Oxysterol-binding protein homologs mediate sterol transport from the endoplasmic reticulum to mitochondria in yeast
Oxysterol-binding protein homologs mediate sterol transport from the endoplasmic reticulum to mitochondria in yeast
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DOI：
10.1074/jbc.ra117.000596
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发表时间：
2018-04-13
影响因子：
4.8
通讯作者：
Fukuda, Ryouichi
中科院分区：
文献类型：
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作者：
Tian, Siqi;Ohta, Akinori;Fukuda, Ryouichi
甾醇存在于真核生物膜中，并显著影响膜的流动性、渗透性和微结构域的形成。它们在内质网（ER）中合成并转运到其他细胞器和质膜。甾醇在线粒体膜的生物发生和维持中起着重要作用。然而，内质网到线粒体的固醇转运机制仍有待确定。本研究利用富含内质网和线粒体的纯化酵母膜组分，研究人员发现酵母中OSH基因编码的甾醇结合蛋白同源物介导了甾醇从内质网到线粒体的转运。在体外实验中，所有7种Osh蛋白的联合缺失会损害固醇从内质网到线粒体的运输；然而，添加一种奥什蛋白后，甾醇转运恢复到不同水平。值得注意的是，在所有其他OSH基因被删除的遗传背景下，Osh4失活后，线粒体片段中的甾醇含量在体内显著降低。我们还发现Osh5-Osh7在体外与胆固醇结合。我们提出了一个模型，其中奥什蛋白具有在膜间运输甾醇的共同功能，这些蛋白的贡献不同，取决于靶膜。总之，我们已经开发了一种体外系统来检测细胞内固醇运输，并提供证据证明奥什蛋白参与了酵母从内质网到线粒体的固醇运输。
Sterols are present in eukaryotic membranes and significantly affect membrane fluidity, permeability, and microdomain formation. They are synthesized in the endoplasmic reticulum (ER) and transported to other organelles and the plasma membrane. Sterols play important roles in the biogenesis and maintenance of mitochondrial membranes. However, the mechanisms underlying ER-to-mitochondrion sterol transport remain to be identified. Here, using purified yeast membrane fractions enriched in ER and mitochondria, we show that the oxysterol-binding protein homologs encoded by the OSH genes in the yeast Saccharomyces cerevisiae mediate sterol transport from the ER to mitochondria. Combined depletion of all seven Osh proteins impaired sterol transport from the ER to mitochondria in vitro; however, sterol transport was recovered at different levels upon adding one of the Osh proteins. Of note, the sterol content in the mitochondrial fraction was significantly decreased in vivo after Osh4 inactivation in a genetic background in which all the other OSH genes were deleted. We also found that Osh5-Osh7 bind cholesterol in vitro. We propose a model in which Osh proteins share a common function to transport sterols between membranes, with varying contributions by these proteins, depending on the target membranes. In summary, we have developed an in vitro system to examine intracellular sterol transport and provide evidence for involvement of Osh proteins in sterol transport from the ER to mitochondria in yeast.