Phosphatidylethanolamine in Trypanosoma brucei Is Organized in Two Separate Pools and Is Synthesized Exclusively by the Kennedy Pathway

Abstract

Phosphatidylethanolamine is a major phospholipid class of all eukaryotic cells. It can be synthesized via the CDP-ethanolamine branch of the Kennedy pathway, by decarboxylation of phosphatidylserine, or by base exchange with phosphatidylserine. The contributions of these pathways to total phosphatidylethanolamine synthesis have remained unclear. Although Trypanosoma brucei, the causative agent of human and animal trypanosomiasis, has served as a model organism to elucidate the entire reaction sequence for glycosylphosphatidylinositol biosynthesis, the pathways for the synthesis of the major phospholipid classes have received little attention. We now show that disruption of the CDP-ethanolamine branch of the Kennedy pathway using RNA interference results in dramatic changes in phosphatidylethanolamine, phosphatidylserine, and phosphatidylcholine. By targeting individual enzymes of the pathway, we demonstrate that de novo phosphatidylethanolamine synthesis in T. brucei procyclic forms is strictly dependent on the CDPethanolamine route. Interestingly, the last step in the Kennedy pathway can be mediated by two separate activities leading to two distinct pools of phosphatidylethanolamine, consisting of predominantly alk-1-enyl-acyl-or diacyl-type molecular species. In addition, we show that phosphatidylserine in T. brucei procyclic forms is synthesized exclusively by base exchange with phosphatidylethanolamine.

An essential bacterial-type cardiolipin synthase mediates cardiolipin formation in a eukaryote

“…A more refined blast to identify predicted T. brucei proteins having a CDP-alcohol phosphatidyltransferase domain, which is typical of eukaryotictype Cls and other enzymes of the glycerophospholipid metabolism (23,24), revealed three proteins: phosphatidylinositol synthase (Tb09.160.0530), choline/ethanolamine phosphotransferase (Tb927.10.8900), and ethanolamine phosphotransferase (Tb927.10.13290). However, all three enzymes have been characterized experimentally in T. brucei and are involved in glycerophospholipid synthesis (36,37) and thus are not part of the CL biosynthetic pathway. These findings suggested that T. brucei may synthesize CL by a route not involving eukaryotic-type Cls.…”

Formation and function of phosphatidylserine and phosphatidylethanolamine in mammalian cells

“…In addition, soluble truncated PSD proteins have been detected in the parasite Plasmodium knowlesi [191]. Interestingly, another parasite, T. brucei, synthesizes PE entirely by the CDP-ethanolamine pathway [172]. It is noteworthy that the PS that is used for decarboxylation to PE in mitochondria is synthesized in the ER/MAM from PC (via PSS1) and PE (via PSS2) (Fig.…”

“…3) appears to depend on the cell type. In rat liver/hepatocytes [167][168][169][170] and hamster heart [171] the CDP-ethanolamine pathway has been reported to provide the majority of PE; in T. brucei, PE is made solely by this pathway [172]. On the other hand, in other cells, such as baby hamster kidney cells and CHO cells, > 80% of PE is derived from the PSD pathway even when ethanolamine is supplied as a substrate for the CDP-ethanolamine pathway [173,174].…”

Lipid synthesis in protozoan parasites: A comparison between kinetoplastids and apicomplexans

“…Although the presence of PS in Leishmania parasites has been reported in several studies [151, 154, 155], recent analyses using mass spectrometry and serine labeling failed to detect this lipid in L. major promastigotes [156–158] (see also below). Interestingly, the glycerophospholipid classes in T. brucei and Leishmania consist of high amounts of ether-type molecular species [137, 147, 159]. In particular, PE in T. brucei procyclic and bloodstream forms [147, 159] and in L. major promastigotes [152] is composed mostly of alkenyl-acyl and alkyl-acyl glycerol, also called plasmenyl or plasmalogen and plasmanyl, respectively, molecular species.…”

“…Interestingly, the glycerophospholipid classes in T. brucei and Leishmania consist of high amounts of ether-type molecular species [137, 147, 159]. In particular, PE in T. brucei procyclic and bloodstream forms [147, 159] and in L. major promastigotes [152] is composed mostly of alkenyl-acyl and alkyl-acyl glycerol, also called plasmenyl or plasmalogen and plasmanyl, respectively, molecular species. The most prominent glycerophospholipids of Leishmania promastigotes contain saturated and unsaturated C18 fatty acids [152], and most ether-type phospholipids in T. brucei contain C18:0 at the sn -1 and mainly unsaturated fatty acids (C18:2, C22:2) at the sn- 2 position [147].…”