Phosphatidylserine synthase 2 and phosphatidylserine decarboxylase are essential for aminophospholipid synthesis in Trypanosoma brucei.

Luce Farine,Jae‐Yeon Choi,Terry K Smith,Jennifer Jelk,Jon Nunes,Dennis R Voelker,Peter Bütikofer

doi:10.1111/mmi.13637

Abstract

SummaryPhosphatidylethanolamine (PE) and phosphatidylserine (PS) are ubiquitously expressed and metabolically interconnected glycerophospholipids in eukaryotes and prokaryotes. In Trypanosoma brucei, PE synthesis has been shown to occur mainly via the Kennedy pathway, one of the three routes leading to PE synthesis in eukaryotes, while PS synthesis has not been studied experimentally. We now reveal the importance of T. brucei PS synthase 2 (TbPSS2) and T. brucei PS decarboxylase (TbPSD), two key enzymes involved in aminophospholipid synthesis, for trypanosome viability. By using tetracycline‐inducible down‐regulation of gene expression and in vivo and in vitro metabolic labeling, we found that TbPSS2 (i) is necessary for normal growth of procyclic trypanosomes, (ii) localizes to the endoplasmic reticulum and (iii) represents the unique route for PS formation in T. brucei. In addition, we identified TbPSD as type I PS decarboxylase in the mitochondrion and found that it is processed proteolytically at a WGSS cleavage site into a heterodimer. Down‐regulation of TbPSD expression affected mitochondrial integrity in both procyclic and bloodstream form trypanosomes, decreased ATP production via oxidative phosphorylation in procyclic form and affected parasite growth.

Highlights

Glycerophospholipids are major building blocks of all biological membranes
In Trypanosoma brucei, PE synthesis has been shown to occur mainly via the Kennedy pathway, one of the three routes leading to PE synthesis in eukaryotes, while PS synthesis has not been studied experimentally
We reveal the importance of T. brucei PS synthase 2 (TbPSS2) and T. brucei PS decarboxylase (TbPSD), two key enzymes involved in aminophospholipid synthesis, for trypanosome viability

Summary

Introduction

Glycerophospholipids are major building blocks of all biological membranes. The relative abundance of the different classes and their subclass and molecular species compositions modulate membrane characteristics, such as fluidity, curvature and membrane tension, and affect properties of membraneassociated proteins (reviewed by Lee, 2004). The aminophospholipid classes, phosphatidylethanolamine (PE) and phosphatidylserine (PS), are present in membranes of most eukaryotes and prokaryotes (reviewed by Vance, 2008; Vance and Tasseva, 2013). PE has been shown to be involved in a wide range of biological processes, including cell division (Emoto et al, 1996) and protein folding (Bogdanov and Dowhan, 1998), and represents the ethanolamine donor for the synthesis of glycosylphosphatidylinositol (GPI) anchors (Menon and Stevens, 1992) and other protein modifications (Ichimura et al, 2000; Signorell et al, 2008a; Cullen and Trent, 2010). The pathways for the synthesis of PS and PE are often coupled, but the contributions of the individual pathways and their interconnections differ considerably among eukaryotes (reviewed by Vance and Tasseva, 2013)

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