Zara V, Rassow J, Wachter E, Tropschug M, Palmieri F, Neupert W, Pfanner N
Dipartimento Farmaco-Biologico, Università di Bari, Italy.
Eur J Biochem. 1991 Jun 1;198(2):405-10. doi: 10.1111/j.1432-1033.1991.tb16029.x.
The mitochondrial phosphate carrier (PiC) is a member of the family of inner-membrane carrier proteins which are generally synthesized without a cleavable presequence. Surprisingly, the cDNA sequences of bovine and rat PiC suggested the existence of an amino-terminal extension sequence in the precursor of PiC. By expressing PiC in vitro, we found that PiC is indeed synthesized as a larger precursor. This precursor was imported and proteolytically processed by mitochondria, whereby the correct amino-terminus of the mature protein was generated. Import of PiC showed the characteristics of mitochondrial protein uptake, such as dependence on ATP and a membrane potential and involvement of contact sites between mitochondrial outer and inner membranes. The precursor imported in vitro was correctly assembled into the functional form, demonstrating that the authentic import and assembly pathway of PiC was reconstituted when starting with the presequence-carrying precursor. These results are discussed in connection with the recently postulated role of PiC as an import receptor located in the outer membrane.
线粒体磷酸载体（PiC）是内膜载体蛋白家族的成员，这类蛋白通常在合成时没有可切割的前导序列。令人惊讶的是，牛和大鼠PiC的cDNA序列表明PiC前体中存在氨基末端延伸序列。通过体外表达PiC，我们发现PiC确实是以更大的前体形式合成的。该前体被线粒体导入并进行蛋白水解加工，从而产生成熟蛋白正确的氨基末端。PiC的导入显示出线粒体蛋白摄取的特征，如对ATP和膜电位的依赖性以及线粒体外膜和内膜之间接触位点的参与。体外导入的前体正确组装成功能形式，表明从携带前导序列的前体开始时，PiC的真实导入和组装途径得以重建。结合最近推测的PiC作为位于外膜的导入受体的作用对这些结果进行了讨论。
