Characterising de novo purine biosynthesis as a platform to antifungal drug design

JL Chitty1,2, KL Blake1, SJ Williams3, U Kappler1, MA Cooper2, B Kobe1,2 and JA Fraser1

  1. AID, SCMB, The University of Queensland, Brisbane, QLD, Australia
  2. IMB, The University of Queensland, Brisbane, QLD, Australia
  3. ANU College of Medicine, The Australian National University, Acton, ACT, Australia

Cryptococcus neoformans is the leading cause of fungal meningoencephalitis and one of the major causes of death in immunocompromised individuals, particularly AIDS patients. Despite the existence of three commonly employed antifungals, mortality can reach almost 100% in some countries where the disease is highly prevalent, such as sub-Saharan Africa. It is therefore essential that we develop additional classes of antifungal drugs, particularly ones that are more effective than those currently available. Due to the shared eukaryotic physiology of fungi and humans, gross differences that can be exploited as drug targets are limited. An alternative approach is to exploit subtle differences in otherwise conserved pathways. Recent analysis by our group revealed de novo purine biosynthesis is essential for C. neoformans virulence. To facilitate our rational drug design program targeting de novo purine biosynthesis we have characterised and solved structures of several enzymes in the pathway to find potential other exploitable differences. One excellent example is adenylosuccinate lyase, an enzyme required for both the production of ATP and GTP via β-elimination of fumarate to convert SAICAR to AICAR and ADS to AMP. Given its dual activity and the short half-life of the substrate SAICAR it requires, it has been hypothesized this ADS lyase is involved in interactions with neighbouring enzyme in order to channel substrates. These interactions are thought to be transient, occurring in purine-depleted conditions, such as host infection. By determining if assemblies occur we hope to determine exposed domains that could be accessed by inhibitors.