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 BBOV_IV005200
Diacylglycerol O-acyltransferase 2.3.1.20 BBOV_IV004970
1-Acylglycerol-3-phosphate O-acyltransferase 2.3.1.51 BBOV_II006950
Diacylglycerol kinase 2.7.1.107 BBOV_III004760
Ethanolamine kinase 2.7.1.82 BBOV_IV008310
Ethanolamine kinase 2.7.1.82 BBOV_IV008320
Ethanolamine-phosphate cytidylyltransferase 2.7.7.14 BBOV_I004300
Phosphatidate cytidylyltransferase 2.7.7.41 BBOV_II005070
Cardiolipin synthetase 2.7.8.- BBOV_II002000
Ethanolaminephosphotransferase 2.7.8.1 BBOV_IV011360
CDP-diacylglycerol-glycerol-3-phosphate 3-phosphatidyltransferase 2.7.8.5 BBOV_IV011790
Phospholipase A2 3.1.1.4 BBOV_III000510
Phospholipase A2 3.1.1.4 BBOV_III009800
Phospholipase A2 3.1.1.4 BBOV_III011780
Phospholipase A2 3.1.1.4 BBOV_IV003440
Lysohospholipase 3.1.1.5 BBOV_IV010560
Phosphatidylglycerophosphatase 3.1.3.27 Missing in annotation
Phospholipase C 3.1.4.3 BBOV_IV011070
Glycerophosphodiester phosphodiesterase 3.1.4.46 BBOV_IV010120
Phosphatidylserine decarboxylase 4.1.1.65 Missing in annotation (May be absent)
Long-chain-fatty-acid-CoA-ligase 6.2.1.3 BBOV_III002500
Long-chain-fatty-acid-CoA-ligase 6.2.1.3 BBOV_III010400
Long-chain-fatty-acid-CoA-ligase 6.2.1.3 BBOV_IV000960
MSF-1 none BBOV_I004560
Acyl-CoA binding protein none BBOV_IV000490

 

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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