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.

Open in a new window

Sources and fates of metabolites