Disruption of de Novo Adenosine Triphosphate (ATP) Biosynthesis Abolishes Virulence in Cryptococcus neoformans

Wizrah

et al. 2017

Sci Rep

Self Cite

Virulence of Cryptococcus neoformans is regulated by a range of transcription factors, and is also influenced by the acquisition of adaptive mutations during infection. Beyond the temporal regulation of virulence factor production by transcription factors and these permanent microevolutionary changes, heritable epigenetic modifications such as histone deacetylation may also play a role during infection. Here we describe the first comprehensive analysis of the sirtuin class of NAD+ dependent histone deacetylases in the phylum Basidiomycota, identifying five sirtuins encoded in the C. neoformans genome. Each sirtuin gene was deleted and a wide range of phenotypic tests performed to gain insight into the potential roles they play. Given the pleiotropic nature of sirtuins in other species, it was surprising that only two of the five deletion strains revealed mutant phenotypes in vitro. However, cryptic consequences of the loss of each sirtuin were identified through whole cell proteomics, and mouse infections revealed a role in virulence for SIR2, HST3 and HST4. The most intriguing phenotype was the repeated inability to complement mutant phenotypes through the reintroduction of the wild-type gene. These data support the model that regulation of sirtuin activity may be employed to enable a drastic alteration of the epigenetic landscape and virulence of C. neoformans.

Section: Discussionmentioning

confidence: 99%

Sirtuins in the phylum Basidiomycota: A role in virulence in Cryptococcus neoformans

Arras

Wizrah

et al. 2017

Sci Rep

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“…The nucleoside hydrolases are required for the hydrolysis of nucleotides to nucleosides; hypoxanthine-xanthine-guanine phosphoribosyltransferase (CNAG_02546, HPT1 ) (HXGPRT) and adenine phosphoribosyltransferase (CNAG_01390, APH1 ) phosphorylate the nucleotides hypoxanthine, xanthine, guanine, and adenine to IMP, XMP, GMP and ATP, respectively [108,109]. The phosphoribosyltransferases have been studied in this organism, and the deletion of the genes encoding these enzymes did not result in any phenotypic differences from the wild-type, nor affect virulence in a murine model of cryptococcosis suggesting purine salvage is not important during the infection process [108,109]. …”

Section: Purine Metabolism In Cryptococcus Neoformansmentioning

confidence: 99%

“…Analysis of the enzymes from the IMP branchpoint to either adenine or guanine synthesis has been carried out for four enzymes in C. neoformans : adenylosuccinate synthetase (ADSS) (CNAG_02858, ADE12 ), adenylosuccinate lyase (ADSL) (CNAG_03270, ADE13 ), inosine monophosphate dehydrogenase (IMPDH) (CNAG_00441, IMD1 ) and guanine monophosphate synthase (GMP synthase) (CNAG_01877, GUA1 ) [108,109,113,114]. Deletion of the genes encoding these enzymes leads to strains that are purine auxotrophs, are attenuated for virulence factor production and are avirulent in a murine inhalation model, contrasting starkly with the salvage mutants and highlighting the importance of de novo purine biosynthesis during infection [108,109,113,114].…”

Section: Purine Metabolism In Cryptococcus Neoformansmentioning

confidence: 99%

“…Deletion of the genes encoding these enzymes leads to strains that are purine auxotrophs, are attenuated for virulence factor production and are avirulent in a murine inhalation model, contrasting starkly with the salvage mutants and highlighting the importance of de novo purine biosynthesis during infection [108,109,113,114]. Biochemical and structural analyses have determined potential differences between these fungal enzymes and their human counterparts that may be exploited in the development of fungal-specific therapeutics [108,109,111,112,113,114]. …”

Section: Purine Metabolism In Cryptococcus Neoformansmentioning

confidence: 99%

See 1 more Smart Citation

Purine Acquisition and Synthesis by Human Fungal Pathogens

Fraser

2017

Microorganisms

While members of the Kingdom Fungi are found across many of the world’s most hostile environments, only a limited number of species can thrive within the human host. The causative agents of the most common invasive fungal infections are Candida albicans, Aspergillus fumigatus, and Cryptococcus neoformans. During the infection process, these fungi must not only combat the host immune system while adapting to dramatic changes in temperature and pH, but also acquire sufficient nutrients to enable growth and dissemination in the host. One class of nutrients required by fungi, which is found in varying concentrations in their environmental niches and the human host, is the purines. These nitrogen-containing heterocycles are one of the most abundant organic molecules in nature and are required for roles as diverse as signal transduction, energy metabolism and DNA synthesis. The most common life-threatening fungal pathogens can degrade, salvage and synthesize de novo purines through a number of enzymatic steps that are conserved. While these enable them to adapt to the changing purine availability in the environment, only de novo purine biosynthesis is essential during infection and therefore an attractive antimycotic target.

“…The pathway is already a target for anticancer drugs (such as mercaptopurine and lometrexol) and immunosuppressants (such as mycophenolic acid) (20 -24). However, the investigation of purine metabolism as an antifungal target has been limited (25)(26)(27).…”

mentioning

confidence: 99%

GMP Synthase Is Required for Virulence Factor Production and Infection by Cryptococcus neoformans

Journal of Biological Chemistry

Tatzenko

Williams

et al. 2017

Self Cite

Edited by John M. DenuOver the last four decades the HIV pandemic and advances in medical treatments that also cause immunosuppression have produced an ever-growing cohort of individuals susceptible to opportunistic pathogens. Of these, AIDS patients are particularly vulnerable to infection by the encapsulated yeast Cryptococcus neoformans. Most commonly found in the environment in purine-rich bird guano, C. neoformans experiences a drastic change in nutrient availability during host infection, ultimately disseminating to colonize the purine-poor central nervous system. Investigating the consequences of this challenge, we have characterized C. neoformans GMP synthase, the second enzyme in the guanylate branch of de novo purine biosynthesis. We show that in the absence of GMP synthase, C. neoformans becomes a guanine auxotroph, the production of key virulence factors is compromised, and the ability to infect nematodes and mice is abolished. Activity assays performed using recombinant protein unveiled differences in substrate binding between the C. neoformans and human enzymes, with structural insights into these kinetic differences acquired via homology modeling. Collectively, these data highlight the potential of GMP synthase to be exploited in the development of new therapeutic agents for the treatment of disseminated, life-threatening fungal infections.In the past four decades there has been a dramatic escalation in the number of immunocompromised individuals (1). Although many of these are due to advances in immunosuppressive and chemotherapeutic technologies, the largest cohort is a direct result of the AIDS pandemic. Foreshadowed in 1981 with the occurrence of opportunistic Pneumocystis or human herpesvirus 8 infections in previously healthy individuals in Los Angeles (2, 3), AIDS and the lentivirus causing the disease soon gained broad public awareness (4 -6). With the advent of commercial blood testing, national blood bank screening programs were commenced in an effort to slow the spread of this emerging pandemic (7), and in 1987 the first treatment, zidovudine, marked what was thought to be an end to the crisis (8, 9). It was not, as was hoped, a miracle drug; the spread of AIDS continued across the globe and is now believed to have infected over 70 million people and killed 55 million to date (10).Since the discovery of the very first patients identified with Pneumocystis pneumonia, opportunistic fungal pathogens have been tightly linked with the AIDS pandemic. One of the key fungi often encountered in this context is Cryptococcus neoformans, a basidiomycete yeast responsible for cryptococcosis and a major cause of AIDS-related mortality (11). Most commonly found associated with purine-rich bird guano, spores or desiccated yeast cells from this environmental niche are inhaled into the lungs where, in an immunocompromised individual, the fungus can disseminate to the purine-poor central nervous system to cause meningoencephalitis.The fundamental treatment for cryptococcosis has not changed significantly ...