Innovations in Antifungal Drug Discovery among Cell Envelope Synthesis Enzymes through Structural Insights

In vitro and In silico investigation deciphering novel antifungal activity of endophyte Bacillus velezensis CBMB205 against Fusarium oxysporum

Endophytes from medicinal plants are potential biocontrol agents against Fusarium oxysporum f. sp. cubense (Foc), which is the causative fungus of banana wilt disease. In the present study, the endophytic bacterium was isolated from Globba racemosa and their antagonistic activities against Foc were studied, and the probable molecular mechanism of antagonism was predicted by molecular docking studies. The 16SrRNA sequencing confirmed the endophytic isolate to be Bacillus velezensis CBMB205 (EG2). The antagonistic activities of the isolates by distortion of fungal hyphae were illustrated in SEM. The probable metabolites present in endophytic isolate were identified by FTIR, suggesting the presence of C-H, CH3 and O-H groups. Two major metabolites such as β-amyrin and dihydroxy octadecenoic acid (DA) were confirmed by LC-MS analysis. Molecular docking studies suggested that these metabolites showed potential binding with chitin synthase 1 and fungal 1,3-glucan synthase of pathogenic fungi. The binding energy (BE) of the molecular interaction between β-amyrin and chitin synthase-1 (CS-1), and 1,3-glucan synthase (1,3-GS) were estimated to be -10.17 kcal/mol and - 9.5 kcal/mol, respectively. The BE of the interaction between β-amyrin and CS-1 and 1,3-GS were determined to be -2.43 kcal/mol and 3.4 kcal/mol, respectively. The current study demonstrated the antagonistic activities of EG2 towards Foc and provided a probable molecular mechanism by in silico studies. The study also provides a potential insight into developing endophytic metabolite-based antifungal agents for various agricultural applications.

Garlic-Derived Quorum Sensing Inhibitors: A Novel Strategy Against Fungal Resistance

In recent years, the incidence of fungal infections has been rising annually, especially among immunocompromised populations, posing a significant challenge to public health. Although antifungal medications provide some relief, the escalating problem of resistance sharply curtails their effectiveness, presenting an urgent clinical dilemma that demands immediate attention. Research has shown that fungal resistance is closely related to quorum sensing (QS), and QS inhibitors (QSIs) are considered an effective solution to this issue. Garlic, as a natural QSI, has demonstrated significant effects in inhibiting fungal growth, preventing biofilm formation, enhancing immunity, and combating resistance. This study explores the potential of garlic in mitigating fungal drug resistance and identifies its key role in inhibiting the QS mechanism, these findings offer a new perspective for the treatment of fungal infections, especially in addressing the increasingly severe problem of resistance. However, the clinical application of garlic still faces several challenges, such as ensuring the standardization of active ingredient extraction, as well as issues of safety and stability. Future research should focus on the QS mechanism and promote interdisciplinary collaboration to develop more natural, effective, and safe QSI drugs like garlic, while actively conducting clinical trials to validate their efficacy and safety. Additionally, incorporating advanced technologies such as nanotechnology to enhance drug stability and targeting, provide a more comprehensive strategy for the treatment of fungal infections. Overall, Our study provides scientific evidence supporting the potential of garlic as a novel antifungal treatment and lays the groundwork for the development of future natural QSIs for therapeutic use. It offers new insights, particularly for the treatment of immunocompromised populations and drug-resistant fungal strains.

The small molecule CBR-5884 inhibits the Candida albicans phosphatidylserine synthase

Systemic infections by Candida spp. are associated with high mortality rates, partly due to limitations in current antifungals, highlighting the need for novel drugs and drug targets. The fungal phosphatidylserine synthase, Cho1, from Candida albicans is a logical antifungal drug target due to its importance in virulence, absence in the host, and conservation among fungal pathogens. Inhibitors of Cho1 could serve as lead compounds for drug development, so we developed a target-based screen for inhibitors of purified Cho1. This enzyme condenses serine and cytidyldiphosphate-diacylglycerol (CDP-DAG) into phosphatidylserine (PS) and releases cytidylmonophosphate (CMP). Accordingly, we developed an in vitro nucleotidase-coupled malachite-green-based high throughput assay for purified C. albicans Cho1 that monitors CMP production as a proxy for PS synthesis. Over 7,300 molecules curated from repurposing chemical libraries were interrogated in primary and dose-responsivity assays using this platform. The screen had a promising average Z' score of ~0.8, and seven compounds were identified that inhibit Cho1. Three of these, ebselen, LOC14, and CBR-5884, exhibited antifungal effects against C. albicans cells, with fungicidal inhibition by ebselen and fungistatic inhibition by LOC14 and CBR-5884. Only CBR-5884 showed evidence of disrupting in vivo Cho1 function by inducing phenotypes consistent with the cho1∆∆ mutant, including a reduction of cellular PS levels. Kinetics curves and computational docking indicate that CBR-5884 competes with serine for binding to Cho1 with a Ki of 1,550 ± 245.6 nM. Thus, this compound has the potential for development into an antifungal compound.

IMPORTANCE

Fungal phosphatidylserine synthase (Cho1) is a logical antifungal target due to its crucial role in the virulence and viability of various fungal pathogens, and since it is absent in humans, drugs targeted at Cho1 are less likely to cause toxicity in patients. Using fungal Cho1 as a model, there have been two unsuccessful attempts to discover inhibitors for Cho1 homologs in whole-cell screens prior to this study. The compounds identified in these attempts do not act directly on the protein, resulting in the absence of known Cho1 inhibitors. The significance of our research is that we developed a high-throughput target-based assay and identified the first Cho1 inhibitor, CBR-5884, which acts both on the purified protein and its function in the cell. This molecule acts as a competitive inhibitor with a Ki value of 1,550 ± 245.6 nM and, thus, has the potential for development into a new class of antifungals targeting PS synthase.