Depletion of phosphatidylcholine in yeast induces shortening and increased saturation of the lipid acyl chains

To study the consequences of depleting the major membrane phospholipid phosphatidylcholine (PC), exponentially growing cells of a yeast cho2opi3 double deletion mutant were transferred from medium containing choline to choline-free medium. Cell growth did not cease until the PC level had dropped below 2 % of total phospholipids after 4-5 generations. Increasing contents of phosphatidylethanolamine (PE) and phosphatidylinositol (PI) made up for the loss of PC. During PC depletion the remaining PC was subject to acyl chain remodeling with monounsaturated species replacing diunsaturated species, as shown by mass spectrometry. The remodeling of PC did not require turnover by the SPO14-encoded phospholipase D. The changes in the PC species profile were found to reflect an overall shift in the cellular acyl chain composition that exhibited a 40 % increase in the ratio of C16 over C18 acyl chains, and a 10 % increase in the degree of saturation. The shift was stronger in the phospholipid than in the neutral lipid fraction, and strongest in the species profile of PE. The shortening and increased saturation of the PE acyl chains were shown to decrease the non-bilayer propensity of PE. The results point to a regulatory mechanism in yeast that maintains intrinsic membrane curvature in an optimal range.