Isolation and identification of a 92-kDa stress induced protein from Candida albicans

Moonlighting Proteins at the Candidal Cell Surface

The cell wall in Candida albicans is not only a tight protective envelope but also a point of contact with the human host that provides a dynamic response to the constantly changing environment in infection niches. Particularly important roles are attributed to proteins exposed at the fungal cell surface. These include proteins that are stably and covalently bound to the cell wall or cell membrane and those that are more loosely attached. Interestingly in this regard, numerous loosely attached proteins belong to the class of “moonlighting proteins” that are originally intracellular and that perform essentially different functions in addition to their primary housekeeping roles. These proteins also demonstrate unpredicted interactions with non-canonical partners at an a priori unexpected extracellular location, achieved via non-classical secretion routes. Acting both individually and collectively, the moonlighting proteins contribute to candidal virulence and pathogenicity through their involvement in mechanisms critical for successful host colonization and infection, such as the adhesion to host cells, interactions with plasma homeostatic proteolytic cascades, responses to stress conditions and molecular mimicry. The documented knowledge of the roles of these proteins in C. albicans pathogenicity has utility for assisting the design of new therapeutic, diagnostic and preventive strategies against candidiasis.

Suppression of a methionine synthase by calmodulin under environmental stress in the entomopathogenic fungus Beauveria bassiana

Methionine synthase (MetE, EC 2.1.1.14) catalyses the final step in the methionine biosynthetic pathway. Methionine biosynthesis plays a major role in protein biogenesis and is the source of S-adenosyl methionine (SAM), the universal donor of methyl groups. In this study, we demonstrated that BbMetE acts as a typical MetE enzyme in the entomopathogenic fungus Beauveria bassiana. In addition, we found that BbMetE binds to calmodulin (CaM) in vitro and in vivo. The functional role of CaM binding to BbMetE was to negatively regulate BbMetE activity in B. bassiana. Our proton-nuclear magnetic resonance data revealed that CaM inhibitor W-7 increases methionine content in B. bassiana, suggesting that CaM negatively regulates the BbMetE activity. Environmental stress stimuli such as salt, H₂ O₂ and heat suppressed BbMetE activity in B. bassiana. W-7 reversed this effect, suggesting that the inhibitory mechanism is mediated through stimulation of CaM activity. Therefore, this work suggests that BbMetE plays an important role in methionine biosynthesis, which is mediated by environmental stress stimuli via the CaM signalling pathway.

Potential molecular mechanisms for fruiting body formation of Cordyceps illustrated in the case of Cordyceps sinensis

The fruiting body formation mechanisms of Cordyceps sinensis are still unclear. To explore the mechanisms, proteins potentially related to the fruiting body formation, proteins from fruiting bodies, and mycelia of Cordyceps species were assessed by using two-dimensional fluorescence difference gel electrophoresis, and the differential expression proteins were identified by matrix-assisted laser desorption/ionisation tandem time of flight mass spectrometry. The results showed that 198 differential expression proteins (252 protein spots) were identified during the fruiting body formation of Cordyceps species, and 24 of them involved in fruiting body development in both C. sinensis and other microorganisms. Especially, enolase and malate dehydrogenase were first found to play an important role in fruiting body development in macro-fungus. The results implied that cAMP signal pathway involved in fruiting body development of C. sinensis, meanwhile glycometabolism, protein metabolism, energy metabolism, and cell reconstruction were more active during fruiting body development. It has become evident that fruiting body formation of C. sinensis is a highly complex differentiation process and requires precise integration of a number of fundamental biological processes. Although the fruiting body formation mechanisms for all these activities remain to be further elucidated, the possible mechanism provides insights into the culture of C. sinensis.

Mycologic Endocrinology

The interactions of fungi and chemical messenger molecules, hormones or pheromones, are addressed in this chapter. These interactions include mammalian fungal pathogens, also plant pathogens, or non-pathogenic fungi, which can result in functional responses in receptor- or non-receptor-mediated fashions. Endogenous ligands in the fungi have been demonstrated to be important for mating in a number of systems. Mammalian hormones have been demonstrated to have stimulatory or inhibitory effects on growth for organisms such as Candida albicans, Paracoccidioides brasiliensis, Saccharomyces cerevisiae, Rhizopus nigricans, Aspergillus fumigatus, Coccidioides, and dermatophytic fungi. A number of fungi have been shown to have specific binding proteins for corticosteroid, estrogen and progesterone that are stereo-specific and high affinity. In some instances, the interactions of a mammalian hormone with the organism, in vivo, affects pathogenesis. Genome expression profiles of C. albicans in the presence of estradiol or progesterone, and S. cerevisiae with progesterone, indicate major up-regulation of various drug resistance pumps, like CDR1, and CDR2, can affect antifungal susceptibility. Azole antifungal interactions occur with fungal hormone binding proteins. Azoles also can block mammalian steroidogenesis. The finding of interactions of mammalian hormones with fungi and subsequent functional responses by the fungi, suggest that hormonal interactions with fungal systems has been conserved throughout evolution and have an important role in fungal pathogenesis, as well as in the overall biology of the organisms.

Allergens from Fusarium solani identified by immunoblotting in asthma patients In Iran

We extracted Fusarium solani antigens to evaluate specific anti-F. solani IgE in fifty-one patients with asthma (33 men and 18 women) and in 22 non-atopic healthy subjects (15 men and 7 women). F. solani strains were cultured in Sabouraud glucose agar and subjected to cell disruption using the freeze-and-thaw method. The obtained cytoplasmic extracts were analysed using sodium dodecyl sulphate-polyacrylamide gel electrophoresis (SDS-PAGE). Sensitisation to F. solani antigens has been evaluated in asthmatic patients using the immunoblotting assay. The SDS-PAGE identified 29 protein bands in the cytoplasmic extracts of F. solani isolates, with molecular weights ranging from 24 kDa to 112 kDa. Immunoblotting detected specific anti-F. solani IgE antibody in all asthma patients, but not in the control group. The predominant reactive allergens in patients corresponded to the bands with molecular weights of 24 kDa, 58.5 kDa, 64.5 kDa, 69 kDa, 72 kDa, and 97 kDa. Our results suggest that various allergenic components of F. solani may produce symptoms of asthma in susceptible individuals and they call for further research.

Prediction of the clinical outcome in invasive candidiasis patients based on molecular fingerprints of five anti-Candida antibodies in serum

Better prognostic predictors for invasive candidiasis (IC) are needed to tailor and individualize therapeutic decision-making and minimize its high morbidity and mortality. We investigated whether molecular profiling of IgG-antibody response to the whole soluble Candida proteome could reveal a prognostic signature that may serve to devise a clinical-outcome prediction model for IC and contribute to known IC prognostic factors. By serological proteome analysis and data-mining procedures, serum 31-IgG antibody-reactivity patterns were examined in 45 IC patients randomly split into training and test sets. Within the training cohort, unsupervised two-way hierarchical clustering and principal-component analyses segregated IC patients into two antibody-reactivity subgroups with distinct prognoses that were unbiased by traditional IC prognostic factors and other patients-related variables. Supervised discriminant analysis with leave-one-out cross-validation identified a five-IgG antibody-reactivity signature as the most simplified and accurate IC clinical-outcome predictor, from which an IC prognosis score (ICPS) was derived. Its robustness was confirmed in the test set. Multivariate logistic-regression and receiver-operating-characteristic curve analyses demonstrated that the ICPS was able to accurately discriminate IC patients at high risk for death from those at low risk and outperformed conventional IC prognostic factors. Further validation of the five-IgG antibody-reactivity signature on a multiplexed immunoassay supported the serological proteome analysis results. The five IgG antibodies incorporated in the ICPS made biologic sense and were associated either with good-prognosis and protective patterns (those to Met6p, Hsp90p, and Pgk1p, putative Candida virulence factors and antiapoptotic mediators) or with poor-prognosis and risk patterns (those to Ssb1p and Gap1p/Tdh3p, potential Candida proapoptotic mediators). We conclude that the ICPS, with additional refinement in future larger prospective cohorts, could be applicable to reliably predict patient clinical-outcome for individualized therapy of IC. Our data further provide insights into molecular mechanisms that may influence clinical outcome in IC and uncover potential targets for vaccine design and immunotherapy against IC.

Methods for functional analysis of macroautophagy in filamentous fungi

Autophagy is a bulk degradative process responsible for the turnover of membranes, organelles, and proteins in eukaryotic cells. Genetic and molecular regulation of autophagy has been independently elucidated in budding yeast and mammalian cells. In filamentous fungi, autophagy is required for several important physiological functions, such as asexual and sexual differentiation, pathogenic development, starvation stress and programmed cell death during heteroincompatibility. Here, we detail biochemical and microscopy methods useful for measuring the rate of induction of autophagy in filamentous fungi, and we summarize the methods that have been routinely used for monitoring macroautophagy in both yeast and filamentous fungi. The role of autophagy in carbohydrate catabolism and cell survival is discussed along with the specific functions of macroautophagy in fungal development and pathogenesis.

Reliability of antibodies to Candida methionine synthase for diagnosis, prognosis and risk stratification in systemic candidiasis: A generic strategy for the prototype development phase of proteomic markers

To be able to diagnose systemic candidiasis (SC) and to predict outcomes in SC patients are still challenging tasks for physicians. Previous proteomic studies suggest that anti-Candida methionine synthase (Met6p) IgG antibodies may be a candidate marker for SC. To evaluate their reliability for diagnosis, prognosis and risk stratification in SC, we developed a generic prototype strategy for their measurement in SC. Receiver-operating-characteristic curve analyses revealed a high diagnostic accuracy for this prototype format, which was slightly better to that for the widely used Western blot assays. Multivariate logistic-regression models showed a positive association between serum anti-Met6p IgG antibody levels and SC risk that was independent from established SC risk factors and other baseline variables. After adjusting for and stratifying according to known prognostic factors, a significant trend toward a lower two-month mortality risk with increasing levels was evidenced in SC patients at presentation. We conclude that these antibodies may be useful in discriminating SC from non-SC patients and determining risk stratification in SC. These may also confer protection against SC and be valuable for the design of future immunotherapies. Furthermore, our prototype format has the potential to make impact on other infectious diseases, cancers, allergies or autoimmune disorders.

Key physiological differences in Candida albicans CDR1 induction by steroid hormones and antifungal drugs

The Candida albicans CDR1 gene, encoding an ABC transporter that functions as an efflux pump, is thought to be involved in pathogenic adaptation and uses mammalian hormones and other environmental cues to regulate its activity. Exposure of several clinical isolates of C. albicans to 1 x 10(-8) M 17beta-oestradiol increased CDR1 expression and the isolates showed a positive correlation between oestrogen induction of CDR1 and growth in the presence of oestrogen. A reporter strain carrying the GFP gene under the control of the CDR1 promoter was used to analyse the effect of steroid hormones and antifungal drugs on CDR1 expression by flow cytometry. We found that among the many hormones tested, only oestradiol and progesterone induce CDR1 expression. CDR1 induction requires hormone concentrations greater than 10(-8) M, a threshold reached in vivo only by progesterone. Using the GFP-reporter strain, we show CDR1 induction by female but not male human serum and demonstrate that exposure of C. albicans to physiological concentrations of progesterone measurably increases resistance to fluconazole, miconazole and 5-fluorouracil. Simultaneous exposure of C. albicans to hormones and antifungal drugs provided evidence that both agents induce CDR1 expression via different mechanisms with different saturation points.

Fungal heat-shock proteins in human disease

Heat-shock proteins (hsps) have been identified as molecular chaperones conserved between microbes and man and grouped by their molecular mass and high degree of amino acid homology. This article reviews the major hsps of Saccharomyces cerevisiae, their interactions with trehalose, the effect of fermentation and the role of the heat-shock factor. Information derived from this model, as well as from Neurospora crassa and Achlya ambisexualis, helps in understanding the importance of hsps in the pathogenic fungi, Candida albicans, Cryptococcus neoformans, Aspergillus spp., Histoplasma capsulatum, Paracoccidioides brasiliensis, Trichophyton rubrum, Phycomyces blakesleeanus, Fusarium oxysporum, Coccidioides immitis and Pneumocystis jiroveci. This has been matched with proteomic and genomic information examining hsp expression in response to noxious stimuli. Fungal hsp90 has been identified as a target for immunotherapy by a genetically recombinant antibody. The concept of combining this antibody fragment with an antifungal drug for treating life-threatening fungal infection and the potential interactions with human and microbial hsp90 and nitric oxide is discussed.

Decoding Serological Response to Candida Cell Wall Immunome into Novel Diagnostic, Prognostic, and Therapeutic Candidates for Systemic Candidiasis by Proteomic and Bioinformatic Analyses

In an effort to bring novel diagnostic and prognostic biomarkers or even potential targets for vaccine design for systemic candidiasis (SC) into the open, a systematic proteomic approach coupled with bioinformatic analysis was used to decode the serological response to Candida wall immunome in SC patients. Serum levels of IgG antibodies against Candida wall-associated proteins (proteins secreted from protoplasts in active wall regeneration, separated by two-dimensional gel electrophoresis, and identified by mass spectrometry) were measured in 45 SC patients, 57 non-SC patients, and 61 healthy subjects by Western blotting. Two-way hierarchical clustering and principal component analysis of their serum anti-Candida wall antibody expression patterns discriminated SC patients from controls and highlighted the heterogeneity of their expression profiles. Multivariate logistic regression models demonstrated that high levels of antibodies against glucan 1,3-beta-glucosidase (Bgl2p) and the anti-wall phosphoglycerate kinase antibody seropositivity were the only independent predictors of SC. Receiver operating characteristic curve analysis revealed no difference between their combined evaluation and measurement of anti-Bgl2p antibodies alone. In a logistic regression model adjusted for known prognostic factors for mortality, SC patients with high anti-Bgl2p antibody levels or a positive anti-wall enolase antibody status, which correlated with each other, had a reduced 2-month risk of death. After controlling for each other, only the seropositivity for anti-wall enolase antibodies was an independent predictor of a lower risk of fatality, supporting that these mediated the protective effect. No association between serum anti-cytoplasmic enolase antibody levels and outcomes was established, suggesting a specific mechanism of enolase processing during wall biogenesis. We conclude that serum anti-Bgl2p antibodies are a novel accurate diagnostic biomarker for SC and that, at high levels, they may provide protection by modulating the anti-wall enolase antibody response. Furthermore serum anti-wall enolase antibodies are a new prognostic indicator for SC and confer protection against it. Bgl2p and wall-associated enolase could be valuable candidates for future vaccine development.

Genetically recombinant antibodies: new therapeutics against candidiasis

Historically, the therapy of serious fungal infection has been dominated by monotherapy with the polyene antibiotic amphotericin B. Clinical failures, side effects, the lack of alternatives and the toxicity of this drug have heightened the need to produce alternative therapies, which have included fluconazole, voriconazole and caspofungin. The observation that recovery from disseminated candidiasis was associated with an antibody response to the 47 kDa Candida heat-shock protein (HSP)90 homologue, coupled with the ability to sequence all the antibodies from patients who have recovered from the infection and to re-express the dominant ones as fragments in Escherichia coli, has opened the possibility of immunotherapy. The first recombinant antibody fragment, Mycograb (Neu Tec Pharma plc), against Candida HSP90 is now in clinical trials in patients with disseminated candidiasis in Europe and the US. Laboratory and early clinical data support the concept of synergy between Mycograb and amphotericin B. This should improve outcome and diminish the risk of resistance occurring to either drug, without an increase in toxicity, as this should be minimal in a human antibody fragment representing the natural antibody that a patient produces on recovery.

Oxidative stress inactivates cobalamin-independent methionine synthase (MetE) in Escherichia coli

In nature, Escherichia coli are exposed to harsh and non-ideal growth environments-nutrients may be limiting, and cells are often challenged by oxidative stress. For E. coli cells confronting these realities, there appears to be a link between oxidative stress, methionine availability, and the enzyme that catalyzes the final step of methionine biosynthesis, cobalamin-independent methionine synthase (MetE). We found that E. coli cells subjected to transient oxidative stress during growth in minimal medium develop a methionine auxotrophy, which can be traced to an effect on MetE. Further experiments demonstrated that the purified enzyme is inactivated by oxidized glutathione (GSSG) at a rate that correlates with protein oxidation. The unique site of oxidation was identified by selectively cleaving N-terminally to each reduced cysteine and analyzing the results by liquid chromatography mass spectrometry. Stoichiometric glutathionylation of MetE by GSSG occurs at cysteine 645, which is strategically located at the entrance to the active site. Direct evidence of MetE oxidation in vivo was obtained from thiol-trapping experiments in two different E. coli strains that contain highly oxidizing cytoplasmic environments. Moreover, MetE is completely oxidized in wild-type E. coli treated with the thiol-oxidizing agent diamide; reduced enzyme reappears just prior to the cells resuming normal growth. We argue that for E. coli experiencing oxidizing conditions in minimal medium, MetE is readily inactivated, resulting in cellular methionine limitation. Glutathionylation of the protein provides a strategy to modulate in vivo activity of the enzyme while protecting the active site from further damage, in an easily reversible manner. While glutathionylation of proteins is a fairly common mode of redox regulation in eukaryotes, very few proteins in E. coli are known to be modified in this manner. Our results are complementary to the independent findings of Leichert and Jakob presented in the accompanying paper (Leichert and Jakob 2004), which provide evidence that MetE is one of the proteins in E. coli most susceptible to oxidation. In eukaryotes, glutathionylation of key proteins involved in protein synthesis leads to inhibition of translation. Our studies suggest a simpler mechanism is employed by E. coli to achieve the same effect.

Transcriptional regulation of methionine synthase by homocysteine and choline in Aspergillus nidulans

Roles played by homocysteine and choline in the regulation of MS (methionine synthase) have been examined in fungi. The Aspergillus nidulans metH gene encoding MS was cloned and characterized. Its transcription was not regulated by methionine, but was enhanced by homocysteine and repressed by choline and betaine. MS activity levels were regulated in a similar way. The repression by betaine was due to its metabolic conversion to choline, which was found to be very efficient in A. nidulans. Betaine and choline supplementation stimulated growth of leaky metH mutants apparently by decreasing the demand for methyl groups and thus saving methionine and S -adenosylmethionine. We have also found that homocysteine stimulates transcription of MS-encoding genes in Saccharomyces cerevisiae and Schizosaccharomyces pombe.

Preclinical assessment of the efficacy of mycograb, a human recombinant antibody against fungal HSP90

Mycograb (NeuTec Pharma plc) is a human genetically recombinant antibody against fungal heat shock protein 90 (HSP90). Antibody to HSP90 is closely associated with recovery in patients with invasive candidiasis who are receiving amphotericin B (AMB). Using in vitro assays developed for efficacy assessment of chemotherapeutic antifungal drugs, Mycograb showed activity against a wide range of yeast species (MICs against Candida albicans [fluconazole [FLC]-sensitive and FLC-resistant strains], Candida krusei, Candida tropicalis, Candida glabrata, and Candida parapsilosis, 128 to 256 microg/ml). Mycograb (4 or 8 microg/ml) showed synergy with AMB, the fractional inhibitory index being 0.09 to 0.31. Synergy was not evident with FLC, except for FLC-sensitive C. albicans. Murine kinetics showed that Mycograb at 2 mg/kg produced a maximum concentration of drug in serum of 4.7 microg/ml, a half-life at alpha phase of 3.75 min, a half-life at beta phase of 2.34 h, and an area under the concentration-time curve from 0 to t h of 155 microg. min/ml. Mycograb (2 mg/kg) alone produced significant improvement in murine candidiasis caused by each species: (i). a reduction (Scheffe's test, P < 0.05) in the mean organ colony count for the FLC-resistant strain of C. albicans (kidney, liver, and spleen), C. krusei (liver and spleen), C. glabrata (liver and spleen), C. tropicalis (kidney), and C. parapsilosis (kidney, liver, and spleen) and (ii). a statistically significant increase in the number of negative biopsy specimens (Fisher's exact test, P < 0.05) for C. glabrata (kidney), C. tropicalis (liver and spleen), and C. parapsilosis (liver). AMB (0.6 mg/kg) alone cleared the C. tropicalis infection but failed to clear infections caused by C. albicans, C. krusei, C. glabrata, or C. parapsilosis. Synergy with AMB, defined as an increase (Fisher's exact test, P < 0.05) in the number of negative biopsy specimens compared with those obtained using AMB alone, occurred with the FLC-resistant strain of C. albicans (kidney), C. krusei (spleen), C. glabrata (spleen), and C. parapsilosis (liver and spleen). Only by combining Mycograb with AMB was complete resolution of infection achieved for C. albicans, C. krusei, and C. glabrata.