Biomedical subjects

R Sentandreu

Publications and source records attributed to R Sentandreu.

At least 37 records · Page 2Linked to original sources

PubMed1996

A Candida albicans gene expressed in Saccharomyces cerevisiae results in a distinct pattern of mRNA processing.

Two plasmids (derived from YCplac22 and YEplac112) carrying a Candida albicans gene (including the 5' non-coding promoter sequences) coding for a 30 kDa membrane-bound protein, were used to transform Saccharomyces cerevisiae cells. A 30 kDa protein was immunodetected by Western blot in the membrane fraction of transformants. Northern analysis showed the presence of three mRNA species (of about 1.1, 0.7 and 0.5 kb) hybridizing with the C. albicans gene as a probe. The same result was obtained using the 5' and 3' regions of the gene as probes, whereas only a 1.1 kb mRNA was found in C. albicans and none was detected in S. cerevisiae control transformants. Thus, heterologous expression of this gene in S. cerevisiae results in a distinct pattern of mRNA processing, either due to the location on plasmid vectors and/or to differences in the mRNA processing systems in the two microorganisms.

Candida albicans↗

PubMed1995

Cloning of a DNA fragment encoding part of a 70-kDa heat shock protein of Candida albicans.

Immunoscreening of a mycelial expression library with polyclonal antibodies raised against mycelial cell wall resulted in the detection of a cDNA encoding a heat shock protein of Candida albicans. Sequence analysis of a 0.8-kb cDNA subclone, 2M-1, revealed an open reading frame encoding 244 amino acids. Southern blot analysis with this fragment as a probe demonstrated hybridization to C. albicans DNA. Northern analysis showed a substantial increase in 2M RNA expression levels after cells were subjected to heat shock. Western blot analysis with 2M monospecific antibodies recognized a 70-kDa protein which was present in membrane particles and cytosolic fractions.

Amino Acid Sequence↗

PubMed1995

Involvement of transglutaminase in the formation of covalent cross-links in the cell wall of Candida albicans.

Activity of the enzyme glutaminyl-peptide--glutamylyl-transferase (EC 2.3.2.13; transglutaminase), which forms the interpeptidic cross-link N epsilon-(gamma-glutamic)-lysine, was demonstrated in cell-free extracts obtained from both the yeast like and mycelial forms of Candida albicans. Higher levels of enzymatic activity were observed in the cell wall fraction, whereas the cytosol contained only trace amounts of activity. Cystamine, a highly specific inhibitor of the enzyme, was used to analyze a possible role of transglutaminase in the organization of the cell wall structure of the fungus. Cystamine delayed protoplast regeneration and inhibited the yeast-to-mycelium transition and the incorporation of proteins into the cell wall. The incorporation of covalently bound high-molecular-weight proteins into the wall was sensitive to cystamine. Proteic epitopes recognized by two monoclonal antibodies, one of which is specific for the mycelial walls of the fungus, were also sensitive to cystamine. These data suggest that transglutaminase may be involved in the formation of covalent bonds between different cell wall proteins during the final assembly of the mature cell wall.

Antibodies, Fungal↗

PubMed1995

Specific immunohistochemical identification of Candida albicans in paraffin-embedded tissue with a new monoclonal antibody (1B12).

In invasive candidiasis, the identification of Candida organisms in tissue samples or in normally sterile fluids is essential for an accurate diagnosis. Species identification is an important clue for the source of infection and in epidemiological studies. In this article, the authors have tested the value of a new monoclonal antibody (1B12) to detect C albicans in culture by immunofluorescence, and in tissue samples by immunohistochemistry. MAb 1B12 was found to specifically recognize C albicans, does not cross-react with other Candida species or other structurally similar fungi, and is very sensitive and specific in paraffin-embedded tissue, having no reactivity in normal human tissues or necrotic areas. Therefore, MAb may be a valuable tool in the evaluation of fungal infections in paraffin-embedded tissue, particularly when Candida species identification is needed.

Antibodies, Monoclonal↗

PubMed1995

Identification of glucan-mannoprotein complexes in the cell wall of Candida albicans using a monoclonal antibody that reacts with a (1,6)-beta-glucan epitope.

The use of a novel monoclonal antibody (mAb) that reacts with (1,6)-beta-glucan has permitted the study of the different covalent linkages between glucan and mannoproteins in the cell wall of Candida albicans. The mAb JRR1 was originally raised by immunization with Zymolyase extracts from C. albicans cell walls, but it soon became apparent that it reacted with a (1,6)-beta-glucan epitope. By using this antibody, we show the existence of glucan-mannoprotein complexes between the (1,6)-beta-glucan epitope recognized by the antibody and cell wall mannoproteins. The topology of the (1,6)-beta-glucan in the cell wall of C. albicans has also been studied.

Antibodies, Monoclonal↗

PubMed1994

Structural mannoproteins released by beta-elimination from Candida albicans cell walls.

Mild alkaline solutions (beta-elimination), after removing the non-covalently bonded wall materials by hot SDS, released 13% and 26% of remaining wall proteins from mycelial and yeast cells of Candida albicans, respectively. When the beta-elimination was carried out after digestion of the walls with chitinase, four-fold more proteinaceous materials were released from mycelium and a similar amount in yeast walls. The solubilized materials were shown to be highly polydisperse, and endo-glycosidase H reduced their polydispersity and molecular masses, revealing different electrophoretic patterns in yeast and mycelial cell walls. The solubilized mycelial proteins carried N-glycosidic sugar chains and the epitopes recognized by two monoclonal antibodies were preserved, although showing a different behaviour in yeast walls. These results are consistent with the idea that significant amounts of intrinsic O-glycosylated mannoproteins are interconnected in the walls of C. albicans.

Antibodies, Monoclonal↗

PubMed1994

Incorporation of specific wall proteins during yeast and mycelial protoplast regeneration in Candida albicans.

The kinectics of incorporation of two precursor mannoproteins into the regenerating cell wall of Candida albicans protoplasts have been followed at 28 degrees C and 37 degrees C using two monoclonal antibodies specific for protein epitopes (MAb 1B12 and 4C12) as probes. Both molecules were secreted from the beginning of the regeneration process, and their incorporation was retarded significantly. Analysis of the secreted materials by Western immunoblotting with MAb 1B12 allowed the identification of two closely migrating bands at apparent Mr higher than 170 kDa and significant amounts of a highly polydisperse material of even greater molecular mass. Some of these mannoproteinaceous species carried both N- and O-glycosidically linked mannose residues, as deduced from their drop in apparent Mr when synthesized in the presence of tunicamycin and by their reactivity with Concanavalin A. Following secretion, the molecules reacting with MAb 1B12 were incorporated into the regenerating walls by covalent binding. Then, when the antigen molecules were solubilized from partially regenerated walls, their mobility differed when regeneration took place at 28 degrees C (blastoconidia) or 37 degrees C (mycelial cells).

Antibodies, Monoclonal↗

PubMed1994

Structural organization of the components of the cell wall from Candida albicans.

The organization of the components of the cell wall from Candida albicans was studied by means of sequential treatment with hot SDS, anhydrous ethylenediamine (EDA) and lytic enzymes, followed by chemical and microscopic analyses of the different separated fractions. The EDA-insoluble fraction retained the original morphology of the wall, which was destroyed by beta-glucanase, but not by chitinase treatments. Staining with fluorescent lectins revealed distinct distributions of mannoproteins, glucans and chitin in the wall. Amino acid analysis of SDS-extracted walls, and the EDA-soluble and -resistant fractions gave similar results, with seven amino acids making up about 70% of the total protein weight. Treatment of the EDA-insoluble fraction with Zymolyase or chitinase released fragments of variable size whose susceptibility to these and other hydrolases suggests that they are made of glucan, chitin and mannan oligomers associated with proteins. Treatment of the Zymolyase-insoluble residue with chitinase released a series of low-molecular-mass oligomers made of neutral sugars, GlcNAc and amino acids, mainly lysine. It is suggested that they represent fragments of the core making up the scaffold of the cell wall of the fungus.

Amino Acids↗

PubMed1994

Isolation and characterization of yeast monomorphic mutants of Candida albicans.

A method was devised for the isolation of yeast monomorphic (LEV) mutants of Candida albicans. By this procedure, about 20 stable yeast-like mutants were isolated after mutagenesis with ethyl methane sulfonate. The growth rate of the mutants in different carbon sources, both fermentable and not, was indistinguishable from that of the parental strain, but they were unable to grow as mycelial forms after application of any of the common effective inducers, i.e., heat shock, pH alterations, proline addition, or use of GlcNAc as the carbon source. Studies performed with one selected strain demonstrated that it had severe alterations in the chemical composition of the cell wall, mainly in the levels of chitin and glucans, and in specific mannoproteins, some of them recognizable by specific polyclonal and monoclonal antibodies. It is suggested that these structural alterations hinder the construction of a normal hyphal wall.

Candida albicans↗

PubMed1993

A kinetic study on the regeneration of Candida albicans protoplasts in the presence of cell wall synthesis inhibitors.

Aculeacin A and papulacandin B block cell wall regeneration in Candida albicans protoplasts at an intermediate step in which the protoplasts have not yet synthesized the rigid structure of the cell wall and are therefore still osmotically sensitive. In the presence of the antibiotics, total synthesis of glucan is not significantly lowered with respect to control cells, although most of it appears either in the culture medium or in the regenerating wall as alkali-soluble glucan. Thus, it is proposed that echinocandins (such as aculeacin A) and papulacandins may not inhibit glucan synthesis per se but instead inhibit its incorporation into the supramolecular organization of the cell wall.

Aminoglycosides↗

PubMed1993

Cloning and characterization of the SEC18 gene from Candida albicans.

The SEC18 gene product is required for protein transport at different stages in the Saccharomyces cerevisiae secretory pathway. The homologous SEC18 gene from Candida albicans has been cloned by complementation of a sec18-1 S. cerevisiae thermosensitive mutant using a C. albicans genomic library in YRp7. Sequence analysis of the gene revealed a 2382-bp open reading frame which coded for a protein of 88,926 kDa. By an in vitro transcription-translation coupled reaction of the C. albicans SEC18 gene, a protein of approximately 85 kDa was obtained. Hydrophobicity analysis of the protein did not show any predicted signal sequence nor transmembrane anchor domain. These results and the fact that glycosylation was absent in the protein indicated that C. albicans Sec18p did not enter in the secretory pathway. The alignment of the amino acid sequence revealed that the SEC18 gene from C. albicans was homologous to the SEC18 from S. cerevisiae (50% amino acid identity) and to the gene that coded the N-ethylmaleimide-sensitive factor (NSF) protein (43% amino acid identity). Moreover, the C. albicans Sec18p also showed the putative ATP binding site present in S. cerevisiae Sec18p and in NSF.

Adenosine Triphosphatases↗

PubMed1993

Effect of digitonin on membrane-bound and chitosomal chitin synthetase activity in protoplasts from yeast cells of Candida albicans.

The effect of digitonin on chitin synthetase present in membrane (MMF) and cytoplasmic fractions (chitosomes) (CF) from C. albicans yeast protoplasts has been determined. The zymogen is preferentially, but not exclusively, solubilized by digitonin from MMF. Centrifugation of distinct solubilized preparations, containing either zymogen, in vivo active enzyme and/or trypsin activated enzyme, on linear sucrose gradients suggests that both zymogen and trypsin activated enzyme sediment slightly slower than the active enzyme, pointing out differences between the activation processes in vivo and in vitro or, alternatively, that both enzyme activities (active in vivo and zymogenic) correspond to different gene products. The detection of a zymogenic activity under certain conditions (0.5 mg ml-1 of digitonin and 64 micrograms ml-1 of trypsin) also suggests the existence of more than one pool of zymogenic enzyme in the MMF. Digitonin sensitizes the chitosomal (CF) proenzyme to trypsin: activation is enhanced by low digitonin concentrations in the presence of 8 micrograms ml-1 of protease, whereas activity strongly decreases in the presence of 64 micrograms ml-1 of trypsin. Digitonin does not produce zymogen activation per se in absence of exogenous protease. Furthermore, chitosome structure is modified into particles with low buoyant densities.

Candida albicans↗

PubMed1993

A method for taxonomic determination of Candida albicans with DNA probes.

Determination of Candida species represents an important problem derived from the clinical implications of the species belonging to this genus. DNA probes have already been used for the epidemiology of Candida albicans, as well as for taxonomic analysis of Candida and other genera, although these probes are based on non-species-specific DNA sequences. In this work we carried out a 48-h assay, allowing the identification of C. albicans from clinical isolates, using DNA probes based on C. albicans LEU2 and URA3 genes. Another probe related to C. albicans SEC18 gene was shown not to be C. albicans specific.

Candida albicans↗

PubMed1993

Critical steps in fungal cell wall synthesis: strategies for their inhibition.

Development of new effective antifungal drugs is limited by the absence of specific target sites in the fungal cells. Knowledge of the fungal cell wall structure and biosynthesis is of interest in searching for a potential target site for new chemotherapeutic agents. Our group has demonstrated that the fungal cell wall is a metabolically active structure where interaction between distinct components occurs to give rise to the mature cell wall structure. Mannoproteins play an essential role in the cell wall organization, and there is evidence for the formation of covalent bonds between these molecules and the structural polymers (glucans and chitin) outside the plasma membrane. Such interactions, which specifically occur at the fungal cell wall, are of great interest in defining target sites for potential new chemotherapeutic agents, which may inhibit the interactions and, thus, lead to a defective cell wall formation and cell death.

Antifungal Agents↗

PubMed1993

Wall formation by Candida albicans yeast cells: synthesis, secretion and incorporation of two types of mannoproteins.

The mannoprotein components solubilized from the walls of Candida albicans blastoconidia following degradation of the glucan network with beta-glucanase (Zymolyase) have higher molecular masses than their probable precursors present in the supernatant of regenerating protoplasts. It therefore appears that the mannoproteins are released from the walls as part of supramolecular complexes. Immunological analysis using both polyclonal and monoclonal antibodies has demonstrated the probable relationship between molecules found in a mixed membrane preparation, those secreted by regenerating protoplasts, and those present in yeast cell walls. Some mannoproteins secreted by protoplasts incubated in the presence of tunicamycin had significantly increased mobility on SDS-PAGE, whereas others were not affected by the treatment. It is therefore possible that two types of mannoproteins are secreted by protoplasts: one carrying N-glycosylated chains (mannan) and one lacking them. All the proteins secreted in the presence of tunicamycin stained with Concanavalin A-peroxidase, demonstrating that they all, including the N-glycosylated ones, carried O-glycosylated sugar residues. Both classes of mannoproteins, secreted independently of each other, were found in the molecular complexes rendered soluble from the wall by Zymolyase digestion. Data obtained with a monoclonal antibody demonstrated the presence of a repeated epitope within one wall protein(s) detectable in a mixed membrane preparation and in the wall complexes released by Zymolyase.

Animals↗

PubMed1993

Characterization of epitopes recognized by Candida factor 1 and 9 antisera by use of Saccharomyces cerevisiae mnn mutants.

The use of Saccharomyces cerevisiae mnn mutants has facilitated the study of the epitopes recognized by antisera against several antigenic factors of the genus Candida (Candida Check; Iatron Laboratories, Tokyo, Japan). We have taken advantage of the very well characterized structure of the mannans of the different mnn mutants to compare their reactivities with the factor antisera used in the identification of different species of the genus Candida. The results of this study provide evidence that one of the antigenic determinants recognized by factor 1 antisera is the O-linked mannose chains of the cell wall mannoproteins, while that recognized by factor 9 antiserum is the alpha 1-6-linked mannose backbone of the outer chain of the N-linked oligosaccharide.

Agglutination↗

PubMed1993

Linkages between macromolecules in Candida albicans cell wall.

Wall mannoproteins can be divided into two major groups depending upon their degree of interaction with the structural network: one type interacts by non-covalent bonds while the second group seems covalently bound to other wall components (intrinsic or structural mannoproteins). Cytological and biochemical studies have shown that mannoproteins are distributed randomly throughout cell wall interacting with glucan, chitin and other mannoproteins. Experimental results obtained using regenerating protoplasts have shown that building of the wall occurs in two steps: during the first one the skeleton of chitin is formed retaining protein molecules by non-covalent bonds. The second steps take place by deposition of glucan molecules that allows incorporation of mannoproteins probably by covalent linkages. Using two monoclonal antibodies, one of them reacting with a mycelial specific antigen and a second one with an epitope found in yeast and mycelial cells, two families of proteins are detected, that are secreted independently. The antigens reacting with both monoclonal antibodies are solubilized from the walls of each morphologic structure forming part of supramolecular structures.

Antibodies, Fungal↗

PubMed1992

Chitin synthetase activity is bound to the plasma membrane and to a cytoplasmic particulate fraction in Candida albicans germ tube cells.

Subcellular distribution of chitin synthetase has been studied in germ tubes of Candida albicans. Two fractions with synthetase activity were separated from cell homogenates: (i) a mixed membrane fraction where the enzyme, partly in an active form, is associated with the plasma membrane (isopycnic centrifugation of mixed membrane fraction on linear sucrose gradients resolved a unique peak of activity matching with [3H]ConA-labelled membranes at a buoyant density of 1.195 g/ml); and (ii) a cytoplasmic fraction containing fully zymogenic enzyme associated with particles whose buoyant density (determined by isopycnic centrifugation on linear sucrose gradients) depended on the cell breakage conditions. The actual cytoplasmic fraction-enzyme may correspond to particles with buoyant density 1.135 g/ml (chitosomes), whereas the enzyme particles with other densities (1.085 and 1.165 g/ml) probably originated during cell disruption, as has been reported previously to occur during the preparation of yeast cell homogenates.

Candida albicans↗