Synthetic Lethal Interaction of the Mitochondrial Phosphatidylethanolamine and Cardiolipin Biosynthetic Pathways in Saccharomyces cerevisiae

Abstract

Saccharomyces cerevisiae mitochondria contain enzymes required for synthesis of the phospholipids cardiolipin (CL) and phosphatidylethanolamine (PE), which are enriched in mitochondrial membranes. Previous studies indicated that PE may compensate for the lack of CL, and vice versa. These data suggest that PE and CL have overlapping functions and that the absence of both lipids may be lethal. To address this hypothesis, we determined whether the crd1⌬ mutant, which lacks CL, was viable in genetic backgrounds in which PE synthesis was genetically blocked. Deletion of the mitochondrial PE pathway gene PSD1 was synthetically lethal with the crd1⌬ mutant, whereas deletion of the Golgi and endoplasmic reticulum pathway genes PSD2 and DPL1 did not result in synthetic lethality. A 20-fold reduction in phosphatidylcholine did not affect the growth of crd1⌬ cells. Supplementation with ethanolamine, which led to increased PE synthesis, or with propanolamine, which led to synthesis of the novel phospholipid phosphatidylpropanolamine, failed to rescue the synthetic lethality of the crd1⌬psd1⌬ cells. These results suggest that mitochondrial biosynthesis of PE is essential for the viability of yeast mutants lacking CL.The phospholipid composition of the mitochondrial membrane is unique in that it is highly enriched in cardiolipin (CL) 2 and phosphatidylethanolamine (PE) (1, 2). CL is a dimeric glycerophospholipid that is synthesized exclusively in mitochondria and plays an important role in oxidative phosphorylation and mitochondrial membrane biogenesis (3). In contrast, PE biosynthesis occurs via multiple pathways (4). PE is commonly present in all subcellular membranes, although PE levels are highest in the mitochondrial membrane (2). PE and CL have similar physical properties in that they have a propensity toward the formation of nonbilayer, inverted hexagonal (H II ) phase structures (5, 6). The local, transient formation of nonbilayer structures is thought to play an important role in vital cellular processes, such as vesicle formation, vesicle-mediated protein trafficking, and membrane fusion (7). In addition, nonbilayer lipids affect integration of proteins into the membrane, their lateral movement within the membrane, and the function and folding of certain integral membrane proteins (8).In the yeast Saccharomyces cerevisiae, phospholipid biosynthesis is compartmentalized in various subcellular organelles, including the Golgi body, endoplasmic reticulum, and mitochondria (Fig. 1). CL biosynthesis occurs in three steps, all catalyzed by enzymes present in the mitochondria. The first step, catalyzed by phosphatidylglycerol phosphate (PGP) synthase, is the synthesis of PGP from CDP-diacylglycerol and glycerol 3-phosphate. PGP phosphatase dephosphorylates PGP to phosphatidylglycerol. In the final step, CL synthase catalyzes the formation of CL from phosphatidylglycerol and CDP-diacylglycerol (9, 10). PGP synthase and CL synthase have been characterized in yeast, and the genes encoding these enzymes, PGS1 (11, 12) and CRD1 ...

Thematic Review Series: Glycerolipids. Cardiolipin synthesis for the assembly of bacterial and mitochondrial membranes

“…Also, cardiolipin has the ability to form clusters (93) and nonbilayer structures (5-7). The potential significance of nonbilayer structures is supported by the absolute requirement for phosphatidylethanolamine, another phospholipid with nonbilayer properties, in cardiolipin-deficient yeast (94). The ability of cardiolipin to trap protons (Fig.…”

Phosphatidylcholine Affects Inner Membrane Protein Translocases of Mitochondria

“…Both phospholipids are crucial for mitochondrial function and morphology (44 -46). Double deletion of Psd1 with the cardiolipin synthase Crd1 is lethal confirming the closely related functions of CL and PE (47).…”

Lipid map of the mammalian cell

“…Under conditions of charge neutralization (divalent cations or high salt), mitochondrial CL also acquires a preference for a non-bilayer configuration. Inactivation of CL synthase and mitochondrial PSD in yeast is synthetically lethal (Gohil et al, 2005), indicating a requirement for mitochondrial non-bilayer lipids. The non-bilayer propensity of PE and CL depends on the length and level of unsaturation of their acyl chains.…”