Surface hydrophobicity changes of two Candida albicans serotype B mnn4delta mutants.
ABSTRACT Cell surface hydrophobicity (CSH) of Candida species enhances virulence by promoting adhesion to host tissues. Biochemical analysis of yeast cell walls has demonstrated that the most significant differences between hydrophobic and hydrophilic yeasts are found in the acid-labile fraction of Candida albicans phosphomannoprotein, suggesting that this fraction is important in the regulation of the CSH phenotype. The acid-labile fraction of C. albicans is unique among fungi, in that it is composed of an extended polymer of beta-1,2-mannose linked to the acid-stable region of the N-glycan by a phosphodiester bond. C. albicans serotype A and B strains both contain a beta-1,2-mannose acid-labile moiety, but only serotype A strains contain additional beta-1,2-mannose in the acid-stable region. A knockout of the C. albicans homolog of the Saccharomyces cerevisiae MNN4 gene was generated in two serotype B C. albicans patient isolates by using homologous gene replacement techniques, with the anticipation that they would be deficient in the acid-labile fraction and, therefore, demonstrate perturbed CSH. The resulting mnn4delta-deficient derivative has no detectable phosphate-linked beta-1,2-mannose in its cell wall, and hydrophobicity is increased significantly under conditions that promote the hydrophilic phenotype. The mnn4delta mutant also demonstrates an unanticipated perturbation in the acid-stable mannan fraction. The present study reports the first genetic knockout constructed in a serotype B C. albicans strain and represents an important step for dissecting the regulation of CSH.
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ABSTRACT: Ywp1 is a prominent glycosylphosphatidylinositol (GPI)-anchored glycoprotein of the cell wall of Candida albicans; it is present in the yeast form of this opportunistic fungal pathogen but absent from filamentous forms and chlamydospores. Yeast cells that lack Ywp1 are more adhesive and form thicker biofilms, implying an antiadhesive activity for Ywp1, with a possible role in yeast dispersal. The antiadhesive effect of Ywp1 is transplantable from yeast to hyphae, as hyphae that are forced to express YWP1 lose adhesion in an in vitro assay. Deletion of the GPI anchor results in loss of Ywp1 to the surrounding medium and reduction of the antiadhesive effect, implying an importance of time-dependent residency in the cell wall. Anchor-negative versions of Ywp1 possessing or lacking a C-terminal green fluorescent protein (GFP) tag were created in C. albicans and harvested from culture supernatants; in addition to serving as quantifiable markers for Ywp1 secretion, they revealed that the cleaved 11-kDa propeptide of Ywp1 remains strongly but noncovalently associated with the Ywp1 core. This association is resistant to highly acidic and basic solutions, 8 M urea, and 1% SDS (below 45°C). Above 50°C, SDS dissociates the isolated complex, but even higher temperatures are required to dissociate the propeptide from native Ywp1 that is anchored in a cell wall. This property has permitted detection, for the first time, of orthologs of Ywp1 in other members of the Candida clade. The cleaved propeptide, which carries the sole N-glycan of Ywp1, must participate in the antiadhesive effect of Ywp1.Eukaryotic Cell 04/2012; 11(6):795-805. · 3.18 Impact Factor
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ABSTRACT: Candida species are unusual causes of urinary tract infection (UTI) in healthy individuals, but common in the hospital setting or among patients with predisposing diseases and structural abnormalities of the kidney and collecting system. The urinary tract may be invaded in either an antegrade fashion from the bloodstream or retrograde via the urethra and bladder. Candida species employ a repertoire of virulence factors, including phenotypic switching, dimorphism, galvano - and thigmotropism, and hydrolytic enzymes, to colonize and then invade the urinary tract. Antegrade infection occurs primarily among patients predisposed to candidemia. The process of adherence to and invasion of the glomerulus, renal blood vessels, and renal tubules by Candida species was elegantly described in early histopathologic studies. Armed with modern molecular biologic techniques, the various virulence factors involved in bloodborne infection of the kidney are gradually being elucidated. Disturbances of urine flow, whether congenital or acquired, instrumentation of the urinary tract, diabetes mellitus, antimicrobial therapy, and immunosuppression underlie most instances of retrograde Candida UTI. In addition, bacterial UTIs caused by Enterobacteriaceae may facilitate the initial step in the process. Ascending infections generally do not result in candidemia in the absence of obstruction.Clinical Infectious Diseases 05/2011; 52 Suppl 6:S437-51. · 9.42 Impact Factor
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ABSTRACT: The fungal cell wall is a dynamic organelle required for cell shape, protection against the environment and, in pathogenic species, recognition by the innate immune system. The outer layer of the cell wall is comprised of glycosylated mannoproteins with the majority of these posttranslational modifications being the addition of O- and N-linked mannosides. These polysaccharides are exposed on the outer surface of the fungal cell wall and are, therefore, the first point of contact between the fungus and the host immune system. This review focuses on O- and N-linked mannan biosynthesis in the fungal pathogen Candida albicans and highlights new insights gained from the characterisation of mannosylation mutants into the role of these cell wall components in host-fungus interactions. In addition, we discuss the use of fungal mannan as a diagnostic marker of fungal disease.Molecular Microbiology 10/2013; · 5.03 Impact Factor