The United Graduate School of Agricultural Sciences, Iwate University, Morioka, Iwate, 020-8550, Japan.
Cryobiofrontier Research Center, Faculty of Agriculture, Iwate University, Morioka, Iwate, 020-8550, Japan.
Sci Rep. 2019 Feb 4;9(1):1372. doi: 10.1038/s41598-018-37809-8.
MPIase is a glycolipid that is involved in membrane protein integration. Despite evaluation of its functions in vitro, the lack of information on MPIase biosynthesis hampered verification of its involvement in vivo. In this study, we found that depletion of CdsA, a CDP-diacylglycerol synthase, caused not only a defect in phospholipid biosynthesis but also MPIase depletion with accumulation of the precursors of both membrane protein M13 coat protein and secretory protein OmpA. Yeast Tam41p, a mitochondrial CDP-diacylglycerol synthase, suppressed the defect in phospholipid biosynthesis, but restored neither MPIase biosynthesis, precursor processing, nor cell growth, indicating that MPIase is essential for membrane protein integration and therefore for cell growth. Consistently, we observed a severe defect in protein integration into MPIase-depleted membrane vesicles in vitro. Thus, the function of MPIase as a factor involved in protein integration was proven in vivo as well as in vitro. Moreover, Cds1p, a eukaryotic CdsA homologue, showed a potential for MPIase biosynthesis. From these results, we speculate the presence of a eukaryotic MPIase homologue.
MPIase 是一种参与膜蛋白整合的糖脂。尽管已经评估了其在体外的功能，但由于缺乏 MPIase 生物合成的信息，阻碍了其在体内参与的验证。在这项研究中，我们发现 CdsA（一种 CDP-二酰基甘油合酶）的耗竭不仅导致磷脂生物合成缺陷，而且还导致 MPIase 耗竭，同时积累了膜蛋白 M13 外壳蛋白和分泌蛋白 OmpA 的前体。酵母 Tam41p，一种线粒体 CDP-二酰基甘油合酶，抑制了磷脂生物合成缺陷，但既没有恢复 MPIase 生物合成、前体加工，也没有恢复细胞生长，表明 MPIase 是膜蛋白整合所必需的，因此也是细胞生长所必需的。一致地，我们观察到在体外 MPIase 耗竭的膜泡中蛋白质整合严重缺陷。因此，MPIase 作为一种参与蛋白质整合的因子的功能在体内和体外都得到了证明。此外，真核 CdsA 同源物 Cds1p 显示出 MPIase 生物合成的潜力。根据这些结果，我们推测存在真核 MPIase 同源物。
