The acquisition of lysophosphatidylcholine by African trypanosomes

Bloodstream forms of the African trypanosome, Trypanosoma brucei, can acquire substantial amounts of exogenous lysophospholipid. Lysophosphatidylcholine uptake is through a pathway consisting of three enzymes, phospholipase A1, acyl-CoA ligase, and lysophosphatidylcholine:acyl-CoA acyltransferase. The pathway enables the organism to acquire fatty acids and phospholipid head groups such as choline. Radiolabeling and 13C NMR studies show that two molecules of lysophosphatidylcholine are used to generate one molecule of cellular phosphatidylcholine. The three enzymes are associated with the trypanosomal plasma membrane and are accessible to exogenous substrates. The first enzyme, phospholipase A1, generates free fatty acid from exogenous lysophospholipid, which the second enzyme, a ligase, uses to form acyl-CoA. The fatty acyl-CoA formed by this route is in a separate pool from that derived from exogenous free fatty acid and is used by the third enzyme, acyltransferase, to acylate a second molecule of exogenous lysophospholipid. Acyltransferase is accessible to exogenous and endogenous acyl-CoA. The high activity of this pathway in bloodstream forms, compared with procyclic culture form trypanosomes, suggests that it may play a role in the acquisition of fatty acids for synthesis of the membrane form of the variant surface glycoprotein. Extracellular myristoyllysophosphatidylcholine can be used by trypanosomes as a source of myristate in remodeling the lipid anchor of the variant surface glycoprotein.