Shiao Y J, Balcerzak B, Vance J E
Lipid and Lipoprotein Research Group, Department of Medicine, University of Alberta, Edmonton, AB, Canada T6G 2S2.
Biochem J. 1998 Apr 1;331 ( Pt 1)(Pt 1):217-23. doi: 10.1042/bj3310217.
The mechanism of import of phosphatidylserine (PtdSer) into mitochondria was investigated using a reconstituted system of isolated organelles in vitro in which PtdSer was translocated from donor membranes to mitochondria and was decarboxylated therein. Neither phosphatidylcholine nor phosphatidylethanolamine (PtdEtn) was translocated under the same conditions. Transfer of PtdSer from its site of synthesis on the endoplasmic reticulum and mitochondria-associated membranes [J. E.Vance (1990) J. Biol. Chem. 265, 7248-7256] to its site of decarboxylation on mitochondrial inner membranes is predicted to be mediated by membrane contact. A mitochondrial membrane protein appears to be involved in the translocation event since proteolysis of proteins exposed on the mitochondrial surface potently inhibited PtdSer transfer, whereas proteolysis of surface proteins of mitochondria-associated membranes did not impair the transfer. The nature of the membranes that donate PtdSer to mitochondria in vitro is not crucial since PtdSer of mitochondria-associated membranes, endoplasmic reticulum and microsomes was decarboxylated to PtdEtn with approximately equal efficiency. The translocation of PtdSer to mitochondria was stimulated by magnesium and calcium ions and was inhibited by incubation of mitochondria with sulphydryl group-modifying reagents. Reconstitution of PtdSer translocation/decarboxylation using digitonin-solubilized mitochondria and PtdSer-donor membranes suggested that the putative PtdSer-translocation protein is primarily localized to contract sites between mitochondrial inner and outer membranes. These studies provide evidence for the involvement of a mitochondrial membrane protein in the import of newly-synthesized PtdSer into mitochondria.
利用体外分离细胞器的重组系统，研究了磷脂酰丝氨酸（PtdSer）导入线粒体的机制，在该系统中，PtdSer从供体膜转运至线粒体并在其中脱羧。在相同条件下，磷脂酰胆碱和磷脂酰乙醇胺（PtdEtn）均未发生转运。预测PtdSer从内质网和线粒体相关膜上的合成位点[J. E.万斯（1990年）《生物化学杂志》265, 7248 - 7256]转运至线粒体内膜上的脱羧位点是由膜接触介导的。一种线粒体膜蛋白似乎参与了转运过程，因为线粒体表面暴露蛋白的蛋白水解作用强烈抑制了PtdSer的转运，而线粒体相关膜表面蛋白的蛋白水解作用并未损害转运。体外向线粒体提供PtdSer的膜的性质并不关键，因为线粒体相关膜、内质网和微粒体的PtdSer以大致相同的效率脱羧生成PtdEtn。镁离子和钙离子刺激了PtdSer向线粒体的转运，而线粒体与巯基修饰试剂孵育则抑制了转运。使用洋地黄皂苷溶解的线粒体和PtdSer供体膜对PtdSer转运/脱羧进行重组表明，假定的PtdSer转运蛋白主要定位于线粒体内外膜之间的接触位点。这些研究为线粒体膜蛋白参与将新合成的PtdSer导入线粒体提供了证据。
