Compromising UDP-sugar nucleotide biosynthesis attenuates Candida albicans viability, virulence and drug sensitivity.

In certain niches, microbes encounter environmental challenges that are temporally linked. In such cases, microbial fitness is enhanced by the evolution of anticipatory responses where the initial challenge simultaneously activates pre-emptive protection against the second impending challenge. The accumulation of anticipatory responses in domesticated yeasts, which have been termed 'adaptive prediction', has led to the emergence of 'core stress responses' that provide stress cross-protection. Protective anticipatory responses also seem to be common in fungal pathogens of humans. These responses reflect the selective pressures that these fungi have faced relatively recently in their evolutionary history. Consequently, some pathogens have evolved 'core environmental responses' which exploit host signals to trigger immune evasion strategies that protect them against imminent immune attack.

The emergence of human immunodeficiency virus (HIV) in the 1980s has led to an increase in infections from previously rare pathogens. Many of these now cause widespread infection among individuals with compromised immune systems, not just limited to AIDS patients but also to those placed on immunosuppressive medication. The encapsulated yeast Cryptococcus neoformans causes widespread disease in the immunocompromised population, particularly in sub-Saharan Africa where it is a major cause of AIDS-related mortality due in part to limited resources and variable drug availability. Current treatment options are restricted to three out-dated antifungals amphotericin B, flucytosine and fluconazole; where possible they are used in combination as nephrotoxicity and resistance are contributing factors in the unacceptably high mortality rates. Alternative therapeutic agents are urgently required to improve survival rates and combat antifungal drug resistance. Two main routes of compound development can be taken: classical drug screening or rational drug design. Classical design requires groups of compounds to be screened against pathogens and those identified with high efficacy and low cytotoxicity are pursued. Rational drug design requires a detailed characterization of the proposed target; exploitable differences between the pathogen and human host are sought out as potential druggable targets. In this thesis both classical and rational methods have been investigated. A classical approach was taken to investigate a class of octapeptin compounds, produced as secondary metabolites by the soil dwelling bacterium, Bacillus circulans. Related compounds, such as the polymxyins, have become last resort drugs against gram-negative bacteria. The physiological target of poylmxyins against gram-negative bacteria is thought to be its charged cell wall surface. Like gram-negative bacteria C. neoformans also has a charged surface; comprised of a polysaccharide capsule and melanin. These features have been investigated as a potential target of octapeptin C4. The fungal pathogen C. neoformans is commonly associated with bird guano, a particularly purine rich environment. Investigation into novel antifungals targeting enzymes of the purine biosynthetic pathway has been limited. Gertrude Elion’s pivotal work in developing inhibitors of the de novo purine biosynthesis pathway in a rational manner successfully led to the development of anticancer agents still used today. To enable development of such compounds against fungal pathogens, enzymes from the de novo purine biosynthesis pathway have been characterized in C. neoformans. In this thesis GMP synthase and ADS lyase were be presented. Gene deletion and subsequent complementation of the genes encoding GMP synthase and ADS lyase was performed. The deletion mutants in both showed defects in the production of virulence traits as well as being avirulent in a murine inhalation model of infection. Recombinantly expressed and purified protein was obtained for enzyme kinetics assays and structural studies. These have enabled the first in-depth analysis of these enzymes in fungi for comparison to previously characterized human enzymes. Collectively, these data highlight the potential of enzymes of the purine biosynthesis pathway to be exploited in the development of new therapeutic agents for the treatment of disseminated, life threatening fungal infections.

Candida albicans is an opportunistic fungal pathogen that causes candidiasis in human hosts. Candidiasis includes a multitude of fungal infections, including invasive fungal infections, where most patients are immunocompromised; hence, the success of treatment is determined by the efficacy of the antifungal agent. However, with the increase in resistance to the existing drugs, the availability of effective antifungal agents is becoming scarce. Many pyrimidine derivatives exhibit powerful antifungal activity. In this study, In silico antifungal activity was carried out on twenty novel aminopyrimidine derivatives to identify the specificity of the pyrimidine analogues for the antifungal targets using ‘Glide’. Molecular docking studies were conducted on two antifungal targets; Dihydrofolate reductase of C. albicans (PDB ID: 4HOE); N-myristoyl transferase of C. albicans (PDB ID: 1IYK); energy minimization of title compounds was carried out using LigPrep, the protein targets were optimized and minimized, a 3-dimensional grid was generated at the active site, and molecular docking was carried out at both the standard precision (SP) and extra precision (XP) modes. The docking poses were ranked according to their docking scores (GScore) and their binding energy with the enzyme (Emodel). The obtained results for the docking of the title compounds with dihydrofolate reductase of C. albicans are quite promising. Molecular docking suggest that compounds 2N and 2A are potential inhibitors of dihyfrofolate reductase and are specific in binding at the active site of the enzyme. They form pi-pi stacking interactions with PHE 36 at the active site of the protein, similar to the standard drug. However the test compounds show lower docking scores against N-myristoyl transferase of C. albicans indicating that they may not be effective against the fungal protein.

Candida glabrata is an opportunistic human fungal pathogen causing infections due to its innate antifungal drug resistance and ability to adhere to mucocutaneous surfaces. Epigenetic pathways may be important factors in the development of drug resistance. Our previous studies showed that deubiquitination of H2B, regulated by a module comprised of Ubp8, Sgf11, Sgf73, and Sus1, plays important roles in oxidative stress tolerance and biofilm formation of C. glabrata. However, the roles of the Rad6 and Bre1 ligase in regulating the ubiquitination of H2B in C. glabrata remain unclear. We characterized the functions of Rad6 and Bre1 in C. glabrata by generating deletion mutants (rad6, bre1, and rad6 bre1). We analyzed biofilm formation, gene expression of key adhesins (EPA1, EPA6, EPA20) and protease (YPS4), antifungal drug susceptibility, stress responses, and virulence in a murine model of systemic candidiasis. Deletion of RAD6 and BRE1 resulted in enhanced biofilm formation, correlating with upregulation of key adhesin genes and the protease gene YPS4. The mutants showed distinct patterns of antifungal drug susceptibility: rad6 and rad6 bre1 mutants exhibited increased sensitivity to azoles, while bre1 mutant showed enhanced resistance to azoles in solid YPD agar plates but no significant difference in liquid RPMI medium. All mutants demonstrated decreased resistance to echinocandins and amphotericin B, associated with altered expression of ergosterol biosynthesis genes (ERG11) and glucan synthase genes (FKS1, FKS2). The mutants also displayed decreased resistance to oxidative and cell wall stresses despite elevated basal expression of antioxidant genes (SOD1, GPX2, CTA1). In a murine model of systemic candidiasis, both rad6 and bre1 mutants exhibited enhanced virulence compared to the wild type. Rad6 and Bre1 in C. glabrata function as negative regulators of biofilm formation and adhesion, and their related-genes expression, while RAD6 deletion also suppresses macrophage ROS production and enhances fungal survival. The enhanced virulence observed in the rad6 and bre1 mutants is primarily attributed to these combined effects of increased biofilm formation, enhanced adhesion capability, and macrophage immune evasion.

When grown in medium containing urea and nitrate, wild type Aspergillus nidulans possesses approximately 2-fold higher activities of four enzymes of the pentose phosphate pathway and 3-fold higher activity of glucose phosphate isomerase than when grown in medium containing urea. The activities of one enzyme of the pentose phosphate pathway and of three enzymes of the Embden-Meyerhof-Parnas pathway and of NADP-isocitrate dehydrogenase are either not affected, or only slightly affected, by the presence of nitrate during growth. The results obtained from mutants of the nitrate reduction pathway show that neither nitrate nor nitrite directly causes the increases in the activities of the four enzymes of the pentose phosphate pathway and glucose phosphate isomerase, that the increases in these activities do not depend upon the metabolism of nitrate and probably do not result from changes in the concentrations of either NADP+ or NADPH. The results suggest that the product of the nirA gene, which is the inducer of the enzymes of the nitrate reduction pathway, is responsible for bringing about the increases in the activities of the enzymes of the pentose phosphate pathway and glucose phosphate isomerase and that the state of activity of the product of the nirA gene for its stimulatory effect on the activities of the four pentose phosphate pathway enzymes and glucose phosphate isomerase is regulated in exactly the same way as is its state of activity for inducing the enzymes of the nitrate reduction pathway.

Antifungal therapeutics is confronted today with the challenge of drug resistance of most fungal germs to current antifungal drugs. Faced with this situation, the search for new and more efficient antifungal molecules that avoid the phenomenon of drug resistance becomes an urgent task. The design of new antifungal drugs acting on new biological targets and/or by innovative mechanisms of action is essential in the fight against fungal infections. Current advances in molecular biology have identified new targets for the development of new antifungal therapy. Several biological targets for the development of new antifungal agents are currently being explored. Amongst these, the most promising are BET (Bromodomain and Extra-Terminal) proteins, Homoserine transacetylase (HTA), mannan cell wall, Glycosylphosphatidylinositols (GPI) anchor biosynthesis, Histone deacetylases, Sphingolipid biosynthesis, D9 fatty acid desaturase and Chitin biosynthesis. This review summarizes the new biological targets and their inhibitors under development as potential new antifungal drugs.

l-2,4-diaminobutyric acid (DABA) aminotransferases can catalyze the formation of amines at the distal ω-position of substrates, and is the intial andrate-limiting enzyme in the biosynthesis pathway of the cytoprotecting molecule (S)-2-methyl-1,4,5,6-tetrahydro-4-pyrimidine carboxylic acid (ectoine). Although there is an industrial interest in the biosynthesis of ectoine, the DABA aminotransferases remain poorly characterized. Herein, we present the crystal structure of EctB (2.45Å), a DABA aminotransferase from Chromohalobactersalexigens DSM 3043, a well-studied organism with respect to osmoadaptation by ectoine biosynthesis. We investigate the enzyme's oligomeric state to show that EctB from C.salexigens is a tetramer of two functional dimers, and suggest conserved recognition sites for dimerization that also includes the characteristic gating loop that helps shape the active site of the neighboring monomer. Although ω-transaminases are known to have two binding pockets to accommodate for their dual substrate specificity, we herein provide the first description of two binding pockets in the active site that may account for the catalytic character of DABA aminotransferases. Furthermore, our biochemical data reveal that the EctB enzyme from C.salexigens is a thermostable, halotolerant enzyme with a broad pH tolerance which may be linked to its tetrameric state. Put together, this study creates a solid foundation for a deeper structural understanding of DABA aminotransferases and opening up for future downstream studies of EctB's catalytic character and its redesign as a better catalyst for ectoine biosynthesis. In summary, we believe that the EctB enzyme from C.salexigens can serve as a benchmark enzyme for characterization of DABA aminotransferases. DATABASE: Structural data are available in PDB database under the accession number 6RL5.

Lignan is the main medicinal component of Eucommia ulmoides, and lignin is involved in the defense of plants against diseases and insect pests.They are synthesized from coniferyl alcohol with the help of dirigent(DIR) and peroxidase(POD), respectively.In this study, transcriptome assembly of stems and leaves of E.ulmoides was performed, yielding 112 578 unigenes.Among them, 70 459 were annotated in seven databases.A total of 59 unigenes encodes 11 key enzymes in the biosynthesis pathways of lignin and lignin, of which 11 encode POD and 8 encode DIR.A total of 13 unigenes encoding transcription factors are involved in phenylpropanoid metabolism. Compared with leaves of E.ulmoides, 7 575 unigenes were more highly expressed in stems, of which 462 were involved in phenylpropanoid biosynthesis.Our results extend the public transcriptome dataset of E.ulmoides, which provide valuable information for the analysis of biosynthesis pathways of lignan and lignin in E.ulmoides and lay a foundation for further study on the functions and regulation mechanism of key enzymes in lignan and lignin biosynthesis pathways.

The calcineurin pathway is a critical signal transduction pathway in fungi that mediates growth, morphology, stress responses, and pathogenicity. The importance of the calcineurin pathway in fungal physiology creates an opportunity for the development of new antifungal therapies that target this critical signaling pathway. In this study, we examined the role of the zinc finger transcription factor Crz1 homolog (CrzA) in the physiology and pathogenicity of the opportunistic human fungal pathogen Aspergillus fumigatus. Genetic replacement of the crzA locus in A. fumigatus resulted in a strain with significant defects in conidial germination, polarized hyphal growth, cell wall structure, and asexual development that are similar to but with differences from defects seen in the A. fumigatus DeltacnaA (calcineurin A) strain. Like the DeltacnaA strain, the DeltacrzA strain was incapable of causing disease in an experimental persistently neutropenic inhalational murine model of invasive pulmonary aspergillosis. Our results suggest that CrzA is an important downstream effector of calcineurin that controls morphology in A. fumigatus, but additional downstream effectors that mediate calcineurin signal transduction are likely present in this opportunistic fungal pathogen. In addition, the importance of CrzA to the production of disease is critical, and thus CrzA is an attractive fungus-specific antifungal target for the treatment of invasive aspergillosis.

The exploring AI-generated pyrazalone derivatives as antifungal agents: Bringing together molecular docking and quantum chemical approaches.

Microbial interactions represent an understudied facet of human health and disease. In this study, the interactions that occur between Chlamydia trachomatis and the opportunistic fungal pathogen, Candida albicans were investigated. Candida albicans is a common component of the oral and vaginal microbiota responsible for thrush and vaginal yeast infections. Normally, Candida exist in the body as yeast. However, disruptions to the microbiota create conditions that allow expanded growth of Candida, conversion to the hyphal form, and tissue invasion. Previous studies have shown that a myriad of outcomes can occur when Candida albicans interacts with pathogenic bacteria. To determine if C. trachomatis physically interacts with C. albicans, we incubated chlamydial elementary bodies (EB) in medium alone or with C. albicans yeast or hyphal forms for 1 h. Following incubation, the samples were formaldehyde-fixed and processed for immunofluorescence assays using anti-chlamydial MOMP or anti- chlamydial LPS antibodies. Replicate samples were replenished with culture medium and incubated at 35°C for 0–120 h prior to fixation for immunofluorescence analysis or collection for EB infectivity assays. Data from this study indicates that both C. trachomatis serovar E and C. muridarum EB bind to C. albicans yeast and hyphal forms. This interaction was not blocked by pre-incubation of EB with the Candida cell wall components, mannan or β-glucans, suggesting that EB interact with a Candida cell wall protein or other structure. Bound EB remained attached to C. albicans for a minimum of 5 days (120 h). Infectivity assays demonstrated that EB bound to C. albicans are infectious immediately following binding (0h). However, once bound to C. albicans, EB infectivity decreased at a faster rate than EB in medium alone. At 6h post binding, 40% of EB incubated in medium alone remained infectious compared to only 16% of EB bound to C. albicans. Likewise, pre-incubation of EB with laminarin, a soluble preparation of β-glucan, alone or in combination with other fungal cell wall components significantly decreases chlamydial infectivity in HeLa cells. These data indicate that interactions between EB and C. albicans inhibit chlamydial infectivity, possibly by physically blocking EB interactions with host cell receptors.

To describe the constituent ratio of different kinds of antifungal agents as first choice in empirical or preemptive antifungal therapy for patients with hematological malignancies received chemotherapy or hematopoietic stem cell transplantation (HSCT). Between 2008 January and 2009 December, 367 patients received chemotherapy or HSCT from 15 medical centers in China were collected. The strategies of antifungal therapy and the first-choice antifungal agents were analyzed. Of them, 282(76.8%) patients received empirical antifungal therapy, 85(23.2%) preemptive therapy. The number of first choice antifungal agents were 55(15.0%) of fluconazole, 174(47.4%) of itraconazole, 39(10.6%) of voriconazole, 57(15.5%) of traditional/lipid formulation amphotericin B, 26(7.1%) of caspofungin, 7(1.9%) of micafungin, and 9(2.5%) of combination antifungal therapy respectively. Moreover, voriconazole and combination antifungal agents were more often selected for preemptive antifungal therapy, while the probabilities of itraconazole were the highest in both empirical and preemptive strategies. More patients undergoing HSCT were first given itraconazole or caspofungin for antifungal therapy, while amphotericin B, fluconazole and voriconazole were more administered in patients received chemotherapy. Caspofungin and combined antifungal agents were more often used for patients with secondary antifungal prophylaxis, while itraconazole was usually used for patients with no prophylaxis or primary antifungal prophylaxis. Empirical antifungal therapy was more administered in hematological malignancies patients received chemotherapy or HSCT. Itraconazole was the most commonly used agent for antifungal therapy followed by amphotericin, fluconazole, voriconazole and echinocandin agents.

GTP cyclohydrolase II catalyzes the conversion of GTP into a mixture of 2,5-diamino-6-ribosylamino-4(3H)-pyrimidinone 5'-phosphate (Compound 2), formate, and pyrophosphate. Moreover, GMP was recently shown to be formed as a minor product. The major product (Compound 2) serves as the first committed intermediate in the biosynthesis of the vitamin, riboflavin. Numerous pathogenic microorganisms are absolutely dependent on endogenous synthesis of riboflavin. The enzymes of this pathway are therefore potential drug targets, and mechanistic studies appear relevant for development of bactericidal inhibitors. Pre-steady state quenched flow analysis of GTP cyclohydrolase II shows the rate-determining step to be located at the beginning of the reaction sequence catalyzed by the enzyme. Thus, GTP is consumed at a rate constant of 0.064 s(-1), and the reaction product, Compound 2, is formed at an apparent rate constant of 0.062 s(-1). Stopped flow experiments monitored by multiwavelength photometry are well in line with these data. 2-Amino-5-formylamino-6-ribosylamino-4(3H)-pyrimidinone triphosphate can serve as substrate for GTP cyclohydrolase II but does not fulfill the criteria for a kinetically competent intermediate. A hypothetical reaction mechanism involves the slow formation of a phosphoguanosyl derivative of the enzyme under release of pyrophosphate. The covalently bound phosphoguanosyl moiety is proposed to undergo rapid hydrolytic release of formate from the imidazole ring and/or hydrolytic cleavage of the phosphodiester bond.

The incidence of opportunistic invasive fungal infections (IFIs) is on the rise, largely driven by the growing number of immunocompromised patients who are at high risk of contracting fungal infections. Patients with haematological malignancies and lung transplantation are particularly vulnerable to IFIs caused by moulds, with Aspergillus species being the predominant fungal pathogen. At the same time, the less well-known moulds such as members of the Scedosporium genera are an emerging cause of IFIs. To date, the management of IFIs in immunocompromised patients remains to be optimised from the aspects of diagnostics, therapeutic antifungal drug monitoring and pharmacoeconomics of antifungal therapy. This thesis aimed to derive critical data to improve the clinical management of IFIs in immunocompromised patients. Specifically, the work in this thesis addresses: the utility of newer diagnostic platforms i.e. Aspergillus galactomannan (GM) and polymerase chain reaction (PCR) assays in haematology patients, voriconazole concentrations in lung transplant recipients, and the pharmacoeconomic of antifungal prophylaxis and invasive scedosporiosis in the haematology population. Non-culture-based diagnostic tests may assist the diagnosis of invasive aspergillosis and guide directed antifungal therapy. However, the clinical utility of Aspergillus GM antigen and Aspergillus genome when tested on bronchoalveolar lavage (BAL) fluid of patients with haematological malignancies remains uncertain. A systematic review and meta-analysis evaluating the diagnostic performance of BAL GM assay in haematology patients was performed. Results from the meta-analysis confirmed the usefulness of GM quantification in BAL fluid for the diagnosis of invasive aspergillosis, yielding a sensitivity, specificity, positive likelihood ratio and negative likelihood ratio of 92%, 98%, 53.7 and 0.08, respectively, at the index cutoff value of 1.5. Combining BAL GM with serum GM or PCR led to a marginal increase in overall sensitivity. Test specificity was significantly decreased by administration of a β-lactam antibiotic at the time of BAL, but sensitivity was not significantly reduced by receipt of mould-active antifungal agents. Many of the previous studies (included in the meta-analysis aforementioned) evaluating the diagnostic accuracy of BAL GM or PCR have restricted study population or bias, which could affect the test performance estimated. As such, to assess the utility of BAL GM and PCR for the diagnosis of invasive pulmonary aspergillosis in routine clinical practice, a multicentre retrospective study involving high-risk haematology patients undergoing BAL was conducted. Our data showed that, in this unselected group of haematology patients in receipt of mould-active antifungal agents and β-lactam antibiotic, BAL GM had lower sensitivity than PCR (61% versus 78%) at an index cutoff of 0.8, but the specificity was higher (93% versus 81%). The optimal OD index cutoff for BAL GM determined in this observational study was lower than that in the aforementioned meta-analysis, probably related to the case-mix of haematology patients, use of therapeutic agents, and BAL protocol. Similar to the findings in our meta-analysis, the sensitivity of both tests was not significantly decreased by administration of mould-active antifungal agent, and the detection rate of invasive pulmonary aspergillosis was not improved by a combination of BAL GM and PCR diagnostic modalities. The thesis also investigated the relationship between trough plasma and pulmonary epithelial lining fluid (ELF) concentrations of voriconazole in lung transplant recipients, with the intention of exploring if plasma voriconazole concentration can be used as a surrogate for the corresponding concentration in ELF. A high-performance liquid chromatographic fluorescence detection method was developed and validated to facilitate measurement of voriconazole concentration in human BAL fluid; a modification of the method was used to quantify voriconazole in plasma. Simultaneous trough concentrations of voriconazole in plasma and ELF (the latter determined from BAL concentration) of 12 lung transplant recipients were determined in a prospective pilot study. Voriconazole achieved consistently higher concentration in the ELF than plasma (mean ± SD ELF:plasma ratio = 12.5 ± 6.3). A strong positive linear relationship between trough plasma and ELF voriconazole concentrations was observed (r2=0.868), which can be described by the equation [VRC]ELF=15.4*[VRC]plasma–1.16, where [VRC]ELF is the voriconazole concentration in ELF and [VRC]plasma is the plasma voriconazole concentration. Findings from this preliminary study suggested the potential for using trough plasma voriconazole concentration as a surrogate for the corresponding concentration in ELF. Another major work of this thesis focuses on the pharmacoeconomics of managing IFIs in the haematology population. Antifungal therapy has a large impact on health resource utilisation and there is currently a paucity of data to guide the selection of antifungal agent for prophylactic use in patients undergoing consolidation chemotherapy for acute myeloid leukaemia. Hence, a pharmacoeconomic evaluation comparing fluconazole, posaconazole and voriconazole prophylaxis was conducted, using retrospective data collected from medical records and cost inputs obtained from Australian databases. The decision-analytical modelling was performed from the perspective of Australian public hospitals. Fluconazole prophylaxis was the most cost-effective approach, with a mean per-patient cost saving of AU$8430 (95% CI AU$5803–AU$11 054) versus posaconazole, and AU$3681 (95% CI AU$990–AU$6319) versus voriconazole. The robustness of the model was confirmed in one-way sensitivity analyses. Little is known about the costs of treating scedosporiosis despite its increasing importance. A multicentre retrospective case-control study was undertaken. Case patients with scedosporiosis were matched (1:2) to controls. Median regression modelling was used to adjust for variables that were not accounted for in the matched-pairs analysis. Invasive scedosporiosis was shown to impose substantial impact on the hospital resources at an adjusted median excess cost of AU$23611, increased median duration of hospitalisation by 13 days and result in a 38-fold elevation in the mortality rate in haematology patients. This is the first report of the attributable economic and clinical outcomes of invasive scedosporiosis in patients with haematological malignancies. In conclusion, this thesis has explored several critical aspects related to the management of IFIs in immunocompromised patients. Importantly, the data generated will assist healthcare providers such as clinicians and pharmacists in moving towards enhanced utilisation of newer fungal diagnostics and antifungal therapy to manage IFIs.

Invasive fungal infections cause significant morbidity and mortality in part due to a limited antifungal drug arsenal. One therapeutic challenge faced by clinicians is the significant host toxicity associated with antifungal drugs. Another challenge is the fungistatic mechanism of action of some drugs. Consequently, the identification of fungus-specific drug targets essential for fitness in vivo remains a significant goal of medical mycology research. The trehalose biosynthetic pathway is found in a wide variety of organisms, including human-pathogenic fungi, but not in humans. Genes encoding proteins involved in trehalose biosynthesis are mechanistically linked to the metabolism, cell wall homeostasis, stress responses, and virulence of Candida albicans, Cryptococcus neoformans, and Aspergillus fumigatus. While there are a number of pathways for trehalose production across the tree of life, the TPS/TPP (trehalose-6-phosphate synthase/trehalose-6-phosphate phosphatase) pathway is the canonical pathway found in human-pathogenic fungi. Importantly, data suggest that proteins involved in trehalose biosynthesis play other critical roles in fungal metabolism and in vivo fitness that remain to be fully elucidated. By further defining the biology and functions of trehalose and its biosynthetic pathway components in pathogenic fungi, an opportunity exists to leverage this pathway as a potent antifungal drug target. The goal of this review is to cover the known roles of this important molecule and its associated biosynthesis-encoding genes in the human-pathogenic fungi studied to date and to employ these data to critically assess the opportunities and challenges facing development of this pathway as a therapeutic target.