Abstract
Pneumocystis jirovecii is a World Health Organization listed “high priority” opportunistic fungus that causes Pneumocystis pneumonia (PCP) in immunocompromised individuals, in particular recipients of solid organ transplants (SOTs) and AIDS patients. Mycophenolic acid (MPA) is used as an immunosuppressant treatment for SOT recipients and also displays antifungal activity. MPA inhibits inosine monophosphate dehydrogenase (IMPDH), which is an essential enzyme in de novo purine synthesis. Six mutations in the IMPDH gene in P. jirovecii were observed in samples collected in outbreaks across six countries in North America, Europe and Asia. These mutations are strongly linked to MPA treatment. We hypothesize MPA treatment may provide selective pressure towards MPA-resistant PjIMPDH-containing strains of P. jirovecii. Structural modeling suggests that these mutations destabilize the enzyme and weaken the binding affinity of MPA. My study investigates the activity and MPA resistance of the mutant PjIMPDHs. I developed a purification protocol for recombinant His-tagged PjIMPDH. The characterization of wild type and mutant PjIMPDH has determined that the mutant enzymes are MPA resistant, leading to the emergence of PCP in MPA treated patients.