Phosphatidylethanolamine metabolism

Phospholipids are crucial components of the cell membrane bilayers. Most of these phospholipids are composed of a diglyceride (diacylglycerol) moiety, a phosphate group and a simple organic molecule such as choline, serine or ethanolamine. The anionic phosphate group and polar groups such as choline forms the hydrophilic head and the fatty acid chains in diacylglycerol forms the hydrophobic tails in the membrane bilayer. Phosphatidic acids with ethanolamine and serine attached are referred to as phosphatidylethanolamine (cephalin) and phosphatidylserine respectively. Phosphatidylethanolamine is found in all living cells and it is the principal phospholipid in bacteria.

 

The apicomplexan parasites, Plasmodium falciparum and Toxoplasma gondii can de novo synthesise phospholipids such as phosphatidylcholine, phosphatidylethanolamine and phosphatidylserine from choline, ethanolamine and serine respectively [1, 2]. The analysis of Piroplasma genomes showed that they can also de novo synthesise phosphatidylethanolamine from ethanolamine. The phosphatidylserine synthase enzyme of both type 1 (P. falciparum) and type 2 (T. gondii) is absent in these genomes suggesting the absence of the de novo biosynthesis of phosphatidylserine. The phosphatidylserine decarboxylase enzyme catalysing the conversion of phosphatidylserine to phosphatidylethanolamine is present in the gene models of Theileria species, although it is missing in the genome of Babesia bovis. The enzymes which belong to the catabolism branch of phosphatidylethanolamine metabolism and cardiolipin biosynthesis present in other apicomplexans are also present in Piroplasma. The phosphatidylethanolamine N-methyltransferase enzyme (2.1.1.17, produces monomethyl-phosphatidylethanolamine) present in T. gondii is absent in other apicomplexans including Piroplasma species.

 

Enzyme EC Number Gene id
Glycerol-3-phosphate O-acyltransferase 2.3.1.15 TP01_0222
Diacylglycerol O-acyltransferase 2.3.1.20 TP01_0247
1-Acylglycerol-3-phosphate O-acyltransferase 2.3.1.51 TP02_0668
Diacylglycerol kinase 2.7.1.107 TP02_0475
Ethanolamine kinase 2.7.1.82 TP01_0942
Ethanolamine-phosphate cytidylyltransferase 2.7.7.14 TP04_0187
Phosphatidate cytidylyltransferase 2.7.7.41 TP04_0048
Cardiolipin synthetase 2.7.8.- TP04_0329
Ethanolaminephosphotransferase 2.7.8.1 TP01_1171
CDP-diacylglycerol-glycerol-3-phosphate 3-phosphatidyltransferase 2.7.8.5 TP01_1130
Phospholipase A2 3.1.1.4 TP01_1049
Phospholipase A2 3.1.1.4 TP03_0786
Phospholipase A2 3.1.1.4 TP04_0897
Lysohospholipase 3.1.1.5 TP01_0667
Lysohospholipase 3.1.1.5 TP01_1185
Lysohospholipase 3.1.1.5 TP03_0200
Lysohospholipase 3.1.1.5 TP03_0738
Lysohospholipase 3.1.1.5 TP03_0739
Lysohospholipase 3.1.1.5 TP04_0044
Lysohospholipase 3.1.1.5 TP04_0172
Phosphatidylglycerophosphatase 3.1.3.27 Missing in annotation
Phospholipase C 3.1.4.3 TP01_0775
Glycerophosphodiester phosphodiesterase 3.1.4.46 TP01_0659
Phosphatidylserine decarboxylase 4.1.1.65 TP01_1219
Long-chain-fatty-acid-CoA-ligase 6.2.1.3 TP01_0119
Long-chain-fatty-acid-CoA-ligase 6.2.1.3 TP01_0520
Long-chain-fatty-acid-CoA-ligase 6.2.1.3 TP02_0107
Acyl-CoA binding protein none TP01_0067
MSF-1 none TP03_0643

 

Open in a new window

 

 

Sources and fates of metabolites

 

Substrate Source pathways Product Fate pathways
Ethanolamine Host    
Fatty acid Host Cardiolipin Inner mitochondrial membrane
Glycerol-3P Glycolysis, Phosphatidylcholine metabolism Triacylglycerol Recycling of phospholipids, Storage in lipid bodies
Phosphatidylserine Host