Department of Molecular Physiology and Biophysics, University of Iowa, Iowa City, IA 52242, USA.
Mol Biol Cell. 2010 Feb 1;21(3):443-55. doi: 10.1091/mbc.e09-06-0519. Epub 2009 Dec 16.
Control of lipid composition of membranes is crucial to ensure normal cellular functions. Saccharomyces cerevisiae has two different phosphatidylserine decarboxylase enzymes (Psd1 and Psd2) that catalyze formation of phosphatidylethanolamine. The mitochondrial Psd1 provides roughly 70% of the phosphatidylethanolamine (PE) biosynthesis in the cell with Psd2 carrying out the remainder. Here, we demonstrate that loss of Psd2 causes cells to acquire sensitivity to cadmium even though Psd1 remains intact. This cadmium sensitivity results from loss of normal activity of a vacuolar ATP-binding cassette transporter protein called Ycf1. Measurement of phospholipid levels indicates that loss of Psd2 causes a specific reduction in vacuolar membrane PE levels, whereas total PE levels are not significantly affected. The presence of a phosphatidylinositol transfer protein called Pdr17 is required for Psd2 function and normal cadmium tolerance. We demonstrate that Pdr17 and Psd2 form a complex in vivo that seems essential for maintenance of vacuolar PE levels. Finally, we refine the localization of Psd2 to the endosome arguing that this enzyme controls vacuolar membrane phospholipid content by regulating phospholipids in compartments that will eventually give rise to the vacuole. Disturbance of this regulation of intracellular phospholipid balance leads to selective loss of membrane protein function in the vacuole.
控制膜的脂质组成对于确保正常的细胞功能至关重要。酿酒酵母有两种不同的磷脂酰丝氨酸脱羧酶（Psd1 和 Psd2），它们催化磷脂酰乙醇胺的形成。线粒体 Psd1 提供细胞中大约 70%的磷脂酰乙醇胺（PE）生物合成，而 Psd2 则进行其余的生物合成。在这里，我们证明尽管 Psd1 保持完整，但 Psd2 的缺失会导致细胞对镉变得敏感。这种镉敏感性源自液泡 ATP 结合盒转运蛋白 Ycf1 的正常活性丧失。磷脂水平的测量表明，Psd2 的缺失导致液泡膜 PE 水平的特异性降低，而总 PE 水平没有明显影响。一种称为 Pdr17 的磷酸肌醇转移蛋白的存在对于 Psd2 功能和正常的镉耐受性是必需的。我们证明 Pdr17 和 Psd2 在体内形成复合物，对于维持液泡 PE 水平似乎是必不可少的。最后，我们将 Psd2 的定位细化到内体，表明该酶通过调节最终将形成液泡的隔室中的磷脂来控制液泡膜磷脂含量。这种细胞内磷脂平衡的调节紊乱会导致液泡中膜蛋白功能的选择性丧失。
