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The Trypanosome UDP-Glucose Pyrophosphorylase Is Imported by Piggybacking into Glycosomes, Where Unconventional Sugar Nucleotide Synthesis Takes Place

Abstract : Glycosomes are peroxisome-related organelles of trypanosomatid parasites containing metabolic pathways, such as glycolysis and biosynthesis of sugar nucleotides, usually present in the cytosol of other eukaryotes. UDP-glucose pyrophosphorylase (UGP), the enzyme responsible for the synthesis of the sugar nucleotide UDP-glucose, is localized in the cytosol and glycosomes of the bloodstream and procyclic trypanosomes, despite the absence of any known peroxisome-targeting signal (PTS1 and PTS2). The questions that we address here are (i) is the unusual glycosomal biosynthetic pathway of sugar nucleotides functional and (ii) how is the PTS-free UGP imported into glycosomes? We showed that UGP is imported into glycosomes by piggybacking on the glycosomal PTS1-containing phosphoenolpyruvate carboxykinase (PEPCK) and identified the domains involved in the UGP/PEPCK interaction. Proximity ligation assays revealed that this interaction occurs in 3 to 10% of glycosomes, suggesting that these correspond to organelles competent for protein import. We also showed that UGP is essential for the growth of trypanosomes and that both the glycosomal and cytosolic metabolic pathways involving UGP are functional, since the lethality of the knockdown UGP mutant cell line (RNAi UGP, where RNAi indicates RNA interference) was rescued by expressing a recoded UGP (rUGP) in the organelle (RNAi UGP/ EXP rUGP-GPDH, where GPDH is glycerol-3-phosphate dehydrogenase). Our conclusion was supported by targeted metabolomic analyses (ion chromatography-high-resolution mass spectrometry [IC-HRMS]) showing that UDPglucose is no longer detectable in the RNAi UGP mutant, while it is still produced in cells expressing UGP exclusively in the cytosol (PEPCK null mutant) or glycosomes (RNAi UGP/ EXP rUGP-GPDH). Trypanosomatids are the only known organisms to have selected functional peroxisomal (glycosomal) sugar nucleotide biosynthetic pathways in addition to the canonical cytosolic ones. IMPORTANCE Unusual compartmentalization of metabolic pathways within organelles is one of the most enigmatic features of trypanosomatids. These unicellular eukaryotes are the only organisms that sequestered glycolysis inside peroxisomes (glycosomes), although the selective advantage of this compartmentalization is still not
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Submitted on : Tuesday, October 5, 2021 - 5:40:03 PM
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Oriana Villafraz, Hélène Baudouin, Muriel Mazet, Hanna Kulyk, Jean-William Dupuy, et al.. The Trypanosome UDP-Glucose Pyrophosphorylase Is Imported by Piggybacking into Glycosomes, Where Unconventional Sugar Nucleotide Synthesis Takes Place. mBio, 2021, 12 (3), ⟨10.1128/mbio.00375-21⟩. ⟨hal-03366680⟩

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