Acyl Lipids: pathways

ARABIDOPSIS
ACYL-LIPID METABOLISM

Legend: G3P produced by GPDH is converted to PA by sequential acylation reactions regulated by GPAT and LPAAT. PA is converted to CDP-DAG, from which PI is produced by PIS. Alternatively, the PA is hydrolyzed to DAG by PP. DAGs are combined with CDP-choline and CDP-ethanolamine to produce PC and PE, respectively; the enzyme responsible for these reactions (AAPTs) may have dual substrate specificity. Phosphoethanolamine produced by EK is an important intermediate for PE and PC biosyntheses. Cytosolic CKs also provide phosphocholine for PC biosynthesis from free choline, which may be recovered from PC by PLDs or derived from other tissues by phloem translocation. Phosphoethanlamine is converted to PE via CDP-ethanolamine, whereas the same substrate is methylated to phosphocholine by PEAMT and then converted to PC via CDP-choline. PE is a substrate for PS biosynthesis by BE-PSS, whereas PS is converted to PE by PSD. PC is the major substrate for desaturation and acyl editing. Acyl editing involves a dynamic exchange of fatty acids predominantly between the sn-2 (but also sn-1) position of PC and acyl-CoA pools, which may occur via the reverse reaction of LPCAT or by PLA2, LACS, and LPCAT. Two lyso-PE acyltransferases (LPEAT) have also been identified.but PE has a minor role in the acyl editing that occurs during initial phospholipid assembly and LPEAT may instead be involved in membrane maintenance. PLMT catalyzes a pathway to PC via methylation of methyl-PE. In addition to above pathways, the conversion of PGP to PG by PGP phosphatase (PGPP) is not shown.
Abbreviations: G3P, glycerol-3-phosphate; PA, phasphatidic acid; LPA, lysophosphatidic acid; DAG, diacylglycerol; PI, phosphatidylinositol; PC, phosphatidylcholine; LPC, lysophosphatidylcholine; PE, phosphatidylethanolamine; PS, phosphatidylserine; PGP, phosphatidyglycerophosphate; PG, phosphatidylglycerol; AAPT, aminoalchoholphosphotransferase; BE-PSS, base-exchange-type phosphatydylserine synthase; CCT, CTP:phosphorylcholine cytidylyltransferase; CDP-DAGS, CDP-diacylglycerol synthetase; PECT, CTP:phosphorylethanolamine cytidyltransferase; DAG-CPT, CDP-choline:diacylglycerol cholinephosphotransferase; DAG-EPT, CDP-ethanolamine:diacylglycerol cholinephosphotransferase; PGPS, phosphatidylglycerophosphate synthase; DHAP: dihydroxyacetone phosphate; FAD2, oleate desaturase; FAD3, linoleate desaturase; GPDH, glycerol-phosphate dehydrogenase; GPAT, glycerol-3-phosphate acyltransferase;. LPAAT, lysophosphatidic acid acyltransferase; PP, phosphatidate phosphatase; PIS, phosphatidylinositol synthase; PSD, phosphatidylserine decarboxylase; EK, ethanolamine kinase; CK, choline kinase; PEAMT, phosphoethanolamine N-methyltransferase; PLA2, PLMT, N-methylphospholipid methyltransferase; phospholipase A2 (Cytosolic); PLD, phospholipase D; LACS, long chain acyl-CoA synthetase; LPCAT: lysophosphatidylcholine acyltransferase, LPEAT, lysophosphatidyl ethanolamine acyltransferase.

Contributors: Ikuo Nishida and Philip Bates

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