Benghezal Mohammed, Roubaty Carole, Veepuri Vijayanath, Knudsen Jens, Conzelmann Andreas
Department of Medicine, University of Fribourg, CH-1700 Fribourg, Switzerland.
J Biol Chem. 2007 Oct 19;282(42):30845-55. doi: 10.1074/jbc.M702719200. Epub 2007 Aug 3.
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 slc1Delta cells. The simultaneous deletion of SLC1 and SLC4 is lethal. Mass spectrometric analysis of lipids from slc1Delta and slc4Delta cells demonstrates that in vivo Slc1p and Slc4p generate almost the same glycerophospholipid profile. Microsomes from slc1Delta and slc4Delta cells incubated with [14C]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 slc1Delta and slc4Delta 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 Mg2+-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.
磷脂酸是所有甘油磷脂合成的中间体。在酵母中，它由溶血磷脂酸生成，溶血磷脂酸由Slc1p进行酰化，Slc1p是一种sn-2特异性的、依赖酰基辅酶A的1-酰基甘油-3-磷酸O-酰基转移酶。删除SLC1并不致命，也不会消除所有微粒体1-酰基甘油-3-磷酸O-酰基转移酶活性，这表明可能存在另外一种酶。在此我们表明，SLC4（Yor175c），一个迄今功能未知的基因，编码第二种1-酰基-sn-甘油-3-磷酸酰基转移酶。SLC4含有一个膜结合的O-酰基转移酶基序，SLC4的下调会强烈降低来自slc1Δ细胞微粒体中的1-酰基-sn-甘油-3-磷酸酰基转移酶活性。同时删除SLC1和SLC4是致命的。对来自slc1Δ和slc4Δ细胞的脂质进行质谱分析表明，在体内Slc1p和Slc4p产生几乎相同的甘油磷脂谱。来自slc1Δ和slc4Δ细胞的微粒体在不存在溶血磷脂酸且没有CTP的情况下与[14C]油酰辅酶A一起孵育时，仍然会将标记物掺入甘油磷脂中，这表明Slc1p和Slc4p也可以使用内源性溶血甘油磷脂作为底物。然而，来自slc1Δ和slc4Δ细胞的微粒体产生的脂质谱不同，这表明Slc1p和Slc4p具有不同的底物特异性，或者由于亚细胞定位不同而能够接触到不同的溶血甘油磷脂底物。实际上，亲和纯化的Slc1p不仅对溶血磷脂酸显示出Mg2+依赖性酰基转移酶活性，而且对磷脂酰丝氨酸和磷脂酰肌醇的溶血形式也显示出该活性。因此，Slc1p和Slc4p可能不仅作为1-酰基甘油-3-磷酸O-酰基转移酶具有活性，而且还参与成熟甘油磷脂sn-2位的脂肪酸交换。
