title: Characterization of the complete uric acid degradation pathway in the fungal pathogen Cryptococcus neoformans.
abstract: Degradation of purines to uric acid is generally conserved among organisms, however, the end product of uric acid degradation varies from species to species depending on the presence of active catabolic enzymes. In humans, most higher primates and birds, the urate oxidase gene is non-functional and hence uric acid is not further broken down. Uric acid in human blood plasma serves as an antioxidant and an immune enhancer; conversely, excessive amounts cause the common affliction gout. In contrast, uric acid is completely degraded to ammonia in most fungi. Currently, relatively little is known about uric acid catabolism in the fungal pathogen Cryptococcus neoformans even though this yeast is commonly isolated from uric acid-rich pigeon guano. In addition, uric acid utilization enhances the production of the cryptococcal virulence factors capsule and urease, and may potentially modulate the host immune response during infection. Based on these important observations, we employed both Agrobacterium-mediated insertional mutagenesis and bioinformatics to predict all the uric acid catabolic enzyme-encoding genes in the H99 genome. The candidate C. neoformans uric acid catabolic genes identified were named: URO1 (urate oxidase), URO2 (HIU hydrolase), URO3 (OHCU decarboxylase), DAL1 (allantoinase), DAL2,3,3 (allantoicase-ureidoglycolate hydrolase fusion protein), and URE1 (urease). All six ORFs were then deleted via homologous recombination; assaying of the deletion mutants' ability to assimilate uric acid and its pathway intermediates as the sole nitrogen source validated their enzymatic functions. While Uro1, Uro2, Uro3, Dal1 and Dal2,3,3 were demonstrated to be dispensable for virulence, the significance of using a modified animal model system of cryptococcosis for improved mimicking of human pathogenicity is discussed.
authors.affiliation: Australian Infectious Diseases Research Centre, University of Queensland, Brisbane, Queensland, Australia.
authors.forename: I Russel
authors.initials: IR
authors.lastname: Lee
authors.forename: Liting
authors.initials: L
authors.lastname: Yang
authors.forename: Gaseene
authors.initials: G
authors.lastname: Sebetso
authors.forename: Rebecca
authors.initials: R
authors.lastname: Allen
authors.forename: Thi H N
authors.initials: TH
authors.lastname: Doan
authors.forename: Ross
authors.initials: R
authors.lastname: Blundell
authors.forename: Edmund Y L
authors.initials: EY
authors.lastname: Lui
authors.forename: Carl A
authors.initials: CA
authors.lastname: Morrow
authors.forename: James A
authors.initials: JA
authors.lastname: Fraser
mesh_terms: D060054:Agrobacterium / Q000378:metabolism; D000818:Animals; D017173:Caenorhabditis elegans / Q000382:microbiology; D019295:Computational Biology; D003453:Cryptococcosis / Q000382:microbiology; D003455:Cryptococcus neoformans / Q000166:cytology / Q000201:enzymology / Q000378:metabolism* / Q000472:pathogenicity; D062607:Fungal Capsules / Q000378:metabolism; D005656:Fungal Proteins / Q000378:metabolism; D017353:Gene Deletion; D054884:Host-Pathogen Interactions; D006801:Humans; D006867:Hydrolases / Q000378:metabolism; D008543:Melanins; D053858:Metabolic Networks and Pathways; D051379:Mice; D016254:Mutagenesis, Insertional / Q000235:genetics; D009584:Nitrogen / Q000378:metabolism; D010641:Phenotype; D011687:Purines / Q000378:metabolism; D015203:Reproducibility of Results; D012098:Reproduction; D059386:Reverse Genetics; D013696:Temperature; D014510:Urease / Q000378:metabolism; D014527:Uric Acid / Q000378:metabolism*
chemical_list: D005656:Fungal Proteins; D008543:Melanins; D011687:Purines; D014527:Uric Acid; D006867:Hydrolases; D014510:Urease; D009584:Nitrogen