Modified histidine containing amphipathic ultrashort antifungal peptide, His[2-p-(n-butyl)phenyl]-Trp-Arg-OMe exhibits potent anticryptococcal activity

Computer-made peptide RQ18 acts as a dual antifungal and antibiofilm peptide though membrane-associated mechanisms of action

The spread of fungi resistant to conventional drugs has become a threatening problem. In this context, antimicrobial peptides (AMPs) have been considered as one of the main alternatives for controlling fungal infections. Here, we report the antifungal and antibiofilm activity and some clues about peptide RQ18's mechanism of action against Candida and Cryptococcus. This peptide inhibited yeast growth from 2.5 μM and killed all Candida tropicalis cells within 2 h incubation. Moreover, it showed a synergistic effect with antifungal agent the amphotericin b. RQ18 reduced biofilm formation and promoted C. tropicalis mature biofilms eradication. RQ18's mechanism of action involves fungal cell membrane damage, which was confirmed by the results of RQ18 in the presence of free ergosterol in the medium and fluorescence microscopy by Sytox green. No toxic effects were observed in murine macrophage cell lines and Galleria mellonella larvae, suggesting fungal target selectivity. Therefore, peptide RQ18 represents a promising strategy as a dual antifungal and antibiofilm agent that contributes to infection control without damaging mammalian cells.

Synthesis and Evaluation of Biological Activities for a Novel 1,2,3,4-Tetrahydroisoquinoline Conjugate with Dipeptide Derivatives: Insights from Molecular Docking and Molecular Dynamics Simulations

Peptide synthesis has opened new frontiers in the quest for bioactive molecules with limitless biological applications. This study presents the synthesis of a series of novel isoquinoline dipeptides using advanced spectroscopic techniques for characterization. These compounds were designed with the goal of discovering unexplored biological activities that could contribute to the development of novel pharmaceuticals. We evaluated the biological activities of novel compounds including their antimicrobial, antibacterial, and antifungal properties. The results show promising activity against Escherichia coli and potent antibacterial activity against MTCC 443 and MTCC 1688. Furthermore, these compounds demonstrate strong antifungal activity, outperforming existing standard drugs. Computational binding affinity studies of tetrahydroisoquinoline-conjugated dipeptides against E. coli DNA gyrase displayed significant binding interactions and binding affinity, which are reflected in antimicrobial activities of compounds. Our integrative significant molecular findings from both wet and dry laboratories would help pave a path for the development of antimicrobial therapeutics. The findings suggest that these isoquinoline-conjugated dipeptides could be excellent candidates for drug development, with potential applications in the fight against bacterial and fungal infections. This research represents an exciting step forward in the field of peptide synthesis and its potential to discover novel bioactive molecules with significant implications for human health.

Novel antimicrobial peptide DvAMP serves as a promising antifungal agent against Cryptococcus neoformans

Cryptococcus neoformans is an important opportunistic human fungal pathogen that causes cryptococcosis in immunocompromised patients. However, the number of drugs for the treatment of cryptococcosis is restricted, and the development of novel antifungal drugs and innovative strategies for the treatment of cryptococcosis is urgently needed. In this study, we validated that DvAMP is a novel antimicrobial peptide with antimicrobial activity and that it was obtained by pre-screening from the UniProt database of more than three million unknown functional sequences based on the quantitative structure-activity relationships (QSARs) protocol (http://www.chemoinfolab.com/antifungal). The peptide exhibited satisfactory biosafety and physicochemical properties, and relatively rapid fungicidal activity against C. neoformans. Meanwhile, DvAMP was able to inhibit the static biofilm of C. neoformans and cause a reduction in the thickness of the capsule. In addition, DvAMP exerts antifungal effects through membrane-mediated mechanisms (membrane permeability and depolarization) and mitochondrial dysfunction, involving a hybrid multi-hit mechanism. Furthermore, by using the C. neoformans-Galleria mellonella infection model, we demonstrated that DvAMP has significant therapeutic effects in vivo and that it significantly reduces the mortality and fungal burden of infected larvae. These results suggest that DvAMP may be a potential antifungal drug candidate for the treatment of cryptococcosis.

A novel series of dipeptide derivatives containing indole-3-carboxylic acid conjugates as potential antimicrobial agents: the design, solid phase peptide synthesis, in vitro biological evaluation, and molecular docking study

A new library of peptide-heterocycle hybrids consisting of an indole-3-carboxylic acid constituent conjugated with short dipeptide motifs was designed and synthesized by using the solid phase peptide synthesis methodology. All the synthesized compounds were characterized by spectroscopic techniques. Additionally, the synthesized compounds were subjected to in vitro antimicrobial activities. Two Gram-negative bacteria (Escherichia coli and Pseudomonas aeruginosa) and two Gram-positive (Streptococcus pyogenes and Staphylococcus aureus) were used for the evaluation of the antibacterial activity of the targeted dipeptide derivatives. Good antibacterial activity was observed for the screened analogues by comparing their activities with that of ciprofloxacin, the standard drug. Also, two fungi (Aspergillus niger and Candida albicans) were employed for the evaluation of the antifungal activity of the synthesized compounds. When compared to the standard drug Fluconazole, it was observed that the screened analogues exhibited good antifungal activity. In continuation, all the synthesized derivatives were subjected to integrated molecular docking studies and molecular dynamics simulations to investigate binding affinities, intermolecular interaction networks, and conformational flexibilities with deoxyribonucleic acid (DNA) gyrase and lanosterol-14-alpha demethylase. The molecular docking studies revealed that indole-3-carboxylic acid conjugates exhibited encouraging binding interaction networks and binding affinity with DNA gyrase and lanosterol-14 alpha demethylase to show antibacterial and antifungal activity, respectively. Such synthesis, biological activity, molecular dynamics simulations, and molecular docking studies of short peptides with an indole conjugate unlock the door for the near future advancement of novel medicines containing peptide-heterocycle hybrids with the ability to be effective as antimicrobial agents.

Identification and Characterization of an Antifungal Gene Mt1 from Bacillus subtilis by Affecting Amino Acid Metabolism in Fusarium graminearum

Fusarium head blight is a devastating disease that causes significant economic losses worldwide. Fusarium graminearum is a crucial pathogen that requires close attention when controlling wheat diseases. Here, we aimed to identify genes and proteins that could confer resistance to F. graminearum. By extensively screening recombinants, we identified an antifungal gene, Mt1 (240 bp), from Bacillus subtilis 330-2. We recombinantly expressed Mt1 in F. graminearum and observed a substantial reduction in the production of aerial mycelium, mycelial growth rate, biomass, and pathogenicity. However, recombinant mycelium and spore morphology remained unchanged. Transcriptome analysis of the recombinants revealed significant down-regulation of genes related to amino acid metabolism and degradation pathways. This finding indicated that Mt1 inhibited amino acid metabolism, leading to limited mycelial growth and, thus, reduced pathogenicity. Based on the results of recombinant phenotypes and transcriptome analysis, we hypothesize that the effect of Mt1 on F. graminearum could be related to the metabolism of branched-chain amino acids (BCAAs), the most affected metabolic pathway with significant down-regulation of several genes. Our findings provide new insights into antifungal gene research and offer promising targets for developing novel strategies to control Fusarium head blight in wheat.

Synthesis, biological evaluation and mechanistic studies of 4-(1,3-thiazol-2-yl)morpholine-benzimidazole hybrids as a new structural class of antimicrobials

In spite of several attempts to develop newer pharmacophores as potential antimicrobial agents, the benzimidazole scaffold is still considered as one of the most sought after structural component towards the design of compounds that act against a wide spectrum of microbes. Herein, we report the design and synthesis of a new structural class of 4-(1,3-thiazol-2-yl)morpholine-benzimidazole hybrids as antimicrobial agents. The most potent analog, 6g shows IC₅₀ of 1.3 µM, 2.7 µM, 10.8 µM, 5.4 µM and 10.8 µM against Cryptococcus neoformans, Candida albicans, Candida parapsilosis, Escherichia coli and Staphylococcus aureus, respectively. Interestingly 6g exhibits selectivity towards the cryptococcal cells with fungicidal behavior. Propidium iodide uptake study shows permeabilization of pathogenic cells in the presence of 6g. Flow cytometric analysis confirms that cell death is predominantly due to apoptosis. Moreover, electron microscopic analysis specifies that it shrinks, disrupts and initiate pore(s) formation in the cell membrane leading to cell lysis.

Synthetic amino acids-based short amphipathic peptides exhibit antifungal activity by targeting cell membrane disruption

Availability of a limited number of antifungal drugs created a necessity to develop new antifungals with distinct mode of action. Investigation on a new series of peptides led us to identify Boc-His-Trp-His[1-(4-tert-butylphenyl)] (10g) as the most promising inhibitor exhibiting IC₅₀ value of 4.4 µg/mL against Cryptococcus neoformans. Analog 10g exhibit high selectivity to fungal cells and was nonhemolytic and noncytotoxic at its minimum inhibitory concentration. 10g produced fungicidal effect on growing cryptococcal cells and displayed synergistic effect with amphotericin B. Overall cationic character of 10g resulted in interaction with negatively charged fungal membrane while hydrophobicity enhanced penetration inside the cryptococcal cells causing hole(s) formation and disruption to the membrane as evident by the scanning electron microscopy, transmission electron microscopy, and confocal laser scanning microscopy analyses. Flow cytometric investigation revealed rapid death of fungal cells by apopotic pathway.

Peptide-based drug discovery: Current status and recent advances

The progressive development of peptides from reaction vessels to life-saving drugs via rigorous preclinical and clinical assessments is fascinating. Peptide therapeutics have gained momentum with the evolution of techniques in peptide chemistry, such as microwave irradiation in solid- and solution-phase synthesis, ligation chemistry, recombinant synthesis, and amalgamation with synthetic tools, including metal catalysis. Diverse emerging technologies, such as DNA-encoded libraries (DELs) and display techniques, are changing the status quo in the discovery of peptide therapeutics. In this review, we analyzed US Food and Drug Administration (FDA)-approved peptide drugs and those in clinical trials, highlighting recent advances in peptide-based drug discovery.

Design, synthesis, and applications of ring-functionalized histidines in peptide-based medicinal chemistry and drug discovery

Modified and synthetic α-amino acids are known to show diverse applications. Histidine, which possesses numerous applications when subjected to synthetic modifications, is one such amino acid. The utility of modified histidines varies widely from remarkable biological activities to catalysis, and from nanotechnology to polymer chemistry. This renders histidine residue an important place in scientific research. Histidine is a well-studied scaffold and constitutes the active site of various enzymes catalyzing important reactions in the biological systems. A rational modification in histidine structure with a distinctly developed protocol extensively changes its physical and chemical properties. The utilization of modified histidines in search of potent, target selective and proteostable scaffolds is vital in the development of bioactive peptides with enhanced drug-likeliness. This review is a compilation and analysis of reported side-chain ring modifications at histidine followed by applications of ring-modified histidines in the synthesis of various categories of bioactive peptides and peptidomimetics.

Anticryptococcal activity and mechanistic studies of short amphipathic peptides

Cryptococcus neoformans, an opportunistic fungal pathogen, causes cryptococcosis in immunocompromised persons. A series of modified L-histidines-containing peptides are synthesized that exhibit promising activity against C. neoformans. Analog 11d [L-His(2-adamantyl)-L-Trp-L-His(2-phenyl)-OMe] produced potency with an IC₅₀ of 3.02 µg/ml (MIC = 5.49 µg/ml). This peptide is noncytotoxic and nonhaemolytic at the MIC and displays synergistic effects with amphotericin B at subinhibitory concentration. Mechanistic investigation of 11d using microscopic tools indicates cell wall and membrane disruption of C. neoformans, while flow cytometric analysis confirms cell death by apoptosis. This study indicates that 11d exhibits antifungal potential and acts via the rapid onset of action.

Ring-Modified Histidine-Containing Cationic Short Peptides Exhibit Anticryptococcal Activity by Cellular Disruption

Delineation of clinical complications secondary to fungal infections, such as cryptococcal meningitis, and the concurrent emergence of multidrug resistance in large population subsets necessitates the need for the development of new classes of antifungals. Herein, we report a series of ring-modified histidine-containing short cationic peptides exhibiting anticryptococcal activity via membrane lysis. The N-1 position of histidine was benzylated, followed by iodination at the C-5 position via electrophilic iodination, and the dipeptides were obtained after coupling with tryptophan. In vitro analysis revealed that peptides Trp-His[1-(3,5-di-tert-butylbenzyl)-5-iodo]-OMe (10d, IC₅₀ = 2.20 μg/mL; MIC = 4.01 μg/mL) and Trp-His[1-(2-iodophenyl)-5-iodo)]-OMe (10o, IC₅₀ = 2.52 μg/mL; MIC = 4.59 μg/mL) exhibit promising antifungal activities against C. neoformans. When administered in combination with standard drug amphotericin B (Amp B), a significant synergism was observed, with 4- to 16-fold increase in the potencies of both peptides and Amp B. Electron microscopy analysis with SEM and TEM showed that the dipeptides primarily act via membrane disruption, leading to pore formation and causing cell lysis. After entering the cells, the peptides interact with the intracellular components as demonstrated by confocal laser scanning microscopy (CLSM).

His-Ala-Phe-Lys peptide from Burkholderia arboris possesses antifungal activity

Burkholderia arboris, which belongs to the Burkholderia cepacia complex, has been shown to possess antifungal activity against several plant fungal pathogens; however, the antifungal compounds are yet to be identified. Here, we identified the antifungal compounds produced by B. arboris using genetic and metabolomic approaches. We generated a Tn5 transposon mutation library of 3,000 B. arboris mutants and isolated three mutants with reduced antifungal activity against the plant fungal pathogen Fusarium oxysporum. Among the mutants, the M464 mutant exhibited the weakest antifungal activity. In the M464 genome, the transposon was inserted into the cobA gene, encoding uroporphyrin-III methyltransferase. Deletion of the cobA gene also resulted in reduced antifungal activity, indicating that the cobA gene contributed to the antifungal activity of B. arboris. Furthermore, a comparison of the differential metabolites between wild type B. arboris and the ∆cobA mutant showed a significantly decreased level of tetrapeptide His-Ala-Phe-Lys (Hafk) in the ∆cobA mutant. Therefore, a Hafk peptide with D-amino acid residues was synthesized and its antifungal activity was evaluated. Notably, the Hafk peptide displayed significant antifungal activity against F. oxysporum and Botrytis cinerea, two plant pathogens that cause destructive fungal diseases. Overall, a novel antifungal compound (Hafk) that can be used for the biocontrol of fungal diseases in plants was identified in B. arboris.