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 (RNAiUGP, where RNAi indicates RNA interference) was rescued by expressing a recoded UGP (rUGP) in the organelle (RNAiUGP/EXPrUGP-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 UDP-glucose is no longer detectable in the RNAiUGP mutant, while it is still produced in cells expressing UGP exclusively in the cytosol (PEPCK null mutant) or glycosomes (RNAiUGP/EXPrUGP-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 clear. Trypanosomatids are also unique for the glycosomal localization of enzymes of the sugar nucleotide biosynthetic pathways, which are also present in the cytosol. Here, we showed that the cytosolic and glycosomal pathways are functional. As in all other eukaryotes, the cytosolic pathways feed glycosylation reactions; however, the role of the duplicated glycosomal pathways is currently unknown. We also showed that one of these enzymes (UGP) is imported into glycosomes by piggybacking on another glycosomal enzyme (PEPCK); they are not functionally related. The UGP/PEPCK association is unique since all piggybacking examples reported to date involve functionally related interacting partners, which broadens the possible combinations of carrier-cargo proteins being imported as hetero-oligomers.

Glycerol suppresses glucose consumption in trypanosomes through metabolic contest

“…In the ATP-bound form, the ε subunit retracts to bring the 2 fluorescent proteins close to each other, which increases FRET efficiency and allows detection of changes in ATP level upon fluorescence quantification (Fig 4B). To focus on the glycosomal ATP levels, the ATeam cassette was fused to the N-terminal extremity of a Myc-tagged glycosomal protein containing a C-terminal peroxisomal targeting motif (PTS1), i.e., glycerol-3-phosphate dehydrogenase (GPDH; EC 1.1.1.8; Tb927.8.3530), which was recently used to target a cytosolic protein exclusively inside this organelle [25]. Upon tetracycline induction, the anti-GPDH and anti-Myc immune sera recognized a 111-kDa protein corresponding to the expected size of the ATeam-Myc-GPDH recombinant protein (Fig 4C).…”

Biogenesis and metabolic homeostasis of trypanosomatid glycosomes: New insights and new questions

“…This has recently also been demonstrated for a T . brucei glycosomal enzyme (Villafraz et al, 2021). UDP‐glucose pyrophosphorylase, an enzyme involved in the nucleotide‐sugar synthesis, is imported due to binding to the phosphoenolpyruvate carboxykinase that possesses a PTS1.…”

Selene-Ethylenelacticamides and N-Aryl-Propanamides as Broad-Spectrum Leishmanicidal Agents

“…The following supporting information can be downloaded at: , Sections S1–S7; Figures S1–S72; Tables S1–S8. References [ 62 , 63 , 64 , 65 , 66 , 67 , 68 , 69 , 70 , 71 , 72 , 73 , 74 , 75 , 76 , 77 , 78 , 79 , 80 , 81 , 82 , 83 , 84 , 85 , 86 ] are cited in the Supplementary Materials.…”