SLC1 and SLC4 Encode Partially Redundant Acyl-Coenzyme A 1-Acylglycerol-3-phosphate O-Acyltransferases of Budding Yeast

Abstract

Phosphatidic acid is the intermediate, from which all glycerophospholipids are synthesized. In yeast, it is generated from lysophosphatidic acid, which is acylated by Slc1p, an sn-2-specific, acyl-coenzyme A-dependent 1-acylglycerol-3-phosphate O-acyltransferase. Deletion of SLC1 is not lethal and does not eliminate all microsomal 1-acylglycerol-3-phosphate O-acyltransferase activity, suggesting that an additional enzyme may exist. Here we show that SLC4 (Yor175c), a gene of hitherto unknown function, encodes a second 1-acyl-sn-glycerol-3-phosphate acyltransferase. SLC4 harbors a membrane-bound O-acyltransferase motif and down-regulation of SLC4 strongly reduces 1-acyl-sn-glycerol-3-phosphate acyltransferase activity in microsomes from slc1⌬ cells. The simultaneous deletion of SLC1 and SLC4 is lethal. Mass spectrometric analysis of lipids from slc1⌬ and slc4⌬ cells demonstrates that in vivo Slc1p and Slc4p generate almost the same glycerophospholipid profile. Microsomes from slc1⌬ and slc4⌬ cells incubated with [ 14 C]oleoyl-coenzyme A in the absence of lysophosphatidic acid and without CTP still incorporate the label into glycerophospholipids, indicating that Slc1p and Slc4p can also use endogenous lysoglycerophospholipids as substrates. However, the lipid profiles generated by microsomes from slc1⌬ and slc4⌬ cells are different, and this suggests that Slc1p and Slc4p have a different substrate specificity or have access to different lyso-glycerophospholipid substrates because of a different subcellular location. Indeed, affinity-purified Slc1p displays Mg 2؉ -dependent acyltransferase activity not only toward lysophosphatidic acid but also lyso forms of phosphatidylserine and phosphatidylinositol. Thus, Slc1p and Slc4p may not only be active as 1-acylglycerol-3-phosphate O-acyltransferases but also be involved in fatty acid exchange at the sn-2-position of mature glycerophospholipids.

Discovery of a lysophospholipid acyltransferase family essential for membrane asymmetry and diversity

“…Recently, four different research groups independently reported the identification of a yeast orthologue of this family as a LPLAT with most similarity to mLPCAT4 (MBOAT2) (46)(47)(48)(49). Notably, the enzymatic properties of yeast MBOAT are different from those of mouse MBOAT.…”

Caenorhabditis elegans mboa-7, a Member of the MBOAT Family, Is Required for Selective Incorporation of Polyunsaturated Fatty Acids into Phosphatidylinositol

“…It is not clear at present whether another lysoPI-specific acyltransferase with different acyl donor specificity exists or if lysophospholipid acyltransferase with no head group specificity catalyzes the transfer of these fatty acids into PI exists. Very recently, a novel lysophospholipid acyltransferase was identified from yeast that catalyzes the transfer of unsaturated fatty acids into major lysophospholipids such as lysoPE, lysoPC, lysoPS, lysoPI, and lysoPA (Benghezal et al, 2007;Jain et al, 2007;Riekhof et al, 2007;Tamaki et al, 2007). Because other MBOAT family genes were found in C. elegans, one or more of these gene products may express the remaining LPIAT activity in mboa-7 mutants.…”

“…Biochemically characterized members of the family encode enzymes that transfer organic acids, typically fatty acids, onto hydroxyl groups of membrane-embedded targets. As mentioned above, several groups very recently cloned a yeast gene named ALE1 (Riekhof et al, 2007), SLC4 (Benghezal et al, 2007), or LPT1 (Jain et al, 2007;Tamaki et al, 2007) that encodes an acyltransferase of the MBOAT family. Deletion of this gene in yeast results in strong reduction of the activities of various lysophospholipid acyltransferases such as LPEAT, LPCAT, LPSAT, LPIAT, and LPAAT, suggesting that this newly identified acyltransferase is involved in the metabolism of a variety of lysophospholipids in the cells.…”

“…These enzymes have conserved motifs in common with the enzymes involved in the de novo phospholipid synthesis pathway (Kennedy pathway) such as acylglycerolphosphate acyltransferase and lysophosphatidic acid acyltransferase (LPAAT). Very recently, a novel lysophospholipid acyltransferase was identified from yeast that catalyzes the transfer of unsaturated fatty acids into most major lysophospholipids (Benghezal et al, 2007;Jain et al, 2007;Riekhof et al, 2007;Tamaki et al, 2007). In contrast to LPCAT1 and LPCAT2, this enzyme harbors a membrane-bound O-acyltransferase (MBOAT) motif present in a variety of acyltransferases of bacteria and mammals (Hofmann, 2000).…”

Global analysis of the yeast lipidome by quantitative shotgun mass spectrometry

“…Altogether, this is currently the most comprehensive description of the S. cerevisiae lipidome achieved with Ϸ125-fold better sensitivity and Ͼ3-fold increased lipidome coverage compared with previous approaches (14,16,17). To demonstrate its efficacy for functional genomics studies, we monitored in molecular detail how the full lipidome adapted to growth temperature and genomic deletion of 3-ketoacyl-CoA synthases.…”