Synthesis and properties of cyclic gomesin and analogues

Non-canonical amino acid bioincorporation into antimicrobial peptides and its challenges

The rise of antimicrobial resistance and multi-drug resistant pathogens has necessitated explorations for novel antibiotic agents as the discovery of conventional antibiotics is becoming economically less viable and technically more challenging for biopharma. Antimicrobial peptides (AMPs) have emerged as a promising alternative because of their particular mode of action, broad spectrum and difficulty that microbes have in becoming resistant to them. The AMPs bacitracin, gramicidin, polymyxins and daptomycin are currently used clinically. However, their susceptibility to proteolytic degradation, toxicity profile, and complexities in large-scale manufacture have hindered their development. To improve their proteolytic stability, methods such as integrating non-canonical amino acids (ncAAs) into their peptide sequence have been adopted, which also improves their potency and spectrum of action. The benefits of ncAA incorporation have been made possible by solid-phase peptide synthesis. However, this method is not always suitable for commercial production of AMPs because of poor yield, scale-up difficulties, and its non-'green' nature. Bioincorporation of ncAA as a method of integration is an emerging field geared towards tackling the challenges of solid-phase synthesis as a green, cheaper, and scalable alternative for commercialisation of AMPs. This review focusses on the bioincorporation of ncAAs; some challenges associated with the methods are outlined, and notes are given on how to overcome these challenges. The review focusses particularly on addressing two key challenges: AMP cytotoxicity towards microbial cell factories and the uptake of ncAAs that are unfavourable to them. Overcoming these challenges will draw us closer to a greater yield and an environmentally friendly and sustainable approach to make AMPs more druggable.

Unlocking the Potential of the Antimicrobial Peptide Gomesin: From Discovery and Structure-Activity Relationships to Therapeutic Applications

Gomesin is a cationic antimicrobial peptide which is isolated from the haemocytes of the Brazilian tarantula Acanthoscurria gomesiana and can be produced chemically by Fmoc solid-phase peptide synthesis. Gomesin exhibits a range of biological activities, as demonstrated by its toxicity against therapeutically relevant pathogens such as Gram-positive or Gram-negative bacteria, fungi, cancer cells, and parasites. In recent years, a cyclic version of gomesin has been used for drug design and development as it is more stable than native gomesin in human serum and can penetrate and enter cancer cells. It can therefore interact with intracellular targets and has the potential to be developed as a drug lead for to treat cancer, infectious diseases, and other human diseases. This review provides a perspective on the discovery, structure-activity relationships, mechanism of action, biological activity, and potential clinical applications of gomesin.

A designed cyclic analogue of gomesin has potent activity against Staphylococcus aureus biofilms

BACKGROUND

Infections caused by bacterial biofilms are very difficult to treat. The use of currently approved antibiotics even at high dosages often fails, making the treatment of these infections very challenging. Novel antimicrobial agents that use distinct mechanisms of action are urgently needed.

OBJECTIVES

To explore the use of [G1K,K8R]cGm, a designed cyclic analogue of the antimicrobial peptide gomesin, as an alternative approach to treat biofilm infections.

METHODS

We studied the activity of [G1K,K8R]cGm against biofilms of Staphylococcus aureus, a pathogen associated with several biofilm-related infections. A combination of atomic force and real-time confocal laser scanning microscopies was used to study the mechanism of action of the peptide.

RESULTS

The peptide demonstrated potent activity against 24 h-preformed biofilms through a concentration-dependent ability to kill biofilm-embedded cells. Mechanistic studies showed that [G1K,K8R]cGm causes morphological changes on bacterial cells and permeabilizes their membranes across the biofilm with a half-time of 65 min. We also tested an analogue of [G1K,K8R]cGm without disulphide bonds, and a linear unfolded analogue, and found both to be inactive.

CONCLUSIONS

The results suggest that the 3D structure of [G1K,K8R]cGm and its stabilization by disulphide bonds are essential for its antibacterial and antibiofilm activities. Moreover, our findings support the potential application of this stable cyclic antimicrobial peptide to fight bacterial biofilms.

Silva L, Gonçales RA, Neves BJ, Soares CM, Pereira M. Setting New Routes for Antifungal Drug Discovery Against Pathogenic Fungi

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Fungal diseases are life-threatening to human health and responsible for millions of deaths around the world. Fungal pathogens lead to a high number of morbidity and mortality. Current antifungal treatment comprises drugs, such as azoles, echinocandins, and polyenes and the cure is not guaranteed. In addition, such drugs are related to severe side effects and the treatment lasts for an extended period. Thus, setting new routes for the discovery of effective and safe antifungal drugs should be a priority within the health care system. The discovery of alternative and efficient antifungal drugs showing fewer side effects is time-consuming and remains a challenge. Natural products can be a source of antifungals and used in combinatorial therapy. The most important natural products are antifungal peptides, antifungal lectins, antifungal plants, and fungi secondary metabolites. Several proteins, enzymes, and metabolic pathways could be targets for the discovery of efficient inhibitor compounds and recently, heat shock proteins, calcineurin, salinomycin, the trehalose biosynthetic pathway, and the glyoxylate cycle have been investigated in several fungal species. HSP protein inhibitors and echinocandins have been shown to have a fungicidal effect against azole-resistant fungi strains. Transcriptomic and proteomic approaches have advanced antifungal drug discovery and pointed to new important specific-pathogen targets. Certain enzymes, such as those from the glyoxylate cycle, have been a target of antifungal compounds in several fungi species. Natural and synthetic compounds inhibited the activity of such enzymes and reduced the ability of fungal cells to transit from mycelium to yeast, proving to be promisor antifungal agents. Finally, computational biology has developed effective approaches, setting new routes for early antifungal drug discovery since normal approaches take several years from discovery to clinical use. Thus, the development of new antifungal strategies might reduce the therapeutic time and increase the quality of life of patients.

The Biological and Biophysical Properties of the Spider Peptide Gomesin

This review summarises the current knowledge of Gomesin (Gm), an 18-residue long, cationic anti-microbial peptide originally isolated from the haemocytes of the Brazilian tarantula Acanthoscurria gomesiana. The peptide shows potent cytotoxic activity against clinically relevant microbes including Gram-positive and Gram-negative bacteria, fungi, and parasites. In addition, Gm shows in-vitro and in-vivo anti-cancer activities against several human and murine cancers. The peptide exerts its cytotoxic activity by permeabilising cell membranes, but the underlying molecular mechanism of action is still unclear. Due to its potential as a therapeutic agent, the structure and membrane-binding properties, as well as the leakage and cytotoxic activities of Gm have been studied using a range of techniques. This review provides a summary of these studies, with a particular focus on biophysical characterisation studies of peptide variants that have attempted to establish a structure-activity relationship. Future studies are still needed to rationalise the binding affinity and cell-type-specific selectivity of Gm and its variants, while more pre-clinical studies are required to develop Gm into a therapeutically useful peptide.

Insights into Antimicrobial Peptides from Spiders and Scorpions

The venoms of spiders and scorpions contain a variety of chemical compounds. Antimicrobial peptides (AMPs) from these organisms were first discovered in the 1990s. As of May 2015, there were 42 spider's and 63 scorpion's AMPs in the Antimicrobial Peptide Database (http://aps.unmc.edu/AP). These peptides have demonstrated broad or narrow-spectrum activities against bacteria, fungi, viruses, and parasites. In addition, they can be toxic to cancer cells, insects and erythrocytes. To provide insight into such an activity spectrum, this article discusses the discovery, classification, structure and activity relationships, bioinformatics analysis, and potential applications of spider and scorpion AMPs. Our analysis reveals that, in the case of linear peptides, spiders use both glycine-rich and helical peptide models for defense, whereas scorpions use two distinct helical peptide models with different amino acid compositions to exert the observed antimicrobial activities and hemolytic toxicity. Our structural bioinformatics study improves the knowledge in the field and can be used to design more selective peptides to combat tumors, parasites, and viruses.

The effect of amidation on the behaviour of antimicrobial peptides

Aurein 2.6-COOH and aurein 3.1-COOH were studied along with their naturally occurring C-terminally amidated analogues. Circular dichroism (CD) and molecular dynamic (MD) simulations were used to study the effects of amidation on the interaction of antimicrobial peptides (AMPs) with lipid bilayers. CD measurements and MD analysis suggested that both peptide analogues were predominantly random coil and adopted low levels of \documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$$\alpha$$\end{document}α-helical structure in solution (<30 %) and in the presence of a lipid bilayer the peptides formed a stable \documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$$\alpha$$\end{document}α-helical structure. In general, amidated analogues have a greater propensity than the non-amidated peptides to form a \documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$$\alpha$$\end{document}α-helical structure. MD simulations predicted that aurein 2.6-COOH and aurein 3.1-CHOOH destabilised lipid bilayers from 1,2-dimyristoyl-sn-glycero-3-phosphocholine and 1,2-dimyristoyl-sn-glycero-3-phosphoserine via angled bilayer penetration. They also showed that aurein 2.6-CONH\documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$$_2$$\end{document}2 and aurein 3.1-CONH\documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$$_2$$\end{document}2 formed a helix horizontal to the plane of an asymmetric interface.

Small lipidated anti-obesity compounds derived from neuromedin U

A small library of truncated/lipid-conjugated neuromedin U (NmU) analogs was synthesized and tested in vitro using an intracellular calcium signaling assay. The selected, most active analogs were then tested in vivo, and showed potent anorexigenic effects in a diet-induced obese (DIO) mouse model. The most promising compound, NM4-C16 was effective in a once-weekly-dose regimen. Collectively, our findings suggest that short, lipidated analogs of NmU are suitable leads for the development of novel anti-obesity therapeutics.

The role of imidazole in peptide cyclization by transesterification: parallels to the catalytic triads of serine proteases

The improved bioavailability, stability and selectivity of cyclic peptides over their linear counterparts make them attractive structures in the design and discovery of novel therapeutics. In our previous work, we developed an imidazole-promoted preparation of cyclic depsipeptides in which we observed that increasing the concentration of imidazole resulted in the concomitant increase in the yield of cyclic product and reduction in dimerization, but also resulted in the generation of an acyl-substituted side product. In this work, we used transition state analysis to explore the mechanism of the imidazole-catalyzed esterification of one such peptide, Ac-SAFYG-SCH2φ, and determined the acyl substitution product to be an intermediate in a competing reaction pathway involving acyl substitution of the thioester by imidazole. Our findings indicate that imidazole plays an essential role in this side-chain to C-terminal coupling, and by extension, in transesterifications in general, through a concerted mechanism wherein imidazole deprotonates the nucleophile as the nucleophile attacks the carbonyl. The system under study is identical to the histidine-serine portion of the catalytic triads in serine proteases and it is likely that these enzymes employ the same concerted mechanism in the first step of peptide cleavage. Additionally, relatively high concentrations of imidazole must be used to effectively catalyze reactions in aprotic solvents since the overall reaction involves imidazole acting both as an acid and as a base, existing in solution as an equilibrium distribution between the neutral form and its conjugate acid.

Microwave-mediated reduction of disulfide bridges with supported (tris(2-carboxyethyl)phosphine) as resin-bound reducing agent

We report on the synthesis and use of a new supported reagent consisting in tris(2-carboxyethyl)phosphine (TCEP) immobilized on hydrophilic PEG based resin beads. Used in conjunction with a 5 min microwave (MW) irradiation, "supported TCEP" reduced disulfide bridges in free thiols in peptides having two or more cysteine residues. Separation of reaction products from reducing agent was easily performed by simple filtration.