Lysophosphatidylcholine metabolism in Saccharomyces cerevisiae -: The role of P-type ATPases in transport and a broad specificity acyltransferase in acylation

We recently described a new route for the synthesis of phosphatidylethanolamine (PtdEtn) from exogenous lyso-PtdEtn, which we have termed the exogenous lysolipid metabolism ( ELM) pathway. The ELM pathway for lyso-PtdEtn requires the action of plasma membrane P-type ATPases Dnf1p and Dnf2p and their requisite beta-subunit, Lem3p, for the active uptake of lyso-PtdEtn. In addition, the acyl-CoA-dependent acyltransferase, Ale1p, mediates the acylation of the imported lysolipid to form PtdEtn. We now report that these components of the lyso-PtdEtn ELM pathway are also active with lyso-1-acyl-2-hydroxyl-sn-glycero-3-phosphocholine (PtdCho) as a substrate. Lyso-PtdCho supports the growth of a choline auxotrophic pem1 Delta pem2 Delta strain. Uptake of radiolabeled lyso- PtdCho was impaired by the dnf2 Delta and lem3 Delta mutations. Introduction of a lem3 Delta mutation into a pem1 Delta pem2 Delta background impaired the ability of the resulting strain to grow with lyso- PtdCho as the sole precursor of PtdCho. After import of lyso- PtdCho, the recently characterized lyso- PtdEtn acyltransferase, Ale1p, functioned as the sole lyso- PtdCho acyltransferase in yeast. A pem1 Delta pem2 Delta ale1 Delta strain grew with lyso- PtdCho as a substrate but showed a profound reduction in PtdCho content when lysoPtdCho was the only precursor of PtdCho. Ale1p acylates lyso- PtdCho with a preference for monounsaturated acyl-CoA species, and the specific LPCAT activity of Ale1p in yeast membranes is >50-fold higher than the basal rate of de novo aminoglycerophospholipid biosynthesis from phosphatidylserine synthase activity. In addition to lyso- PtdCho, lyso- PtdEtn, and lyso- phosphatidic acid, Ale1p was also active with lysophosphatidylserine, lysophosphatidylglycerol, and lysophosphatidylinositol as substrates. These results establish a new pathway for the net synthesis of PtdCho in yeast and provide new tools for the study of PtdCho synthesis, transport, and remodeling.