Trypanosoma brucei Bloodstream Forms Depend upon Uptake of myo -Inositol for Golgi Complex Phosphatidylinositol Synthesis and Normal Cell Growth

Abstract

ABSTRACT myo -Inositol is a building block for all inositol-containing phospholipids in eukaryotes. It can be synthesized de novo from glucose-6-phosphate in the cytosol and endoplasmic reticulum. Alternatively, it can be taken up from the environment via Na + - or H + -linked myo -inositol transporters. While Na + -coupled myo -inositol transporters are found exclusively in the plasma membrane, H + -linked myo -inositol transporters are detected in intracellular organelles. In Trypanosoma brucei , the causative agent of human African sleeping sickness, myo -inositol metabolism is compartmentalized. De novo -synthesized myo -inositol is used for glycosylphosphatidylinositol production in the endoplasmic reticulum, whereas the myo -inositol taken up from the environment is used for bulk phosphatidylinositol synthesis in the Golgi complex. We now provide evidence that the Golgi complex-localized T. brucei H + -linked myo -inositol transporter (TbHMIT) is essential in bloodstream-form T. brucei . Downregulation of TbHMIT expression by RNA interference blocked phosphatidylinositol production and inhibited growth of parasites in culture. Characterization of the transporter in a heterologous expression system demonstrated a remarkable selectivity of TbHMIT for myo -inositol. It tolerates only a single modification on the inositol ring, such as the removal of a hydroxyl group or the inversion of stereochemistry at a single hydroxyl group relative to myo -inositol.