Enhancement of the Antifungal Activity of Chitinase by Palmitoylation and the Synergy of Palmitoylated Chitinase with Amphotericin B

Topical Delivery of Artificial Lipidated Antifungal Proteins for the Treatment of Subcutaneous Fungal Infections Using a Biocompatible Ionic Liquid-Based Microemulsion

The rising incidence of fungal infections, compounded by the emergence of severe antifungal resistance, has resulted in an urgent need for innovative antifungal therapies. We developed an antifungal protein-based formulation as a topical antifungal agent by combining an artificial lipidated chitin-binding domain of antifungal chitinase (LysM-lipid) with recently developed ionic liquid-in-oil microemulsion formulations (MEFs). Our findings demonstrated that the lipid moieties attached to LysM and the MEFs effectively disrupted the integrity of the stratum corneum in a mouse skin model, thereby enhancing the skin permeability of the LysM-lipids. Among the MEFs incorporating LysM modified with lauric (C12), myristic (C14), and palmitic (C16) acids, the LysM-C14-loaded MEF emerged as the most promising candidate, exhibiting potent antifungal activity against Trichoderma viride growing actively beneath the skin. The stability of the MEFs was investigated after a 28 day storage period at room temperature, and both LysM-C14- and LysM-C16-loaded MEFs retained comparable antifungal activity with that of the freshly prepared MEFs. These results highlight the considerable potential of LysM-lipid-loaded MEFs as effective topical antifungal agents.

The Biosynthesis and Applications of Protein Lipidation

Protein lipidation dramatically affects protein structure, localization, and trafficking via remodeling protein-membrane and protein-protein interactions through hydrophobic lipid moieties. Understanding the biosynthesis of lipidated proteins, whether natural ones or mimetics, is crucial for reconstructing, validating, and studying the molecular mechanisms and biological functions of protein lipidation. In this Perspective, we first provide an overview of the natural enzymatic biosynthetic pathways of protein lipidation in mammalian cells, focusing on the enzymatic machineries and their chemical linkages. We then discuss strategies to biosynthesize protein lipidation in mammalian cells by engineering modification machineries and substrates. Additionally, we explore site-specific protein lipidation biosynthesis in vitro via enzyme-mediated ligations and in vivo primarily through genetic code expansion strategies. We also discuss the use of small molecule tools to modulate the process of protein lipidation biosynthesis. Finally, we provide concluding remarks and discuss future directions for the biosynthesis and applications of protein lipidation.

Overcoming amphotericin B resistance in Candida auris using the antiemetic drug rolapitant

The emergence of Candida auris poses a significant health challenge that has led to a new era of multidrug-resistant fungal infections. Invasive infections caused by C. auris are usually associated with remarkable morbidity and mortality. For many years, amphotericin B (AmB) remained the most efficient and the last line of treatment against most hard-to-treat fungal infections. However, strains of C. auris possess extraordinary resistance to most antifungal agents, including AmB. In this study, we screened ~2,600 FDA-approved drugs and clinical compounds to identify the antiemetic drug rolapitant as a promising enhancer to AmB against C. auris. Rolapitant exhibited potent synergistic interactions with AmB against all tested (29/29) C. auris isolates. In a time-kill assay, rolapitant restored the fungicidal activity of AmB within 4 h. Additionally, the synergistic relationship between rolapitant and AmB was observed against other medically crucial Candida, Cryptococcus, and Aspergillus species. A transcriptomic study revealed that exposure to rolapitant affects oxidation reduction processes, ion transporters, and ATP production. Rolapitant triggers an elevation in cytosolic and mitochondrial calcium levels and induces oxidative stress within fungal cells. An ATP luminescence assay confirmed that rolapitant, at sub-inhibitory concentrations, significantly interfered with ATP production in C. auris. Moreover, rolapitant enhanced the in vivo activity of AmB in a mouse model of disseminated C. auris infection, as the combination reduced the fungal burden in murine kidneys by ~1 log (~90%) colony forming units. Our findings warrant further investigation of using rolapitant to overcome AmB resistance in C. auris and other fungal species.

Design of Protease-Responsive Antifungal Liposomal Formulation Decorated with a Lipid-Modified Chitin-Binding Domain

Candida albicans is a prevalent fungal pathogen that displays antibiotic resistance. The polyene antifungal amphotericin B (AmB) has been the gold standard because of its broad antifungal spectra, and its liposomal formulation, AmBisome, has been used widely and clinically in treating fungal infections. Herein, we explored enhancing the antifungal activity of AmBisome by integrating a small chitin-binding domain (LysM) of chitinase A derived from Pteris ryukyuensis. LysM conjugated with a lipid (LysM-lipid) was initially prepared through microbial transglutaminase (MTG)-mediated peptide tag-specific conjugation of LysM with a lipid-peptide substrate. The AmBisome formulation modified with LysM-lipid conjugates had a size distribution that was comparable to the native liposomes but an increased zeta potential, indicating that LysM-lipid conjugates were anchored to AmBisome. LysM-lipid-modified AmBisome exhibited long-term stability at 4 °C while retaining the capacity to bind chitin. Nevertheless, the antifungal efficacy of LysM-lipid-modified AmBisome against C. albicans was modest. We then redesigned a new LysM-lipid conjugate by introducing a peptide linker containing a thrombin digestion (TD) site at the C-terminus of LysM (LysM-TD linker-lipid), thereby facilitating the liberation of the LysM domain from AmBisome upon the addition of thrombin. This new AmBisome formulation anchored with LysM-TD linker-lipid exhibited superior performance in suppressing C. albicans growth in the presence of thrombin compared with the LysM-lipid formulation. These results provide a platform to design stimuli-responsive AmBisome formulations that respond to external environments and thus advance the treatment of pathogenic fungi infections.

The chitin-binding domain of Bacillus thuringiensis ChiA74 inhibits gram-negative bacterial and fungal pathogens of humans and plants

The chitinase ChiA74 is synthesized by Bacillus thuringiensis and possesses a modular organization composed of four domains. In the C-terminal of the enzyme is located the chitin-binding domain (CBD), which has not been isolated as a single unit or characterized. Here, we aimed to isolate the ChiA74's CBD as a single unit, determine the binding properties, and evaluate its antimicrobial and hemolytic activities. We cloned the ChiA74's CBD and expressed it in Escherichia coli BL21. The single domain was purified, analyzed by SDS-PAGE, and characterized. The recombinant CBD (rCBD) showed a molecular mass of ∼14 kDa and binds strongly to α-chitin, with Kd and Bmax of ∼4.7 ± 0.9 μM and 1.5 ± 0.1 μmoles/g chitin, respectively. Besides, the binding potential (Bmax/Kd) was stronger for α-chitin (∼0.31) than microcrystalline cellulose (∼0.19). It was also shown that the purified rCBD inhibited the growth of the clinically relevant Gram-negative bacteria (GNB) Vibrio cholerae, and V. parahemolyticus CVP2 with minimum inhibitory concentrations (MICs) of 121 ± 9.9 and 138 ± 3.2 μg/mL, respectively, and of one of the most common GNB plant pathogens, Pseudomonas syringae with a MIC of 230 ± 13.8 μg/mL. In addition, the rCBD possessed antifungal activity inhibiting the conidia germination of Fusarium oxysporum (MIC = 192 ± 37.5 μg/mL) and lacked hemolytic and agglutination activities against human erythrocytes. The significance of this work lies in the fact that data provided here show for the first time that ChiA74's CBD from B. thuringiensis has antimicrobial activity, suggesting its potential use against significant pathogenic microorganisms. Future works will be focused on testing the inhibitory effect against other pathogenic microorganisms and elucidating the mechanism of action.

Genomic Insights into Paucibacter aquatile DH15, a Cyanobactericidal Bacterium, and Comparative Genomics of the Genus Paucibacter

Microcystis blooms threaten ecosystem function and cause substantial economic losses. Microorganism-based methods, mainly using cyanobactericidal bacteria, are considered one of the most ecologically sound methods to control Microcystis blooms. This study focused on gaining genomic insights into Paucibacter aquatile DH15 that exhibited excellent cyanobactericidal effects against Microcystis. Additionally, a pan-genome analysis of the genus Paucibacter was conducted to enhance our understanding of the ecophysiological significance of this genus. Based on phylogenomic analyses, strain DH15 was classified as a member of the species Paucibacter aquatile. The genome analysis supported that strain DH15 can effectively destroy Microcystis, possibly due to the specific genes involved in the flagellar synthesis, cell wall degradation, and the production of cyanobactericidal compounds. The pan-genome analysis revealed the diversity and adaptability of the genus Paucibacter, highlighting its potential to absorb external genetic elements. Paucibacter species were anticipated to play a vital role in the ecosystem by potentially providing essential nutrients, such as vitamins B7, B12, and heme, to auxotrophic microbial groups. Overall, our findings contribute to understanding the molecular mechanisms underlying the action of cyanobactericidal bacteria against Microcystis and shed light on the ecological significance of the genus Paucibacter.

Natural product osthole can significantly disrupt cell wall integrity and dynamic balance of Fusarium oxysporum

Dendrobium officinale Kimura et Migo is a traditional Chinese herbal medicinal plant. However, the frequent occurrence of soft rot disease (SRD) is one of the most harmful diseases in D. officinale production in recent years, which can seriously affect its yield and quality. In this study, the major pathogenic fungus (SR-1) was isolated from D. officinale with typical symptoms of SRD, and was identified as Fusarium oxysporum through morphological and molecular identification. The biological activities of five natural products were determined against F. oxysporum using a mycelial growth inhibition assay. The results showed that osthole had the highest antifungal activity against F. oxysporum, with an EC50 value of 6.40 mg/L. Scanning electron microscopy (SEM) showed that osthole caused F. oxysporum mycelia to shrink and deform. Transmission electron microscopy (TEM) showed that the organelles were blurred and the cell wall was thickened in the presence of osthole. The sensitivity of F. oxysporum to calcofluor white (CFW) staining was significantly enhanced by osthole. Relative conductivity measurements and propidium iodide (PI) observation revealed that osthole had no significant effect on the cell membrane. Further experiments showed that the activity of chitinase and β-1,3-glucanase were decreased, and expression levels of chitinase and β-1,3-glucanase related genes were significantly down-regulated after treatment with osthole. In conclusion, osthole disrupted the cell wall integrity and dynamic balance of F. oxysporum, thereby inhibiting normal mycelial growth.

Liposomal Amphotericin B Formulation Displaying Lipid-Modified Chitin-Binding Domains with Enhanced Antifungal Activity

Fungal infections affect more than one billion people worldwide and cause more than one million deaths per year. Amphotericin B (AmB), a polyene antifungal drug, has been used as the gold standard for many years because of its broad antifungal spectrum, high activity, and low tendency of drug resistance. However, the side effects of AmB, such as nephrotoxicity and hepatotoxicity, have hampered its widespread use, leading to the development of a liposome-type AmB formulation, AmBisome. Herein, we report a simple but highly effective strategy to enhance the antifungal activity of AmBisome with a lipid-modified protein. The chitin-binding domain (LysM) of the antifungal chitinase, Pteris ryukyuensis chitinase A (PrChiA), a small 5.3 kDa protein that binds to fungal cell wall chitin, was engineered to have a glutamine-containing peptide tag at the C-terminus for the microbial transglutaminase (MTG)-catalyzed crosslinking reaction (LysM-Q). LysM-Q was site-specifically modified with a lysine-containing lipid peptide substrate of MTG with a palmitoyl moiety (Pal-K). The resulting palmitoylated LysM (LysM-Pal) exhibited negligible cytotoxicity to mammalian cells and can be easily anchored to yield LysM-presenting AmBisome (LysM-AmBisome). LysM-AmBisome exhibited a dramatic enhancement of antifungal activity toward Trichoderma viride and Cryptococcus neoformans, demonstrating the marked impact of displaying a cell-wall binder protein on the targeting ability of antifungal liposomal formulations. Our simple strategy with enzymatic protein lipidation provides a potent approach to upgrade other types of lipid-based drug formulations.

Identification of New Fusarium sulawense Strains Causing Soybean Pod Blight in China and Their Control Using Carbendazim, Dipicolinic Acid and Kojic Acid

Soybean plants are highly susceptible to Fusarium species, which significantly reduce soybean production and quality. Several Fusarium species have been reported to synthesize mycotoxins, such as trichothecene, which have been related to major human diseases. In November 2021, soybean pods in Nantong municipality, China, showed black necrotic lesions during the harvest stage. The disease incidence reached 69%. The pathogen was identified as Fusarium sulawense via morphological analysis and sequencing of ITS, EF1-α and RPB2 genes. A PCR assay with primers targeting the trichothecene biosynthesis genes suggested that the three isolates could synthesize trichothecenes. The effectiveness of fungicide carbendazim and natural metabolites dipicolinic acid and kojic acid was screened for the management of F. sulawense on postharvest soybean pods. The highest efficacy was obtained when combining 3.8 mg/mL carbendazim and 0.84 mg/mL dipicolinic acid (curative efficacy: 49.1% lesion length inhibition; preventive efficacy: 82.7% lesion length inhibition), or 1.9 mg/mL carbendazim and 0.71 mg/mL kojic acid (preventive efficacy: 84.9% lesion length inhibition). Collectively, this report will lead to a better understanding of the safety hazards found in soybean products in China and reveals the application of dipicolinic and kojic acids to reduce the use of carbendazim.

Preparation of amphotericin B-loaded hybrid liposomes and the integration of chitin-binding proteins for enhanced antifungal activity

Amphotericin B (AMB) is a gold standard antifungal drug because of its broad-spectrum activity toward pathogenic yeasts and molds. Because of its low solubility in water and toxicity toward humans, several lipid-based formulations that either increase the aqueous solubility or decrease the side effects have been employed in practical use. In our previous research, we found that the combination of AMB with an artificial palmitoylated chitin-binding domain from Pteris ryukyuensis chitinase (LysM-Pal) resulted in synergistic antifungal action against Trichoderma viride. Herein, we prepared hybrid liposomal formulations by combining a commercially available AMB formulation and liposomes with different surface charges to explore key factors in the antifungal activity. The characterization of AMB-loaded liposomal formulations (AMB-LFs), including particle size distribution and zeta potential, showed that anionic and neutral AMB-LFs could stably encapsulate AMB. The combination of either anionic or neutral AMB-LFs with unmodified LysM decreased the minimum inhibitory concentration of AMB. The combination of neutral AMB-LF with LysM-Pal resulted in a further decrease in the MIC, up to 15-fold compared with that of the neutral AMB-LF alone. Our results demonstrate the potential utility of lipid-based liposomal formulations of AMB combined with lipid-modified proteinaceous binders to tackle fungal infections.