Schuiki Irmgard, Schnabl Martina, Czabany Tibor, Hrastnik Claudia, Daum Günther
Institute of Biochemistry, Graz University of Technology, Petersgasse 12/2, A-8010 Graz, Austria.
Biochim Biophys Acta. 2010 Apr;1801(4):480-6. doi: 10.1016/j.bbalip.2009.12.008. Epub 2009 Dec 28.
In this study, we examined the contribution of the four different pathways of phosphatidylethanolamine (PE) synthesis in the yeast Saccharomyces cerevisiae to the supply of this phospholipid to the plasma membrane. These pathways of PE formation are decarboxylation of phosphatidylserine (PS) by (i) phosphatidylserine decarboxylase 1 (Psd1p) in mitochondria and (ii) phosphatidylserine decarboxylase 2 (Psd2p) in a Golgi/vacuolar compartment, (iii) incorporation of exogenous ethanolamine and ethanolamine phosphate derived from sphingolipid catabolism via the CDP-ethanolamine pathway in the endoplasmic reticulum (ER), and (iv) synthesis of PE through acylation of lyso-PE catalyzed by the acyl-CoA-dependent acyltransferase Ale1p in the mitochondria associated endoplasmic reticulum membrane (MAM). Deletion of PSD1 and/or PSD2 led to depletion of total cellular and plasma membrane PE level, whereas mutation in the other pathways had practically no effect. Analysis of wild type and mutants, however, revealed that all four routes of PE synthesis contributed not only to PE formation but also to the supply of PE to the plasma membrane. Pulse-chase labeling experiments with L[(3)H(G)]serine and [(14)C]ethanolamine confirmed the latter finding. Fatty acid profiling demonstrated a rather balanced incorporation of PE species into the plasma membrane irrespective of mutations suggesting that all four pathways of PE synthesis provide at least a basic portion of "correct" PE species required for plasma membrane biogenesis. In summary, the PE level in the plasma membrane is strongly influenced by total cellular PE synthesis, but fine tuned by selective assembly mechanisms.
在本研究中，我们检测了酿酒酵母中磷脂酰乙醇胺（PE）合成的四种不同途径对质膜中这种磷脂供应的贡献。这些PE形成途径包括：（i）线粒体中的磷脂酰丝氨酸脱羧酶1（Psd1p）对磷脂酰丝氨酸（PS）进行脱羧；（ii）高尔基体/液泡区室中的磷脂酰丝氨酸脱羧酶2（Psd2p）对磷脂酰丝氨酸进行脱羧；（iii）在内质网（ER）中通过CDP - 乙醇胺途径掺入源自鞘脂分解代谢的外源性乙醇胺和磷酸乙醇胺；以及（iv）在线粒体相关内质网膜（MAM）中由酰基辅酶A依赖性酰基转移酶Ale1p催化溶血PE的酰化作用合成PE。缺失PSD1和/或PSD2导致总细胞和质膜PE水平降低，而其他途径的突变几乎没有影响。然而，对野生型和突变体的分析表明，PE合成的所有四条途径不仅有助于PE的形成，还有助于向质膜供应PE。用L[（3）H（G）]丝氨酸和[（14）C]乙醇胺进行的脉冲追踪标记实验证实了后一发现。脂肪酸分析表明，无论有无突变，PE种类都相当平衡地掺入质膜，这表明PE合成的所有四条途径至少提供了质膜生物合成所需的“正确”PE种类的基本部分。总之，质膜中的PE水平受总细胞PE合成的强烈影响，但通过选择性组装机制进行微调。
