Phosphatidylethanolamine Has an Essential Role inSaccharomyces cerevisiae That Is Independent of Its Ability to Form Hexagonal Phase Structures

Abstract

Two yeast enzymes, Psd1p and Psd2p, catalyze the decarboxylation of phosphatidylserine to produce phosphatidylethanolamine (PtdEtn). Mitochondrial Psd1p provides ϳ90% of total cellular phosphatidylserine decarboxylase activity. When the PSD1 gene is deleted, the resultant strain (psd1⌬) grows normally at 30°C in glucose and in the absence of exogenous choline or ethanolamine. However, at elevated temperature (37°C) or on the nonfermentable carbon source lactate, the growth of psd1⌬ strains is minimal without ethanolamine supplementation. The reduced growth and viability correlate with a PtdEtn content below 4% of total phospholipid. These results suggest that there is a critical level of PtdEtn required to support growth. This theory is supported by growth data revealing that a psd1⌬ psd2⌬ dpl1⌬ strain can only grow in the presence of ethanolamine. In contrast, a psd1⌬ psd2⌬ strain, which makes low levels of PtdEtn from sphingolipid breakdown, can be rescued by ethanolamine, choline, or the ethanolamine analogue propanolamine. psd1⌬ psd2⌬ cells grown in 2 mM propanolamine accumulate a novel lipid, which was determined by mass spectrometry to be phosphatidylpropanolamine (PtdPrn). PtdPrn can comprise up to 40% of the total phospholipid content in supplemented cells at the expense of phosphatidylcholine and PtdEtn. The absolute level of PtdEtn required for growth when PtdPrn is present appears to be 1% of the total phospholipid content. The essential function of the PtdEtn in the presence of propanolamine does not appear to be the formation of hexagonal phase lipid, insofar as PtdPrn readily forms hexagonal phase structures detectable by 31 P NMR.

From Protease to Decarboxylase

“…The autonomous generation of PE at specific subcellular sites appears to play an important role in organelle structure and function (7,8,10). PSDs belong to a small family of enzymes that contain a pyruvoyl prosthetic group, which includes S-adenosylmethionine decarboxylase (27), histidine decarboxylase (28), aspartate decarboxylase (29), and arginine decarboxylase (30) Pyruvoyl enzymes are first synthesized as single polypeptide precursors that undergo autoendoproteolytic cleavage to produce dissimilar ␣-and ␤-subunits.…”

Identification of Gene Encoding Plasmodium knowlesi Phosphatidylserine Decarboxylase by Genetic Complementation in Yeast and Characterization of in Vitro Maturation of Encoded Enzyme

“…Pk-cDNA Library Screening-Pk-cDNA library plasmids were transformed into an Etn auxotrophic strain, HKY44 (MAT␣ psd1-⌬1::TRP1 psd2-⌬1::HIS3 dpl1⌬::KanMX trp1 ura3 his3 lys2 leu2) (21). Transformants that stably acquired a plasmid from the library were isolated based on the growth on minimal glucose, uracil dropout (SC-U) medium, supplemented with 2 mM Etn.…”

Phosphatidylserine Transport to the Mitochondria Is Regulated by Ubiquitination

“…Despite the ability of choline to enable synthesis of PtdCho via the Kennedy pathway, this lipid cannot replace PtdEtn. This latter finding reflects both the need for critical levels of PtdEtn in the mitochondria, under respiratory conditions, and the essential role of PtdEtn in cells that has only recently been recognized (13,14). Although the pstA1-1 strain is an Etn auxotroph, the level and rate of PtdEtn synthesis is only modestly depressed in these cells under nutrient-restrictive conditions.…”

“…PtdEtn and PtdCho can also be synthesized via the Kennedy pathways from the precursors ethanolamine or choline (3). Both PtdEtn and PtdCho are thought to be essential for S. cerevisiae growth in medium that contains glucose or nonfermentable carbon sources (5,(12)(13)(14).…”