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PubMed2006

The Hsp70 member, Ssa1, acts as a DNA-binding transcriptional co-activator of laccase in Cryptococcus neoformans.

Hsp70 proteins are a well-known class of chaperones that have also been described to have roles in cellular regulation. Here, we show that a Cryptococcus neoformans Hsp70 homologue Ssa1 acts as a DNA-binding transcriptional co-activator of the fungal virulence factor, laccase, via binding to a GC-rich element within the 5'-UAS in response to glucose starvation, iron, copper, calcium and temperature. In addition, Ssa1 forms a regulatory complex with heat shock transcription factor and TATA-binding protein during laccase induction. Furthermore, deletion of Ssa1 results in reduced laccase and attenuated virulence using a mouse model. These results indicate that Hsp70 functions as a stress-related transcriptional co-activator required for fungal virulence.

Animals↗
PubMed1980

Xylan-degrading enzymes of the yeast Cryptococcus albidus. Identification and cellular localization.

During growth on wood beta-1,4-xylans the yeast Cryptococcus albidus produced at least two enzymes which convert the polysaccharide to xylose catabolized by the cells. The enzyme almost completely secreted into culture fluid was identified as an endo-1,4-beta-xylanase. The function of the extracellular beta-xylanase is to hydrolyze xylan to oligosaccharides, mainly to xylobiose and xylotriose, which enter the cell where they are split by the second identified enzyme, a cell-bound beta-xylosidae (xylobiase). Aryl beta-xylosidase activity detected in the culture fluid was snown to be due to low affinity of beta-xylanase for p-nitrophenyl beta-D-xylopyranoside. This property of beta-xylanase was preserved after purification of the enzyme by chromatography on DEAE-cellulose, CM-Sephadex and Biogel A 1.5 m or Biogel P 100. Purified beta-xylanase exhibited certain microheterogeneity after polyacrylamide gel electrophoresis. Both extracellular beta-xylanase and intracellular beta-xylosidase were produced in much lower amounts by the cells grown on glucose than by the cells grown on xylan. This suggested that they are not produced constitutively. The investigated strain was not able to grow on cellulose and the crude and purified beta-xylanase were unable to hydrolyze cellulose or its soluble derivatives.

Cellulose↗
PubMed1980

Induction and inducers of endo-1,4-beta-xylanase in the yeast Cryptococcus albidus.

Extracellular endo-1,4-beta-xylanase synthesis in the yeast Cryptococcus albidus is largely inducible. During growth on wood xylans the yeast produces the enzyme in amounts two orders of magnitude greater than on other carbon sources, including xylose. The enzyme can be induced in washed glucose-grown cells by xylan and beta-1,4-xylooligosaccharides. Among the oligosaccharides only xylobiose was not degraded extracellularly, therefore it appears to be the natural inducer of the enzyme. Xylobiose as a metabolisable inducer is effective at low concentrations and constant availability to cells. At high concentration of xylobiose the inductive effect is less pronounced because of catabolic repression by degradation products. Methyl beta-D-xylopyranoside was found to serve as a non-utilizable inducer of beta-xylanase. The enzyme induced by the glycoside appears to be identical with that produced by the cells during growth on xylan.

Cryptococcus↗
PubMed1980

Inducible beta-xyloside permease as a constituent of the xylan-degrading enzyme system of the yeast Cryptococcus albidus.

The yeast, Cryptococcus albidus, depending on whether it is grown on xylan or glucose, differs remarkably in the ability to take up inducers of extracellular endo-1,4-beta-xylanase synthesis. In washed, glucose-grown cells the initially low ability to take up xylobiose or methyl beta-D-xylopyranoside, increases during incubation with these compounds after a lag-phase shorter than the induction time of the extracellular beta-xylanase. Using of methyl beta-D-[U-14C]xylopyranoside as a very slowly metabolizable inducer of beta-xylanase it has been established that the increase of the rate of xylobiose or methyl xyloside uptake is due to induction of an active transport system for methyl beta-D-xyloside and beta-1,4-xylooligosaccharides. The system is called beta-xyloside permease. The permease activity of induced cells decreases in the absence of beta-xylanase inducers. The induction of permease as well as its inactivation (degradation) can be prevented with cycloheximide, thus both events appear to be dependent on de novo protein synthesis. In analogy with other active transport systems, beta-xyloside permease function can be effectively blocked by inhibitors of energy metabolism in the cells. The demonstrated example of induction of a permease, for inducers and products of hydrolysis of an extracellular polysaccharide hydrolase, points to a new feature of induction of extracellular enzymes in eucaryotic microorganisms.

Biological Transport, Active↗
PubMed1980

Complex reaction pathway of aryl beta-xyloside degradation by beta-xylanase of Cryptococcus albidus.

The extracellular endo-1,4-beta-xylanase of the yeast Cryptococcus albidus catalyzes degradation of aryl beta-xylosides by other reactions than simple hydrolytic cleavage. Liberation of phenol or p-nitrophenol from the corresponding beta-xylosides is accompanied by formation of xylose oligosaccharides and only small amounts of xylose. With the aid of phenyl beta-[U-14C]xyloside synthesized from [U-14C]xylose, it was established that the reaction followed a complex pattern with the rate of phenyl beta-xyloside digestion and appearance of various products varying markedly with time. The reaction involves multiple transglycosylic reaction leading first to phenyl glycosides of xylooligosaccharides, which are subsequently hydrolyzed mainly to xylobiose and xylotriose. At concentrations of phenyl beta-xyloside lower than 100 mM the reaction exhibited a significant lag phase, which was followed by period during which the rate of the degradation of the substrate could be determined. The rate showed a strong sigmoidal dependence on phenyl-beta-xyloside concentration. The lag phase could be eliminated and the initial rate accelerated by addition of xylose oligosaccharides, which are hydrolyzed by beta-xylanase. After disappearance of the added oligosaccharides, the reaction transitionally ceased and then resumed again at a rate comparable to the control without added oligosaccharides. It is proposed that beta-xylanase utilizes for degradation of phenyl beta-xyloside two reaction pathways differing in the nature of glycosyl donors.

Carbon Radioisotopes↗
PubMed1981

Substrate-binding site of endo-1,4-beta-xylanase of the yeast Cryptococcus albidus.

The substrate-binding site of endo-1,4-beta-xylanase of the yeast Cryptococcus albidus was investigated using, 1,4-beta-xylooligosaccharides (1-3H)-labelled at the reducing end. Evaluation of the affinities of ten imaginary subsites by the method of Suganuma et al. [1978, J. Biochem. (Tokyo) 84, 293--316] pointed out that the substrate-binding site of the enzyme is composed of four subsites and that the catalytic groups are localized in the centre. The imaginary subsites on the left-hand side of the binding site ('non-reducing-end' side) showed little or no affinity to bind xylosyl residues. For the subsites on the right-hand side of the binding site ('reducing-end' side) negative values of affinity were obtained, which means this region of the enzyme is unfavourable for complexing with xylosyl residues. As a consequence of the asymmetric distribution of negative values of affinity around the binding site, the enzyme displays a strong preference for attacking near the reducing end of the substrate. Regardless of the length of [1-3H]xylooligosaccharides, [1-3H]xylobiose was the prevailing reaction product at an early stage of hydrolysis, and frequency distribution of bond cleavage decreased from the second glycosidic bond towards the non-reducing end. Additional information on the substrate-binding site of C. albidus beta-xylanase was obtained by evaluating the efficiency of xylose, xylobiose, methyl beta-D-xyloside and phenyl beta-D-xyloside to serve as glycosyl acceptors in the transglycosylic reactions proceeding at high concentrations of xylotriose.

Binding Sites↗
PubMed1981

Mechanisms of substrate digestion by endo-1,4-beta-xylanase of Cryptococcus albidus. Lysozyme-type pattern of action.

The action pattern and reaction mechanism of the endo-1,4-beta-xylanase of the yeast Cryptococcus albidus were investigated using reducing-end (1-3H)-labelled and uniformly 14C-labelled beta-1,4-xylooligosaccharides up to xylopentaose. The enzyme was found to catalyze degradation of oligosaccharides also by other pathways than a simple hydrolytic cleavage. Bond-cleavage frequency of xylotriose, xylotetraose and xylopentaose were found to be concentration dependent. At high substrate concentration reactions such as xylosyl, xylobiosyl and xylotriosyl transfer occur and result in the formation of products larger than the starting substrate. Xylose and xylobiose to significant extent enter the reaction pathways as glycosyl acceptors. None of the transglycosylic reactions observed with reducing-end-labelled substrates or acceptors were accompanied by a significant label redistribution from the reducing-end unit, suggesting that the enzyme-glycosyl intermediates effective in the transfer reactions can be formed from the non-reducing-end units of oligosaccharides. Evidence for the formation of a termomolecular shifted complex of beta-xylanase with xylotriose has also been obtained. All features of the degradation of oligosaccharides by beta-xylanase are consistent with the lysozyme-type reaction mechanism.

Catalysis↗
PubMed1983

Synthesis and hydrolysis of 1,3-beta-xylosidic linkages by endo-1,4-beta-xylanase of Cryptococcus albidus.

Purified extracellular endo-1,4-beta-xylanase (EC 3.2.1.8) of the yeast Cryptococcus albidus was found to catalyze not only the known 1,4-beta-transfer, but an alternative transglycosylation reaction leading to the formation of 1,3-beta-glycosidic linkages. From a mixture of products of beta-xylanase degradation of phenyl beta-D-xylopyranoside three xylooligosaccharide fractions, differing chromatographically from the 1,4-beta-linked products, were isolated by preparative paper chromatography. Their structure was elucidated by mass spectrometry, 13C-NMR spectroscopy and enzymic hydrolysis by beta-xylanase and beta-xylosidase. The isomeric xylotriose was identified as 3-O-beta-D-xylopyranosyl-4-O-beta-D-xylopyranosyl-D-xylose. The fraction of isomeric tetrasaccharides was found to be represented mainly by 4-O-beta-D-xylopyranosyl-3-O-beta-D-xylopyranosyl-4-O-beta-D-xylopyranosyl- D-xylose. The xylooligosaccharides containing one 1,3-beta-linkage were also produced on the enzyme treatment of 1,4-beta-xylotriose and 1,4-beta-xylan. When treated with the enzyme responsible for their synthesis, the isomeric xylooligosaccharides were hydrolyzed at the 1,3-beta-linkage, despite the fact the enzyme does not attack 1,3-beta-xylan. The results are interpreted in the relation to the characterized four-subsite substrate-binding site of the enzyme.

Binding Sites↗
PubMedDate not supplied

Feline meningitis due to Cryptococcus neoformans var. neoformans and review of feline cryptococcosis.

Cryptococcus neoformans var. neoformans was ascertained as the prime cause of fatal meningitis in a young-adult female domestic cat who was suspected of rabies. The pathogen was isolated in heavy growth from the infected brain specimen on simplified sunflower seed (Helianthus annuus) medium at 30 degrees C. Periodic acid-Schiff stained impression smear revealed numerous cryptococcal cells. Histologically, pia-arachnoid showed thickening along with many circular yeast cells with and without budding morphologically consistent with Cr. neoformans. The detailed typing of the strain indicated that it belonged to serotype AD and Filobasidiella neoformans var. neoformans mating type 'alpha'. The emphasis is given on early diagnosis by immunological and mycological techniques and prompt chemotherapy to avert the fatal consequences of this enigmatic mycosis.

Animals↗
PubMedDate not supplied

Infection due to Cryptococcus neoformans of unusual morphology in a patient with AIDS.

Cryptococcus neoformans with a rare morphology of hand-mirror appearance was demonstrated by direct microscopic preparation of both cerebrospinal fluid (CSF) and sputum of a patient with AIDS. In addition, one to six blastoconidia were seen at the tip of a germ-tube like structure. Cr. neoformans was isolated in pure culture and the identification was confirmed by biochemical and serological tests as well as by animal pathogenicity.

Acquired Immunodeficiency Syndrome↗
PubMedDate not supplied

Turbidimetric and visual criteria for in vitro susceptibility testing of Cryptococcus neoformans clinical isolates.

The drug concentration which inhibited 50% of growth (IC50), the lowest drug concentration at which growth was less than 30% of that in a positive control well (IC30), the visual minimal inhibitory concentration (MIC visual), were applied to study the effects of fluconazole, itraconazole, amphotericin B and flucytosine against 27 isolates of Cryptococcus neoformans by a broth microdilution technique. When the recommendations established by NCCLS Subcommittee on Antifungal Susceptibility Test were applied for the visual reading of the microplates, the results were comparable with those obtained by the turbidimetric method. No statistically significant differences between MIC visual and IC30 readings were observed with the azoles. There were, however, differences with amphotericin B and flucytosine. In absolute terms MICs of amphotericin B and flucytosine showed higher values than IC30s and IC50s.

AIDS-Related Opportunistic Infections↗
PubMedDate not supplied

Effects of three azole derivatives on the lipids of different strains of Cryptococcus neoformans.

The comparative effects of ketoconazole, itraconazole and fluconazole on the lipids of four Cryptococcus neoformans strains were investigated. Quantitative analysis of lipids and sterols was completed, as well as qualitative analysis of sterols by thin-layer chromatography and by the ultraviolet spectrum. Growth of the cryptococcal isolates in the presence of the azoles derivatives concentrations below the minimum inhibitory concentration resulted in significant alterations in the lipid and sterol contents as compared with the control values. Furthermore, lanosterol was detected in these azole-treated cells. These results were in complete agreement with the proposed mechanism of action of azoles, which act through the inhibition of ergosterol biosynthesis, with resultant accumulation of lanosterol. Ketoconazole was found to be the least effective drug, as determined from a comparison of the effect of the three azoles on the sterol content of the four strains. Itraconazole showed to be the most effective drug, probably because of its high lipophilicity, which allows the drug to penetrate into fungi cells more efficiently.

Antifungal Agents↗
PubMed1996

[Osteomyelitis from Cryptococcus neoformans].

A forty-three-year old patient suspected of having a bone tumor in his left femur, was submitted to the hospital. However, osteomyelitis caused by Cryptococcus neoformans has been demonstrated by culture. The history of the patient revealed a long-term therapy with corticosteroids due to sarcoidosis. The osteomyelitis was treated with fluconazole (200 mg daily p.o.) for three months. Under this therapy the infection resolved.

Adrenal Cortex Hormones↗
PubMed1997

Comparison of broth macrodilution, broth microdilution and E-test susceptibility tests of Cryptococcus neoformans for fluconazole.

Forty Cryptococcus neoformans strains isolated from cerebral spinal fluid specimens collected from 39 patients were included in the study. The MICs for fluconacole were determined by YNB macrodilution test, microdilution tests using both RPMI1640 and YNB medium and E-tests on solidified RPMI1640 medium, Casitone and YNB agar. In comparison with the reference macrodilution method NCCLS M27-P both the microdilution as well as the E-test techniques can be used for fluconacole susceptibility testing of Cr. neoformans.

Antifungal Agents↗
PubMed1997

Serotyping of Cryptococcus neoformans isolates from environmental and clinical sources in extreme southern Italy (Calabria and Sicily, central Mediterranean area).

Ninety-seven environmental and four clinical isolates of Cryptococcus neoformans from several localities in extreme southern Italy were serotyped. All proved to be Cr. neoformans var. neoformans serotype A. The homogeneity of the serotypes suggests that geographical climatological conditions may play a role in Cr. neoformans serotype diffusion. It was furthermore revealed that, unlike the data reported for the serotypes of Cr. neoformans in mainland Italy, Cr. neoformans serotype D was not present in the examined sites in extreme southern Italy.

Animals↗
PubMed1997

Prevalence of serotype D in Cryptococcus neoformans isolates from HIV positive and HIV negative patients in Italy.

Cryptococcus neoformans strains isolated from 207 HIV positive and HIV negative patients hospitalized in Northern Italy were serotyped by slide agglutination. One Brazilian HIV negative woman was infected by var. gattii serotype B and all the other patients by var. neoformans, serotype D in 71%, serotype A in 24.6% and serotype AD in 3.4%. No difference was observed between subjects with serotypes A and D in HIV coinfection, exposure categories for AIDS, age, sex, and CD4 count of HIV positive patients. Meningeal and respiratory tract involvements and prostatic reservoir occurred with comparable frequency in AIDS patients infected by serotypes A and D. Skin lesions were observed only in serotype D infections, occurring in 12.6% of HIV positive and 58.3% of HIV negative patients infected by this serotype. Serotype A was found less susceptible to fluconazole than serotype D: 53.7% of serotype A strains had a MIC > or = 25 micrograms ml-1 compared to 17.7% of the serotype D isolates. On the other hand, both serotypes were highly susceptible to itraconazole.

Adolescent↗
PubMedDate not supplied

Molecular subtyping of clinical and environmental strains of Cryptococcus neoformans variety neoformans serotype A isolated from southern Italy.

Analysis of ribosomal DNA (rDNA) restriction fragment-length polymorphism (RFLP) and random amplification of polymorphic DNA (RAPD) was used to investigate the genetic variability and biogeographic distribution of clinical and environmental strains of Cryptococcus neoformans isolated from a limited area of southern Italy, where the selection of a predominant cryptococcal genotype could be expected. All isolates belonged to the species Cr. neoformans variety neoformans serotype A. RFLP analysis of a specific rDNA fragment allowed the distinction of strains of Cr. neoformans from closely related fungal reference species, but neither intraspecies nor intravarieties polymorphism was detected. On the contrary, RAPD fingerprints produced by priming with four different primers [(GTG)5, (GACA)4, M13 core sequence and the 8-mer oligonucleotide (GCGGACGG)] were able to characterize the isolates up to the individual level, indicating the presence of marked heterogeneity among Cr. neoformans serotype A strains in southern Italy.

Cryptococcosis↗
PubMedDate not supplied

Rapid and easy method to extract and preserve DNA from Cryptococcus neoformans and other pathogenic yeasts.

The mucopolysaccharide capsule of Cryptococcus neoformans and other pathogenic yeasts prevent the extraction of DNA from these important zoonotic agents. We report that the use of a lysis buffer containing a high concentration of urea is an easy, efficient and time-saving technique to obtain high yields of good-quality DNA for molecular diagnosis. The use of urea also prevents the degradation of DNA during storage of samples at room temperature for up to 6 months.

Cryptococcus neoformans↗