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Proteomic identification of the UDP-GlcNAc : PI α1-6 GlcNAc-transferase subunits of the glycosylphosphatidylinositol biosynthetic pathway of Trypanosoma brucei.

ABSTRACT: The first step of glycosylphosphatidylinositol (GPI) anchor biosynthesis in all eukaryotes is the addition of N-acetylglucosamine (GlcNAc) to phosphatidylinositol (PI) which is catalysed by a UDP-GlcNAc : PI α1-6 GlcNAc-transferase. This enzyme has been shown to be a complex of at least seven subunits in mammalian cells and a similar complex of homologous subunits has been postulated in yeast. Homologs of most of these mammalian and yeast subunits were identified in the Trypanosoma brucei predicted protein database. The putative catalytic subunit of the T. brucei complex,TbGPI3, was epitope tagged with three consecutive c-Myc sequences at its C-terminus. Immunoprecipitation of TbGPI3-3Myc followed by native polyacrylamide gel electrophoresis and anti-Myc Western blot showed that it is present in a ~240 kDa complex. Label-free quantitative proteomics were performed to compare anti-Myc pull-downs from lysates of TbGPI-3Myc expressing and wild type cell lines. TbGPI3-3Myc was the most highly enriched protein in the TbGPI3-3Myc lysate pull-down and partner proteins TbGPI15, TbGPI9, TbGPI2, TbGPI1 and TbERI1 were also identified with significant enrichment. Our proteomics data also suggest that an Arv-1 like protein (TbArv1) is a subunit of the T. brucei complex. Yeast and mammalian Arv1 have been previously implicated in GPI biosynthesis, but here we present the first experimental evidence for physical association of Arv1 with GPI biosynthetic machinery. A putative E2-ligase has also been tentatively identified as part of the T. brucei UDP-GlcNAc : PI α1-6 GlcNAc-transferase complex.

INSTRUMENT(S): Q Exactive Plus

ORGANISM(S): Trypanosoma Brucei

SUBMITTER: Michele Tinti

LAB HEAD: Mike Ferguson

PROVIDER: PXD022979 | Pride | 2021-02-26

REPOSITORIES: Pride

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Project description:The bloodstream forms of Trypanosoma brucei (BSF), responsible for the sleeping sickness, primarily evaluate in the blood of its mammalian hosts. The skin and the adipose tissues were recently identified as additional major sites for the parasite proliferation and transmission through its insect vector blood ingestion. Glucose is the only carbon source used by the blood parasites to feed its central metabolism, however, the metabolic behavior of the tissue-adapted parasites has not yet been addressed. Since production of glycerol is an important primary function of adipocytes, we have adapted the BSF trypanosomes to glucose-depleted and glycerol-rich growth medium (CMM_Gly/GlcNAc) and compared its metabolism and proteome with standard glucose-rich growth conditions (CMM_Glu). BSF consume 2-times more oxygen per carbon consumed in CMM_Gly/GlcNAc and is 11.5-times more sensitive to SHAM, a specific inhibitor of the alternative oxidase, which is consistent with the expected absolute requirement of the mitochondrial respiratory chain activity to convert glycerol into dihydroxyacetone phosphate. Metabolomic analyses by mass spectrometry showed that 13C-labeled glycerol is incorporated into hexose phosphates through gluconeogenesis. After several weeks of growth in CMM_Gly/GlcNAc, BSF adapt their metabolism by increasing and decreasing the rate of glycerol and glucose consumption, respectively. As expected RNAi-mediated down-regulation of glycerol kinase expression abolished glycerol degradation and is lethal for BSF growth in CMM_Gly/GlcNAc. However, the glycerol kinase activity is 7.8-fold decreased in CMM_Gly/GlcNAc, as confirms by western blotting and proteomic analyses, which suggests that the huge excess of glycerol kinase, which is not necessary for glycerol metabolism, is required for another yet undetermined non-essential function in glucose rich-conditions. Altogether these data shows that BSF trypanosomes are well adapted to glycerol-rich conditions, which could be encountered by the parasite in extravascular niches, such as skin and adipose tissues.

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Dataset Information

Proteomic identification of the UDP-GlcNAc : PI α1-6 GlcNAc-transferase subunits of the glycosylphosphatidylinositol biosynthetic pathway of Trypanosoma brucei.

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