Fig. 3.

Lipid metabolism at MAMs. Historically, MAMs were identified as essential regions for phospholipid metabolism. For phosphatidylethanolamine (PE) synthesis, phosphatidylserine (PS) synthesized in the endoplasmic reticulum (ER) from phosphatidic acid (PA) by the PS synthetases 1 and 2 (Pss1/2) needs to be shuttled to the inner mitochondrial membrane (IMM), where it is decarboxylated to PE by the PS decarboxylase (Psd). This PE can then be shuttled back to the ER and used in further lipid metabolism, such as conversion to phosphatidylcholine (PC) by the PE-N-methyltransferase (PEMT). In addition, the synthesis of sterols requires the import of cholesterol (chol) from the ER into mitochondria