De Novo GTP Biosynthesis Is Critical for Virulence of the Fungal Pathogen Cryptococcus Neoformans

PLoS Pathog. 2012;8(10):e1002957. doi: 10.1371/journal.ppat.1002957. Epub 2012 Oct 11.

Abstract

We have investigated the potential of the GTP synthesis pathways as chemotherapeutic targets in the human pathogen Cryptococcus neoformans, a common cause of fatal fungal meningoencephalitis. We find that de novo GTP biosynthesis, but not the alternate salvage pathway, is critical to cryptococcal dissemination and survival in vivo. Loss of inosine monophosphate dehydrogenase (IMPDH) in the de novo pathway results in slow growth and virulence factor defects, while loss of the cognate phosphoribosyltransferase in the salvage pathway yielded no phenotypes. Further, the Cryptococcus species complex displays variable sensitivity to the IMPDH inhibitor mycophenolic acid, and we uncover a rare drug-resistant subtype of C. gattii that suggests an adaptive response to microbial IMPDH inhibitors in its environmental niche. We report the structural and functional characterization of IMPDH from Cryptococcus, revealing insights into the basis for drug resistance and suggesting strategies for the development of fungal-specific inhibitors. The crystal structure reveals the position of the IMPDH moveable flap and catalytic arginine in the open conformation for the first time, plus unique, exploitable differences in the highly conserved active site. Treatment with mycophenolic acid led to significantly increased survival times in a nematode model, validating de novo GTP biosynthesis as an antifungal target in Cryptococcus.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Animals
  • Antifungal Agents / pharmacology
  • Caenorhabditis elegans / microbiology
  • Cryptococcus gattii / drug effects
  • Cryptococcus gattii / genetics
  • Cryptococcus gattii / isolation & purification
  • Cryptococcus neoformans / drug effects
  • Cryptococcus neoformans / enzymology*
  • Cryptococcus neoformans / metabolism
  • Cryptococcus neoformans / pathogenicity*
  • Crystallography, X-Ray
  • Drug Resistance, Fungal / genetics
  • Enzyme Inhibitors / pharmacology
  • Guanosine Triphosphate / biosynthesis*
  • IMP Dehydrogenase / antagonists & inhibitors
  • IMP Dehydrogenase / chemistry*
  • IMP Dehydrogenase / genetics
  • IMP Dehydrogenase / metabolism*
  • Meningoencephalitis / microbiology
  • Mycophenolic Acid / pharmacology*

Substances

  • Antifungal Agents
  • Enzyme Inhibitors
  • Guanosine Triphosphate
  • IMP Dehydrogenase
  • Mycophenolic Acid

Grant support

This work was supported by NHMRC Project Grant 455980 and NHMRC CDA 569673 to JAF. CAM was supported by an ANZ Trustees PhD Scholarship in Medical Research. BK is a National Health and Medical Research Council Research Fellow. JMH was supported by NHMRC RD Wright Fellowship 401748. The funders had no role in study design, data collection and analysis, decision to publish, or preparation of the manuscript.