Background: Intracellular myo-inositol homeostasis involves both de novo synthesis and uptake of myo-inositol from the environment. Results: Down-regulation of the myo-inositol transporter in Trypanosoma brucei causes depletion of bulk inositol lipids, but not glycosylphosphatidylinositols, and leads to parasite death. Conclusion: De novo synthesis of myo-inositol is not sufficient to ensure bulk inositol lipid production. Significance: myo-Inositol metabolism in T. brucei is compartmentalized.

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Aspergillus species included in section Nigri are common in plant products and processed food, such as grapes, cereals, coffee and derivatives, particularly in warm and tropical climates. Two of these species, A. carbonarius and A. niger, are known to produce ochratoxin A (OTA), a potent nephrotoxin and carcinogenic to human (group 2B). Recognition of the several species of this section is difficult and requires considerable expertise using conventional methods based on morphological features. In this work we describe rapid, sensitive and robust assays based on the PCR technique to discriminate the main species included in section Nigri: A. japonicus, A. heteromorphus, A. ellipticus and the two morphologically indistinguishable species of the A. niger aggregate: A. niger and A. tubingensis. The species-specific primers have been designed on the basis of ITS (internal transcribed spacers of rDNA units) sequence comparisons obtained from several Aspergillus strains and have been tested in a number of strains from different origins and hosts. These PCR assays, based on multi-copy sequences, are highly sensitive and specific and represent a good tool for an early detection of OTA-producing Aspergillus species in order to prevent OTA from entering the food chain.

The membrane protein RFT1 is essential for normal protein N-glycosylation, but its precise function is not known. RFT1 was originally proposed to translocate the glycolipid ManGlcNAc-PP-dolichol (needed to synthesize N-glycan precursors) across the endoplasmic reticulum membrane, but subsequent studies showed that it does not play a direct role in transport. In contrast to the situation in yeast, RFT1 is not essential for growth of the parasitic protozoan Trypanosoma brucei, enabling the study of its function in a null background. We now report that lack of T. brucei RFT1 (TbRFT1) not only affects protein N-glycosylation but also glycosylphosphatidylinositol (GPI) anchor side-chain modification. Analysis by immunoblotting, metabolic labeling, and mass spectrometry demonstrated that the major GPI-anchored proteins of T. brucei procyclic forms have truncated GPI anchor side chains in TbRFT1 null parasites when compared with wild-type cells, a defect that is corrected by expressing a tagged copy of TbRFT1 in the null background. In vivo and in vitro labeling experiments using radiolabeled GPI precursors showed that GPI underglycosylation was not the result of decreased formation of the GPI precursor lipid or defective galactosylation of GPI intermediates in the endoplasmic reticulum, but rather due to modifications that are expected to occur in the Golgi apparatus. Unexpectedly, immunofluorescence microscopy localized TbRFT1 to both the endoplasmic reticulum and the Golgi, consistent with the proposal that TbRFT1 plays a direct or indirect role in GPI anchor glycosylation in the Golgi apparatus. Our results implicate RFT1 in a wider range of glycosylation processes than previously appreciated.

Discovery of novel drug targets may lead to improved treatment of trypanosomiasis. We characterize here 2 gene products of Trypanosoma brucei that are essential for the growth of bloodstream form (BSF) parasites, as shown by RNA interference (RNAi)-mediated down-regulation of the individual mRNAs. The primary sequences of the 2 proteins-protein encoded by gene Tb927.1.4450 (TbK1) and protein encoded by gene Tb927.9.4820 (TbK2)-indicate that both belong to the family of putative, Ca 2+ -activated potassium channels. The proteins were expressed in Xenopus laevis oocytes and their functions investigated by use of electrophysiological techniques. Only combined expression of TbK1 and TbK2 results in the formation of sizeable currents, indicating that these proteins probably assemble into a heteromeric ion channel. The current mediated by this channel shows little time and voltage dependence and displays a permeability ratio of K + /Na + of >20. The known potassium channel blocker barium inhibits this channel with a half-maximal inhibitory concentration (IC 50 ) of 98 6 15 mM. The membrane potential of trypanosomes was measured with a fluorescent dye. Individual RNAi-mediated downregulation of TbK1 or TbK2 eliminates a potassium conductance in the plasma membrane of BSF. Thus, this heteromeric potassium channel is involved in the modulation of the plasma membrane potential and represents a novel drug target in T. brucei.-Steinmann, M. E., González-Salgado, A., Bütikofer, P., Mäser, P., Sigel, E. A heteromeric potassium channel involved in the modulation of the plasma membrane potential is essential for the survival of African trypanosomes. FASEB J. 29, 3228-3237 (2015). www.fasebj.org