Tu S L, Li H M
Graduate Institute of Life Sciences, National Defense Medical Center, Taipei 112, Taiwan.
Plant Cell. 2000 Oct;12(10):1951-60. doi: 10.1105/tpc.12.10.1951.
Most chloroplastic outer envelope membrane proteins are synthesized in the cytosol at their mature size without a cleavable targeting signal. Their insertion into the outer membrane is insensitive to thermolysin pretreatment of chloroplasts and does not require ATP. The insertion has been assumed to be mediated by a spontaneous mechanism or by interaction solely with the lipid components of the outer membrane. However, we show here that insertion of an outer membrane protein requires some trypsin-sensitive and some N-ethylmaleimide-sensitive components of chloroplasts. Association and insertion of the outer membrane protein are saturable and compete with the import of another outer membrane protein. These data suggest that import of chloroplastic outer membrane proteins occurs at specific proteinaceous sites on chloroplasts.
大多数叶绿体外被膜蛋白是在细胞质中以成熟大小合成的，没有可切割的靶向信号。它们插入外膜对叶绿体的嗜热菌蛋白酶预处理不敏感，且不需要ATP。这种插入被认为是由自发机制介导的，或者仅仅是通过与外膜的脂质成分相互作用介导的。然而，我们在此表明，外膜蛋白的插入需要叶绿体的一些对胰蛋白酶敏感和对N-乙基马来酰亚胺敏感的成分。外膜蛋白的结合和插入是可饱和的，并与另一种外膜蛋白的导入相互竞争。这些数据表明，叶绿体外膜蛋白的导入发生在叶绿体上特定的蛋白质位点。
