Secretion of cryptococcal phospholipase B1 (PLB1) is regulated by a glycosylphosphatidylinositol (GPI) anchor

Reveal key genes and factors affecting athletes performance in endurance sports using bioinformatic technologies

Medium-intensity activities comprise the major proportion of many sorts of sports. The energy consumption of athletes has been a research emphasis for the purpose of improving both training efficiency and competition performance. However, the evidence based on large-scale gene screen has been rarely performed. This is a bioinformatic study revealing the key factors contributed to the metabolic difference between subjects with different endurance activity capacities. A dataset comprised of high- (HCR) and low-capacity running (LCR) rats was used. Differentially expressed genes (DEGs) were identified and analysed. The Gene Ontology (GO) and Kyoto Encyclopaedia of Genes and Genomes (KEGG) pathway enrichment was obtained. The DEGs' protein-protein interaction (PPI) network was built, and the enriched terms of the PPI network were also analysed. Our findings showed that the GO terms were enriched in lipid metabolism-related terms. The KEGG signalling pathway analysis enriched in the ether lipid metabolism. Plb1, Acad1, Cd2bp2, and Pla2g7 were identified as the hub genes. This study provides a theoretical foundation showing lipid metabolism plays an important role in the performance of endurance activities. Plb1, Acad1, and Pla2g7 may be the key genes involved. The training plan and diet for athletes can be designed based on above results and expecting a better competitive performance.

Phospholipase B Is Critical for Cryptococcus neoformans Survival in the Central Nervous System

Cryptococcus neoformans (Cn) is an opportunistic, encapsulated, yeast-like fungus that causes severe meningoencephalitis, especially in countries with high HIV prevalence. In addition to its well-known polysaccharide capsule, Cn has other virulence factors such as phospholipases, a heterogeneous group of enzymes that hydrolyze ester linkages in glycerophospholipids. Phospholipase B (PLB1) has been demonstrated to play a key role in Cn pathogenicity. In this study, we used a PLB1 mutant (plb1) and its reconstituted strain (Rec1) to assess the importance of this enzyme on Cn brain infection in vivo and in vitro. Mice infected with the plb1 strain survive significantly longer, have lower peripheral and central nervous system (CNS) fungal loads, and have fewer and smaller cryptococcomas or biofilm-like brain lesions compared to H99- and Rec1-infected animals. PLB1 causes extensive brain tissue damage and changes microglia morphology during cryptococcal disease, observations which can have important implications in patients with altered mental status or dementia as these manifestations are related to poorer survival outcomes. plb1 cryptococci are significantly more phagocytosed and killed by NR-9460 microglia-like cells. plb1 cells have altered capsular polysaccharide biophysical properties which impair their ability to stimulate glial cell responses or morphological changes. Here, we provide significant evidence demonstrating that Cn PLB1 is an important virulence factor for fungal colonization of and survival in the CNS as well as in the progression of cryptococcal meningoencephalitis. These findings may potentially help fill in a gap of knowledge in our understanding of cerebral cryptococcosis and provide novel research avenues in Cn pathogenesis. IMPORTANCE Cryptococcal meningoencephalitis (CME) is a serious disease caused by infection by the neurotropic fungal pathogen Cryptococcus neoformans. Due to the increasing number of cases in HIV-infected individuals, as well as the limited therapies available, investigation into potential targets for new therapeutics has become critical. Phospholipase B is an enzyme synthesized by Cn that confers virulence to the fungus through capsular enlargement, immunomodulation, and intracellular replication. In this study, we examined the properties of PLB1 by comparing infection of a Cn PLB1 mutant strain with both the wild-type and a PLB1-reconstituted strain. We show that PLB1 augments the survival and proliferation of the fungus in the CNS and strengthens virulence by modulating the immune response and enhancing specific biophysical properties of the fungus. PLB1 expression causes brain tissue damage and impacts glial cell functions, which may be responsible for the dementia observed in patients which may persist even after resolving from CME. The implications of PLB1 inhibition reveal its involvement in Cn infection and suggest that it may be a possible molecular target in the development of antifungal therapies. The results of this study support additional investigation into the mechanism of PLB1 to further understand the intricacies of cerebral Cn infection.

pH-Dependent Expression, Stability, and Activity of Malassezia restricta MrLip5 Lipase

Background

The lipophilic yeasts Malassezia spp. are normally resident on the surface of the human body, and often associated with various skin diseases. Of the 18 known Malassezia spp., Malassezia restricta is the most predominantly identified Malassezia sp. found on the human skin. Malassezia possesses a large number of genes encoding lipases to degrade human sebum triglycerides into fatty acids, which are required not only for their growth, but also trigger skin diseases. Previously, we have shown that MrLIP5 (MRET_0930), one of the 12 lipase genes in the genome of M. restricta, and is the most frequently expressed lipase gene in the scalp of patients with dandruff.

Objective

In this study, we aimed to analyze the activity, stability, and expression of MrLip5, with particular focus on pH.

Methods

We heterologously expressed MrLip5 in Escherichia coli, and purified and analyzed its activity and expression under different pH conditions.

Results

We found that MrLip5 was most active and stable and highly expressed under alkaline conditions, which is similar to that of the diseased skin surface.

Conclusion

Our results suggest that the activity and expression of MrLip5 are pH-dependent, and that this lipase may play an essential role at the M. restricta-host interface during disease progression.

Calcium Binding Protein Ncs1 Is Calcineurin Regulated in Cryptococcus neoformans and Essential for Cell Division and Virulence

Intracellular calcium (Ca2+) is crucial for signal transduction in Cryptococcus neoformans, the major cause of fatal fungal meningitis. The calcineurin pathway is the only Ca2+-requiring signaling cascade implicated in cryptococcal stress adaptation and virulence, with Ca2+ binding mediated by the EF-hand domains of the Ca2+ sensor protein calmodulin. In this study, we identified the cryptococcal ortholog of neuronal calcium sensor 1 (Ncs1) as a member of the EF-hand superfamily. We demonstrated that Ncs1 has a role in Ca2+ homeostasis under stress and nonstress conditions, as the ncs1Δ mutant is sensitive to a high Ca2+ concentration and has an elevated basal Ca2+ level. Furthermore, NCS1 expression is induced by Ca2+, with the Ncs1 protein adopting a punctate subcellular distribution. We also demonstrate that, in contrast to the case with Saccharomyces cerevisiae, NCS1 expression in C. neoformans is regulated by the calcineurin pathway via the transcription factor Crz1, as NCS1 expression is reduced by FK506 treatment and CRZ1 deletion. Moreover, the ncs1Δ mutant shares a high temperature and high Ca2+ sensitivity phenotype with the calcineurin and calmodulin mutants (cna1Δ and cam1Δ), and the NCS1 promoter contains two calcineurin/Crz1-dependent response elements (CDRE1). Ncs1 deficiency coincided with reduced growth, characterized by delayed bud emergence and aberrant cell division, and hypovirulence in a mouse infection model. In summary, our data show that Ncs1 has a significant role as a Ca2+ sensor in C. neoformans, working with calcineurin to regulate Ca2+ homeostasis and, consequently, promote fungal growth and virulence.IMPORTANCECryptococcus neoformans is the major cause of fungal meningitis in HIV-infected patients. Several studies have highlighted the important contributions of Ca2+ signaling and homeostasis to the virulence of C. neoformans Here, we identify the cryptococcal ortholog of neuronal calcium sensor 1 (Ncs1) and demonstrate its role in Ca2+ homeostasis, bud emergence, cell cycle progression, and virulence. We also show that Ncs1 function is regulated by the calcineurin/Crz1 signaling cascade. Our work provides evidence of a link between Ca2+ homeostasis and cell cycle progression in C. neoformans.

Role of clathrin-mediated endocytosis in the use of heme and hemoglobin by the fungal pathogen Cryptococcus neoformans

Heme is a major source of iron for pathogens of humans, and its use is critical in determining the outcome of infection and disease. Cryptococcus neoformans is an encapsulated fungal pathogen that causes life-threatening infections in immunocompromised individuals. C. neoformans effectively uses heme as an iron source, but the underlying mechanisms are poorly defined. Non-iron metalloporphyrins (MPPs) are toxic analogues of heme and are thought to enter microbial cells via endogenous heme acquisition systems. We therefore carried out a mutant screen for susceptibility against manganese MPP (MnMPP) to identify new components for heme uptake in C. neoformans. We identified several genes involved in signalling, DNA repair, sugar metabolism, and trafficking that play important roles in susceptibility to MnMPP and in the use of heme as an iron source. We focused on investigating the role of clathrin-mediated endocytosis (CME) and found that several components of CME including Chc1, Las17, Rvs161, and Rvs167 are required for growth on heme and hemoglobin and for endocytosis and intracellular trafficking of these molecules. We show that the hemoglobin uptake process in C. neoformans involves clathrin heavy chain, Chc1, which appears to colocalise with hemoglobin-containing vesicles and to potentially assist in proper delivery of hemoglobin to the vacuole. Additionally, C. neoformans strains lacking Chc1, Las17, Rvs161, or Rvs167 were defective in the elaboration of several key virulence factors, and a las17 mutant was avirulent in a mouse model of cryptococcosis. Overall, this study unveils crucial functions of CME in the use of heme iron by C. neoformans and reveals a role for CME in fungal pathogenesis.

Understanding the Mechanism of Action of the Anti-Dandruff Agent Zinc Pyrithione against Malassezia restricta

Dandruff is known to be associated with Malassezia restricta. Zinc pyrithione (ZPT) has been used as an ingredient in anti-dandruff treatments. The mechanism of ZPT has been investigated in several studies; however, a non-pathogenic model yeast, such as Saccharomyces cerevisiae was most often used. The aim of the present study was to understand how ZPT inhibits the growth of M. restricta. We analyzed the cellular metal content and transcriptome profile of ZPT-treated M. restricta cells and found that ZPT treatment dramatically increased cellular zinc levels, along with a small increase in cellular copper levels. Moreover, our transcriptome analysis showed that ZPT inhibits Fe-S cluster synthesis in M. restricta. We also observed that ZPT treatment significantly reduced the expression of lipases, whose activities contribute to the survival and virulence of M. restricta on human skin. Therefore, the results of our study suggest that at least three inhibitory mechanisms are associated with the action of ZPT against M. restricta: (i) an increase in cellular zinc levels, (ii) inhibition of mitochondrial function, and (iii) a decrease in lipase expression.

Cryptococcal Traits Mediating Adherence to Biotic and Abiotic Surfaces

Several species in the genus Cryptococcus are facultative intracellular pathogens capable of causing disease associated with high mortality and morbidity in humans. These fungi interact with other organisms in the soil, and these interactions may contribute to the development of adaptation mechanisms that function in virulence by promoting fungal survival in animal hosts. Fungal adhesion molecules, also known as adhesins, have been classically considered as cell-surface or secreted proteins that play critical roles in microbial pathogenesis or in biofilm formation as structural components. Pathogenic Cryptococcus spp. differ from other pathogenic yeasts in having a polysaccharide capsule that covers the cell wall surface and precludes interactions of those structures with host cell receptors. Hence, pathogenic Cryptococcus spp. use unconventional tools for surface attachment. In this essay, we review the unique traits and mechanisms favoring adhesion of Cryptococcus spp. to biotic and abiotic surfaces. Knowledge of the traits that mediate adherence could be exploited in the development of therapeutic, biomedical, and/or industrial products.

In vitro synthesis of phospholipids with yeast phospholipase B, a phospholipid deacylating enzyme

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Saccharomyces cerevisiae PLB enzyme was expressed in E. coli.

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Purified Scplb1p exhibited deacylation activity.

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Purified Scplb1p transacylated LPC to PC and esterified LPC with FFA.

The gene encoding the Saccharomyces cerevisiae phospholipid deacylation enzyme, phospholipase B (ScPLB1), was successfully expressed in E. coli. The enzyme (Scplb1p) was engineered to have a histidine-tag at the C-terminal end and was purified by metal (Ni) affinity chromatography. Enzymatic properties, optimal pH, and substrate specificity were similar to those reported previously. For example, deacylation activity was observed in acidic pH in the absence of Ca²⁺ and was additive in neutral pH in the presence of Ca²⁺, and the enzyme had the same substrate priority as reported previously, with the exception of PE, suggesting that yeast phospholipase B could be produced in its native structure in bacterial cells. Scplb1p retained transacylation activity in aqueous medium, and esterified lysophosphatidylcholine with free fatty acid to form phosphatidylcholine in a non-aqueous, glycerin medium. We propose that phospholipase B could serve as an additional tool for in vitro enzyme-mediated phospholipid synthesis.

The putative flippase Apt1 is required for intracellular membrane architecture and biosynthesis of polysaccharide and lipids in Cryptococcus neoformans

Flippases are responsible for the asymmetric distribution of phospholipids in biological membranes. In the encapsulated fungal pathogen Cryptococcus neoformans, the putative flippase Apt1 is an important regulator of polysaccharide secretion and pathogenesis in mice by unknown mechanisms. In this study, we analyzed the role of C. neoformans Apt1 in intracellular membrane architecture and synthesis of polysaccharide and lipids. Analysis of wild type (WT), apt1Δ (mutant) and apt1Δ::APT1 (complemented) strains by transmission electron microscopy revealed that deletion of APT1 resulted in the formation of irregular vacuoles. Disorganization of vacuolar membranes in apt1Δ cells was accompanied by a significant increase in the amounts of intra-vacuolar and pigment-containing vesicles. Quantitative immunogold labeling of C. neoformans cells with a monoclonal antibody raised to a major capsular component suggested impaired polysaccharide synthesis. APT1 deletion also affected synthesis of phosphatidylserine, phosphatidylethanolamine, inositolphosphoryl ceramide, glucosylceramide and ergosterylglycoside. These results reveal novel functions of Apt1 and are in agreement with the notion that this putative flippase plays an important role in the physiology of C. neoformans.

Titan cell production in Cryptococcus neoformans reshapes the cell wall and capsule composition during infection

Cryptococcus neoformans is a human fungal pathogen that often causes infections in immunocompromised individuals. Upon inhalation into the lungs C. neoformans differentiates into cells with altered size and morphology, including production of large titan cells. Titan cells possess thickened cell wall and dense, cross-linked capsule when compared to in vitro grown cells. In addition, titan cells have increased cell wall chitin that is associated with a detrimental anti-inflammatory immune response. Here we examined the cell wall and capsule composition of in vitro, in vivo typical-sized and in vivo titan cells using High Performance Liquid Chromatography (HPLC). The monomer composition of cell wall polysaccharides showed that in vivo C. neoformans cells contained more glucosamine and less glucose than in vitro cells, suggesting alteration in abundance of both chitin and glucans, respectively. Low levels of galactosamine were also detected in carbohydrates from both in vivo and vitro cells. Within the in vivo cell population, differences in the proportions of cell wall and capsule monomers between typical and titan cells were also observed. Taken together, these results demonstrate that C. neoformans reshapes its cell wall and capsule composition during infection. These cell wall and capsule alterations likely help C. neoformans escape recognition by, and allow modulation of, the host immune system.

IP3-4 kinase Arg1 regulates cell wall homeostasis and surface architecture to promote clearance of Cryptococcus neoformans infection in a mouse model

We previously identified a series of inositol polyphosphate kinases (IPKs), Arg1, Ipk1, Kcs1 and Asp1, in the opportunistic fungal pathogen Cryptococcus neoformans. Using gene deletion analysis, we characterized Arg1, Ipk1 and Kcs1 and showed that they act sequentially to convert IP₃ to PP-IP₅ (IP₇), a key metabolite promoting stress tolerance, metabolic adaptation and fungal dissemination to the brain. We have now directly characterized the enzymatic activity of Arg1, demonstrating that it is a dual specificity (IP₃/IP₄) kinase producing IP₅. We showed previously that IP₅ is further phosphorylated by Ipk1 to produce IP₆, which is a substrate for the synthesis of PP-IP₅ by Kcs1. Phenotypic comparison of the arg1Δ and kcs1Δ deletion mutants (both PP-IP₅-deficient) reveals that arg1Δ has the most deleterious phenotype: while PP-IP₅ is essential for metabolic and stress adaptation in both mutant strains, PP-IP₅ is dispensable for virulence-associated functions such as capsule production, cell wall organization, and normal N-linked mannosylation of the virulence factor, phospholipase B1, as these phenotypes were defective only in arg1Δ. The more deleterious arg1Δ phenotype correlated with a higher rate of arg1Δ phagocytosis by human peripheral blood monocytes and rapid arg1Δ clearance from lung in a mouse model. This observation is in contrast to kcs1Δ, which we previously reported establishes a chronic, confined lung infection. In summary, we show that Arg1 is the most crucial IPK for cryptococcal virulence, conveying PP-IP₅-dependent and novel PP-IP₅-independent functions.

A P4-ATPase subunit of the Cdc50 family plays a role in iron acquisition and virulence in Cryptococcus neoformans

The pathogenic fungus Cryptococcus neoformans delivers virulence factors such as capsule polysaccharide to the cell surface to cause disease in vertebrate hosts. In this study, we screened for mutants sensitive to the secretion inhibitor brefeldin A to identify secretory pathway components that contribute to virulence. We identified an ortholog of the cell division control protein 50 (Cdc50) family of the noncatalytic subunit of type IV P-type ATPases (flippases) that establish phospholipid asymmetry in membranes and function in vesicle-mediated trafficking. We found that a cdc50 mutant in C. neoformans was defective for survival in macrophages, attenuated for virulence in mice and impaired in iron acquisition. The mutant also showed increased sensitivity to drugs associated with phospholipid metabolism (cinnamycin and miltefosine), the antifungal drug fluconazole and curcumin, an iron chelator that accumulates in the endoplasmic reticulum. Cdc50 is expected to function with catalytic subunits of flippases, and we previously documented the involvement of the flippase aminophospholipid translocases (Apt1) in virulence factor delivery. A comparison of phenotypes with mutants defective in genes encoding candidate flippases (designated APT1, APT2, APT3, and APT4) revealed similarities primarily between cdc50 and apt1 suggesting a potential functional interaction. Overall, these results highlight the importance of membrane composition and homeostasis for the ability of C. neoformans to cause disease.

High-Resolution Genetics Identifies the Lipid Transfer Protein Sec14p as Target for Antifungal Ergolines

Invasive infections by fungal pathogens cause more deaths than malaria worldwide. We found the ergoline compound NGx04 in an antifungal screen, with selectivity over mammalian cells. High-resolution chemogenomics identified the lipid transfer protein Sec14p as the target of NGx04 and compound-resistant mutations in Sec14p define compound-target interactions in the substrate binding pocket of the protein. Beyond its essential lipid transfer function in a variety of pathogenic fungi, Sec14p is also involved in secretion of virulence determinants essential for the pathogenicity of fungi such as Cryptococcus neoformans, making Sec14p an attractive antifungal target. Consistent with this dual function, we demonstrate that NGx04 inhibits the growth of two clinical isolates of C. neoformans and that NGx04-related compounds have equal and even higher potency against C. neoformans. Furthermore NGx04 analogues showed fungicidal activity against a fluconazole resistant C. neoformans strain. In summary, we present genetic evidence that NGx04 inhibits fungal Sec14p and initial data supporting NGx04 as a novel antifungal starting point.

Emerging resistance to antibiotics led to an inglorious revival of infectious diseases. Furthermore, in the past 30 years, only one novel anti-fungal target has been discovered which was used to develop therapies against. Therefore pathogen-selective targets and knowledge about possible resistance determinants are of utmost importance to successfully develop new medicines. Here we describe the identification of anti-fungal ergolines, targeting the lipid transfer protein Sec14p, and inhibiting the growth of two clinical isolates of the pathogenic fungus Cryptococcus neoformans. Both, compound and target represent attractive points for further investigations: Sec14p as it differs significantly from the human homolog and as it has been implicated in fungal viability and pathogenicity, and, ergolines as they are used in the clinic against a variety of diseases demonstrating both efficacy and safety.

Extracellular vesicles from Paracoccidioides brasiliensis induced M1 polarization in vitro

Extracellular vesicles (EVs) released by eukaryotes, archaea, and bacteria contain proteins, lipids, polysaccharides, and other molecules. The cargo analysis of EVs shows that they contain virulence factors suggesting a role in the pathogenesis of infection. The proteome, lipidome, RNA content, and carbohydrate composition of EVs from Paracoccidioides brasiliensis and Paracoccidioides lutzii were characterized. However, the effects of P. brasiliensis EVs on the host immune system have not yet been investigated. Herein, we verified that EVs from P. brasiliensis induce the production of proinflammatory mediators by murine macrophages in a dose-dependent manner. Addition of EV to macrophages also promoted transcription of the M1-polarization marker iNOs and diminish that of the M2 markers Arginase-1, Ym-1, and FIZZ-1. Furthermore, the augmented expression of M2-polarization markers, stimulated by IL-4 plus IL-10, was reverted toward an M1 phenotype in response to secondary stimulation with EVs from P. brasiliensis. The ability of EVs from P. brasiliensis to promote M1 polarization macrophages favoring an enhanced fungicidal activity, demonstrated by the decreased CFU recovery of internalized yeasts, with comparable phagocytic efficacy. Our results suggest that EVs from P. brasiliensis can modulate the innate immune response and affect the relationship between P. brasiliensis and host immune cells.

All about that fat: Lipid modification of proteins in Cryptococcus neoformans

Lipid modification of proteins is a widespread, essential process whereby fatty acids, cholesterol, isoprenoids, phospholipids, or glycosylphospholipids are attached to polypeptides. These hydrophobic groups may affect protein structure, function, localization, and/or stability; as a consequence such modifications play critical regulatory roles in cellular systems. Recent advances in chemical biology and proteomics have allowed the profiling of modified proteins, enabling dissection of the functional consequences of lipid addition. The enzymes that mediate lipid modification are specific for both the lipid and protein substrates, and are conserved from fungi to humans. In this article we review these enzymes, their substrates, and the processes involved in eukaryotic lipid modification of proteins. We further focus on its occurrence in the fungal pathogen Cryptococcus neoformans, highlighting unique features that are both relevant for the biology of the organism and potentially important in the search for new therapies.

Cryptococcus and Phagocytes: Complex Interactions that Influence Disease Outcome

Cryptococcus neoformans and C. gattii are fungal pathogens that cause life-threatening disease. These fungi commonly enter their host via inhalation into the lungs where they encounter resident phagocytes, including macrophages and dendritic cells, whose response has a pronounced impact on the outcome of disease. Cryptococcus has complex interactions with the resident and infiltrating innate immune cells that, ideally, result in destruction of the yeast. These phagocytic cells have pattern recognition receptors that allow recognition of specific cryptococcal cell wall and capsule components. However, Cryptococcus possesses several virulence factors including a polysaccharide capsule, melanin production and secretion of various enzymes that aid in evasion of the immune system or enhance its ability to thrive within the phagocyte. This review focuses on the intricate interactions between the cryptococci and innate phagocytic cells including discussion of manipulation and evasion strategies used by Cryptococcus, anti-cryptococcal responses by the phagocytes and approaches for targeting phagocytes for the development of novel immunotherapeutics.

Fungal Inositol Pyrophosphate IP7 Is Crucial for Metabolic Adaptation to the Host Environment and Pathogenicity

Inositol pyrophosphates (PP-IPs) comprising inositol, phosphate, and pyrophosphate (PP) are essential for multiple functions in eukaryotes. Their role in fungal pathogens has never been addressed. Cryptococcus neoformans is a model pathogenic fungus causing life-threatening meningoencephalitis. We investigate the cryptococcal kinases responsible for the production of PP-IPs (IP₇/IP₈) and the hierarchy of PP-IP importance in pathogenicity. Using gene deletion and inositol polyphosphate profiling, we identified Kcs1 as the major IP₆ kinase (producing IP₇) and Asp1 as an IP₇ kinase (producing IP₈). We show that Kcs1-derived IP₇ is the most crucial PP-IP for cryptococcal drug susceptibility and the production of virulence determinants. In particular, Kcs1 kinase activity is essential for cryptococcal infection of mouse lungs, as reduced fungal burdens were observed in the absence of Kcs1 or when Kcs1 was catalytically inactive. Transcriptome and carbon source utilization analysis suggested that compromised growth of the KCS1 deletion strain (Δkcs1 mutant) in the low-glucose environment of the host lung is due to its inability to utilize alternative carbon sources. Despite this metabolic defect, the Δkcs1 mutant established persistent, low-level asymptomatic pulmonary infection but failed to elicit a strong immune response in vivo and in vitro and was not readily phagocytosed by primary or immortalized monocytes. Reduced recognition of the Δkcs1 cells by monocytes correlated with reduced exposure of mannoproteins on the Δkcs1 mutant cell surface. We conclude that IP₇ is essential for fungal metabolic adaptation to the host environment, immune recognition, and pathogenicity.

Cryptococcus neoformans is responsible for 1 million cases of AIDS-associated meningitis and ~600,000 deaths annually. Understanding cellular pathways responsible for pathogenicity might have an impact on new drug development. We characterized the inositol polyphosphate kinases Kcs1 and Asp1, which are predicted to catalyze the production of inositol pyrophosphates containing one or two diphosphate moieties (PP-IPs). Using gene deletion analysis and inositol polyphosphate profiling, we confirmed that Kcs1 and Asp1 are major IP₆ and IP₇ kinases, respectively. Kcs1-derived IP₇, but not Asp1-derived IP₈, is crucial for pathogenicity. Global expression profiling and carbon source utilization testing suggest that IP₇-deficient cryptococci cannot adapt their metabolism to allow growth in the glucose-poor environment of the host lung, and consequently, fungal burdens are significantly reduced. Persistent asymptomatic Δkcs1 mutant infection correlated with decreased mannoprotein exposure on the Δkcs1 mutant surface and reduced phagocytosis. We conclude that IP₇ is crucial for the metabolic adaptation of C. neoformans to the host environment and for pathogenicity.

Cryptococcal phospholipase B1 is required for intracellular proliferation and control of titan cell morphology during macrophage infection

Cryptococcus neoformans is an opportunistic fungal pathogen and a leading cause of fungal-infection-related fatalities, especially in immunocompromised hosts. Several virulence factors are known to play a major role in the pathogenesis of cryptococcal infections, including the enzyme phospholipase B1 (Plb1). Compared to other well-studied Cryptococcus neoformans virulence factors such as the polysaccharide capsule and melanin production, very little is known about the contribution of Plb1 to cryptococcal virulence. Phospholipase B1 is a phospholipid-modifying enzyme that has been implicated in multiple stages of cryptococcal pathogenesis, including initiation and persistence of pulmonary infection and dissemination to the central nervous system, but the underlying reason for these phenotypes remains unknown. Here we demonstrate that a Δplb1 knockout strain of C. neoformans has a profound defect in intracellular growth within host macrophages. This defect is due to a combination of a 50% decrease in proliferation and a 2-fold increase in cryptococcal killing within the phagosome. In addition, we show for the first time that the Δplb1 strain undergoes a morphological change during in vitro and in vivo intracellular infection, resulting in a subpopulation of very large titan cells, which may arise as a result of the attenuated mutant's inability to cope within the macrophage.

Identification of Aph1, a phosphate-regulated, secreted, and vacuolar acid phosphatase in Cryptococcus neoformans

Cryptococcus neoformans strains isolated from patients with AIDS secrete acid phosphatase, but the identity and role of the enzyme(s) responsible have not been elucidated. By combining a one-dimensional electrophoresis step with mass spectrometry, a canonically secreted acid phosphatase, CNAG_02944 (Aph1), was identified in the secretome of the highly virulent serotype A strain H99. We created an APH1 deletion mutant (Δaph1) and showed that Δaph1-infected Galleria mellonella and mice survived longer than those infected with the wild type (WT), demonstrating that Aph1 contributes to cryptococcal virulence. Phosphate starvation induced APH1 expression and secretion of catalytically active acid phosphatase in the WT, but not in the Δaph1 mutant, indicating that Aph1 is the major extracellular acid phosphatase in C. neoformans and that it is phosphate repressible. DsRed-tagged Aph1 was transported to the fungal cell periphery and vacuoles via endosome-like structures and was enriched in bud necks. A similar pattern of Aph1 localization was observed in cryptococci cocultured with THP-1 monocytes, suggesting that Aph1 is produced during host infection. In contrast to Aph1, but consistent with our previous biochemical data, green fluorescent protein (GFP)-tagged phospholipase B1 (Plb1) was predominantly localized at the cell periphery, with no evidence of endosome-mediated export. Despite use of different intracellular transport routes by Plb1 and Aph1, secretion of both proteins was compromised in a Δsec14-1 mutant. Secretions from the WT, but not from Δaph1, hydrolyzed a range of physiological substrates, including phosphotyrosine, glucose-1-phosphate, β-glycerol phosphate, AMP, and mannose-6-phosphate, suggesting that the role of Aph1 is to recycle phosphate from macromolecules in cryptococcal vacuoles and to scavenge phosphate from the extracellular environment.

Infections with the AIDS-related fungal pathogen Cryptococcus neoformans cause more than 600,000 deaths per year worldwide. Strains of Cryptococcus neoformans isolated from patients with AIDS secrete acid phosphatase; however, the identity and role of the enzyme(s) are unknown. We have analyzed the secretome of the highly virulent serotype A strain H99 and identified Aph1, a canonically secreted acid phosphatase. By creating an APH1 deletion mutant and an Aph1-DsRed-expressing strain, we demonstrate that Aph1 is the major extracellular and vacuolar acid phosphatase in C. neoformans and that it is phosphate repressible. Furthermore, we show that Aph1 is produced in cryptococci during coculture with THP-1 monocytes and contributes to fungal virulence in Galleria mellonella and mouse models of cryptococcosis. Our findings suggest that Aph1 is secreted to the environment to scavenge phosphate from a wide range of physiological substrates and is targeted to vacuoles to recycle phosphate from the expendable macromolecules.

Functional disruption of yeast metacaspase, Mca1, leads to miltefosine resistance and inability to mediate miltefosine-induced apoptotic effects

Miltefosine (MI) is a novel, potential antifungal agent with activity against some yeast and filamentous fungal pathogens. We previously demonstrated in the model yeast, Saccharomyces cerevisiae, that MI causes disruption of mitochondrial membrane potential and apoptosis-like cell death via interaction with the Cox9p sub-unit of cytochrome c oxidase (COX). To identify additional mechanisms of antifungal action, MI resistance was induced in S. cerevisiae by exposure to the mutagen, ethyl methanesulfonate, and gene mutation(s) responsible for resistance were investigated. An MI-resistant haploid strain (H-C101) was created. Resistance was retained in the diploid strain (D-C101) following mating, confirming dominant inheritance. Phenotypic assessment of individual D-C101 tetrads revealed that only one mutant gene contributed to the MI-resistance phenotype. To identify this gene, the genome of H-C101 was sequenced and 17 mutated genes, including metacaspase-encoding MCA1, were identified. The MCA1 mutation resulted in substitution of asparagine (N) with aspartic acid (D) at position 164 (MCA1(N164D)). MI resistance was found to be primarily due to MCA1(N164D), as single-copy episomal expression of MCA1(N164D), but not two other mutated genes (FAS1(T1417I) and BCK2(T104A)), resulted in MI resistance in the wild-type strain. Furthermore, an MCA1 deletion mutant (mca1Δ) was MI-resistant. MI treatment led to accumulation of reactive oxygen species (ROS) in MI-resistant (MCA1(N164D)-expressing and mca1Δ) strains and MI-susceptible (MCA1-expressing) strains, but failed to activate Mca1 in the MI-resistant strains, demonstrating that ROS accumulation does not contribute to the fungicidal effect of MI. In conclusion, functional disruption of Mca1, leads to MI resistance and inability to mediate MI-induced apoptotic effects. Mca1-mediated apoptosis is therefore a major mechanism of MI-induced antifungal action.

Phospholipase B is activated in response to sterol removal and stimulates acrosome exocytosis in murine sperm

Despite a strict requirement for sterol removal for sperm to undergo acrosome exocytosis (AE), the mechanisms by which changes in membrane sterols are transduced into changes in sperm fertilization competence are poorly understood. We have previously shown in live murine sperm that the plasma membrane overlying the acrosome (APM) contains several types of microdomains known as membrane rafts. When characterizing the membrane raft-associated proteomes, we identified phospholipase B (PLB), a calcium-independent enzyme exhibiting multiple activities. Here, we show that sperm surface PLB is activated in response to sterol removal. Both biochemical activity assays and immunoblots of subcellular fractions of sperm incubated with the sterol acceptor 2-hydroxypropyl-β-cyclodextrin (2-OHCD) confirmed the release of an active PLB fragment. Specific protease inhibitors prevented PLB activation, revealing a mechanistic requirement for proteolytic cleavage. Competitive inhibitors of PLB reduced the ability of sperm both to undergo AE and to fertilize oocytes in vitro, suggesting an important role in fertilization. This was reinforced by our finding that incubation either with protein concentrate released from 2-OHCD-treated sperm or with recombinant PLB peptide corresponding to the catalytic domain was able to induce AE in the absence of other stimuli. Together, these results lead us to propose a novel mechanism by which sterol removal promotes membrane fusogenicity and AE, helping confer fertilization competence. Importantly, this mechanism provides a basis for the newly emerging model of AE in which membrane fusions occur during capacitation/transit through the cumulus, prior to any physical contact between the sperm and the oocyte's zona pellucida.

Lipolytic enzymes involved in the virulence of human pathogenic fungi

Pathogenic microbes secrete various enzymes with lipolytic activities to facilitate their survival within the host. Lipolytic enzymes include extracellular lipases and phospholipases, and several lines of evidence have suggested that these enzymes contribute to the virulence of pathogenic fungi. Candida albicans and Cryptococcus neoformans are the most commonly isolated human fungal pathogens, and several biochemical and molecular approaches have identified their extracellular lipolytic enzymes. The role of lipases and phospholipases in the virulence of C. albicans has been extensively studied, and these enzymes have been shown to contribute to C. albicans morphological transition, colonization, cytotoxicity, and penetration to the host. While not much is known about the lipases in C. neoformans, the roles of phospholipases in the dissemination of fungal cells in the host and in signaling pathways have been described. Lipolytic enzymes may also influence the survival of the lipophilic cutaneous pathogenic yeast Malassezia species within the host, and an unusually high number of lipase-coding genes may complement the lipid dependency of this fungus. This review briefly describes the current understanding of the lipolytic enzymes in major human fungal pathogens, namely C. albicans, C. neoformans, and Malassezia spp.

A glycosylphosphatidylinositol anchor is required for membrane localization but dispensable for cell wall association of chitin deacetylase 2 in Cryptococcus neoformans

Cell wall proteins (CWPs) mediate important cellular processes in fungi, including adhesion, invasion, biofilm formation, and flocculation. The current model of fungal cell wall organization includes a major class of CWPs covalently bound to β-1,6-glucan via a remnant of a glycosylphosphatidylinositol (GPI) anchor. This model was established by studies of ascomycetes more than a decade ago, and relatively little work has been done with other fungi, although the presumption has been that proteins identified in the cell wall which contain a predicted GPI anchor are covalently linked to cell wall glucans. The pathogenic basidiomycete Cryptococcus neoformans encodes >50 putatively GPI-anchored proteins, some of which have been identified in the cell wall. One of these proteins is chitin deacetylase 2 (Cda2), an enzyme responsible for converting chitin to chitosan, a cell wall polymer recently established as a virulence factor for C. neoformans infection of mammalian hosts. Using a combination of biochemistry, molecular biology, and genetics, we show that Cda2 is GPI anchored to membranes but noncovalently associated with the cell wall by means independent of both its GPI anchor and β-1,6-glucan. We also show that Cda2 produces chitosan when localized to the plasma membrane, but association with the cell wall is not essential for this process, thereby providing insight into the mechanism of chitosan biosynthesis. These results increase our understanding of the surface of C. neoformans and provide models of cell walls likely applicable to other undercharacterized basidiomycete pathogenic fungi.

The surface of a pathogenic microbe is a major interface with its host. In fungi, the outer surface consists of a complex matrix known as the cell wall, which includes polysaccharides, proteins, and other molecules. The mammalian host recognizes many of these surface molecules and mounts appropriate responses to combat the microbial infection. Cryptococcus neoformans is a serious fungal pathogen that kills over 600,000 people annually. It converts most of its chitin, a cell wall polysaccharide, to chitosan, which is necessary for virulence. Chitin deacetylase enzymes have been identified in the cell wall, and our studies were undertaken to understand how the deacetylase is linked to the wall and where it has activity. Our results have implications for the current model of chitosan biosynthesis and further challenge the paradigm of covalent linkages between cell wall proteins and polysaccharides through a lipid modification of the protein.

Membrane microdomain components of Histoplasma capsulatum yeast forms, and their role in alveolar macrophage infectivity

Analysis of membrane lipids of Histoplasma capsulatum showed that ~40% of fungal ergosterol is present in membrane microdomain fractions resistant to treatment with non-ionic detergent at 4°C. Specific proteins were also enriched in these fractions, particularly Pma1p a yeast microdomain protein marker (a plasma membrane proton ATPase), a 30kDa laminin-binding protein, and a 50kDa protein recognized by anti-α5-integrin antibody. To better understand the role of ergosterol-dependent microdomains in fungal biology and pathogenicity, H. capsulatum yeast forms were treated with a sterol chelator, methyl-beta-cyclodextrin (mβCD). Removal of ergosterol by mβCD incubation led to disorganization of ergosterol-enriched microdomains containing Pma1p and the 30kDa protein, resulting in displacement of these proteins from detergent-insoluble to -soluble fractions in sucrose density gradient ultracentrifugation. mβCD treatment did not displace/remove the 50kDa α5-integrin-like protein nor had effect on the organization of glycosphingolipids present in the detergent-resistant fractions. Ergosterol-enriched membrane microdomains were also shown to be important for infectivity of alveolar macrophages; after treatment of yeasts with mβCD, macrophage infectivity was reduced by 45%. These findings suggest the existence of two populations of detergent-resistant membrane microdomains in H. capsulatum yeast forms: (i) ergosterol-independent microdomains rich in integrin-like proteins and glycosphingolipids, possibly involved in signal transduction; (ii) ergosterol-enriched microdomains containing Pma1p and the 30kDa laminin-binding protein; ergosterol and/or the 30kDa protein may be involved in macrophage infectivity.

Unravelling secretion in Cryptococcus neoformans: more than one way to skin a cat

Secretion pathways in fungi are essential for the maintenance of cell wall architecture and for the export of a number of virulence factors. In the fungal pathogen, Cryptococcus neoformans, much evidence supports the existence of more than one route taken by secreted molecules to reach the cell periphery and extracellular space, and a significant degree of crosstalk between conventional and non-conventional secretion routes. The need for such complexity may be due to differences in the nature of the exported cargo, the spatial and temporal requirements for constitutive and non-constitutive protein secretion, and/or as a means of compensating for the extra burden on the secretion machinery imposed by the elaboration of the polysaccharide capsule. This review focuses on the role of specific components of the C. neoformans secretion machinery in protein and/or polysaccharide export, including Sec4, Sec6, Sec14, Golgi reassembly and stacking protein and extracellular exosome-like vesicles. We also address what is known about traffic of the lipid, glucosylceramide, a target of therapeutic antibodies and an important regulator of C. neoformans pathogenicity, and the role of signalling pathways in the regulation of secretion.

A xylosylphosphotransferase of Cryptococcus neoformans acts in protein O-glycan synthesis

Cryptococcal meningoencephalitis is an AIDS-defining illness caused by the opportunistic pathogen Cryptococcus neoformans. This organism possesses an elaborate polysaccharide capsule that is unique among pathogenic fungi, and the glycobiology of C. neoformans has been a focus of research in the field. The capsule and other cellular glycans and glycoconjugates have been described, but the machinery responsible for their synthesis remains largely unexplored. We recently discovered Xpt1p, an enzyme with the unexpected activity of generating a xylose-phosphate-mannose linkage. We now demonstrate that this novel activity is conserved throughout the C. neoformans species complex, localized to the Golgi apparatus, and functions in the O-glycosylation of proteins. We also present the first survey of O-glycans from C. neoformans.

SEC14 is a specific requirement for secretion of phospholipase B1 and pathogenicity of Cryptococcus neoformans

Secreted phospholipase B1 (CnPlb1) is essential for dissemination of Cryptococcus neoformans to the central nervous system (CNS) yet essential components of its secretion machinery remain to be elucidated. Using gene deletion analysis we demonstrate that CnPlb1 secretion is dependent on the CnSEC14 product, CnSec14-1p. CnSec14-1p is a homologue of the phosphatidylinositol transfer protein ScSec14p, which is essential for secretion and viability in Saccharomyces cerevisiae. In contrast to CnPlb1, neither laccase 1-induced melanization within the cell wall nor capsule induction were negatively impacted in CnSEC14-1 deletion mutants (CnΔsec14-1 and CnΔsec14-1CnΔsfh5). Similar to the CnPLB1 deletion mutant (CnΔplb1), CnΔsec14-1 was hypovirulent in mice and did not disseminate to the CNS by day 14 post infection. Furthermore, macrophage expulsion of live CnΔsec14-1 and CnΔplb1 (vomocytosis) was reduced. Individual deletion of CnSEC14-2, a closely related CnSEC14-1 homologue, and CnSFH5, a distantly related SEC fourteen like homologue, did not abrogate CnPlb1 secretion or virulence. However, reconstitution of CnΔsec14-1 with CnSEC14-1 or CnSEC14-2 restored both phenotypes, consistent with functional genetic redundancy. We conclude that CnPlb1 secretion is SEC14-dependent and that C. neoformans preferentially exports virulence determinants to the cell periphery via distinct pathways. We also demonstrate that CnPlb1 secretion is essential for vomocytosis.

Role of phospholipases in fungal fitness, pathogenicity, and drug development - lessons from cryptococcus neoformans

Many pathogenic microbes, including many fungi, produce phospholipases which facilitate survival of the pathogen in vivo, invasion and dissemination throughout the host, expression of virulence traits and evasion of host immune defense mechanisms. These phospholipases are either secreted or produced intracellularly and act by physically disrupting host membranes, and/or by affecting fungal cell signaling and production of immunomodulatory effectors. Many of the secreted phospholipases acquire a glycosylphosphatidylinositol sorting motif to facilitate membrane and/or cell wall association and secretion. This review focuses primarily on the role of two members of the phospholipase enzyme family, phospholipase B (Plb) and phosphatidylinositol (PI)-specific phospholipase C (PI-C/Plc), in fungal pathogenesis and in particular, what has been learnt about their function from studies performed in the model pathogenic yeast, Cryptococcus neoformans. These studies have revealed how Plb has adapted to become an important part of the virulence repertoire of pathogenic fungi and how its secretion is regulated. They have also provided valuable insight into how the intracellular enzyme, Plc1, contributes to fungal fitness and pathogenicity – via a putative role in signal transduction pathways that regulate the production of stress-protecting pigments, polysaccharide capsule, cell wall integrity, and adaptation to growth at host temperature. Finally, this review will address the role fungal phospholipases have played in the development of a new class of antifungal drugs, which mimic their phospholipid substrates.

KRE genes are required for beta-1,6-glucan synthesis, maintenance of capsule architecture and cell wall protein anchoring in Cryptococcus neoformans

The polysaccharide beta-1,6-glucan is a major component of the cell wall of Cryptococcus neoformans, but its function has not been investigated in this fungal pathogen. We have identified and characterized seven genes, belonging to the KRE family, which are putatively involved in beta-1,6-glucan synthesis. The H99 deletion mutants kre5Delta and kre6Deltaskn1Delta contained less cell wall beta-1,6-glucan, grew slowly with an aberrant morphology, were highly sensitive to environmental and chemical stress and were avirulent in a mouse inhalation model of infection. These two mutants displayed alterations in cell wall chitosan and the exopolysaccharide capsule, a primary cryptococcal virulence determinant. The cell wall content of the GPI-anchored phospholipase B1 (Plb1) enzyme, which is required for cryptococcal cell wall integrity and virulence, was reduced in kre5Delta and kre6Deltaskn1Delta. Our results indicate that KRE5, KRE6 and SKN1 are involved in beta-1,6-glucan synthesis, maintenance of cell wall integrity and retention of mannoproteins and known cryptococcal virulence factors in the cell wall of C. neoformans. This study sets the stage for future investigations into the function of this abundant cell wall polymer.

Extracellular vesicles from Cryptococcus neoformans modulate macrophage functions

Cryptococcus neoformans and distantly related fungal species release extracellular vesicles that traverse the cell wall and contain a varied assortment of components, some of which have been associated with virulence. Previous studies have suggested that these extracellular vesicles are produced in vitro and during animal infection, but the role of vesicular secretion during the interaction of fungi with host cells remains unknown. In this report, we demonstrate by fluorescence microscopy that mammalian macrophages can incorporate extracellular vesicles produced by C. neoformans. Incubation of cryptococcal vesicles with murine macrophages resulted in increased levels of extracellular tumor necrosis factor alpha (TNF-alpha), interleukin-10 (IL-10), and transforming growth factor beta (TGF-beta). Vesicle preparations also resulted in a dose-dependent stimulation of nitric oxide production by phagocytes, suggesting that vesicle components stimulate macrophages to produce antimicrobial compounds. Treated macrophages were more effective at killing C. neoformans yeast. Our results indicate that the extracellular vesicles of C. neoformans can stimulate macrophage function, apparently activating these phagocytic cells to enhance their antimicrobial activity. These results establish that cryptococcal vesicles are biologically active.

The trehalose synthesis pathway is an integral part of the virulence composite for Cryptococcus gattii

The trehalose pathway is essential for stress tolerance and virulence in fungi. We investigated the importance of this pathway for virulence of the pathogenic yeast Cryptococcus gattii using the highly virulent Vancouver Island, Canada, outbreak strain R265. Three genes putatively involved in trehalose biosynthesis, TPS1 (trehalose-6-phosphate [T6P] synthase) and TPS2 (T6P phosphatase), and degradation, NTH1 (neutral trehalose), were deleted in this strain, creating the R265tps1 Delta, R265tps2 Delta, and R265nth1 Delta mutants. As in Cryptococcus neoformans, cellular trehalose was reduced in the R265tps1 Delta and R265tps2 Delta mutants, which could not grow and died, respectively, at 37 degrees C on yeast extract-peptone-dextrose agar, suggesting that T6P accumulation in R265tps2 Delta is directly toxic. Characterizations of the cryptococcal hexokinases and trehalose mutants support their linkage to the control of glycolysis in this species. However, unlike C. neoformans, the C. gattii R265tps1 Delta mutant demonstrated, in addition, defects in melanin and capsule production, supporting an influence of T6P on these virulence pathways. Attenuated virulence of the R265tps1 Delta mutant was not due solely to its 37 degrees C growth defect, as shown in worm studies and confirmed by suppressor mutants. Furthermore, an intact trehalose pathway controls protein secretion, mating, and cell wall integrity in C. gattii. Thus, the trehalose synthesis pathway plays a central role in the virulence composites of C. gattii through multiple mechanisms. Deletion of NTH1 had no effect on virulence, but inactivation of the synthesis genes, TPS1 and TPS2, has profound effects on survival of C. gattii in the invertebrate and mammalian hosts. These results highlight the central importance of this pathway in the virulence composites of both pathogenic cryptococcal species.

Role and mechanism of phosphatidylinositol-specific phospholipase C in survival and virulence of Cryptococcus neoformans

Phospholipase B1 (Plb1) is secreted after release from its glycosylphosphatidylinositol anchor and is implicated in initiation and dissemination of infection of the pathogenic fungus, Cryptococcus neoformans. To investigate the role of phosphatidylinositol-specific phospholipase C (PI-PLC) in Plb1 secretion, we identified two putative PI-PLC-encoding genes in C. neoformans var. grubii (PLC1 and PLC2), and created Deltaplc1 and Deltaplc2 deletion mutants. In Deltaplc1, which expressed less PI-PLC activity than wild type (WT), three major cryptococcal virulence traits, Plb1 secretion, melanin production and growth at host temperature (37 degrees C) were abolished and absence of Plb1 secretion coincided with Plb1 accumulation in plasma membranes. In addition, Deltaplc1 cell walls were defective, as indicated by cell clumping and irregular morphology, slower growth and an inability to activate mitogen-activated protein kinase (MAPK) in the presence of cell wall-perturbing agents. In contrast to Deltaplc2, which was as virulent as WT, Deltaplc1 was avirulent in mice and exhibited attenuated killing of Caenorhabditis elegans at 25 degrees C, demonstrating that mechanism(s) independent of the 37 degrees C growth defect contribute to the virulence composite. We conclude that Plc1 is a central regulator of cryptococcal virulence, acting through the protein kinase C/MAPK pathway, that it regulates release of Plb1 from the plasma membrane and is a candidate antifungal drug target.

Unique motifs identify PIG-A proteins from glycosyltransferases of the GT4 family

Background

The first step of GPI anchor biosynthesis is catalyzed by PIG-A, an enzyme that transfers N-acetylglucosamine from UDP-N-acetylglucosamine to phosphatidylinositol. This protein is present in all eukaryotic organisms ranging from protozoa to higher mammals, as part of a larger complex of five to six 'accessory' proteins whose individual roles in the glycosyltransferase reaction are as yet unclear. The PIG-A gene has been shown to be an essential gene in various eukaryotes. In humans, mutations in the protein have been associated with paroxysomal noctural hemoglobuinuria. The corresponding PIG-A gene has also been recently identified in the genome of many archaeabacteria although genes of the accessory proteins have not been discovered in them. The present study explores the evolution of PIG-A and the phylogenetic relationship between this protein and other glycosyltransferases.

Results

In this paper we show that out of the twelve conserved motifs identified by us eleven are exclusively present in PIG-A and, therefore, can be used as markers to identify PIG-A from newly sequenced genomes. Three of these motifs are absent in the primitive eukaryote, G. lamblia. Sequence analyses show that seven of these conserved motifs are present in prokaryote and archaeal counterparts in rudimentary forms and can be used to differentiate PIG-A proteins from glycosyltransferases. Using partial least square regression analysis and data involving presence or absence of motifs in a range of PIG-A and glycosyltransferases we show that (i) PIG-A may have evolved from prokaryotic glycosyltransferases and lipopolysaccharide synthases, members of the GT4 family of glycosyltransferases and (ii) it is possible to uniquely classify PIG-A proteins versus glycosyltransferases.

Conclusion

Besides identifying unique motifs and showing that PIG-A protein from G. lamblia and some putative PIG-A proteins from archaebacteria are evolutionarily closer to glycosyltransferases, these studies provide a new method for identification and classification of PIG-A proteins.

Honeybee Apis mellifera acetylcholinesterase--a biomarker to detect deltamethrin exposure

The purpose of this study is to investigate the possibility to use acetylcholinesterase (AChE) as a biomarker of exposure to deltamethrin insecticide in the honeybee, Apis mellifera and to test its reliability in the presence of other contaminants, as carbamate insecticide. Joined actions of deltamethrin (pyrethroid) and pirimicarb (carbamate), alone or in association, are investigated on AChE activity in surviving and dead honeybees, with a special focus on the relative proportions of its membrane and soluble forms. At the 0.5X dose (12.5 ng of deltamethrin and/or 2.5 microg of pirimicarb per bee), the residual tissue AChE activity in dead bees was 78% with deltamethrin, 43% with pirimicarb and 33% with dual treatment. In surviving bees, tissue AChE activity represented 250%, and 270% of control AChE activity with deltamethrin and dual treatment, respectively. The analysis of membrane and soluble AChE forms revealed an increase in the soluble form in dead bees after deltamethrin and dual treatment. However, in vitro investigations showed no direct interaction of deltamethrin on soluble and membrane AChE activity. The results suggest that the action of deltamethrin on AChE activity, in honeybee intact organisms, could be due to indirect mechanisms. The duality of AChE response to deltamethrin exposure, exhibited by the possibility of increase (surviving bees) or decrease (dead bees) of its activity has been pointed out for the first time. The important increase in AChE activity in response to deltamethrin, not altered by pirimicarb treatment, suggests that AChE activity could represent a robust biomarker specific to deltamethrin exposure in living bees.

Cell wall-linked cryptococcal phospholipase B1 is a source of secreted enzyme and a determinant of cell wall integrity

Phospholipase B (Plb1) is secreted by pathogenic fungi and is a proven virulence determinant in Cryptococcus neoformans. Cell-associated Plb1 is presumptively involved in fungal membrane biogenesis and remodelling. We have also identified it in cryptococcal cell walls. Motif scanning programs predict that Plb1 is attached to cryptococcal membranes via a glycosylphosphatidylinositol (GPI) anchor, which could regulate Plb1 export and secretion. A functional GPI anchor was identified in cell-associated Plb1 by (G)PI-specific phospholipase C (PLC)-induced release of Plb1 from strain H99 membrane rafts and inhibition of GPI anchor synthesis by YW3548, which prevented Plb1 secretion and transport to membranes and cell walls. Plb1 containing beta-1,6-linked glucan was released from H99 (wild-type strain) cell walls by beta-1,3 glucanase, consistent with covalent attachment of Plb1 via beta-1,6-linked glucans to beta-1,3-linked glucan in the central scaffold of the wall. Naturally secreted Plb1 also contained beta-1,6-linked glucan, confirming that it originated from the cell wall. Plb1 maintains cell wall integrity because a H99 deletion mutant, DeltaPLB1, exhibited a morphological defect and was more susceptible than H99 to cell wall disruption by SDS and Congo red. Growth of DeltaPLB1 was unaffected by caffeine, excluding an effect of Plb1 on cell wall biogenesis-related signaling pathways. Environmental (heat) stress caused Plb1 accumulation in cell walls, with loss from membranes and reduced secretion, further supporting the importance of Plb1 in cell wall integrity. This is the first demonstration that Plb1 contributes to fungal survival by maintaining cell wall integrity and that the cell wall is a source of secreted enzyme.

Clonorchis sinensis: expression, characterization, immunolocalization and serological reactivity of one excretory/secretory antigen-LPAP homologue

From a Clonorchis sinensis adult cDNA plasmid library, a cDNA clone encoding a novel lysophosphatidic acid phosphatase (LPAP) homologue was isolated. The predicted molecular weight of putative protein was 48.8 kDa and the deduced amino acid sequence had 45%, 32%, and 29% identity with LPAP of Schistosoma japonicum, Danio rerio, and Homo sapiens, respectively. Prediction of signal peptide and Western blot analysis indicated that the CsLPAP homologue was an excretory-secretory antigen (ES antigen) of C. sinensis. Immunostaining revealed that the CsLPAP was markedly localized in the intestinal cecum, seminal receptacle and eggs of the adult worm. The recombinant CsLPAP showed slightly higher sensitivity (82.14%) and specificity (85.86%) than the crude worm antigen by enzyme-linked immunosorbent assay (ELISA), a result which suggested that the recombinant antigen might be valuable in the serodiagnosis of human clonorchiasis.

Molecular characterization and serodiagnosis analysis of a novel lysophospholipase from Clonorchis sinensis

A cDNA clone encoding a novel lysophospholipase with a predicted molecular weight of 25.2 kDa was isolated from a Clonorchis sinensis adult cDNA library. The enzyme activity of the recombinant protein expressed in Escherichia coli was determined using phosphatidylcholine and lysophosphatidylcholine as substrates. Western blotting analysis indicated that it belonged to excretory/secretory proteins of the adults. The sensitivity and specificity of the recombinant antigen for serodiagnosis were evaluated with immunoglobulin enzyme-linked immunosorbent assay using serum samples from 20 patients with clonorchiasis and 20 patients with schistosomiasis. The sensitivity (75%) and specificity (80%) of the recombinant protein were comparable to those of crude extracts, at 65 and 82.5%, respectively. The sensitivity of the recombinant protein was 77% using 100 serum samples of clonorchiasis patients with various parasite burden. The results suggested that the recombinant lysophospholipase protein was not a satisfactory candidate for diagnosis of clonorchiasis, although it might be an excretory/secretory protein.

Cryptococcal phospholipase B antigen is not detected in serum of patients infected with Cryptococcus neoformans using a sandwich enzyme-linked immunosorbent assay

Extracellular phospholipase B (PLB) is a virulence determinant of Cryptococcus neoformans and Cryptococcus gattii. In this study, we developed a sensitive enzyme-linked immunosorbent assay (ELISA) for PLB antigen with a detection limit of 3.9 ng mL(-1). PLB was detected in culture supernatants of C. neoformans and C. gattii. PLB, however, was not detected in sera of seven human patients and 10 feline patients with active cryptococcosis. Furthermore, none of five rats with extensive pulmonary C. gattii infection had a positive ELISA test result. In conclusion, cryptococcal PLB could not be detected in serum using a PLB antigen-based ELISA. Despite its sensitivity, this ELISA is of limited diagnostic value. Exploration of further extracellular molecules suitable for serodiagnosis of active cryptococcal infection is warranted.

Extracellular glycosylphosphatidylinositol-anchored mannoproteins and proteases of Cryptococcus neoformans

Extracellular proteins of Cryptococcus neoformans are involved in the pathogenesis of cryptococcosis, and some are immunoreactive antigens that may potentially serve as candidates for vaccine development. To further study the extracellular proteome of the human fungal pathogen Cry. neoformans, we conducted a proteomic analysis of secreted and cell wall-bound proteins with an acapsular strain of Cry. neoformans. Proteins were identified from both intact cells and cell walls. In both cases, extracellular proteins were removed with trypsin or beta-glucanase, and then all proteins/peptides were purified by solid-phase extraction, spin dialysis, and HPLC, and identified by liquid chromatography-mass spectrometry. This study identified 29 extracellular proteins with a predicted N-terminal signal sequence and also a predicted glycosylphosphatidylinositol anchor motif in more than half. Among the novel proteins identified were five glycosylphosphatidylinositol-anchored proteins with extensive Ser/Thr-rich regions but no apparent functional domains, a glycosylphosphatidylinositol-anchored aspartic protease, and a metalloprotease with structural similarity to an elastinolytic metalloprotease of Aspergillus fumigatus. This study suggests that Cry. neoformans has the machinery required to target glycosylphosphatidylinositol-anchored proteins to the cell wall, and it confirms the extracellular proteolytic ability of Cry. neoformans.

Cryptococcus neoformans produces authentic prostaglandin E2 without a cyclooxygenase

Many single-celled eukaryotes produce prostaglandin-like molecules, but these have not been absolutely verified by mass spectrometry. We have isolated, and identified by liquid chromatography-tandem mass spectrometry, authentic prostaglandin E(2) from Cryptococcus neoformans. Cyclooxygenase inhibitors did not inhibit prostaglandin synthesis, and the cryptococcal genome lacks a cyclooxygenase homolog. Thus, novel enzymes must exist.

Genomewide analysis of phospholipid signaling genes in Phytophthora spp.: novelties and a missing link

Phospholipids are cellular membrane components in eukaryotic cells that execute many important roles in signaling. Genes encoding enzymes required for phospholipid signaling and metabolism have been characterized in several organisms, but only a few have been described for oomycetes. In this study, the genome sequences of Phytophthora sojae and P. ramorum were explored to construct a comprehensive genomewide inventory of genes involved in the most universal phospholipid signaling pathways. Several genes and gene families were annotated, including those encoding phosphatidylinositol synthase (PIS), phosphatidylinositol (phosphate) kinase (PI[P]K), diacylglycerol kinase (DAG), and phospholipase D (PLD). The most obvious missing link is a gene encoding phospholipase C (PLC). In all eukaryotic genomes sequenced to date, PLC genes are annotated based on certain conserved features; however, these genes seem to be absent in Phytophthora spp. Analysis of the structural and regulatory domains and domain organization of the predicted isoforms of PIS, PIK, PIPK, DAG, and PLD revealed many novel features compared with characterized representatives in other eukaryotes. Examples are transmembrane proteins with a C-terminal catalytic PLD domain, secreted PLD-like proteins, and PIPKs that have an N-terminal G-protein-coupled receptor-transmembrane signature. Compared with other sequenced eukaryotes, the genus Phytophthora clearly has several exceptional features in its phospholipid-modifying enzymes.

Cryptococcal lipid metabolism: phospholipase B1 is implicated in transcellular metabolism of macrophage-derived lipids

Cryptococci survive and replicate within macrophages and can use exogenous arachidonic acid for the production of eicosanoids. Phospholipase B1 (PLB1) has a putative, but uninvestigated, role in these processes. We have shown that uptake and esterification of radiolabeled arachidonic, palmitic, and oleic acids by the Cryptococcus neoformans var. grubii H99 wild-type strain and its PLB1 deletion mutant strain (the Deltaplb1 strain) are independent of PLB1, except under hyperosmolar stress. Similarly, PLB1 was required for metabolism of 1-palmitoyl lysophosphatidylcholine (LysoPC), which is toxic to eukaryotic cell membranes, under hyperosmolar conditions. During both logarithmic and stationary phases of growth, the physiologically relevant phospholipids, dipalmitoyl phosphatidylcholine (DPPC) and dioleoyl phosphatidylcholine, were taken up and metabolized via PLB1. Exogenous DPPC did not enhance growth in the presence of glucose as a carbon source but could support it for at least 24 h in glucose-free medium. Detoxification of LysoPC by reacylation occurred in both the H99 wild-type and the Deltaplb1 strains in the presence of glucose, but PLB1 was required when LysoPC was the sole carbon source. This indicates that both energy-independent (via PLB1) and energy-dependent transacylation pathways are active in cryptococci. Phospholipase A(1) activity was identified by PLB1-independent degradation of 1-palmitoyl-2-arachidonoyl phosphatidylcholine, but the arachidonoyl LysoPC formed was not detoxified by reacylation. Using the human macrophage-like cell line THP-1, we demonstrated the PLB1-dependent incorporation of macrophage-derived arachidonic acid into cryptococcal lipids during cryptococcus-phagocyte interaction. This pool of arachidonate can be sequestered for eicosanoid production by the fungus and/or suppression of host phagocytic activity, thus diminishing the immune response.

Phospholipase A2 and phospholipase B activities in fungi

As saprophytes or disease causing microorganisms, fungi acquire nutrients from dead organic material or living host organisms. Lipids as structural components of cell membranes and storage compartments play an important role as energy-rich food source. In recent years, it also has become clear that lipids have a wide range of bioactive properties including signal transduction and cell to cell communication. Thus, it is not surprising that fungi possess a broad range of hydrolytic enzymes that attack neutral lipids and phospholipids. Especially during infection of a mammalian host, phospholipase A(2) (PLA(2)) enzymes released by fungi could play important roles not only for nutrient acquisition and tissue invasion, but for intricate modulation of the host's immune response. Sequencing of fungal genomes has revealed a wide range of genes encoding PLA(2) activities in fungi. We are just beginning to become aware of the significance these enzymes could have for the fungal cells and their interaction with the host.

Cryptococcosis

In the past 2 decades, Cryptococcus has emerged in its clinical significance and as a model yeast for understanding molecular pathogenesis. C neoformans and C gattii are currently considered major primary and secondary pathogens in a wide array of hosts that are known to be immunocompromised or apparently immunocompetent. A recent outbreak of C gattii infections further underscores the clinical importance of the yeast through its epidemiology and pathogenicity features. With an enlarging immunosuppressed population caused by HIV infection, solid organ transplantation, and clinical use of potent immunosuppressives, such as cancer chemotherapy, monoclonal antibodies, and corticosteroids, this fungus has become a well-established infectious complication of modern medicine. This article examines current issues in cryptococcal infections, including new classification, epidemiology, pathogenesis, and specific clinical aspects.

Glycosyltransferases and their products: cryptococcal variations on fungal themes

Glycosyltransferases are specific enzymes that catalyse the transfer of monosaccharide moieties to biological substrates, including proteins, lipids and carbohydrates. These enzymes are present from prokaryotes to humans, and their glycoconjugate products are often vital for survival of the organism. Many glycosyltransferases found in fungal pathogens such as Cryptococcus neoformans do not exist in mammalian systems, making them attractive potential targets for selectively toxic agents. In this article, we present the features of this diverse class of enzymes, and review the fungal glycosyltransferases that are involved in synthesis of the cell wall, the cryptococcal capsule, glycoproteins and glycolipids. We specifically focus on enzymes that have been identified or studied in C. neoformans, and we consider future directions for research on glycosyltransferases in the context of this opportunistic pathogen.