Schwaiger M, Herzog V, Neupert W
J Cell Biol. 1987 Jul;105(1):235-46. doi: 10.1083/jcb.105.1.235.
Import of proteins into the mitochondrial matrix requires translocation across two membranes. Translocational intermediates of mitochondrial proteins, which span the outer and inner membrane simultaneously and thus suggest that translocation occurs in one step, have recently been described (Schleyer, M., and W. Neupert, 1985, Cell, 43:339-350). In this study we present evidence that distinct membrane areas are involved in the translocation process. Mitochondria that had lost most of their outer membrane by digitonin treatment (mitoplasts) still had the ability to import proteins. Import depended on proteinaceous structures of the residual outer membrane and on a factor that is located between the outer and inner membranes and that could be extracted with detergent plus salt. Translocational intermediates, which had been preformed before fractionation, remained with the mitoplasts under conditions where most of the outer membrane was subsequently removed. Submitochondrial vesicles were isolated in which translocational intermediates were enriched. Immunocytochemical studies also suggested that the translocational intermediates are located in areas where outer and inner membranes are in close proximity. We conclude that the membrane-potential-dependent import of precursor proteins involves translocation contact sites where the two membranes are closely apposed and are linked in a stable manner.
蛋白质导入线粒体基质需要穿过两层膜。最近已经描述了线粒体蛋白质的转位中间体，它们同时跨越外膜和内膜，因此表明转位是一步完成的（施莱尔，M.，和W. 诺伊佩特，1985年，《细胞》，43:339 - 350）。在本研究中，我们提供证据表明不同的膜区域参与了转位过程。经洋地黄皂苷处理失去大部分外膜的线粒体（线粒体膜间颗粒）仍具有导入蛋白质的能力。导入依赖于残余外膜的蛋白质结构以及位于外膜和内膜之间且可用去污剂加盐提取的一种因子。分级分离前预先形成的转位中间体，在随后大部分外膜被去除的条件下仍与线粒体膜间颗粒在一起。分离出了富含转位中间体的亚线粒体小泡。免疫细胞化学研究也表明转位中间体位于外膜和内膜紧密相邻的区域。我们得出结论，前体蛋白的膜电位依赖性导入涉及转位接触位点，在这些位点两层膜紧密并置且以稳定方式相连。
