Jawsamycin exhibits in vivo antifungal properties by inhibiting Spt14/Gpi3-mediated biosynthesis of glycosylphosphatidylinositol

To each its own: Mechanisms of cross-talk between GPI biosynthesis and cAMP-PKA signaling in Candida albicans versus Saccharomyces cerevisiae

Candida albicans is an opportunistic fungal pathogen that can switch between yeast and hyphal morphologies depending on the environmental cues it receives. The switch to hyphal form is crucial for the establishment of invasive infections. The hyphal form is also characterized by the cell surface expression of hyphae-specific proteins, many of which are GPI-anchored and important determinants of its virulence. The coordination between hyphal morphogenesis and the expression of GPI-anchored proteins is made possible by an interesting cross-talk between GPI biosynthesis and the cAMP-PKA signaling cascade in the fungus; a parallel interaction is not found in its human host. On the other hand, in the nonpathogenic yeast, Saccharomyces cerevisiae, GPI biosynthesis is shut down when filamentation is activated and vice versa. This too is achieved by a cross-talk between GPI biosynthesis and cAMP-PKA signaling. How are diametrically opposite effects obtained from the cross-talk between two reasonably well-conserved pathways present ubiquitously across eukarya? This Review attempts to provide a model to explain these differences. In order to do so, it first provides an overview of the two pathways for the interested reader, highlighting the similarities and differences that are observed in C. albicans versus the well-studied S. cerevisiae model, before going on to explain how the different mechanisms of regulation are effected. While commonalities enable the development of generalized theories, it is hoped that a more nuanced approach, that takes into consideration species-specific differences, will enable organism-specific understanding of these processes and contribute to the development of targeted therapies.

Molecular basis of the inositol deacylase PGAP1 involved in quality control of GPI-AP biogenesis

The secretion and quality control of glycosylphosphatidylinositol-anchored proteins (GPI-APs) necessitates post-attachment remodeling initiated by the evolutionarily conserved PGAP1, which deacylates the inositol in nascent GPI-APs. Impairment of PGAP1 activity leads to developmental diseases in humans and fatality and infertility in animals. Here, we present three PGAP1 structures (2.66-2.84 Å), revealing its 10-transmembrane architecture and product-enzyme interaction details. PGAP1 holds GPI-AP acyl chains in an optimally organized, guitar-shaped cavity with apparent energetic penalties from hydrophobic-hydrophilic mismatches. However, abundant glycan-mediated interactions in the lumen counterbalance these repulsions, likely conferring substrate fidelity and preventing off-target hydrolysis of bulk membrane lipids. Structural and biochemical analyses uncover a serine hydrolase-type catalysis with atypical features and imply mechanisms for substrate entrance and product release involving a drawing compass movement of GPI-APs. Our findings advance the mechanistic understanding of GPI-AP remodeling.

Structure and Function of the Glycosylphosphatidylinositol Transamidase, a Transmembrane Complex Catalyzing GPI Anchoring of Proteins

Glycosylphosphatidylinositol (GPI) anchoring of proteins is a ubiquitous posttranslational modification in eukaryotic cells. GPI-anchored proteins (GPI-APs) play critical roles in enzymatic, signaling, regulatory, and adhesion processes. Over 20 enzymes are involved in GPI synthesis, attachment to client proteins, and remodeling after attachment. The GPI transamidase (GPI-T), a large complex located in the endoplasmic reticulum membrane, catalyzes the attachment step by replacing a C-terminal signal peptide of proproteins with GPI. In the last three decades, extensive research has been conducted on the mechanism of the transamidation reaction, the components of the GPI-T complex, the role of each subunit, and the substrate specificity. Two recent studies have reported the three-dimensional architecture of GPI-T, which represent the first structures of the pathway. The structures provide detailed mechanisms for assembly that rationalizes previous biochemical results and subunit-dependent stability data. While the structural data confirm the catalytic role of PIGK, which likely uses a caspase-like mechanism to cleave the proproteins, they suggest that unlike previously proposed, GPAA1 is not a catalytic subunit. The structures also reveal a shared cavity for GPI binding. Somewhat unexpectedly, PIGT, a single-pass membrane protein, plays a crucial role in GPI recognition. Consistent with the assembly mechanisms and the active site architecture, most of the disease mutations occur near the active site or the subunit interfaces. Finally, the catalytic dyad is located ~22 Å away from the membrane interface of the GPI-binding site, and this architecture may confer substrate specificity through topological matching between the substrates and the elongated active site. The research conducted thus far sheds light on the intricate processes involved in GPI anchoring and paves the way for further mechanistic studies of GPI-T.

The Mechanism of Transcription Factor Swi6 in Regulating Growth and Pathogenicity of Ceratocystis fimbriata: Insights from Non-Targeted Metabolomics

Ceratocystis fimbriata (C. fimbriata) is a notorious pathogenic fungus that causes sweet potato black rot disease. The APSES transcription factor Swi6 in fungi is located downstream of the cell wall integrity (CWI)-mitogen-activated protein kinase (MAPK) signaling pathway and has been identified to be involved in cell wall integrity and virulence in several filamentous pathogenic fungi. However, the specific mechanisms by which Swi6 regulates the growth and pathogenicity of plant pathogenic fungi remain elusive. In this study, the SWI6 deletion mutants and complemented strains of C. fimbriata were generated. Deletion of Swi6 in C. fimbriata resulted in aberrant growth patterns. Pathogenicity assays on sweet potato storage roots revealed a significant decrease in virulence in the mutant. Non-targeted metabolomic analysis using LC-MS identified a total of 692 potential differentially accumulated metabolites (PDAMs) in the ∆Cfswi6 mutant compared to the wild type, and the results of KEGG enrichment analysis demonstrated significant enrichment of PDAMs within various metabolic pathways, including amino acid metabolism, lipid metabolism, nucleotide metabolism, GPI-anchored protein synthesis, and ABC transporter metabolism. These metabolic pathways were believed to play a crucial role in mediating the growth and pathogenicity of C. fimbriata through the regulation of CWI. Firstly, the deletion of the SWI6 gene led to abnormal amino acid and lipid metabolism, potentially exacerbating energy storage imbalance. Secondly, significant enrichment of metabolites related to GPI-anchored protein biosynthesis implied compromised cell wall integrity. Lastly, disruption of ABC transport protein metabolism may hinder intracellular transmembrane transport. Importantly, this study represents the first investigation into the potential regulatory mechanisms of SWI6 in plant filamentous pathogenic fungi from a metabolic perspective. The findings provide novel insights into the role of SWI6 in the growth and virulence of C. fimbriata, highlighting its potential as a target for controlling this pathogen.

Virulence traits and novel drug delivery strategies for mucormycosis post-COVID-19: a comprehensive review

The outbreak of a fatal black fungus infection after the resurgence of the cadaverous COVID-19 has exhorted scientists worldwide to develop a nutshell by repurposing or designing new formulations to address the crisis. Patients expressing COVID-19 are more susceptible to Mucormycosis (MCR) and thus fall easy prey to decease accounting for this global threat. Their mortality rates range around 32-70% depending on the organs affected and grow even higher despite the treatment. The many contemporary recommendations strongly advise using liposomal amphotericin B and surgery as first-line therapy whenever practicable. MCR is a dangerous infection that requires an antifungal drug administration on appropriate prescription, typically one of the following: Amphotericin B, Posaconazole, or Isavuconazole since the fungi that cause MCR are resistant to other medications like fluconazole, voriconazole, and echinocandins. Amphotericin B and Posaconazole are administered through veins (intravenously), and isavuconazole by mouth (orally). From last several years so many compounds are developed against invasive fungal disease but only few of them are able to induce effective treatment against the micorals. Adjuvant medicines, more particularly, are difficult to assess without prospective randomized controlled investigations, which are challenging to conduct given the lower incidence and higher mortality from Mucormycosis. The present analysis provides insight into pathogenesis, epidemiology, clinical manifestations, underlying fungal virulence, and growth mechanisms. In addition, current therapy for MCR in Post Covid-19 individuals includes conventional and novel nano-based advanced management systems for procuring against deadly fungal infection. The study urges involving nanomedicine to prevent fungal growth at the commencement of infection, delay the progression, and mitigate fatality risk.

Structures of liganded glycosylphosphatidylinositol transamidase illuminate GPI-AP biogenesis

Many eukaryotic receptors and enzymes rely on glycosylphosphatidylinositol (GPI) anchors for membrane localization and function. The transmembrane complex GPI-T recognizes diverse proproteins at a signal peptide region that lacks consensus sequence and replaces it with GPI via a transamidation reaction. How GPI-T maintains broad specificity while preventing unintentional cleavage is unclear. Here, substrates- and products-bound human GPI-T structures identify subsite features that enable broad proprotein specificity, inform catalytic mechanism, and reveal a multilevel safeguard mechanism against its promiscuity. In the absence of proproteins, the catalytic site is invaded by a locally stabilized loop. Activation requires energetically unfavorable rearrangements that transform the autoinhibitory loop into crucial catalytic cleft elements. Enzyme-proprotein binding in the transmembrane and luminal domains respectively powers the conformational rearrangement and induces a competent cleft. GPI-T thus integrates various weak specificity regions to form strong selectivity and prevent accidental activation. These findings provide important mechanistic insights into GPI-anchored protein biogenesis.

Biosynthesis and Genome Mining Potentials of Nucleoside Natural Products

Nucleoside natural products show diverse biological activities and serve as leads for various application purposes, including human and veterinary medicine and agriculture. Studies in the past decade revealed that these nucleosides are biosynthesized through divergent mechanisms, in which early steps of the pathways can be classified into two types (C5' oxidation and C5' radical extension), while the structural diversity is created by downstream tailoring enzymes. Based on this biosynthetic logic, we investigated the genome mining discovery potentials of these nucleosides using the two enzymes representing the two types of C5' modifications: LipL-type α-ketoglutarate (α-KG) and Fe-dependent oxygenases and NikJ-type radical S-adenosyl-L-methionine (SAM) enzymes. The results suggest that this approach allows discovery of putative nucleoside biosynthetic gene clusters (BGCs) and the prediction of the core nucleoside structures. The results also revealed the distribution of these pathways in nature and implied the possibility of future genome mining discovery of novel nucleoside natural products.

Candidiasis: From cutaneous to systemic, new perspectives of potential targets and therapeutic strategies

Candidiasis is an infection caused by fungi from a Candida species, most commonly Candida albicans. C. albicans is an opportunistic fungal pathogen typically residing on human skin and mucous membranes of the mouth, intestines or vagina. It can cause a wide variety of mucocutaneous barrier and systemic infections; and becomes a severe health problem in HIV/AIDS patients and in individuals who are immunocompromised following chemotherapy, treatment with immunosuppressive agents or after antibiotic-induced dysbiosis. However, the immune mechanism of host resistance to C. albicans infection is not fully understood, there are a limited number of therapeutic antifungal drugs for candidiasis, and these have disadvantages that limit their clinical application. Therefore, it is urgent to uncover the immune mechanisms of the host protecting against candidiasis and to develop new antifungal strategies. This review synthesizes current knowledge of host immune defense mechanisms from cutaneous candidiasis to invasive C. albicans infection and documents promising insights for treating candidiasis through inhibitors of potential antifungal target proteins.

The Investigation and Prediction of Voriconazole-Associated Hepatotoxicity under Therapeutic Drug Monitoring. ANNUAL INTERNATIONAL CONFERENCE OF THE IEEE ENGINEERING IN MEDICINE AND BIOLOGY SOCIETY. IEEE ENGINEERING IN MEDICINE AND BIOLOGY SOCIETY. ANNUAL INTERNATIONAL CONFERENCE 2023;2023:1-4. [PMID: 38082975 DOI: 10.1109/embc40787.2023.10340343] [Citation(s) in RCA: 0] [Impact Index Per Article: 0]

Voriconazole is commonly used as the first-line agent to treat invasive fungal infections (IFIs), but the induction of hepatotoxicity limits its use. To improve the treatment outcomes and minimize toxicity, doctors often administer Therapeutic Drug Monitoring (TDM) to patients receiving voriconazole treatment. Here, we conducted a real-world clinical investigation of voriconazole-treated patients and found significant differences between the TDM (n=318) and non-TDM cohort (n=6,379), and such incidence of hepatotoxicity showed 10.6% in the non-TDM cohort, compared with 21.5% in the TDM cohort. Based on our previous investigation, we presented and compared several machine learning models (including AdaBoost, decision tree, GBDT, logistic regression, neural networks, and random forest) for the early warning of voriconazole-associated hepatoxicity. Through the five-fold cross validation, the logistic model outperformed other models with a mean AUC of 0.7933±0.0934. Our findings offer important insights into the safe and effective application of voriconazole.

Moonlight-like proteins are actually cell wall components in Pseudocercospora fijiensis

The fungal cell wall protects fungi against threats, both biotic and abiotic, and plays a role in pathogenicity by facilitating host adhesion, among other functions. Although carbohydrates (e.g. glucans, chitin) are the most abundant components, the fungal cell wall also harbors ionic proteins, proteins bound by disulfide bridges, alkali-extractable, SDS-extractable, and GPI-anchored proteins, among others; the latter consisting of suitable targets which can be used for fungal pathogen control. Pseudocercospora fijiensis is the causal agent of black Sigatoka disease, the principal threat to banana and plantain worldwide. Here, we report the isolation of the cell wall of this pathogen, followed by extensive washing to eliminate all loosely associated proteins and conserve those integrated to its cell wall. In the HF-pyridine protein fraction, one of the most abundant protein bands was recovered from SDS-PAGE gels, electro-eluted and sequenced. Seven proteins were identified from this band, none of which were GPI-anchored proteins. Instead, atypical (moonlight-like) cell wall proteins were identified, suggesting a new class of atypical proteins, bound to the cell wall by unknown linkages. Western blot and histological analyses of the cell wall fractions support that these proteins are true cell wall proteins, most likely involved in fungal pathogenesis/virulence, since they were found conserved in many fungal pathogens.

Epidemiology, Modern Diagnostics, and the Management of Mucorales Infections

Mucormycosis is an uncommon, yet deadly invasive fungal infection caused by the Mucorales moulds. These pathogens are a WHO-assigned high-priority pathogen group, as mucormycosis incidence is increasing, and there is unacceptably high mortality with current antifungal therapies. Current diagnostic methods have inadequate sensitivity and specificity and may have issues with accessibility or turnaround time. Patients with diabetes mellitus and immune compromise are predisposed to infection with these environmental fungi, but COVID-19 has established itself as a new risk factor. Mucorales also cause healthcare-associated outbreaks, and clusters associated with natural disasters have also been identified. Robust epidemiological surveillance into burden of disease, at-risk populations, and emerging pathogens is required. Emerging serological and molecular techniques may offer a faster route to diagnosis, while newly developed antifungal agents show promise in preliminary studies. Equitable access to these emerging diagnostic techniques and antifungal therapies will be key in identifying and treating mucormycosis, as delayed initiation of therapy is associated with higher mortality.

Clinical Features and Treatment Progress of Invasive Mucormycosis in Patients with Hematological Malignancies

The incidence rate of invasive mucormycosis (IM) in patients with hematological malignancies (HMs) is increasing year by year, ranging from 0.07% to 4.29%, and the mortality rate is mostly higher than 50%. With the ongoing pandemic of COVID-19, COVID-19-associated mucormycosis (CAM) also became a global health threat. Patients with high risk factors such as active HMs, relapsed/refractory leukemia, prolonged neutropenia may still develop breakthrough mucormycosis (BT-MCR) even under the prophylaxis of Mucorales-active antifungals, and such patients often have higher mortality. Rhizopus spp. is the most common genus associated with IM, followed by Mucor spp. and Lichtheimia spp. Pulmonary mucormycosis (PM) is the most common form of IM in patients with HMs, followed by rhino-orbital-cerebral mucormycosis (ROCM) and disseminated mucormycosis. The prognosis of IM patients with neutrophil recovery, localized IM and receiving early combined medical-surgical therapy is usually better. As for management of the disease, risk factors should be eliminated firstly. Liposome amphotericin B (L-AmB) combined with surgery is the initial treatment scheme of IM. Those who are intolerant to L-AmB can choose intravenous formulations or tablets of isavuconazole or posaconazole. Patients who are refractory to monotherapy can turn to combined antifungals therapy.

Target- and prodrug-based design for fungal diseases and cancer-associated fungal infections

Invasive fungal infections (IFIs) are emerging as a serious threat to public health and are associated with high incidence and mortality. IFIs also represent a frequent complication in patients with cancer who are undergoing chemotherapy. However, effective and safe antifungal agents remain limited, and the development of severe drug resistance further undermines the efficacy of antifungal therapy. Therefore, there is an urgent need for novel antifungal agents to treat life-threatening fungal diseases, especially those with new mode of action, favorable pharmacokinetic profiles, and anti-resistance activity. In this review, we summarize new antifungal targets and target-based inhibitor design, with a focus on their antifungal activity, selectivity, and mechanism. We also illustrate the prodrug design strategy used to improve the physicochemical and pharmacokinetic profiles of antifungal agents. Dual-targeting antifungal agents offer a new strategy for the treatment of resistant infections and cancer-associated fungal infections.

Antifungal metabolites, their novel sources, and targets to combat drug resistance

Excessive antibiotic prescriptions as well as their misuse in agriculture are the main causes of antimicrobial resistance which poses a growing threat to public health. It necessitates the search for novel chemicals to combat drug resistance. Since ancient times, naturally occurring medicines have been employed and the enormous variety of bioactive chemicals found in nature has long served as an inspiration for researchers looking for possible therapeutics. Secondary metabolites from microorganisms, particularly those from actinomycetes, have made it incredibly easy to find new molecules. Different actinomycetes species account for more than 70% of naturally generated antibiotics currently used in medicine, and they also produce a variety of secondary metabolites, including pigments, enzymes, and anti-inflammatory compounds. They continue to be a crucial source of fresh chemical diversity and a crucial component of drug discovery. This review summarizes some uncommon sources of antifungal metabolites and highlights the importance of further research on these unusual habitats as a source of novel antimicrobial molecules.

Allicin shows antifungal efficacy against Cryptococcus neoformans by blocking the fungal cell membrane

Allicin, which is generated by the catalytic reaction between alliin and alliinase extracted from garlic, has been shown to have a wide range of antimicrobial activities, but its anti-Cryptococcus efficacy and mechanism are not quite clear. Here, we have determined that the Conversion rate of allicin in the reaction product reached 97.5%. The minimal inhibitory concentration (MIC) of allicin against Cryptococcus neoformans (C. neoformans) H99 was 2 μg/ml, which is comparable to fluconazole (FLU, 1 μg/ml). Furthermore, allicin exhibited effective antifungal activity against 46 clinical isolates of C. neoformans, and the MICs ranged from 1 to 8 μg/ml, even for AmB-insensitive strains. Interestingly, allicin also exerted additive or synergistic effects when combined with amphotericin B (AmB) and FLU. Time-killing curves and long-term live cell imaging of H99 showed that 4 MIC of allicin had fungicide activity. Additionally, allicin (4 and 8 mg/kg) exerted a dose-dependent therapeutic effect on H99-infected mice by significantly reducing the wet pulmonary coefficient and Cryptococcus load and reducing lung damage. Even the efficacy of 8 mg/kg was comparable to FLU (20 mg/kg). Transcriptomics revealed that allicin may act on the cell membrane of H99. Subsequently, transmission electron microscopy (TEM) observations showed that allicin clearly breached the cell membrane and organelles of H99. Confocal laser scanning microscopy (CLSM) results further confirmed that allicin disrupted the permeability of the cell membranes of H99 in a dose-dependent manner. Allicin exhibits strong anti-C. neoformans activity in vitro and in vivo, mainly by destroying the permeability and related functions of Cryptococcus cell membranes.

Novel Promising Antifungal Target Proteins for Conquering Invasive Fungal Infections

Invasive fungal infections (IFIs) pose a serious clinical problem, but the antifungal arsenal is limited and has many disadvantages, such as drug resistance and toxicity. Hence, there is an urgent need to develop antifungal compounds that target novel target proteins of pathogenic fungi for treating IFIs. This review provides a comprehensive summary of the biological functions of novel promising target proteins for treating IFIs in pathogenic fungi and their inhibitors. Inhibitors of inositol phosphoramide (IPC) synthases (such as Aureobasidin A, Khafrefungin, Galbonolide A, and Pleofungin A) have potent antifungal activities by inhibiting sphingolipid synthesis. Disrupting glycosylphosphatidylinositol (GPI) biosynthesis by Jawsamycin (an inhibitor of Spt14), M720 (an inhibitor of Mcd4), and APX001A (an inhibitor of Gwt1) is a promising strategy for treating IFIs. Turbinmicin is a natural-compound inhibitor of Sec14 and has extraordinary antifungal efficacy, broad-antifungal spectrum, low toxicity, and is a promising new compound for treating IFIs. CMLD013075 targets fungal heat shock protein 90 (Hsp90) and has remarkable antifungal efficacy. Olorofim, as an inhibitor of dihydrolactate dehydrogenase, is a breakthrough drug treatment for IFIs. These novel target proteins and their inhibitors may overcome the limitations of currently available antifungal drugs and improve patient outcomes in the treatment of IFIs.

Turning Inside Out: Filamentous Fungal Secretion and Its Applications in Biotechnology, Agriculture, and the Clinic

Filamentous fungi are found in virtually every marine and terrestrial habitat. Vital to this success is their ability to secrete a diverse range of molecules, including hydrolytic enzymes, organic acids, and small molecular weight natural products. Industrial biotechnologists have successfully harnessed and re-engineered the secretory capacity of dozens of filamentous fungal species to make a diverse portfolio of useful molecules. The study of fungal secretion outside fermenters, e.g., during host infection or in mixed microbial communities, has also led to the development of novel and emerging technological breakthroughs, ranging from ultra-sensitive biosensors of fungal disease to the efficient bioremediation of polluted environments. In this review, we consider filamentous fungal secretion across multiple disciplinary boundaries (e.g., white, green, and red biotechnology) and product classes (protein, organic acid, and secondary metabolite). We summarize the mechanistic understanding for how various molecules are secreted and present numerous applications for extracellular products. Additionally, we discuss how the control of secretory pathways and the polar growth of filamentous hyphae can be utilized in diverse settings, including industrial biotechnology, agriculture, and the clinic.

Antifungal natural products

Natural products are specialized small molecules produced in Nature and play pivotal roles in many cellular processes. These compounds possess exquisite chemical diversity and represent some of the most important pharmaceutical agents in human health care. With the rampant rise of fungal pathogens that are becoming resistant to nearly all clinically available antibiotics, there is an increased urgency to find new antifungal therapies with novel modes of action. To meet this need, we must be able to quickly identify new bioactive chemical scaffolds within complex natural extracts, determine their mechanisms of action, and generate appreciable yields for preclinical studies. In this review, we will highlight naturally derived antifungal agents of clinical importance as well as those with strong potential as leads in drug development.

Identification and characterization of enzymes involved in the biosynthesis of pyrimidine nucleoside antibiotics

Covering: up to September 2020 Hundreds of nucleoside-based natural products have been isolated from various microorganisms, several of which have been utilized in agriculture as pesticides and herbicides, in medicine as therapeutics for cancer and infectious disease, and as molecular probes to study biological processes. Natural products consisting of structural modifications of each of the canonical nucleosides have been discovered, ranging from simple modifications such as single-step alkylations or acylations to highly elaborate modifications that dramatically alter the nucleoside scaffold and require multiple enzyme-catalyzed reactions. A vast amount of genomic information has been uncovered the past two decades, which has subsequently allowed the first opportunity to interrogate the chemically intriguing enzymatic transformations for the latter type of modifications. This review highlights (i) the discovery and potential applications of structurally complex pyrimidine nucleoside antibiotics for which genetic information is known, (ii) the established reactions that convert the canonical pyrimidine into a new nucleoside scaffold, and (iii) the important tailoring reactions that impart further structural complexity to these molecules.