Interaction between the antimicrobial peptide Aurein 1.2 dimer and mannans

Programming the Cellular Uptake of Protein-Based Viromimetic Nanoparticles for Enhanced Delivery

Viral mimetics is a noteworthy strategy to design efficient delivery systems without the safety drawbacks and engineering difficulties of modifying viral vectors. The triblock polypeptide CSB was previously designed de novo to self-assemble with DNA into nanocomplexes called artificial virus-like particles (AVLPs) due to their similarities to viral particles. Here, we show how we can incorporate new blocks into the CSB polypeptide to enhance its transfection without altering its self-assembly capabilities and the stability and morphology of the AVLPs. The addition of a short peptide (aurein) and/or a large protein (transferrin) to the AVLPs improved their internalization and specific targeting to cells by up to 11 times. Overall, these results show how we can further program the cellular uptake of the AVLPs with a wide range of bioactive blocks. This can pave the way to develop programmable and efficient gene delivery systems.

Understanding the mechanism of action of peptide (p-BthTX-I)2 derived from C-terminal region of phospholipase A2 (PLA2)-like bothropstoxin-I on Gram-positive and Gram-negative bacteria

Based on the antimicrobial activity of bothropstoxin-I (BthTX-I) and on the premise that a C-terminal peptide of Lys49 myotoxin can reproduce the antimicrobial activity of the parent protein, we aimed to study the mechanism of action of a peptide derived from the C-terminal region of the myotoxin BthTX-I [(p-BthTX-I)₂, sequence: KKYRYHLKPFCKK, disulfide-linked dimer] against Gram-positive and Gram-negative bacteria. Fluorescence quenching technique showed that the carboxyfluorescein labeled-peptide [CF-(p-BthTX-I)₂] when incubated with E. coli displayed a superior penetration activity than when incubated with S. aureus. Cell death induced by the peptide (p-BthTX-I)₂ showed a loss of membrane integrity in E. coli and S. aureus; however, the mechanisms of cell death were different, characterized by the presence of necrosis-like and apoptosis-like deaths, respectively. Scanning electron microscopy studies in E. coli and S. aureus showed morphological changes in the cells, with superficial deformities, appearance of wrinkles and bubbles, and formation of vesicles. Our results demonstrate that the mechanism of action of the peptide (p-BthTX-I)₂ is different in Gram-negative (E. coli) and Gram-positive (S. aureus) bacteria. Knowledge of the mechanism of action of these peptides is important, since they are promising prototypes for new antimicrobial drugs.

Alanine Scanning Studies of the Antimicrobial Peptide Aurein 1.2

Antimicrobial peptides (AMPs) are compounds widely distributed in nature that display activity against a broad spectrum of pathogens. Amphibian skin, as an organ rich in pharmacologically active peptides, appears to be an interesting source of novel AMPs. Aurein 1.2 (GLFDIIKKIAESF-NH₂) is a short 13-residue antimicrobial peptide primarily isolated from the skin secretions of Australian bell frogs. In this study, the alanine scan of aurein 1.2 was performed to investigate the effect of each amino acid residue on its biological and physico-chemical properties. The biological studies included determination of minimum inhibitory concentration, activity against biofilm, and inhibitory effect on its formation. Moreover, the hemolytic activity as well as serum stability was determined. The hydrophobicity of peptides and their self-assembly were investigated using reversed-phase chromatography. In addition, their helicity was calculated from circular dichroism spectra. The results not only provided information on structure-activity relationship of aurein 1.2 but also gave insights into design of novel analogs of AMPs in the future.

Antimicrobial activity of RP-1 peptide conjugate with ferrocene group

Parasitic diseases are a neglected and serious problem, especially in underdeveloped countries. Among the major parasitic diseases, Leishmaniasis figures as an urgent challenge due to its high incidence and severity. At the same time, the indiscriminate use of antibiotics by the population is increasing together with resistance to medicines. To address this problem, new antibiotic-like molecules that directly kill or inhibit the growth of microorganisms are necessary, where antimicrobial peptides (AMPs) can be of great help. In this work, the ferrocene molecule, one active compound with low levels of in vivo toxicity, was coupled to the N-terminus of the RP1 peptide (derived from the human chemokine CXCL4), aiming to evaluate how this change modifies the structure, biological activity, and toxicity of the peptide. The peptide and the conjugate were synthesized using the solid phase peptide synthesis (SPPS). Circular dichroism assays in PBS showed that the RP1 peptide and its conjugate had a typical spectrum for disordered structures. The Fc-RP1 presented anti-amastigote activity against Leishmania amazonensis (IC₅₀ = 0.25 μmol L^–1). In comparison with amphotericin B, a second-line drug approved for leishmaniasis treatment, (IC₅₀ = 0.63 μmol L^-1), Fc-RP1 was more active and showed a 2.5-fold higher selectivity index. The RP1 peptide presented a MIC of 4.3 μmol L^-1 against S. agalactiae, whilst Fc-RP1 was four times more active (MIC = 0.96 μmol L^-1), indicating that ferrocene improved the antimicrobial activity against Gram-positive bacteria. The Fc-RP1 peptide also decreased the minimum inhibitory concentration (MIC) in the assays against E. faecalis (MIC = 7.9 μmol L^-1), E. coli (MIC = 3.9 μmol L^-1) and S. aureus (MIC = 3.9 μmol L^-1). The cytotoxicity of the compounds was tested against HaCaT cells, and no significant activity at the highest concentration tested (500 μg. mL^-1) was observed, showing the high potential of this new compound as a possible new drug. The coupling of ferrocene also increased the vesicle permeabilization of the peptide, showing a direct relation between high peptide concentration and high carboxyfluorescein release, which indicates the action mechanism by pore formation on the vesicles. Several studies have shown that ferrocene destabilizes cell membranes through lipid peroxidation, leading to cell lysis. It is noteworthy that the Fc-RP1 peptide synthesized here is a prototype of a bioconjugation strategy, but it still is a compound with great biological activity against neglected and fish diseases.

Dimerization of Antimicrobial Peptides: A Promising Strategy to Enhance Antimicrobial Peptide Activity

Antimicrobial resistance is a global health problem with strong social and economic impacts. The development of new antimicrobial agents is considered an urgent challenge. In this regard, Antimicrobial Peptides (AMPs) appear to be novel candidates to overcome this problem. The mechanism of action of AMPs involves intracellular targets and membrane disruption. Although the exact mechanism of action of AMPs remains controversial, most AMPs act through membrane disruption of the target cell. Several strategies have been used to improve AMP activity, such as peptide dimerization. In this review, we focus on AMP dimerization, showing many examples of dimerized peptides and their effects on biological activity. Although more studies are necessary to elucidate the relationship between peptide properties and the dimerization effect on antimicrobial activity, dimerization constitutes a promising strategy to improve the effectiveness of AMPs.

Photodynamic and peptide-based strategy to inhibit Gram-positive bacterial biofilm formation

The self-produced extracellular polymeric matrix of biofilms renders them difficult to eliminate once they are established. This makes the inhibition of biofilm formation key to successful treatment of biofilm infection. Antimicrobial photodynamic therapy (aPDT) and antimicrobial peptides offer a new approach as antibiofilm strategies. In this study sub-lethal doses of aPDT (with chlorin-e6 (Ce6-PDT) or methylene blue (MB-PDT)) and the peptides AU (aurein 1.2 monomer) or (AU)₂K (aurein 1.2 C-terminal dimer) were combined to evaluate their ability to prevent biofilm development by Enterococcus faecalis. Biofilm formation was assessed by resazurin reduction, confocal microscopy, and infrared spectroscopy. All treatments successfully prevented biofilm development. The (AU)₂K dimer had a stronger effect, both alone and combined with aPDT, while the monomer AU had significant activity when combined with Ce6-PDT. Additionally, it is shown that the peptides bind to the lipoteichoic acid of the E. faecalis cell wall, pointing to a possible key mechanism of biofilm inhibition.

Evaluation of cytotoxicity features of antimicrobial peptides with potential to control bacterial diseases of citrus

Antimicrobial peptides (AMPs) can be found in various organisms, and could be considered an alternative for pesticides used to control plant pathogens, including those affecting citrus. Brazil is the largest producer and exporter of frozen concentrated orange juice in the world. However, the citrus industry has been affected by several diseases such as citrus canker and huanglongbing (HLB), caused by the bacteria Xanthomonas citri subsp. citri (X.citri) and Candidatus Liberibacter asiaticus (CaLas), respectively. In order to control these pathogens, putative AMPs were prospected in databases containing citrus sequences. Furthermore, AMPs already reported in the literature were also used for in vitro and in vivo assays against X.citri. Since CaLas cannot be cultivated in vitro, surrogates as Sinorhizobium meliloti and Agrobacterium tumefaciens were used. This study reports the evaluation of six AMPs obtained from different sources, two of them from Citrus spp. (citrus-amp1 and citrus-amp2), three from amphibians (Hylin-a1, K⁰-W⁶-Hy-a1 and Ocellatin 4-analogue) and one from porcine (Tritrpticin). Peptides K⁰-W⁶-Hy-a1, Ocellatin 4-analogue, and citrus-amp1 showed bactericidal activity against X.citri and S. meliloti and bacteriostatic effect on A. tumefaciens. These results were confirmed for X.citri in planta. In addition cytotoxicity evaluations of these molecules were performed. The AMPs that showed the lowest hemolytic activities were Triptrpticin, citrus-amp1 and citrus-amp2. Citrus-amp1 and citrus-amp2 not presented toxicity in experiments using in vivo model, G. mellonella and U87 MG cells. To verify the interaction of these AMPs with bacteria and erythrocyte cell membranes, vesicles mimicking these cells were built. Citrus-amp1 and Tritrpticin exhibited higher affinity to bacterial membranes, while Ocellatin 4-analogue and Hylin-a1 showed higher affinity to erythrocyte membranes; exclude their use in citrus. This work demonstrates an essential alternative, trough AMPs obtained from Citrus spp., which can be feasibly used to control bacterial pathogens.

A coarse-grained approach to studying the interactions of the antimicrobial peptides aurein 1.2 and maculatin 1.1 with POPG/POPE lipid mixtures

In the present work we investigated the differential interactions of the antimicrobial peptides (AMPs) aurein 1.2 and maculatin 1.1 with a bilayer composed of a mixture of the lipids 1-palmitoyl-2-oleoyl-sn-glycero-3-phospho-(1'-rac-glycerol) (POPG) and 1-palmitoyl-2-oleoyl-sn-glycero-3-phosphoethanolamine (POPE). We carried out molecular dynamics (MD) simulations using a coarse-grained approach within the MARTINI force field. The POPE/POPG mixture was used as a simple model of a bacterial (prokaryotic cell) membrane. The results were compared with our previous findings for structures of 1-palmitoyl-2-oleoyl-sn-glycero-3-phosphocholine (POPC), a representative lipid of mammalian cells. We started the simulations of the peptide-lipid system from two different initial conditions: peptides in water and peptides inside the hydrophobic core of the membrane, employing a pre-assembled lipid bilayer in both cases. Our results show similarities and differences regarding the molecular behavior of the peptides in POPE/POPG in comparison to their behavior in a POPC membrane. For instance, aurein 1.2 molecules can adopt similar pore-like structures on both POPG/POPE and POPC membranes, but the peptides are found deeper in the hydrophobic core in the former. Maculatin 1.1 molecules, in turn, achieve very similar structures in both kinds of bilayers: they have a strong tendency to form clusters and induce curvature. Therefore, the results of this study provide insight into the mechanisms of action of these two peptides in membrane leakage, which allows organisms to protect themselves against potentially harmful bacteria. Graphical Abstract Aurein pore structure (green) in a lipid bilayer composed by POPE (blue) and POPG (red) mixture. It is possible to see water beads (light blue) inside the pore.

Antimicrobial Photodynamic therapy enhanced by the peptide aurein 1.2

In the past few years, the World Health Organization has been warning that the post-antibiotic era is an increasingly real threat. The rising and disseminated resistance to antibiotics made mandatory the search for new drugs and/or alternative therapies that are able to eliminate resistant microorganisms and impair the development of new forms of resistance. In this context, antimicrobial photodynamic therapy (aPDT) and helical cationic antimicrobial peptides (AMP) are highlighted for the treatment of localized infections. This study aimed to combine the AMP aurein 1.2 to aPDT using Enterococcus faecalis as a model strain. Our results demonstrate that the combination of aPDT with aurein 1.2 proved to be a feasible alternative capable of completely eliminating E. faecalis employing low concentrations of both PS and AMP, in comparison with the individual therapies. Aurein 1.2 is capable of enhancing the aPDT activity whenever mediated by methylene blue or chlorin-e6, but not by curcumin, revealing a PS-dependent mechanism. The combined treatment was also effective against different strains; noteworthy, it completely eliminated a vancomycin-resistant strain of Enterococcus faecium. Our results suggest that this combined protocol must be exploited for clinical applications in localized infections as an alternative to antibiotics.

Retro analog concept: comparative study on physico-chemical and biological properties of selected antimicrobial peptides

Increasing drug resistance of common pathogens urgently needs discovery of new effective molecules. Antimicrobial peptides are believed to be one of the possible solutions of this problem. One of the approaches for improvement of biological properties is reversion of the sequence (retro analog concept). This research is based on investigation of antimicrobial activity against Gram-positive, Gram-negative bacteria, and fungi, hemolysis of erythrocytes, interpretation of the circular dichroism spectra, measurement of counter-ion content, and assessment of the peptide hydrophobicity and self-assembly using reversed-phase chromatography. The experiments were conducted using the following peptides: aurein 1.2, CAMEL, citropin 1.1, omiganan, pexiganan, temporin A, and their retro analogs. Among the compounds studied, only retro omiganan showed an enhanced antimicrobial and a slightly increased hemolytic activity as compared to parent molecule. Moreover, retro pexiganan exhibited high activity towards Klebsiella pneumoniae, whereas pexiganan was in general more or equally active against the rest of tested microorganisms. Furthermore, the determined activity was closely related to the peptide hydrophobicity. In general, the reduced hemolytic activity correlates with lower antimicrobial activity. The tendency to self-association and helicity fraction in SDS seems to be correlated. The normalized RP-HPLC—temperature profiles of citropin 1.1 and aurein 1.2, revealed an enhanced tendency to self-association than that of their retro analogs.

Controls and constrains of the membrane disrupting action of Aurein 1.2

Aurein 1.2 is a 13 residue antimicrobial peptide secreted by the Australian tree frog Litoria Aurea. It is a surface-acting membrane disrupting peptide that permeabilizes bacterial membranes via the carpet mechanism; the molecular details of this process are mostly unknown. Here the mechanism of action of Aurein 1.2 was investigated with an emphasis on the role of membrane charge and C-terminal amidation of the peptide. Using quartz crystal microbalance (QCM) fingerprinting it was found that the membrane charge correlates with membrane affinity of the peptide, however the binding and the membrane disrupting processes are not charge driven; increased membrane charge reduces the membrane disrupting activity. Coarse grain simulations revealed that phenylalanine residues act as membrane anchors. Accordingly Aurein 1.2 has the ability to bind to any membrane. Furthermore, bundling precludes membrane disruption in case of wild type peptides, while non C-terminal amidated peptides form random aggregates leading to detachment from the membrane. Hence C-terminal amidation is crucial for Aurein 1.2 action. Our results suggest that Aurein 1.2 acts via aggregation driven membrane penetration. The concomitant change in the tension of the outer leaflet imposes a spontaneous curvature on the membrane, leading to disintegration.