Pyrimidine Salvage Enzymes Are Essential for De Novo Biosynthesis of Deoxypyrimidine Nucleotides in Trypanosoma brucei.
The human pathogenic parasite Trypanosoma brucei possess both de novo and salvage routes for the biosynthesis of pyrimidine nucleotides. Consequently, they do not require salvageable pyrimidines for growth. Thymidine kinase (TK) catalyzes the formation of dTMP and dUMP and is one of several salvage enzymes that appear redundant to the de novo pathway. Surprisingly, we show through analysis of TK conditional null and RNAi cells that TK is essential for growth and for infectivity in a mouse model, and that a catalytically active enzyme is required for its function. Unlike humans, T. brucei and all other kinetoplastids lack dCMP deaminase (DCTD), which provides an alternative route to dUMP formation. Ectopic expression of human DCTD resulted in full rescue of the RNAi growth phenotype and allowed for selection of viable TK null cells. Metabolite profiling by LC-MS/MS revealed a buildup of deoxypyrimidine nucleosides in TK depleted cells. Knockout of cytidine deaminase (CDA), which converts deoxycytidine to deoxyuridine led to thymidine/deoxyuridine auxotrophy. These unexpected results suggested that T. brucei encodes an unidentified 5'-nucleotidase that converts deoxypyrimidine nucleotides to their corresponding nucleosides, leading to their dead-end buildup in TK depleted cells at the expense of dTTP pools. Bioinformatics analysis identified several potential candidate genes that could encode 5'-nucleotidase activity including an HD-domain protein that we show catalyzes dephosphorylation of deoxyribonucleotide 5'-monophosphates. We conclude that TK is essential for synthesis of thymine nucleotides regardless of whether the nucleoside precursors originate from the de novo pathway or through salvage. Reliance on TK in the absence of DCTD may be a shared vulnerability among trypanosomatids and may provide a unique opportunity to selectively target a diverse group of pathogenic single-celled eukaryotes with a single drug.
Department of Pharmacology University of Texas Southwestern Medical Center at Dallas, Dallas, Texas, United States of America.
Christopher
http://orcid.org/0000-0002-0041-2502
C
Leija
Instituto de Medicina Molecular, Faculdade de Medicina, Universidade de Lisboa, Lisboa, Portugal.|Department of Neuroscience, University of Texas Southwestern Medical Center at Dallas, Dallas, Texas, United States of America.|Graduate Program in Areas of Basic and Applied Biology, Instituto de Ciências Biomédicas Abel Salazar, Universidade do Porto, Porto, Portugal.
Filipa
F
Rijo-Ferreira
Department of Biophysics, University of Texas Southwestern Medical Center at Dallas, Dallas, Texas, United States of America.
Lisa N
LN
Kinch
Department of Biophysics, University of Texas Southwestern Medical Center at Dallas, Dallas, Texas, United States of America.
Nick V
NV
Grishin
Department of Biochemistry, University of Texas Southwestern Medical Center at Dallas, Dallas, Texas, United States of America.
Nicole
http://orcid.org/0000-0002-5209-1958
N
Nischan
Department of Biochemistry, University of Texas Southwestern Medical Center at Dallas, Dallas, Texas, United States of America.
Jennifer J
http://orcid.org/0000-0001-5373-3329
JJ
Kohler
Children's Medical Center Research Institute, University of Texas Southwestern Medical Center at Dallas, Dallas, Texas, United States of America.
Zeping
Z
Hu
Department of Pharmacology University of Texas Southwestern Medical Center at Dallas, Dallas, Texas, United States of America.
Margaret A
MA
Phillips
D000818:Animals; D015153:Blotting, Western; D002853:Chromatography, Liquid; D004195:Disease Models, Animal; D006801:Humans; D051379:Mice; D008810:Mice, Inbred C57BL; D009711:Nucleotides / Q000096:biosynthesis*; D016133:Polymerase Chain Reaction; D011743:Pyrimidines / Q000378:metabolism; D053719:Tandem Mass Spectrometry; D013937:Thymidine Kinase / Q000378:metabolism*; D014162:Transfection; D014346:Trypanosoma brucei brucei / Q000201:enzymology*; D014353:Trypanosomiasis, African / Q000201:enzymology* / Q000469:parasitology*
D009711:Nucleotides; D011743:Pyrimidines; D013937:Thymidine Kinase; C030986:pyrimidine