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.

The role of the de novo pyrimidine biosynthetic pathway in Cryptococcus neoformans high temperature growth and virulence

“…Insertional mutagenesis mediated by Agrobacterium tumefaciens in C. neoformans has been a useful tool for gene function discovery and analysis (Idnurm et al, 2004; Idnurm and Heitman, 2005; Walton et al, 2005; 2006; Feretzaki and Heitman, 2013; Lee et al , 2013). In this paper, this technique was employed to identify genes involved in high temperature growth, an important virulence factor for this yeast.…”

Uric acid in plants and microorganisms: Biological applications and genetics - A review

“…The formed uric acid can either be excreted or degraded in the peroxisomes by active catabolic enzymes [34], Fig. 2.…”

“…The identified catabolic genes of uric acid in C. neoformans were URO1 (urate oxidase), URO2 (HIU hydrolase), URO3 (OHCU decarboxylase), DAL1 (allantoinase), DAL2,3,3 (allantoicase-ureidoglycolate hydrolase fusion protein), and URE1 (urease) [34].…”

Rewiring of the Ppr1 Zinc Cluster Transcription Factor from Purine Catabolism to Pyrimidine Biogenesis in the Saccharomycetaceae

“…The phylogenetic tree is based on Wang et al [29] and the Fungal Orthogroups Repository (https://portals.broadinstitute.org/regev/orthogroups/). (B) Purine catabolism pathway [30]. Blue enzymes: present in C. albicans and regulated by Ppr1 but missing in S. cerevisiae; green enzymes: regulated by both Ppr1 in C. albicans and Dal82 in S. cerevisiae; red enzymes: regulated by Ppr1 in C. albicans and present in S. cerevisiae, but not regulated by Dal82 in S. cerevisiae.…”