipophilic fungistatic agents are poorly water soluble with a low oral adsorption characteristic posing challenges for the precise prescriptions. In this study, a natural antimicrobial cationic peptide of epsilon-poly-l-lysine (EPL) decorated ordered mesoporous silica (SBA-15) was facilely prepared for the efficient loading of antifungal itraconazole (ITZ) drugs. The characterized mesoporous SBA-15/EPL/ITZ composite exhibited remarkable antifungal performance against Aspergillus fumigatus as a model mold, which was attributed to synergistic antifungal activities of ITZ and EPL in the mesopores. Moreover, the in vitro release behaviors of ITZ in the composite nanoexcipients both in simulated gastric fluid and fasted state simulated intestinal fluid were studied. The observed release kinetics of ITZ demonstrated a contributing role of SBA-15/EPL to enhance the solubility of ITZ and thereby may promote its flux across the gastrointestinal epithelium, which is beneficial for the absorption of drugs. Additionally, SBA-15/EPL/ITZ composites showed desirable biocompatibility toward mammalian red blood cells, human cervical cancer cells (Hela) and human embryonic kidney cells (HEK-293T). Furthermore, the pharmacokinetic profiles of obtained nano-formulations were assessed in rats, among which the improved adsorption of SBA-15/EPL/ITZ composites (AUC0–24h sum: 8381.7 nM·h) was identified compared with that of pure ITZ (525.1 nM·h) and the commercial drug of Sporanox (7516.6 nM·h). Collectively, the prepared SBA-15/EPL/ITZ provides an ecofriendly and integrated nanocomposite with enhanced solubility of lipophilic drugs to combat proliferations of infectious fungi.

Discovery of a Short-Chain ε-Poly-l-lysine and Its Highly Efficient Production via Synthetase Swap Strategy.

ε-Poly-l-lysine (ε-PL) is a natural antimicrobial cationic peptide, which is generally recognized as safe for use as a food preservative. To date, the production capacity of strains that produce low-molecular weight ε-PL remains very low and thus unsuitable for industrial production. Here, we report a new low-molecular weight ε-PL-producing Kitasatospora aureofaciens strain. The ε-PL synthase gene of this strain was cloned into a high ε-PL-producing Streptomyces albulus strain. The resulting recombinant strain efficiently produced ε-PL with a molecular weight of 1.3-2.3 kDa and yielded of 23.6 g/L following fed-batch fermentation in a 5 L bioreactor. In addition, circular dichroism spectra showed that this ε-PL takes on a conformation similar to an antiparallel pleated-sheet. Moreover, it demonstrated better antimicrobial activity against yeast compared to the 3.2-4.5 kDa ε-PL. This study provides a highly efficient strategy for production of the low-molecular weight ε-PL, which helps to expand its potential applications.

Copy number variation of PR-39 cathelicidin, and identification of PR-35, a natural variant of PR-39 with reduced mammalian cytotoxicity

Proline-arginine-rich (PR)-39 is neutrophil antimicrobial peptide that has potent antimicrobial activity against a broad spectrum of microorganisms, including bacteria, fungi, and some enveloped viruses as a part of the innate immune system. We analyzed the nucleotide sequence variations of PR-39 exon 4, which is the mature peptide region responsible for antimicrobial activity, from 48 pigs of six breeds using sequence-based typing. The analysis identified four alleles including allele PR-35 with a 12-bp deletion near the N-terminus. Interestingly, 16.7% of individuals showed the presence of three alleles per individual, but only in the Berkshire and Duroc breeds. We further analyzed the genetic diversity of PR-39 for the entire genomic region of the gene from PR-39 exon 1 to the 3′ untranslated region for different alleles by PCR amplification and cloning. The antimicrobial activity of chemically synthesized PR-35 was similar to that of PR-39, but the level of mammalian cell cytotoxicity was lower than the wild type. Better knowledge of the genetic diversity of PR-39 among different individuals and breeds may contribute to improved immune defense of pigs. PR-35, as a natural antimicrobial peptide variant, could be an interesting candidate for the development of peptide antibiotics.

Enhanced antifungal activity of bovine lactoferrin-producing probiotic Lactobacillus casei in the murine model of vulvovaginal candidiasis

BackgroundVulvovaginal candidiasis (VVC) is a common vaginitis caused by Candida species,a frequently recurring condition. Fungal azole-resistant strains with azole-resistance have developed for long and wide explosion to the first-line antifungal azole agent. Bovine lactoferrin (BLF) is a protein from transferrin family secreted by the bovine mammary tissue. Its various biological functions are well known, especially the pronounced antifungal activity.ResultsIn the current study, we constructed a Lactobacillus casei strain (L.casei/pPG612.1-BLF), which secreted BLF encoded by a mature secretion vector plasmid pPG612.1, and evaluated its antifungal activity in vitro and in vivo. In a two-layer agar plate in vitro assay, the number of C. albicans CFUs decreased and the average colony size shrunk upon exposure to L. casei/pPG612.1-BLF. In a murine VVC model, the infection burden of mice intra-vaginally pre-inoculated with L. casei/pPG612.1-BLF was lower than in control groups. Furthermore, the infection burden in mice with VVC was reduced when the animals were continually given L. casei/pPG612.1-BLF as a topical treatment for 5 days.ConclusionCombined, these results suggested that the L. casei/pPG612.1-BLF strain is a promising preventative and therapeutic anti-VVC agent, highlighting the possibility of employing the probiotic L. casei as a vehicle for biotherapy in the female genital tract and exploiting the natural antibiotic antimicrobial peptides for other applications.

Design, expression, and characterization of a novel cecropin A-derived peptide with high antibacterial activity.

In recent years, antimicrobial peptides have received increased interest and are potential substitutes for antibiotics. However, natural antimicrobial peptides are always toxic to mammalian cells and usually exhibit weak antibacterial activity, which restrict their wide application. In this study, a novel antibacterial peptide named PEW300 was designed with three mutations to the parental peptide cecropin A. As predicted by bioinformatic programs, the positive charge of PEW300 increased from + 6 to + 9 compared with cecropin A, and the grand average of hydropathicity increased from - 0.084 to - 0.008. Expression of PEW300 resulted in serious inhibition of Escherichia coli BL21(DE3) cells, indicating designed PEW300 may have stronger antibacterial activity. A simple, fast, and low-cost approach without tedious protein purification steps was selected for the efficient production of PEW300 by fusion with ELK16 and about 7.38μg/mg wet cell weight PEW300 was eventually obtained. Purified PEW300 exhibited strong antibacterial activity against various Gram-positive and Gram-negative bacteria which was enhanced four- to sevenfold compared with the parental peptide cecropin A. Besides, PEW300 had no hemolytic activity toward mammalian cells even at high concentration (224ng/μl). PEW300 showed good stability in neutral and alkaline solutions. Moreover, PEW300 was thermally stable even at up to 100°C and resistant to proteinase K, pepsin, snailase, and trypsin. The incubation with human serum had no effect on the antibacterial activity of PEW300. All these results demonstrated that PEW300 designed in this work may have good potential as a candidate pharmaceutical agent.

Tyrosine based cationic acrylates as potent antimicrobial agents against shigellosis.

Incorporation of tyrosine within synthetic macromolecules via the controlled radical polymerization technique is of particular interest due to the presence of a phenolic group in tyrosine imparting high inhibition potential. Tyrosine incorporation is also fascinating from a medicinal point of view since this particular amino acid is present in several natural antimicrobial peptides as a key constituent. This study describes a facile strategy to integrate the naturally occurring proteinogenic amino acid tyrosine within a polyacrylate system via the reversible addition fragmentation chain transfer polymerization technique to construct potent bioactive macromolecules against the microbial strain S. flexneri 2a causing shigellosis. The cationic charge and amphiphilic features inherited from the amino acid tyrosine mimic the function of natural antimicrobial peptides. A library of tyrosine polyacrylates has been synthesized to investigate the effect of molecular weight on antimicrobial activity. The time-dependent morphological switching observed via FESEM measurement revealed membrane rupture followed by leakage of cellular constituents as an effective mechanism of action of the biomimetic tyrosine-based polymers. The details of membrane disintegration and depolarization due to alteration in membrane potential have been evaluated via flow cytometric and fluorescence microscopic measurements. Most importantly, the side chain tyrosine-based polymers show fascinating biocidal features against the Gram-positive methicillin-resistant Staphylococcus aureus (MRSA) bacterial strain, the major causative agent of nosocomial infections. The broad spectrum nature of the polymers has been further investigated against the fungus Aspergillus niger and another Gram-negative bacterium, Escherichia coli.