Results 1 - 10
of
11
Cryptococcus neoformans laccase catalyses melanin synthesis from both D- and L-DOPA
- Microbiology
, 2007
"... The human fungal pathogen Cryptococcus neoformans produces melanin in the presence of various substrates, including the L enantiomer of 3,4-dihydroxyphenylalanine (DOPA). The enzyme laccase catalyses the formation of melanin by oxidizing L-DOPA, initiating a series of presumably spontaneous reaction ..."
Abstract
-
Cited by 11 (1 self)
- Add to MetaCart
(Show Context)
The human fungal pathogen Cryptococcus neoformans produces melanin in the presence of various substrates, including the L enantiomer of 3,4-dihydroxyphenylalanine (DOPA). The enzyme laccase catalyses the formation of melanin by oxidizing L-DOPA, initiating a series of presumably spontaneous reactions that ultimately leads to the polymerization of the pigment in the yeast cell wall. There, melanin protects the cell from a multitude of environmental and host assaults. Thus, the ability of C. neoformans to produce pigments from a variety of available substrates is likely to confer a survival advantage. A number of C. neoformans isolates of different serotypes produced pigments from D-DOPA, the stereoisomer of L-DOPA. Acid-resistant particles were isolated from pigmented C. neoformans cells grown in the presence of D-DOPA. Biophysical characterization showed the particles had a stably detectable free-radical signal by EPR, and negative zeta potential, similar to L-DOPA-derived particles. No major differences were found between L- and D-DOPA ghosts in terms of binding to anti-melanin antibodies, or in overall architecture when imaged by electron microscopy. C. neoformans cells utilized L- and D-DOPA at a similar rate. Overall, our results indicate that C. neoformans shows little stereoselectivity for utilizing DOPA in melanin synthesis. The ability of C. neoformans to use both L and D enantiomers for melanization implies that this organism has access to a greater potential pool of substrates for melanin synthesis, and this could potentially be exploited in the design of therapeutic inhibitors of laccase.
Comparative analysis of Cryptococcus neoformans acidresistant particles generated from pigmented cells grown in different laccase substrates.
- Fungal Genet. Biol.
, 2005
"... Abstract Cryptococcus neoformans produces pigments in vitro in the presence of exogenous substrate. We characterized acid-resistant particles isolated from pigmented cells grown in L-dopa, methyl-dopa, (¡)-epinephrine or (¡)-norepinephrine. The goals of this study were to determine whether pigments ..."
Abstract
-
Cited by 9 (6 self)
- Add to MetaCart
(Show Context)
Abstract Cryptococcus neoformans produces pigments in vitro in the presence of exogenous substrate. We characterized acid-resistant particles isolated from pigmented cells grown in L-dopa, methyl-dopa, (¡)-epinephrine or (¡)-norepinephrine. The goals of this study were to determine whether pigments made from each of these substrates were melanins and the consequences of pigmentation on related cell characteristics. The greatest yield of acid-resistant particles occurred with methyl-dopa followed by L-dopa. Electron microscopy indicated that L-dopa and methyl-dopa produced particles with thicker shells. The mAb 6D2 reacted with all particles, but a lower reactivity was observed with epinephrine-derived particles. ESR analysis revealed that epinephrine-derived particles failed to produce a stable free radical signal typical of melanins. Growth of C. neoformans in diVerent substrates aVected cell and capsule size but not capsule induction. Hence, the type of pigment produced by C. neoformans is dependent on the substrate and not all pigments meet the criteria for melanins.
The radioprotective properties of fungal melanin are a function of its chemical composition, stable radical presence and spatial arrangement. Pigment cell & melanoma research 21
, 2008
"... Summary Melanized microorganisms are often found in environments with very high background radiation levels such as in nuclear reactor cooling pools and the destroyed reactor in Chernobyl. These findings and the laboratory observations of the resistance of melanized fungi to ionizing radiation sugg ..."
Abstract
-
Cited by 4 (2 self)
- Add to MetaCart
Summary Melanized microorganisms are often found in environments with very high background radiation levels such as in nuclear reactor cooling pools and the destroyed reactor in Chernobyl. These findings and the laboratory observations of the resistance of melanized fungi to ionizing radiation suggest a role for this pigment in radioprotection. We hypothesized that the radioprotective properties of melanin in microorganisms result from a combination of physical shielding and quenching of cytotoxic free radicals. We have investigated the radioprotective properties of melanin by subjecting the human pathogenic fungi Cryptococcus neoformans and Histoplasma capsulatum in their melanized and non-melanized forms to sublethal and lethal doses of radiation of up to 8 kGy. The contribution of chemical composition, free radical presence, spatial arrangement, and Compton scattering to the radioprotective properties of melanin was investigated by high-performance liquid chromatography, electron spin resonance, transmission electron microscopy, and autoradiographic techniques. Melanin protected fungi against ionizing radiation and its radioprotective properties were a function of its chemical composition, free radical quenching, and spherical spatial arrangement.
A Chitin Synthase and Its Regulator Protein Are Critical for Chitosan Production and Growth of the Fungal Pathogen Cryptococcus neoformans†
, 2005
"... This article cites 60 articles, 31 of which can be accessed free ..."
(Show Context)
Address correspondence:
, 2007
"... Antibody-mediated protection through cross-reactivity introduces a fungal heresy into immunological dogma ..."
Abstract
- Add to MetaCart
Antibody-mediated protection through cross-reactivity introduces a fungal heresy into immunological dogma
Edited by:
, 2015
"... doi: 10.3389/fmicb.2015.00113 Endocytotic uptake of FITC-labeled anti-H. pylori egg yolk immunoglobulin Y in Candida yeast for detection of intracellular H. pylori Parastoo Saniee and Farideh Siavoshi* ..."
Abstract
- Add to MetaCart
(Show Context)
doi: 10.3389/fmicb.2015.00113 Endocytotic uptake of FITC-labeled anti-H. pylori egg yolk immunoglobulin Y in Candida yeast for detection of intracellular H. pylori Parastoo Saniee and Farideh Siavoshi*
Vesicular Trans-Cell Wall Transport in Fungi: A Mechanism for the Delivery of Virulence-Associated Macromolecules?
"... Abstract: Fungal cells are encaged in rigid, complex cell walls. Until recently, there was remarkably little information regarding the trans-fungal cell wall transfer of intracellular macromolecules to the extracellular space. Recently, several studies have begun to elucidate the mechanisms that fun ..."
Abstract
- Add to MetaCart
(Show Context)
Abstract: Fungal cells are encaged in rigid, complex cell walls. Until recently, there was remarkably little information regarding the trans-fungal cell wall transfer of intracellular macromolecules to the extracellular space. Recently, several studies have begun to elucidate the mechanisms that fungal cells utilize to secrete a wide variety of macromolecules through the cell wall. The combined use of transmission electron microscopy, serology, biochemistry, proteomics and lipidomics have revealed that the fungal pathogens Cryptococcus neoformans, Histoplasma capsulatum, Candida albicans, Candida parapsilosis and Sporothrix schenckii, as well as the model yeast Saccharomyces cerevisiae, each produces extracellular vesicles that carry lipids, proteins, polysaccharides and pigment-like structures of unquestionable biological signifi cance. Compositional analysis of the C. neoformans and H. capsulatum extracellular vesicles suggests that they may function as ‘virulence bags’, with the potential to modulate the host-pathogen interaction in favor of the fungus. The cellular origin of the extracellular vesicles remains unknown, but morphological and biochemical features indicate that they are similar to
Correspondence
, 2009
"... Recently, several pathogenic fungi were shown to produce extracellular vesicles that contain various components associated with virulence. In the human pathogenic fungus Cryptococcus neoformans, these components included laccase, an enzyme that catalyses melanin synthesis. Spherical melanin granules ..."
Abstract
- Add to MetaCart
Recently, several pathogenic fungi were shown to produce extracellular vesicles that contain various components associated with virulence. In the human pathogenic fungus Cryptococcus neoformans, these components included laccase, an enzyme that catalyses melanin synthesis. Spherical melanin granules have been observed in the cell wall of C. neoformans. Given that melanin granules have dimensions that are comparable to those of extracellular vesicles, and that metazoan organisms produce melanin in vesicular structures known as melanosomes, we investigated the role of vesicles in cryptococcal melanization. Extracellular vesicles melanized when incubated with the melanin precursor L-3,4-dihydroxyphenylalanine (L-DOPA). The kinetics of substrate incorporation into cells and vesicles was analysed using radiolabelled L-DOPA. The results indicated that substrate incorporation was different for cells and isolated vesicles. Acid-generated melanin ghosts stained with lipophilic dyes, implying the presence of associated lipid. A model for C. neoformans melanization is proposed that accounts for these observations and provides a mechanism for the assembly of melanin into relatively uniform spherical particles stacked in an orderly arrangement in the cell wall.
The supramolecular structure of melani
, 2009
"... om are ent ctio a h n y ( nte t p y r den the su pon d o monotonic absorbance; extremely low radiative quantum yield; and condensed phase electrical and photoconductivity.2 This mented neurons and the onset of neurodegenerative diseases like 12 peculation that the electrical ortant in this neural ro ..."
Abstract
- Add to MetaCart
om are ent ctio a h n y ( nte t p y r den the su pon d o monotonic absorbance; extremely low radiative quantum yield; and condensed phase electrical and photoconductivity.2 This mented neurons and the onset of neurodegenerative diseases like 12 peculation that the electrical ortant in this neural role.13 shown to play a variety of les in other organisms. Studies ey structural role in the jaws of the cell walls of certain species at melanin is a virulence factor s.16 Additionally, more recent l. has shown that the robust k are linked to the presence of nlike melanins.17 gical significance the melanins research during the last five acterisation and remain one of sses of bio-macromolecule.2, there has been some recent etic melanins with chemical, physical and processing properties suitable for implementation in PAPER www.rsc.org/softmatter | Soft Matterand detailed experimental methods. See DOI: 10.1039/b902507corganic, bioelectronic and optoelectronic applications,5,18,19 and in the aforementioned multifunctional polydopamine coatings.6,7 We have known since the pioneering work of Watson and Crick that supramolecular organisation of biological macromolecules such as proteins and DNA has a profound influence upon their physical and chemical properties and corresponding function. This organisation is primarily directed by non-covalent interactions such as hydrogen-bonding and van der Waals forces.
Correspondence
, 2006
"... The iron- and cAMP-regulated gene SIT1 influences ferrioxamine B utilization, melanization and cell wall structure in Cryptococcus neoformans ..."
Abstract
- Add to MetaCart
(Show Context)
The iron- and cAMP-regulated gene SIT1 influences ferrioxamine B utilization, melanization and cell wall structure in Cryptococcus neoformans
