Chemical Cleavage of an Asp-Cys Sequence Allows Efficient Production of Recombinant Peptides with an N-Terminal Cysteine Residue

Antibacterial mechanism of lignin and lignin-based antimicrobial materials in different fields

The control of microbial infection transmission often relies on the utilization of synthetic and metal-based antimicrobial agents. However, their non-biodegradability and inadequate disposal practices lead to significant environmental contamination. To address this concern, the quest for natural alternatives has gained paramount importance. Lignin, a widely available renewable aromatic compound, emerges as a promising candidate owing to its inherent phenolic moiety, which lends itself well to acting as a natural antimicrobial agent either independently or in combination with other agents. This article provides a comprehensive account of the structure and primary classes of lignin. Additionally, it elucidates the antimicrobial mechanism of lignin, the factors influencing its efficacy, and the methods employed for its detection. Moreover, it describes the progress made in developing the antimicrobial capacity of lignin in different areas. In conclusion, this paper not only outlines the current state of research on the antimicrobial function of lignin, but also identifies challenges and future possibilities for enhancing its antimicrobial properties. This work holds great significance in the ongoing endeavor to contribute to high-impact research on natural alternatives for controlling infections and fostering environmentally conscious practices.

The Antimicrobial, Antibiofilm and Anti-Inflammatory Activities of P13#1, a Cathelicidin-like Achiral Peptoid

Cationic antimicrobial peptides (CAMPs) are powerful molecules with antimicrobial, antibiofilm and endotoxin-scavenging activities. These properties make CAMPs very attractive drugs in the face of the rapid increase in multidrug-resistant (MDR) pathogens, but they are limited by their susceptibility to proteolytic degradation. An intriguing solution to this issue could be the development of functional mimics of CAMPs with structures that enable the evasion of proteases. Peptoids (N-substituted glycine oligomers) are an important class of peptidomimetics with interesting benefits: easy synthetic access, intrinsic proteolytic stability and promising bioactivities. Here, we report the characterization of P13#1, a 13-residue peptoid specifically designed to mimic cathelicidins, the best-known and most widespread family of CAMPs. P13#1 showed all the biological activities typically associated with cathelicidins: bactericidal activity over a wide spectrum of strains, including several ESKAPE pathogens; the ability to act in combination with different classes of conventional antibiotics; antibiofilm activity against preformed biofilms of Pseudomonas aeruginosa, comparable to that of human cathelicidin LL-37; limited toxicity; and an ability to inhibit LPS-induced proinflammatory effects which is comparable to that of "the last resource" antibiotic colistin. We further studied the interaction of P13#1 with SDS, LPSs and bacterial cells by using a fluorescent version of P13#1. Finally, in a subcutaneous infection mouse model, it showed antimicrobial and anti-inflammatory activities comparable to ampicillin and gentamicin without apparent toxicity. The collected data indicate that P13#1 is an excellent candidate for the formulation of new antimicrobial therapies.

Valorization of lignins from energy crops and agro-industrial byproducts as antioxidant and antibacterial materials

BACKGROUND

Developing eco-friendly antioxidant and antimicrobial substances originating from biomass residues has recently attracted considerable interest. In this study, two lignosulfonates and various oxidized water-soluble lignins were investigated for their antioxidant properties, as assessed by ABTS, DPPH and Folin-Ciocalteu methods, and their antimicrobial activity against some bacterial strains responsible for human pathologies.

RESULTS

The lignosulfonates showed the largest antiradical/antimicrobial capacity, whereas the other substrates were less effective. The observed antioxidant/antibacterial properties were positively correlated with lignin aromatic/phenolic content. The positive correlation between antiradical and antimicrobial activities suggests that lignin scavenging capacity was also involved in its antibacterial activity. A greater antimicrobial performance was generally observed against Gram-positive bacterial strains, and it was attributed to the intrinsic larger susceptibility of Gram-positive bacteria to lignin phenols. A significant though lesser inhibitory activity was also found against Escherichia coli.

CONCLUSION

Our results confirmed the dependence of lignin antioxidant/antibacterial power on its extraction method and chemical structure, as well as on the type of bacterial strains. Identifying the relationship between lignin molecular composition and its antioxidant/antibacterial features represents an advance on the potential future use of renewable and eco-compatible lignin materials in nutraceutical, pharmaceutical and cosmetic sectors. © 2021 Society of Chemical Industry.

Environment-Sensitive Fluorescent Labelling of Peptides by Luciferin Analogues

Environment-sensitive fluorophores are very valuable tools in the study of molecular and cellular processes. When used to label proteins and peptides, they allow for the monitoring of even small variations in the local microenvironment, thus acting as reporters of conformational variations and binding events. Luciferin and aminoluciferin, well known substrates of firefly luciferase, are environment-sensitive fluorophores with unusual and still-unexploited properties. Both fluorophores show strong solvatochromism. Moreover, luciferin fluorescence is influenced by pH and water abundance. These features allow to detect local variations of pH, solvent polarity and local water concentration, even when they occur simultaneously, by analyzing excitation and emission spectra. Here, we describe the characterization of (amino)luciferin-labeled derivatives of four bioactive peptides: the antimicrobial peptides GKY20 and ApoB_L, the antitumor peptide p53pAnt and the integrin-binding peptide RGD. The two probes allowed for the study of the interaction of the peptides with model membranes, SDS micelles, lipopolysaccharide micelles and Escherichia coli cells. K_d values and binding stoichiometries for lipopolysaccharide were also determined. Aminoluciferin also proved to be very well-suited to confocal laser scanning microscopy. Overall, the characterization of the labeled peptides demonstrates that luciferin and aminoluciferin are previously neglected environment-sensitive labels with widespread potential applications in the study of proteins and peptides.

Semisynthesis of a Homogeneous Glycoprotein Using Chemical Transformation of Peptides to Thioester Surrogates

Semisynthesis using recombinant polypeptides as building blocks is a powerful approach for the preparation of proteins with a variety of modifications such as glycosylation. The activation of the C terminus of recombinant peptides is a key step for coupling peptide building blocks and preparing a full-length polypeptide of a target protein. This article reports two chemical approaches for transformation of the C terminus of recombinant polypeptides to thioester surrogates. The first approach relies on efficient substitution of the C-terminal Cys residue with bis(2-sulfanylethyl)amine (SEA) to yield peptide-thioester surrogates. The second approach employs a native tripeptide, cysteinyl-glycyl-cysteine (CGC), to yield peptide-thioesters via a process mediated by a thioester surrogate. Both chemical transformation methods employ native peptide sequences and were thereby successfully applied to recombinant polypeptides. As a consequence, we succeeded in the semisynthesis of a glycosylated form of inducible T cell costimulator (ICOS) for the first time.

Expression of acid cleavable Asp-Pro linked multimeric AFP peptide in E. coli

Background

Difficult to express peptides are usually produced by co-expression with fusion partners. In this case, a significant mass part of the recombinant product falls on the subsequently removed fusion partner. On the other hand, multimerization of peptides is known to improve its proteolytic stability in E. coli due to the inclusion of body formation, which is sequence specific. Thereby, the peptide itself may serve as a fusion partner and one may produce more than one mole of the desired product per mole of fusion protein. This paper proposes a method for multimeric production of a human alpha-fetoprotein fragment with optimized multimer design and processing. This fragment may further find its application in the cytotoxic drug delivery field or as an inhibitor of endogenous alpha-fetoprotein.

Results

Multimerization of the extended alpha-fetoprotein receptor-binding peptide improved its stability in E. coli, and pentamer was found to be the largest stable with the highest expression level. As high as 10 aspartate-proline bonds used to separate peptide repeats were easily hydrolyzed in optimized formic acid-based conditions with 100% multimer conversion. The major product was represented by unaltered functional alpha-fetoprotein fragment while most side-products were its formyl-Pro, formyl-Tyr, and formyl-Lys derivatives. Single-step semi-preparative RP-HPLC was enough to separate unaltered peptide from the hydrolysis mixture.

Conclusions

A recombinant peptide derived from human alpha-fetoprotein can be produced via multimerization with subsequent formic acid hydrolysis and RP-HPLC purification. The reported procedure is characterized by the lower reagent cost in comparison with enzymatic hydrolysis of peptide fusions and solid-phase synthesis. This method may be adopted for different peptide expression, especially with low amino and hydroxy side chain content.

Supplementary Information

The online version contains supplementary material available at 10.1186/s43141-021-00265-5.

Host defence peptides identified in human apolipoprotein B as promising antifungal agents

Abstract

Therapeutic options to treat invasive fungal infections are still limited. This makes the development of novel antifungal agents highly desirable. Naturally occurring antifungal peptides represent valid candidates, since they are not harmful for human cells and are endowed with a wide range of activities and their mechanism of action is different from that of conventional antifungal drugs. Here, we characterized for the first time the antifungal properties of novel peptides identified in human apolipoprotein B. ApoB-derived peptides, here named r(P)ApoB_L^Pro, r(P)ApoB_L^Ala and r(P)ApoB_S^Pro, were found to have significant fungicidal activity towards Candida albicans (C. albicans) cells. Peptides were also found to be able to slow down metabolic activity of Aspergillus niger (A. niger) spores. In addition, experiments were carried out to clarify the mechanism of fungicidal activity of ApoB-derived peptides. Peptides immediately interacted with C. albicans cell surfaces, as indicated by fluorescence live cell imaging analyses, and induced severe membrane damage, as indicated by propidium iodide uptake induced upon treatment of C. albicans cells with ApoB-derived peptides. ApoB-derived peptides were also tested on A. niger swollen spores, initial hyphae and branched mycelium. The effects of peptides were found to be more severe on swollen spores and initial hyphae compared to mycelium. Fluorescence live cell imaging analyses confirmed peptide internalization into swollen spores with a consequent accumulation into hyphae. Altogether, these findings open interesting perspectives to the application of ApoB-derived peptides as effective antifungal agents.

Key points

Human cryptides identified in ApoB are effective antifungal agents.

ApoB-derived cryptides exert fungicidal effects towards C. albicans cells.

ApoB-derived cryptides affect different stages of growth of A. niger.

Graphical abstract

Supplementary Information

The online version contains supplementary material available at 10.1007/s00253-021-11114-3.

Bioactivity and antimicrobial properties of chemically characterized compost teas from different green composts

The acknowledgement of bioactive functions of compost teas promotes the research on characteristics and potential application of these heterogeneous water-soluble extracts from recycled biomasses. In this work, compost teas were isolated from on-farm composts made with agro-industrial residues of artichoke, pepper and coffee husks with the aim to evaluate the structural-activity relationship of dissolved bioactive molecules. The molecular features of compost teas were determined by ¹³C-CPMAS NMR spectroscopy, Infrared spectroscopy, and off-line pyrolysis-Gas Chromatography/Mass Spectrometry. Bioactivity of different compost teas was tested on Basil seeds germination, while the antioxidant capacity was measured by ABTS and DDPH spectrophotometric assays. The antimicrobial activity was measured against some pathogenic human bacterial strains. The seed germination experiment showed no phytotoxic effects and a significant increase of both root and epicotyls upon application of coffee husks and pepper CT samples. The same compost teas revealed the largest antioxidant activity and a clear antimicrobial effect determined by MIC (Minimal Inhibitory Concentration) against some gram-negative bacterial strains such as Pseudomonas aeruginosa, Escherichia coli, and Klebsiella pneumoniae. The bioactivity of CT-samples was related to their general hydrophobic features and to specific molecular composition. In particular, ¹³C-CPMAS NMR spectra and off-line thermochemolysis GC-MS highlighted a close correlation between radical scavenger activity and antibacterial bioactive functions with bio-available soluble aromatic compounds, such as lignin and phenols derivatives. The antioxidant and, antibacterial properties of compost teas from green composts encourages an innovative potential application of these eco-friendly products not only in agricultural applications but also in nutraceutical and pharmaceutical fields.

Enzymes as a Reservoir of Host Defence Peptides

Host defence peptides (HDPs) are powerful modulators of cellular responses to various types of insults caused by pathogen agents. To date, a wide range of HDPs, from species of different kingdoms including bacteria, plant and animal with extreme diversity in structure and biological activity, have been described. Apart from a limited number of peptides ribosomally synthesized, a large number of promising and multifunctional HDPs have been identified within protein precursors, with properties not necessarily related to innate immunity, consolidating the fascinating hypothesis that proteins have a second or even multiple biological mission in the form of one or more bio-active peptides. Among these precursors, enzymes constitute certainly an interesting group, because most of them are mainly globular and characterized by a fine specific internal structure closely related to their catalytic properties and also because they are yet little considered as potential HDP releasing proteins. In this regard, the main aim of the present review is to describe a panel of HDPs, identified in all canonical classes of enzymes, and to provide a detailed description on hydrolases and their corresponding HDPs, as there seems to exist a striking link between these structurally sophisticated catalysts and their high content in cationic and amphipathic cryptic peptides.

Transglutaminase-mediated crosslinking of a host defence peptide derived from human apolipoprotein B and its effect on the peptide antimicrobial activity

Background Microbial transglutaminase (mTG) has been successfully used to produce site-specific protein conjugates derivatized at the level of Gln and/or Lys residues for different biotechnological applications. Here, a recombinant peptide identified in human apolipoprotein B sequence, named r(P)ApoB_L and endowed with antimicrobial activity, was studied as a possible acyl acceptor substrate of mTG with at least one of the six Lys residues present in its sequence. Methods The enzymatic crosslinking reaction was performed in vitro using N,N-dimethylcasein, substance P and bitter vetch (Vicia ervilia) seed proteins, well known acyl donor substrates in mTG-catalyzed reactions. Mass spectrometry analyses were performed for identifying the Lys residue(s) involved in the crosslinking reaction. Finally, bitter vetch protein-based antimicrobial films grafted with r(P)ApoB_L were prepared and, their biological activity evaluated. Results r(P)ApoB_L was able to be enzymatically modified by mTG. In particular, it was demonstrated the highly selective crosslinking of the peptide under study by mTG at level of Lys-18. Interestingly, the biological activity of the peptide when grafted into protein-based films was found to be lost following mTG-catalyzed crosslinking. Conclusions r(P)ApoB_L was shown to be an effective acyl acceptor substrate of mTG. The involvement of Lys-18 in the enzymatic reaction was demonstrated. In addition, films grafted with r(P)ApoB_L in the presence of mTG lost antimicrobial property. General significance A possible role of mTG as biotechnological tool to modulate the r(P)ApoB_L antimicrobial activity was hypothesized, and a potential use in food packaging of protein-based films grafted with r(P)ApoB_L was suggested.

Chemical Digestion of the -Asp-Cys- Sequence for Preparation of Post-translationally Modified Proteins

Numerous studies of native proteins have been reported on protein folding in this half century. Recently, post-translationally modified proteins are also focused on protein folding. However, it is still difficult to prepare such types of proteins because it requires not only the chemical but also the recombinant techniques. Native chemical ligation (NCL) is a powerful technique for producing target proteins when combined with recombinant techniques, such as expressed protein ligation (EPL). NCL basically requires an N-terminal peptide with a thioester and a C-terminal peptide which should possess a Cys residue at the N-terminus. Numerous efforts have been made to prepare N-terminal peptides carrying a thioester or a derivative thereof. However, a method for preparing C-terminal Cys-peptides with post-translational modifications has not been well developed, making it difficult to prepare such C-terminal Cys-peptides, except for chemical syntheses or enzymatic digestion. We report here on the development of a convenient technique that involves acid hydrolysis at the -Asp-Cys- sequence, to effectively obtain a C-terminal peptide fragment that can be used for any protein synthesis when combined with EPL, even under denatured conditions. Thus, this chemical digestion strategy permits the NCL strategy to be dramatically accelerated for protein syntheses in which post-translational modifications, such as glycosylation, phosphorylation, etc. are involved. In addition, this method should be useful to prepare the post-translationally modified proteins for protein folding.

Use of an asparaginyl endopeptidase for chemo-enzymatic peptide and protein labeling

Asparaginyl endopeptidases (AEPs) are ideal for peptide and protein labeling. However, because of the reaction reversibility, a large excess of labels or backbone modified substrates are needed. In turn, simple and cheap reagents can be used to label N-terminal cysteine, but its availability inherently limits the potential applications. Aiming to address these issues, we have created a chemo-enzymatic labeling system that exploits the substrate promiscuity of AEP with the facile chemical reaction between N-terminal cysteine and 2-formyl phenylboronic acid (FPBA). In this approach, AEP is used to ligate polypeptides with a Asn-Cys-Leu recognition sequence with counterparts possessing an N-terminal Gly-Leu. Instead of being a labeling reagent, the commercially available FPBA serves as a scavenger converting the byproduct Cys-Leu into an inert thiazolidine derivative. This consequently drives the AEP labeling reaction forward to product formation with a lower ratio of label to protein substrate. By carefully screening the reaction conditions for optimal compatibility and minimal hydrolysis, conversion to the ligated product in the model reaction resulted in excellent yields. The versatility of this AEP-ligation/FPBA-coupling system was further demonstrated by site-specifically labeling the N- or C-termini of various proteins.