title: GMP synthase is essential for viability and infectivity of Trypanosoma brucei despite a redundant purine salvage pathway.
abstract: The causative agent of human African trypanosomiasis, Trypanosoma brucei, lacks de novo purine biosynthesis and depends on purine salvage from the host. The purine salvage pathway is redundant and contains two routes to guanosine-5'-monophosphate (GMP) formation: conversion from xanthosine-5'-monophosphate (XMP) by GMP synthase (GMPS) or direct salvage of guanine by hypoxanthine-guanine phosphoribosyltransferase (HGPRT). We show recombinant T. brucei GMPS efficiently catalyzes GMP formation. Genetic knockout of GMPS in bloodstream parasites led to depletion of guanine nucleotide pools and was lethal. Growth of gmps null cells was only rescued by supraphysiological guanine concentrations (100 μM) or by expression of an extrachromosomal copy of GMPS. Hypoxanthine was a competitive inhibitor of guanine rescue, consistent with a common uptake/metabolic conversion mechanism. In mice, gmps null parasites were unable to establish an infection demonstrating that GMPS is essential for virulence and that plasma guanine is insufficient to support parasite purine requirements. These data validate GMPS as a potential therapeutic target for treatment of human African trypanosomiasis. The ability to strategically inhibit key metabolic enzymes in the purine pathway unexpectedly bypasses its functional redundancy by exploiting both the nature of pathway flux and the limited nutrient environment of the parasite's extracellular niche.
authors.affiliation: Department of Pharmacology, University of Texas Southwestern Medical Center at Dallas, 6001 Forest Park Rd, Dallas, TX, 75390-9041, USA.
authors.forename: Qiong
authors.initials: Q
authors.lastname: Li
authors.affiliation: Department of Pharmacology, University of Texas Southwestern Medical Center at Dallas, 6001 Forest Park Rd, Dallas, TX, 75390-9041, USA.
authors.forename: Christopher
authors.initials: C
authors.lastname: Leija
authors.affiliation: Department of Neuroscience, University of Texas Southwestern Medical Center at Dallas, 6001 Forest Park Rd, Dallas, TX, 75390-9041, USA.|Instituto de Medicina Molecular, Faculdade de Medicina, Universidade de Lisboa, Lisboa, Portugal.|Graduate Program in Areas of Basic and Applied Biology, Instituto de Ciências Biomédicas Abel Salazar, Universidade do Porto, Porto, Portugal.
authors.forename: Filipa
authors.initials: F
authors.lastname: Rijo-Ferreira
authors.affiliation: Department of Biochemistry, University of Texas Southwestern Medical Center at Dallas, 6001 Forest Park Rd, Dallas, TX, 75390-9041, USA.
authors.forename: Jun
authors.initials: J
authors.lastname: Chen
authors.affiliation: Seattle Biomedical Research Institute, 307 Westlake Avenue North, Suite 500, Seattle, WA, 98109-5219, USA.
authors.forename: Igor
authors.initials: I
authors.lastname: Cestari
authors.affiliation: Seattle Biomedical Research Institute, 307 Westlake Avenue North, Suite 500, Seattle, WA, 98109-5219, USA.
authors.forename: Kenneth
authors.initials: K
authors.lastname: Stuart
authors.affiliation: Department of Biochemistry, University of Texas Southwestern Medical Center at Dallas, 6001 Forest Park Rd, Dallas, TX, 75390-9041, USA.
authors.forename: Benjamin P
authors.initials: BP
authors.lastname: Tu
authors.affiliation: Department of Pharmacology, University of Texas Southwestern Medical Center at Dallas, 6001 Forest Park Rd, Dallas, TX, 75390-9041, USA.
authors.forename: Margaret A
authors.initials: MA
authors.lastname: Phillips
mesh_terms: D000241:Adenosine / Q000378:metabolism; D000818:Animals; D001665:Binding Sites; D019731:Carbon-Nitrogen Ligases / Q000235:genetics* / Q000378:metabolism*; D002453:Cell Cycle; D055786:Gene Knockout Techniques; D006147:Guanine / Q000378:metabolism / Q000494:pharmacology; D006157:Guanosine Monophosphate / Q000378:metabolism; D006801:Humans; D019271:Hypoxanthine / Q000378:metabolism / Q000494:pharmacology; D053858:Metabolic Networks and Pathways / Q000187:drug effects / Q000235:genetics; D008810:Mice, Inbred C57BL; D011687:Purines / Q000378:metabolism*; D011994:Recombinant Proteins / Q000235:genetics / Q000378:metabolism; D014346:Trypanosoma brucei brucei / Q000201:enzymology* / Q000235:genetics / Q000472:pathogenicity / Q000502:physiology*; D014353:Trypanosomiasis, African / Q000469:parasitology / Q000628:therapy
chemical_list: D011687:Purines; D011994:Recombinant Proteins; D019271:Hypoxanthine; D006147:Guanine; D006157:Guanosine Monophosphate; D019731:Carbon-Nitrogen Ligases; C020828:GMP synthase (glutamine-hydrolyzing); D000241:Adenosine